Building Moisture

Field guide

Building moisture

With practical advice, tips and tricks

% RH

C td

C

2

Foreword FOREWORD As a manufacturer of measuring instruments for a wide range of industrial and commercial applications, TESTO is interested not just in supplying users with a particular instrument, but also in helping them meet their specific needs, i.e. carrying out their measuring tasks. The field guides that TESTO has been publishing for several years have become useful sources of reference for users of measurement technology. While the building services sector has already been covered in this series of guides (heating engineering and air-conditioning), guides for other problems associated with buildings, such as moisture and discomfort, have been lacking. Even before the TESTO ACADEMY was established, demand was such that it was decided to offer seminars - for a charge and independent of any brand - for the building industry with the aim of helping users identify measuring tasks and carry them out properly. In these seminars, which were constantly expanded, the hope was sometimes expressed that the learning material could be supplemented and condensed into written form and made available as a handbook. We are happy to respond to this request by publishing this guide. Because of the lack of opportunity to swap experience and perform practical exercises, this guide cannot replace any seminar. Nevertheless, we hope that this book will be widely distributed so that measuring techniques are applied efficiently and correctly, building defects are located quickly and the causes of damage can be clearly demonstrated. Our speaker at the building moisture seminars and symposia, Martin Giebeler of Zwingenberg, collaborated closely in shaping the content of this guide. The guide is aimed at managers of apartment complexes, expert inspectors, planners and engineers and companies providing measurement and building drying services. We would like to encourage the use of measurement technology wherever it is helpful. That requires familiarity with the possibilities and the limits of its proper use. This guide is intended to play its part in that process. It also offers information that would go far beyond the scope of the operating instructions for analysers. What is missing? What has not been dealt with intensively enough? We welcome your ideas, amendments and suggestions for how this guide can be improved. They will be considered in the next issue.

The Board of Directors

Burkart Knospe

Lothar Walleser 3

Overview

Air humidity

Parameter

Design

Recording room climate on first inspection

Parameter

Measuring in cavities (insulating course, screed joint)

Long-term recording of the room climate and ventilation characteristics

Moisture content equilibrium on/in the building component

Air temperature

A

Design

Recording room climate on first inspection

4

Comfort analyses (room climate at workplaces)

Long-term recording of the room climate and ventilation characteristics

Wind determination (meteorology)

Overview

Material moisture

Local or chronological comparative measurements (drying process, leak location)

Non-destructive surface measurement

Air flow

Throw determination and comfort at leakage points; determination of volume flow at defined channel cross-sections of ventilation and airconditioning systems

Penetration probe: rapid overview; brush probe: determination of the moisture horizon; moisture profile in a cross-section of masonry

Material temperature

Determination of the airtightness of a building as a whole; generation of an artificial vacuum for comfort analyses

Recording of radiator running times; assessment of heat bridges; clarification of condensation

Measurement of inaccessible parts of a room; rapid location of hot water leaks or heat bridges

More precise determination of building component temperature on first inspection

5

Contents Field guide to building moisture: Contents 1. Parameters and measuring methods 1.1 Air temperature 1.1.1 The measuring principle 1.1.2 Correct and incorrect application 1.1.2.1 Transport/inertia of the sensor 1.1.2.2 Performing the measurement 1.1.2.3 Special applications 1.2 Air humidity 1.2.1 The measuring principle 1.2.2 Correct and incorrect application 1.2.2.1 Transport/inertia of the sensor 1.2.2.2 Performing the measurement 1.2.2.3 Special applications 1.3 Material temperature 1.3.1 The principle of contact measurement 1.3.1.1 Application and performance 1.3.1.2 Special applications 1.3.2. The principle of non-contact measurement 1.3.2.1 Application and performance 1.4 Material moisture 1.4.1 The different measuring processes: Possibilities and limits 1.4.1.1 The scatter field method 1.4.1.2 Conductivity 1.4.1.3 Moisture ratio at equilibrium 1.4.1.4 Other methods

6

8 8 9 9 10 12 12 14 16 17 18 18 18 19 19 20 21 22 23 26 28 28 31 34 39

2. The basics of measurement

41

2.1 The authority advantage

41

2.2 Blind faith in digital technology

41

2.3 The four basic elements of measurement

43

Contents 3. Typical applications of building practice

47

3.1 Locating leaks in pipes

47

3.2 Locating air leaks in BlowerDoor tests, assessing draughts

50

3.3 Assessing moisture damage 3.3.1 The problem 3.3.2 The procedure 3.4 Assessing mould damage 3.4.1 Procedures in an inspection 3.4.2 Short-term and long-term measurement 3.4.3 Measuring location 3.4.4 Recommended programming for loggers used to record room climate 3.4.5 Narrowing down the causes 3.5 Assessing heat bridges 3.5.1 The problem and its importance 3.5.2 Types of heat bridge 3.5.3 Recording heat bridges

57 57 59 62 63 65 65 67 68 70 70 70 73

4. Reference to other field guides

75

5. General

78

7

Parameters and measuring methods 1. Parameters and measuring methods (See page 4 for an overview).

1.1 Air temperature The measurement of air temperature is a fundamental measuring task. It is carried out in order to control heating and ventilation, and also to assess the level of comfort and mould damage. The measurement of air temperature is straightforward in terms of handling and technical requirements.

Helpful phrase

In principle: It is always the actual temperature of the air that is measured, regardless of whether it is stagnant or agitated Stagnant air and agitated air are felt in different ways. Agitated air has a cooling effect: a breeze, for instance, makes oppressive summer heat more bearable, even if it has the same temperature. On the other hand, cold is felt more keenly the stormier it is (this is known as the wind chill factor). The subjective perception of cold and draught can be indicated with the perceived temperature , which is always lower than the actual temperature. However, empirical anthropological factors (the sensitivity of a person) extending beyond the purely physical indication of a temperature also come into play here. Finding the right definition is crucial when giving weather/climate information, for sporting events and expeditions and when considering comfort levels. It is just as important that radiating elements change both the perceived temperature and the actual temperature! Everyone knows how the embers of a campfire on a cool autumn evening can make you feel pleasantly warm - albeit only on one side. Similarly, an ordinary radiator, tile stove or halogen radiator in an apartment can radiate heat and raise the perceived temperature. If this radiated heat meets a thermometer, the thermometer will display a higher temperature than the ambient air actually has. This radiation component is not normally measured as well.

8

Parameters and measuring methods Air thermometers should in principle be shielded from radiation (meteorological measurements, for instance, are always performed in the shade). If the radiation component and its effect on comfort are to be recorded, though, there are special thermometers (e.g. globe thermometers) for this purpose.

1.1.1 The measuring principle There are a number of different ways of measuring air temperature. The most common are measurement with a temperature-dependent electrical resistor (high-impedance NTC or low-impedance PT100) and measurement with a thermocouple. This thermocouple generates an electric voltage according to the temperature. As in other measuring tasks, there are preferred applications for the one or the other principle depending on the temperature level to be recorded (e.g. 20 C or 200 C?) and the requirements with regard to precision, design and speed. Suitability and precision are indicated by the manufacturer of each device; temperature sensors are often combined with air humidity sensors or an air velocity sensor in one probe. The accuracy of TESTO s standard sensors (combination probe) is about 0.4 K, the response times for agitated sensors about 30 sec.1

1.1.2 Correct and incorrect application Always remember the following: The instrument only ever records the temperature of the sensor, not the temperature of the medium! For that reason the temperature of the sensor must come as close as possible to that of the medium to be measured. That is why the sensor is normally detached from the handheld instrument and accommodated in a handheld probe.2 Handheld probes must be specifically designed for measurements in air (or more generally, in gases). They are markedly different in design from sensors for the surfaces of solids, for bulk goods and for liquids!

1 2

For more about the response time, see chapter 1.1.2.1 For a definition of the terms sensor and probe , see Fig. 1

9

Parameters and measuring methods The temperature should only be recorded in that part of the space in which the sensor is located. Given that the layers of air that prevail in homes can produce a difference of 4 K between near the floor and near the ceiling, the question arises as to the best height for measuring. If in doubt, it is better to measure at several heights and to note all measurements. Otherwise it is normally sufficient to measure at chest height. This corresponds to a height of about 140 cm, which comfort guidelines give as the mean measurement height.3 The middle of the room is taken as representative of the room. If other locations are to be assessed, e.g. a balcony door that is thought to have a draught, they must be measured separately.

Handheld unit

Sensor Sensor/probe

Fig. 1: Components of a measuring instrument

1.1.2.1 Transport/inertia of the sensor As already explained, the temperature of the sensor should approach the temperature of the medium as quickly and without hindrance as possible. After transportation or storage at significantly different temperatures, the sensor must be given a sufficient equalisation time to be able to react to the actual prevailing temperatures (e.g. do not keep the instrument in the car overnight during frosty periods if you are going to perform a measurement in a home the next morning).

3

10

cf. DIN 1946: Head height for seated activity 110 cm, head height for standing activity 170 cm

Parameters and measuring methods If the temperature of the handheld instrument is different, this is not as critical as the temperature of the probe being too low. If the probe was cooled down (or heated) when brought into the room to be measured, however, it would need about 10 minutes lying still in order to adjust. The actual inert mass here is the sensor housing, not the sensor itself. If measurement is carried out with a probe that has cooled down too much, the sensor would fog up. This would result in lower values. If you have not waited long enough, you can see by excessively high or low values that the reading is wandering . Only when the reading is stable has the probe reached the equilibrium and hence correct temperature. In the typical design, in which the sensor sits in a slotted protective cap well exposed to direct flows, a microclimate forms. With the sensor at rest, an insulating air cushion can be maintained in the cap (this is particularly true for fully enclosed sintered caps used in dusty atmospheres). Temperature equalisation can be accelerated by moving the probe around in the ambient air: the microclimate is then broken up. Even with good flows around it, the response time of the sensor depends on its design and especially its mass. The response time of commercial air sensors is a matter of seconds and so has little bearing. In technical language, the response time is expressed as a characteristic value known as t99. This is the time taken for the displayed temperature to approach 99 % of the end value.

11

Parameters and measuring methods 1.1.2.2 Performing the measurement When carrying out a measurement, you must make sure that your own body heat and especially the air that you exhale do not reach the probe. One solution is to move the sensor around. This should not be done vigorously, but nor should it be too gentle. In summary, measurements should be performed as follows: Roughly in the centre of the room At chest height Shield off strong sources of radiation with your body Keep your arm stretched away from your body Use your wrist to swing the instrument. Aim for about 1.5 m/s; this corresponds to about 2 swings per second

Fig. 2: Correct handling when measuring air temperature and air humidity

1.1.2.3 Special applications Measurements of comfort are carried out using a globe thermometer. This is not agitated but is instead fixed immovably in position using a stand at one of three defined heights that are laid down in DIN 1946-2 and VDI 2080. The globe thermometer consists of a hollow sphere painted matt black. The actual sensor is located in the sphere.

12

Parameters and measuring methods Incident heat radiation (e.g. sunlight) has the effect of warming the sphere in a similar way to how the human body would experience it. The reading approximates very closely to the average human sensitivity if the readings are calibrated on the basis of empirical experiments with a large number of test people. The reading given by the globe thermometer cannot, however, indicate whether the radiation was uniform all the way round or just on one side of the sphere. That makes a huge difference with regard to comfort.

Fig. 3: Globe thermometer Long-term recording is advisable if temperature fluctuations are to be recorded. This requires a programmable device with a data memory, known as a data logger. What was said under 1.1.2.2 applies analogously for the positioning of a probe in the room. Because the sensor is not moved around, the inertia of the globe thermometer is theoretically greater. That is irrelevant in practice, however, as the air temperature in rooms does not vary so quickly that the sensor is unable to keep track.

13

Parameters and measuring methods 1.2 Air humidity The parameter of air humidity is very important in any assessment of mould damage. It is also a key indicator in the technical drying of buildings in order to ascertain when a drying process can be terminated. There are a large number of characteristic values which can be used to indicate how much water vapour is in the air. As regards the applications addressed in this field guide, only absolute humidity relative humidity

g water

and

m3gas g actual water g max. possible water

are of interest.4 The absolute humidity describes the mass of water (vapour) which exists in one cubic metre of ambient air (including the vapour). Strictly speaking, you would have to make sure that the standard pressure was maintained. That is irrelevant in practice, however, because the instrumentation and the performance of the actual measurement lead to greater inaccuracies. The relative humidity describes how much of the maximum possible absorbing capacity of the air is actually taken up. This depends on the temperature!

Increasing saturation

Water content of air in g/m3

Flowing water

Water vapour

Air temperature in C Dry, cool air

Warm, moist air

Fig. 4: Saturation curve and dew point temperature curve

14

4

The terms vapour pressure , enthalpy and water content are preferred in some industries (airconditioning, production engineering). The units can be transferred using an h-x diagram ( Mollier diagram ) if the side parameters are known.

Parameters and measuring methods

75 %RH

Troom = 20 C

Tsurface = 15 C

55 %RH

Minimum distance from wall to measurement point for representative room climate measurements

Fig. 5: Temperature dependence of relative humidity

Absolute and relative humidity in practice

5

Room air at

with an assumed water content of

...would be saturated at...

and consequently has a relative humidity of...

20 C

9.5 g/m

17 g/m

55 %

This would be a typical room climate in a lounge, for instance. If this air then gets into a cooled bedroom, in a corner which is only 10 C on the surface,... ...this air cools down to...

At first it still contains...

...but is already saturated at...

In other words:

10 C

9.5 g/m

9 g/m

About 0.5 g, corresponding to 0.5 ml, excess condensates out, on the cold surface first => mould forms! The condensation begins from cooling down to 10.7 C. Mould begins to form before condensation occurs.

Remedy: Move the furniture out, insulate the top of the ceiling, heat the bedroom better. This would help to increase the wall temperature up to 15 C, for instance:

5

So this air only cools down to...

It still contains...

...but is not saturated until... This corresponds to a relative humidity at the wall of:

15 C

9.5 g/m

13 g/m

73 %. This figure is much lower than the critical value for mould to form, namely 85 %. => Problem solved!

For the sake of simplicity, constant values were assumed in this scenario. In practice, the room climate will of course vary. However, mean values can be used.

15

Parameters and measuring methods Different relative humidities within a room

The dew temperature

Relative humidity is the indicator most commonly used, probably due to meteorology and considerations of comfort levels. Relative humidity depends not only on water content, but also on air temperature. Since different air temperatures may prevail within a room (the temperature at floor level and on ceilings next to external walls is smaller than in the centre of the room), a room may have a variety of relative humidities!

That is why absolute humidity is more helpful for considerations relating to the physics of construction, which often involve condensation and drying. Well-designed instruments indicate both characteristic values and also provide information on the dew temperature (often called the dew point temperature ). This is the temperature at which condensation would begin if this ambient air were cooled down. This parameter is very important if you want to know where cool sections of a wall fog up in a given room climate.

1.2.1 The measuring principle The actual sensor is usually located in a handheld probe along with a temperature sensor. It consists of an approx. 0.5 cm2-large lamina comprising three layers and hence forming a capacitor. The middle layer is a moisture-sensitive plastic. Depending on the ambient humidity, it brings about a different dielectric constant, so that the capacity changes. The change in the response of the resonant circuit is analysed electronically. Sensors are available in different tolerance classes. Dust deposits can be rinsed off, but mechanical stresses (scratches) or sweat from your hand can damage the sensor. While today s sensors are considered to have long-term stability, they are subject to unavoidable ageing. For our applications, they must be inspected every 2 years and recalibrated if necessary. This is particularly important if the accuracy of the determined values has a legally binding effect or if several measuring instruments are used at the same time and their values are not allowed to differ (e.g. when diagnosing heat bridges and mould, see chapter 3.5.3). If calibration takes place in the factory, the relevant certification is provided (e.g. a calibration certificate). This helps to allay lack of confidence with regard to the accuracy of measurement. The accuracy of TESTO s standard sensors is + 2 % of relative humidity (not a % of the displayed value). The response time (for agitated combination sensors) is about 30 s. 16

Parameters and measuring methods

Fig. 6: Combination sensor

1.2.2 Correct and incorrect application Before performing any measurement, it is essential to ask yourself this question: what do I want to achieve with this measurement? When it comes to measuring moisture in order to assess mould, it is often unclear where the probe should be positioned: Do I want to find out the air humidity in the corner that is being attacked by mould? Or do I want a representative moisture value for a living space in order to assess the ventilation requirements? Here too, the principle is that: the measurement applies only for the place at which it was taken. It is always advisable to carry out a measurement in each room, this being done roughly in the centre of the room, as when measuring temperature. Humidity can also then be measured in corners, behind cupboards and the like, and these must then be noted separately in the report. The room climate is always influenced by the measurement itself, i.e. by the presence of the person doing the measuring. You should therefore go into the room quickly, close the doors and perform the measurement promptly. Even just opening the door or leaving it ajar, or staying for longer than necessary, will change the air humidity in the room. The report must normally show the measuring location, the time, the weather and the air temperature, as these are indispensable for subsequent interpretation of the results. 17

Parameters and measuring methods Waving the sensor around reduces the equalisation period

Posture during measurement

1.2.2.1 Transport/inertia of the sensor As with temperature sensors, humidity sensors also have a certain equalisation period. This is because the humidity in the air must first penetrate into the plastic layer of the probe. Although the plastic layer has only an ultra-thin, microporous metal layer as the second pole, the process can still take from a few seconds to several minutes. Here too, the inertia depends primarily on how exposed the sensor is to flows, i.e. whether the sensor is moved around in the air. If the probe is hardly moved, an equalisation period of about 10 minutes should be expected. More rapid equalisation takes place if the instrument is agitated at approx. 1.5 m/s. To prevent condensation and reduce the response time, the instrument should not have been stored in a cold place beforehand. The measurement can be taken once the reading is stable. 1.2.2.2 Performing the measurement Everything that applies for temperature measurement must also be observed when measuring humidity: the sensor must be kept away from the body so that it is not exposed to exhaled air (which is saturated with moisture!). The sensor should be agitated using the wrist, at chest height etc. 1.2.2.3 Special applications There are long-term recordings in humidity measurement as well. These are vital for assessing mould. The probes and instruments are positioned in the same way as for a one-off measurement. For measurement in cavities or screed insulating layers, particularly thin probe types which can be pushed into drill holes or edge joints are available. The very slim protective caps that come with them protect against dust and grains, but prolong the response time. Sintered metal protective caps which are permeable to gas but impermeable for particles are available for measurements in dusty atmospheres. Again, these prolong the equalisation period.

18

Parameters and measuring methods

Fig. 7: Measuring in a screed edge joint With special adapters, air humidity sensors can also be used to determine ma terial moisture (see chapter 1.4.1.3).

1.3 Material temperature

1.3.1 The principle of contact measurement Here measurement is performed according to the tried and tested principle that the sensor has to take on the temperature of the medium to be measured. The accuracy of measurement depends on how well that succeeds. Principle: every measuring instrument only measures the temperature of its own sensor. Since with solid bodies the sensor is normally placed only on the surface, it is important that a vital intimate contact of the sensor is achieved, e.g. by having a sufficiently large contact area. This contact area should adapt as fully as possible to the contours of the surface. The part to be placed on the surface should also have little mass so that it equalises quickly. The measured temperature is always a mixed temperature, as the air temperature is unavoidably measured as well.

19

Parameters and measuring methods The accuracies are normally lower here than when measuring air temperatures. For more details, please refer to the following section.

1.3.1.1 Application and performance Of course, air or penetration sensors do not meet these requirements on solid bodies and are not therefore suitable for measuring wall temperatures. This is where disk or spring band sensors come in.

Exact measurements only with intimate contact

Disk sensors are only suitable for very smooth surfaces; they are used in combination with magnetic adhesion for even metallic surfaces, but not for wallpaper, plaster, stone or concrete. Spring band sensors are more suitable for the latter. If the surface is very rough (e.g. rendering), the transmission of heat can be improved by using a thermal conduction paste. The equalisation period for spring band sensors is always longer with poor heat conductors (e.g. insulating material) and can be up to 10 seconds; with good heat conductors (e.g. metal) it is shorter.

Fig. 8: Spring band sensor Where particular accuracy is extremely important in measurements (e.g. for expert reports), the measuring principle and the design and application must be taken into account in measurements. With regard to accuracy, it must be remembered that the manufacturers only give sensor accuracies for defined surface conditions, i.e. the sensor is placed at right angles on a smooth metal plate. Other surfaces may be taken into consideration in a special calibration. 20

Parameters and measuring methods The standard accuracy of spring band sensors for usual room temperatures, for instance, is 2.5 K. More precise measurements, however, are required for applications demanding a high level of accuracy. Calibration is possible and recommended if greater accuracy is desired in the temperature range of 10 C (the typical heat bridge temperature). Penetration probes which could be pushed behind a wallpaper are sometimes more accurate, but also more inert; the transmission of heat is also more undefined. A more accurate type of sensor is described in the next chapter.

1.3.1.2 Special applications There is a need for long-term recording even when measuring surface temperature. Expert assessors require them primarily when assessing mould or in research in the determination of heating response. The equalisation period is virtually irrelevant here. It is much more important that a sensor can be anchored in position. Lamina sensors 1.5 x 4 cm in size which - with thermal conductive paste - can be fixed to the wall using two small nails are available to this end. The rear should be shielded from heat radiation and the air flows in the room by means of a small piece of polystyrene.

Fig. 9: Lamina sensor The achievable accuracy here is much greater than for a sensor simply placed onto a surface. It is about 0.5 K for the lamina itself, which is fitted with a PT100 sensor, and is sufficient for assessing dew. Intimate contact with the surface is essential, which is why an air gap must be avoided and thermal conductive paste must be used. The location of measuring/mounting depends on the particular task. It is often useful to measure at two different locations simultaneously. For more about the procedure for mould damage, please refer to chapter 3.4. Aspects to do with assessing heat bridges can be found in chapter 3.5.3.

21

Parameters and measuring methods 1.3.2. The principle of non-contact measurement All bodies which are warmer than absolute zero (-273 C = 0 Kelvin) radiate heat (also known as infrared radiation). Infrared radiation has a long wavelength (>770 nm) and is thus in a spectral range that the human eye cannot see. The higher the frequency, i.e. the shorter the wavelength, the more energy-rich the radiation. It can be picked up by sensors. The intensity (output) of the heat radiation is a measure of the temperature of the radiating body. Most substances have a clean radiation behaviour that is utilised by the standard measuring instruments in the range from 8 to 14 nm.6 7 What is critical is whether the body really only gives off its own energy at the surface or whether it reflects a considerable proportion of the ambient heat radiation (rather like a polished surface does with visible light). The proportion made up of reflected radiation is described as the emissivity coefficient . It must be remembered that the reflective or transparent property of a body may behave differently in response to radiated heat than in the case of visible light! What is transparent glass to the eye, for instance, may be a matt pane for a measuring instrument. As a rule, however, surfaces which appear to be reflective are also critical for infrared measurement. The colour that we perceive an object to have (white, black, blue etc.) is irrelevant for the purposes of measurement. In principle: Only the temperature of the surface of the solid is measured. The core temperature and the air temperature in front of it are not displayed.8

6 7

8

22

Some infrared cameras also work in ranges of 3 to 5 mm There are some materials (e.g. metal oxides and plastics) that give off radiation in several spectral ranges and change their wavelength erratically when the temperature changes; they are known as coloured emitters . These are technically more difficult to measure. However, this is not relevant for typical building applications. Of course, the temperature that arises on the surface also depends on the core and air temperatures. Cold air that flows in and along the wall, for instance, leads to smear-like cooling zones on the surface. The cold air itself is not recognised , but it can be seen by the effect it achieves on the surface.

Parameters and measuring methods 1.3.2.1 Application and performance The correct emissivity coefficient is crucial for the accuracy of the measurement. For the majority of matt building materials it is 0.93 ... 0.95. Lower-priced devices have a fixed value. With more variable devices, the emissivity coefficient can be adjusted to requirements. The measurement of reflective surfaces (e.g. polished stainless steel rails, anodised surfaces) can be very inaccurate because there is very little characteristic radiation. Glass is not always as reflective or transparent as it may appear. Whether or not glass surfaces act like matt surfaces of building materials depends on the wavelength range in which the instrument is operating. Window panes can be opaque for many thermographic cameras and instead act like a mirror for cosmic radiation. The panes then appear unnaturally cold in the readings. If there are no recommendations from the manufacturer or previous experience, help can be found by covering the surface in question with a matt-effect adhesive tape (heat-resistant adhesive tape for high temperatures is available to this end). Aluminised adhesive tapes are of course out of question. However, the Gaffa tape used by sound engineers, or even masking tape, are also very suitable. These allow glazed tiles, panes, mirrors, radiators, metal railings, galvanised surfaces etc. to be measured more reliably. Consideration must be given to the size of the measuring spot. With thermographic cameras the subject area that goes into the measurement is known because the area is continuously scanned. Handheld devices, however, make only 1-point measurements, and this is normally over a circular spot rather than on one single point. This is due to the lens arrangement (cf. principle of a photo camera). A mean temperature value is obtained for the surface to be measured.

The reflection

The measuring

To let you know where you are measuring, the instruments have a laser beam that picks out the position of the measuring spot. The size of the measuring spot is also significant, however, e.g. in corners, near water pipes or on the adhesive tapes mentioned above. That is why the more convenient instruments have additional laser beams that highlight the contours of the measuring spot. Otherwise the size of the measuring spot must be derived from the distance to the object as detailed in the operating instructions.

23

Parameters and measuring methods The surface to be measured should be viewed as far as possible at right angles. Deviations of up to 30 from the vertical are irrelevant. The measuring instrument should be held away from the side of the body so that the reflected radiation of body heat cannot reach the instrument. Very flat angles of observation not only impair accuracy, but also lead to a distorted, oval-shaped measuring spot. Non-contact measurement is not necessarily more accurate than contact measurement. A direct comparison between the two methods at one and the same location can show up differences. The accuracy is determined not only by the resolution of the digital display, but also by the accuracy of the emission factor, the compensation capability of the electronics with regard to the ambient air temperature and the exactness of the lens. A comparison between both methods on the building site is useful in delivering an impression of the accuracy. 9

9

24

Even if results coincide, this does not mean that the measurement was accurate. The deviation might be in the same direction for both measurements. Nevertheless, it is vital to always employ several methods for critical applications!

Parameters and measuring methods Infrared measurement

Contact measurement

Criterion

Possible remedy

Criterion

Possible remedy

Emission factor estimated correctly?

Find correct value from handbook and adjust

Uneven surface? Does the sensor have a sufficient contact surface?

Select suitable sensor

Reliable surface?

Apply matt adhesive tape on Rough surface? Enclosed metals, anodised surfaces layer of air? and reflective surfaces

Use thermal conductive paste

Strong background radiation Shield with own body, (incandescent bulb, smelting cardboard cover or umbrella furnace, clear winter sky)?

Sensor type generally too inaccurate?

Lens foggy? Wait Device at room temperature?

Sensor and handheld device Wait at room temperature?

Select different principle for recording measurements; select different accuracy class; individual calibration

Measuring spot larger than measuring object? Size of measuring spot known?

Probe heated up at wrong Determine size from operating instructions or use place? device with laser display

Dust or other nonhomogeneous film on measuring object? Measuring object foggy?

Clean

Reading stable?

Wait until room temperature is reached; find more reliable contact surface; avoid tilting when positioning; check device

No reproducibility? Sharp deviations between measuring locations close together?

Surface property not homogeneous! Apply adhesive tape

No reproducibility? Sharp deviations between measuring locations close together?

Surface property or contact surface not homogeneous! Use conductive paste

Table 1:

Hold probe only by the handle, not by the connector and not by the shaft; insulate leaf sensor on room side

Important criteria for the accuracy of measurement in infrared and contact measurements

An accurate measurement also depends to a large extent on having a measuring instrument that is at room temperature, particularly when measuring objects with a low emission factor. The great advantage of infrared measuring instruments is their ease of use. Building components which cannot be reached by hand, e.g. ceilings in sports 25

Parameters and measuring methods halls, coving above bedroom wardrobes and corners of rooms can be measured quickly and with sufficient accuracy. Temperature differences can be measured with much greater accuracy than the absolute temperature, provided that the surface is identical. Joins in brickwork, piping, concrete lintels etc. are identified by their temperature. If the current dew temperature of the room climate is known, it is easy to find zones in which condensation is taking place at the moment. It is even more convenient if the dew temperature can be entered into the instrument as a lower threshold value so that an optical and acoustic signal is given if this lower value is not reached. Infrared measurement measures rough surfaces as well as inaccessible surfaces, something that is critical for building applications.

1.4 Material moisture There are about a dozen different ways of determining the water content in mineral building materials. Some of these methods are destructive, require time-consuming calibration work, a great deal of time, a lot of electricity or radioactive substances. Not all methods are transportable and economically viable for smaller firms. All procedures must be based around a reference procedure, the Darr-W ge (dry-and-weigh) method. For this method a sample is taken (chiselled out), packed in an airtight and steam-tight container and sent to a laboratory. The sample is weighed precisely before all the water is expelled from the sample in a drying oven (the drying temperature for cement building materials is 105 C). The sample is weighed again when a constant weight is reached. The difference in weight corresponds to the quantity of water contained.

The mass of this water is then compared with the dry mass of the sample: U= m -m moist

dried

m dried

It is normally indicated as a %. The indication U of the water content that is obtained in this way, however, reveals nothing about the actual saturation of a substance, i.e. whether or not it is already saturated. 26

Parameters and measuring methods To draw a conclusion about that, a further step is required: the fully dried sample is immersed in a water bath. It is left there until no further increase in weight can be ascertained (complete saturation = maximum possible water absorption). The quantity of water that is contained is then compared with the maximum possible quantity (there are parallels here with the definition of relative air humidity): Moisture penetration =

m contained water m maximum absorbable water

Please note: Some people compare the water volume with the moist sample (in some industries and in the English-speaking world). There is a volume density indication (vol. %) which must not be confused with the mass density figure (m %). All the water is driven out of the dried sample and so it reaches a level of dryness that would never occur under normal circumstances. A level of dryness that is assumed in our home or ambient climate is called the moisture content equilibrium 10. This depends on the ambient air humidity. The Darr-W ge method takes several days due to the drying and saturation processes, assumes air-conditioned drying ovens and precision scales and ultimately supplies values which are primarily of interest for research purposes (materials science, fundamental research, calibration values for other processes etc.). Other methods for determining material moisture which are primarily suited for day-to-day use in terms of financial and practical aspects will be addressed below. However, these methods cannot provide the moisture content U or even the moisture penetration for unknown materials without further calibration with the Darr-W ge method.

10

The terms moisture content equilibrium and moisture ratio at equilibrium are not differentiated properly and consistently in the literature and are used as synonyms. For a definition in this guide, see chapter 1.4.1.3.

27

Parameters and measuring methods 1.4.1 The different measuring processes: Possibilities and limits 1.4.1.1 The scatter field method An electrode with coil is placed on a building component. An applied alternating low voltage generates an electrical field that - depending on the design penetrates the component to a greater or lesser depth. The standard forms are a spherical head and a loop head. The depth of penetration is between 2 and 5 cm. This depends on the geometry of the component and the layer structure. Water contained in the building material has a significant effect on the electrical field. Field changes are therefore a measure of the water content. The type of building material has a considerable influence on the readings. Metals in the substrate (e.g. reinforcing iron and water pipes) lead to sharp changes (cf. functional principle of cable search devices). Different densities can lead to varying readings even in identical types of building material, e.g. bricks. In addition, lack of homogeneity (cavities, mortar in joints, mixed masonry) results in fluctuations and mixed values . It is understandable, then, that the measuring instruments do not supply the water content directly, but instead measure only an output voltage. This is usually converted into dimensionless units or digits or indicates that conditions are dry , moist or wet using LEDs. High-end devices enable individual scaling by the user. Although it is possible to determine the moisture content U from the value displayed, this presupposes prior laboratory calibration for the material used, with its own specific density, according to the Darr-W ge method. In practice, these instruments are often used to locate leaks, as they can penetrate tiles, for instance. Water in the substrate can be narrowed down to a particular area, even under (thin) screeds, rubber floorcoverings or laminate floors. The second advantage, the absence of destruction, is useful in the case of very hard, dense or valuable surfaces (mosaic, frescoes, paving stones). The instruments also enable conclusions about the development of damage to be drawn, e.g. whether building components are tending to dry out, remain just as moist or become increasingly moist. Two or three measurements taken several weeks apart are performed to this end. The location of the measurement points and the readings must be recorded very precisely. A grid is drawn on the building component so that the repeat measurements are performed at exactly the same spots. 28

Parameters and measuring methods Caution: Depending on the shape, the position of the probe (tilted or straight, pressed on firmly or just placed on lightly) also has an effect on the reading! Placing the probe on one location several times givens an indication of whether the measurement was correct. Ideally, identical values will be obtained. Reproducibility can be improved by having a strictly defined probe position. The probe can be laid flat on the surface, for instance, in order to exclude a variety of angles when applying the probe from above.

Fig. 10: How to hold a loop head probe

29

Parameters and measuring methods

Fig. 11: Marking enables repeat measurements Since, as already indicated, the slightest movements (or changes of angle) of the probe have a considerable influence on the reading, corners, coving and rough/uneven surfaces are very difficult to measure precisely. Because of the concentration of masses, corners tend to produce higher readings that usually only simulate an increased water content. Any consideration of accuracy is superfluous with this measuring method because the handling differences outlined above and the lack of homogeneity of the substrate yields far greater fluctuations than the equipment itself. That is why many manufacturers dispense with indicating the accuracy.

30

Parameters and measuring methods 1.4.1.2 Conductivity Water conducts electricity and, through its resistance, influences the electrical conductivity of a building material that contains water. This fact can be utilised in measuring the water content. Two electrodes must be introduced into the building component, or at least placed on top. This can be done using brush probes inserted into previously drilled holes (in concrete and brickwork) drive-in probes that are driven in with blows of a hammer (primarily for analyses in wood) needle points that are pushed in (plasters and screeds).

Fig. 12: Probe types for measuring conductivity The reading is slightly affected by temperature, but this can be compensated through technical means. The penetration depth of the needles or brush probes and their spacing also have an influence on the reading that can be compensated. If the spacing of the holes is not already prescribed by the design, it must be taken from the operating instructions. In the case of drilled holes, the heat of the drilling process causes a certain amount of drying that has to be compensated through a sufficiently long waiting time. The drill hole must be kept closed for that period. This is easily done 31

Parameters and measuring methods using plastic adhesive tape. The biggest unknown in the whole measurement is the chemical composition of the building component. This means that the conductivity - given an identical water content - differs from one material to another: clinker, concrete, sandlime blocks, mortar etc. behave in different ways depending on their density. If the instruments are being used to diagnose damage, it must also be remembered that moisture that has been in the component for some time may have released and relocated salts. Salts conduct electricity, i.e. increased salt loads increase conductivity relative to the standard salt content of the building material, in some cases many times over. Salts are always carried with the water flow to the evaporation surface. Measurement usually takes place on this evaporation surface (interior plaster). This can lead to a higher water content being displayed than actually exists.11 Instruments with contact gauges have proven to enable rapid diagnosis in practice. The main application here is assessing whether wall stains indicate a previous but rectified case or acute damage. If the instrument indicates dry , the wall - at least on the surface - is actually dry. If the instrument indicates moist , water and/or salts may be present: either a lot of water with a few salts or a little water with a lot of salts. Highly reliable conclusions can be drawn by observation (is the plaster discoloured or fragmented?) and another, separate, method of measurement. If the instruments indicates complete wetness , it must be assumed that the building material is actually wet. When measuring thoroughly moist plaster, the force required to push the instrument in often says a lot about the damage: moist plaster which has already been thoroughly penetrated by moisture for a longer period is fragmented and offers no resistance to the gauges. If you always get an end-of-scale reading at different locations, you should check whether an aluminium-backed wallpaper was put up! Moist wallpapers should be removed for the purposes of measuring anyway, as their hygroscopicity means that they retain water well and cause high display readings.

11

32

It is true that salts have a direct influence on the reading, especially in the conductivity measurement method. However, there is a second relationship that applies for all methods: an increased salt concentration causes moisture to be absorbed from the air (hygroscopicity of the salts). These building materials thus have a higher moisture content equilibrium and are never as dry as uncontaminated material under a particular ambient climate. See also chapter 1.4.1.3.

Parameters and measuring methods The conductivity response can - in conjunction with the approx. 30 cm long brush probes - also be used to determine moisture profiles, for instance at various heights (with constant depth) or at various depths in the brickwork (in only one drill hole pair).

Inconsistencies in terms

This allows a conclusion to be drawn e.g. about whether the moisture is coming from outside or is rising moisture. In the ideal scenario, mathematically clean curves would be produced. In practice, however, lack of homogeneity (different types of brick used in wall, joins in the brickwork, cavities) lead to very different curves from which only trends can be ascertained. Inhomogeneity can be identified in advance by the resistance felt when drilling and the colour of the boring dust that is produced. The procedure can also be used to assess readiness for a floorcovering, subject to three conditions: 1. It must be possible to define the recipe of the building material to be assessed (e.g. screed ZE 20) 2. Set or limit values must have been elaborated for this recipe (i.e. this requires one-off calibration in the laboratory using the Darr-W ge method) 3. The immersion path of the brush probes must be defined by a limit stop or similar If the above requirements for calibration are not met, the conductivity method will not supply any direct moisture figures either, merely indicators for classification. This dry-moist-wet statement applies for mineral and industrial building materials. With wood, the situation is different: this is because although the types of wood differ, there is very little deviation among woods of one particular type, so good reference values exist and can be used to determine the moisture content more accurately. Example: Fir has a different conductivity to beech. However, fir that comes from Scandinavia does not differ to any meaningful extent from fir that comes from the Black Forest.12

12

It is not proposed to go into more detail with regard to measuring wood moisture since the method can be taken from the manufacturers operating instructions.

33

Parameters and measuring methods 1.4.1.3 Moisture ratio at equilibrium This method is a special case because, instead of being measured directly, the moisture of the material is measured indirectly via the air humidity. The air humidity is that which occurs on contact with the building component to be examined. The reason is clear from the above explanation of the other methods: in terms of technology, measuring air humidity is very reliable and can be achieved at little expense!

Definitions and terms... Although the term equilibrium is used in both MOISTURE RATIO AT EQUILIBRIUM and MOISTURE CONTENT EQUILIBRIUM, for the purposes of this guide a distinction should be made:

The moisture ratio at equilibrium is the air humidity that corresponds to any particular water content of the building material, i.e. forms a stable equilibrium with it (see below). The unit is % RH or g/m . The moisture content equilibrium is the material moisture that occurs in contact with a normal average room or indoor climate. The unit is usually M %. It must be remembered that these terms are used in different ways in the literature. Other common terms related to these physical phenomena are: moisture equalisation method, hydrometer method, water activity, hygroscopic moisture.

A closed system in miniature must be created if this air humidity (known as the moisture ratio at equilibrium) is to be determined. Either a sealed volume on the surface of the building component. Such a test chamber can be created, for instance, by using film that is glued down all the way round or a funnel that is applied tightly. Or a chamber can be created in the building component itself by drilling a hole which is then sealed up. There are handy aids for both variations.

34

Parameters and measuring methods

Sample Sample Material moisture greater than relative air humidity of the environment Drying out

Material moisture less than relative air humidity of the environment

Sample Moisture equilibrium

Moistening Fig. 13: Moistening, drying, equalisation

Surface measurement

Immersion measurement

Air humidity sensor

Air humidity sensor

Funnel as surface adapter

Dowel for reliable sealing of the hole

Fig. 14: Schematic diagram of a sealed volume 35

Parameters and measuring methods Assuming a sealed volume, there is a physical relationship: Every material moisture can be assigned an air humidity that occurs at the building material. Or vice versa: storing a building material in a certain climate leads to a certain material moisture. This relationship can be mapped by curves known as sorption isotherms. Each sorption isotherm applies only for the specific building material with which it was determined, because every building material has a different sorptive (absorbent) characteristic. Sorption isotherms can be obtained from the literature, or in some cases from the manufacturer of the building materials or equipment.

% RH

Moisture content

In the material

Desorption

Adsorption

Relative air humidity % RH

Fig. 15: Example of a sorption isotherm

36

In the drill hole

Parameters and measuring methods Salinisation will lead to an increase in the moisture content equilibrium! In the diagram the line of a sorption isotherm influenced by salt goes higher than a comparable isotherm for unsalinised material. What this means in reverse is that theoretically much drier ambient air is needed in order to dry salinised components. Salinised brickwork causes problems for painting and conventional plastering. Stains become evident within a very short space of time. Salts can be determined qualitatively and semi-quantitatively on site, and in the laboratory fully quantitatively as well. This is only important for complex cases, e.g. the restoration of historical building fabric with special plasters. Measuring the moisture ratio at equilibrium is straightforward in terms of equipment and does not depend on the make. The disadvantage, however, is the relatively long equalisation period, which is about 1 minute in practice with small funnels on the surface. The air cushion first has to be enriched with diffused moisture. The larger the cushion of air, the longer this process takes. In the case of larger air cushions, e.g. under films or in drill holes (which must be allowed to cool down first), the additional waiting time is at least 30 minutes. Because of this equalisation period and the longer waiting time that may be required, this method is not practical for leak location. The long time taken to scan many points makes the solution unprofitable. On the other hand, the method is very suitable for: Diagnosing mould, addressing the question of: is the air moistening the wall, or is the wall moistening the air? Verifying a different method (where resistance is measured first, for instance, and if the result is not clear the moisture content equilibrium is then measured) Monitoring checks of technical building drying under screeds as well as on plaster Examining readiness for floorcoverings. Only measurement on the surface of the screed is non-destructive, but drilling a hole is more conclusive. The recipe of the material being investigated must be based on a sorption isotherm (determined in the laboratory with the Darr-W ge method) or on own field experience. Complete drying out is identified in residential buildings even without sorption curves, but residual moisture can only be assessed with a sorption curve.

37

Parameters and measuring methods Always remember the following: For funnel measurements: The funnel must offer tight, all-round contact. Tilting or raising it leads to a partial exchange of air, which can prolong the equalisation period. Rough and uneven surfaces cannot normally be measured using a funnel. The funnel must not be warmed up with the hand. However, the effect of the temperature can be negated if the air humidity sensor is used to determine the absolute air humidity rather than the relative air humidity. For drill holes: The heating and drying caused by the drilling process must have abated completely. A waiting period of 1 to 2 hours is recommended. Unless serial drilling/measurements are being carried out on a lot of holes one after the other, a further visit will normally be required. The sealing dowel must have a tight fit. In general: It is normally advisable to note the absolute and relative humidity along with the relevant temperature. The humidity of the room air should also be recorded. If jointing compounds are used to hermetically seal the measuring chamber, these must not give off any water (e.g. chewing gum or water-based jointing compounds are not suitable). Permanently flexible mastic (e.g. as used by the sanitary trade) is very suitable.

38

Parameters and measuring methods 1.4.1.4 Other methods Although the thermal method of infrared measurement that is frequently mentioned (thermography or a non-contact thermometer) is indispensable for locating hot water leaks, the method is not suitable for assessing water content.13 In the chemical CM method, a piece about the size of the thumb is chiselled out of the building material, crushed in a defined procedure, mixed with a reagent and poured into a pressure bottle. Through shaking, the water that is released from the ground sample reacts with the reagent (calcium carbide) and produces the gas acetylene. The pressure rise that this generates in the bottle is a measure of the water it contains. The water contents determined using the CM device are generally lower than those determined using the Darr-W ge method. This fact is already taken into account in the standard limits and values, e.g. for screeds. Limit values are identified as CM % and can only be used in combination with the CM method. For fundamental reasons not all the water contained comes into reaction or the reaction takes place only slowly. That is why the shaking and reading times must be strictly observed. The device must also be examined regularly for pressure tightness and precision of indication; special reagent test capsules can be filled in for this purpose. The CM method is a method that we in Germany all know and recognise (unlike in Scandinavia). This is probably due to its early introduction on the market. Disadvantages are the consumption of reagent, the time-consuming procedure and - if insufficient care is taken - differences in results obtained by a variety of users. As with other consuming processes, the reading is not strictly reproducible (a second material sample which does not necessarily have to be identical with the first is required for verification). Other measuring procedures have the potential to satisfy the required function with the same level of reliability.

13

There are industrial applications in which infrared measurement is used to determine the water content on surfaces. However, there are no instruments of this kind that would be suitable for use on building sites (weight, size, costs).

39

Parameters and measuring methods The best prospects are offered by the moisture content equilibrium method, since this is cost-efficient, does not depend on designs and shows little side sensitivities. As experience grows, the necessary calibration curves are being produced (such as the CM limit values we know today). The microwave method is similar to the scatter field method in its effect, but works with different frequencies and produces greater penetration depths. The probes are roughly the size and shape of a large flashlight and, depending on design, give different penetration depths ranging from 5 to 30 cm. This method too reacts to the properties of the building material (recipe, density) as well as the water content. Metals and the interfaces between building material and air distort the measurement. This means that vertically perforated bricks, with the numerous chambers they contain, cannot be measured. Reinforcing rods can be identified by the higher readings that keep occurring at certain intervals. A microwave measuring instrument has roughly the same dimensions as other handheld units, but is more expensive. Finally, the very cost-intensive neutron probe (Troxler probe) should also be mentioned in passing. It is used with weakly radioactive material and the corresponding handling and transport authorisation documents and is very complicated. Because of the high penetration depth and its shape (similar to an upright vacuum cleaner), it is very suitable for revealing water distribution on flat roofs.

40

The basics of measurement 2. The basics of measurement 2.1 The authority advantage A convincing representation and interpretation of important facts requires a solid basis of data. This solid basis of data is provided by verifiable measurements properly carried out by an expert. Only if the exact and verifiable data and measurements that are obtained are combined with professional presentation and communication of the results, however, will they find broad acceptance across all sections of the population. This acceptance signifies an advantage in authority which can nevertheless only be maintained if the conclusions that are given are actually underpinned by the technology, i.e. there are no gaps in the arguments or data. It is therefore essential to perform the measurements properly in terms of the systems used, to handle the measuring instruments expertly, to document the results clearly and comprehensibly, and to interpret them with the required degree of caution.

2.2 Blind faith in digital technology Even an expert runs the risk of believing what his measuring instruments tell him without reservation. This is even more marked where instruments have digital displays than with traditional pointer devices, because readings given to decimal places give an impression of exactness that does not actually exist. In addition, fluctuations are harder for the eye to pick up than a needle that is swinging back and forth. When performing a measurement, you must always ask yourself: Is the reading obtained at all plausible? Is there a clear explanation for the value? Was it expected to be at that level? Is this value at all physically possible? Am I making a glaring error in how I am conducting the measurement? Can the measurement be reproduced in the event of doubt?

41

The basics of measurement If different readings are obtained when a material moisture sensor, for instance, is repeatedly applied to the same part of the wall, the individual measurement cannot be used. The probable reason is that the position of the sensor is not exactly the same, the surface is too rough, the sensor is not held still, etc. If these chances are to be excluded statistically, a lot of repeat measurements would have to be performed and the mean and standard deviation then calculated. What tolerances can be expected? Inaccuracies can be traced back to several sources: - the sensor - the handheld device - side influences (temperature, salts) - handling differences. - How does the accuracy of measurement compare with the accuracy of the display?

What tolerances can be expected?

42

Example: If a moisture indication of 21 %RH has an error of 5 %RH, it makes little sense to give a decimal place, especially not if this measurement is carried out on a random basis which could deliver very different readings one hour later. No expert should on any account offer a conclusion based on such a value.

The basics of measurement 2.3 The four basic elements of measurement There is more to diagnosis of a building structure than simply measurements. There are four basic elements to it:

Interview Observation

Measurement Combination

Fig. 16: A jigsaw puzzle comprising observation, interview, measurement, combination Observation Experienced inspectors can often deduce the cause of damage from its appearance (observation). Of course, the recognition effect means there is also a risk of coming to a premature conclusion without having examined and then ruled out other possible causes. Measuring technology can offer the critical assistance here that enables a suspicion to be confirmed and other causes to be rejected. Interview The answers provided by the developers are also of great psychological importance. It is better if those concerned feel included. In addition, establishing the timescale over which the damage occurred can often provide valuable information. If interviewees say, for instance, that a damp patch occurred after a very cold period, the possibility of frost damage to the pipes will be investigated and analysed more closely.

43

The basics of measurement Typical questions might be: When did the damage occur? Under what external influences and weather conditions did the damage occur? If there are several symptoms: in what order did they occur? Is the phenomenon continuous or repetitive? If the phenomena reoccur: at what intervals of time or on what occasions? If this interview is carried out, it will often give initial approaches for the best way to carry out the measurements. Combination If the findings are combined together, an all-round picture should finally be obtained. It is not always possible to put the jigsaw puzzle of findings together on site; it often takes several days of intensive consideration for thinking to ripen . In many cases this will also lead to a decision as to how the problem can ultimately be clarified and a solution found during a second visit to the location. Measurement Before measurement begins, it must be clear what the actual problem is. This is often determined intuitively. It is highly advantageous if you are clear in advance as to the readings that your experience tells you to expect and what measurements would prove or contradict a theory. For most cases, it is highly recommended that the readings are recorded exactly. This can be done using a handwritten report, a log produced on a laptop or a paper printout from the measuring instrument. The important details are: date, apartment/room/building component, parameter and ambient climate. Preprinted log forms are very useful. These ensure that nothing is forgotten and mean that the facts are always set down in the same format. You can design these forms yourself, or ready-made forms can be obtained (from the author).

44

The basics of measurement

Fig. 17: Excerpt from a preprinted moisture measurement log form

45

The basics of measurement Supplementary photographs help to recall the process even after a few months and enable further expert processing (this also gives legal certainty in critical legal scenarios). Sufficient experience is essential for many readings to be interpreted. Premature conclusions given to those involved in the process should be avoided.

5

INTERPRETATION

4

RECORDING

3

PERFORMANCE

2

LIMIT VALUES

1

PROBLEM

Fig. 18: Process chain : problem, limit value definition, performance, recording, interpretation

46

Typical applications of building practice 3. Typical applications of building practice 3.1 Locating leaks in pipes If large quantities of water escape from pipes, these are normally quickly identified: the water soaks through the wall or floor within a matter of days. If only a little water escapes, it can take several weeks for the moisture to spread. Such small quantities of water can escape if pipes drip water due to corrosion or soldered joints that have since become detached. Drinking water pipes that are under several bars of pressure often show an ultra-thin, barely visible jet on exposure (the diameter is thinner than that of a pin). Nevertheless, it is not unusual for walls to be completely saturated up to 2 m in height and across the entire cross-section. Once the whole wall is moist, it is very difficult to narrow down the leakage area by measurement. The measuring instrument simply indicates completely moist at every measurement point. If the damaged pipe is located inside a wall, the moisture zone will spread roughly concentrically around the actual leak. If the pipe is in the floor, moisture will penetrate the insulating layer or separating layer from the screed. The water will consequently rise in the walls with a fundamentally horizontal moisture line that can be observed on interior and exterior walls. Leaks in hot water pipes can be easily located using infrared technology. Here the infrared camera is the instrument of choice so that a lot of time does not have to be spent scanning all the surfaces. The coloured printouts (known as thermograms) also illustrate the distribution of the water in a very vivid way (see Fig. 19). The heated zones normally show up clearly. This presupposes, of course, that hot water leaked out. In the case of underfloor heating, it is best to let the screed cool down overnight and start the heating up again about 1 hour before visiting the site. The location of the leaks can then be more easily seen against the cold surface of the floor than if the screed were already uniformly warmed through.

47

Typical applications of building practice

Fig. 19: Thermogram for hot water leaks For cold water pipes, the location of the leak is best narrowed down by using a compact conductivity measuring instrument (e.g. testo 606). There is little need to worry about salt distorting the result in this type of measurement because the period of moisture penetration following a pipe burst is no more than a few weeks. If a moisture pattern on walls indicates moisture under the screed, this can be confirmed by measuring the air humidity in the edge joint. If there is free water below the screed the readings will be in excess of 95 %. Further localisation is impossible using this method as water and water vapour spread in roughly the same way under the screed.

48

Typical applications of building practice

Fig. 20: Measurement in a test hole of a tiled floor If no further localisation is possible (perhaps because a measuring instrument gives an end-of-scale reading everywhere), it is best to trust to instinct and understanding of structural engineering. Now and then there are surprises, especially in old buildings, because pipes run at places no one would ever have suspected. Drawings of the building can be helpful in searching for particular piping in this case. With a drinking water pipe, initial localisation can be carried out by observing the water meter. The loss may of course be slight, e.g. only a few litres per week. That is why it is only possible to establish whether a loss is being caused by a damaged pipe or the like if the building is not occupied for several days and the consumers are switched off. It is important to read the water meter carefully, right down to the last decimal place. If only a slight loss is found, dripping water taps and leaky sink inlets must be ruled out as a cause of the loss (it would be sensible to shut off the corner valves at the start of the observation period).

49

Typical applications of building practice If the water meter does not show any consumption, but the heating system suffers a constant loss of pressure and needs to keep being topped up, further investigation is required. However, low water quantities being lost can also be an indication of leaky pumps or cracked boilers! Caution: In the case of basement flats, moisture under the screed is not always caused by a leaking pipe! It may be that water is also being forced up from the ground, e.g. through the joint between the wall and the floor, the sole plate or even leaking sewage pipes (floor outlets from laundry rooms or the like). All in all, leaks in pipes that are subject to pressure are relatively easy to locate. The plumbing industry offers some special processes such as sound localisation and trace gas snifting devices for the very tough nuts .

3.2 Locating air leaks in BlowerDoor tests, assessing draughts This chapter is concerned with the medium of air. The issues of ventilation heat losses, heatability, draughts, cold air fogging and comfort frequently have to be clarified, particularly where lofts have been converted. Loft conversions have been practically always permeable to air over the last few decades because no attention was paid to the airtight laying of foil.

If proper measurement evidence is to be collected in every single case, the problem must be defined precisely beforehand. This depends primarily on the legal position which the customer finds himself in (e.g. buyer, tenant, landlord, developer, planner). It also hinges on whether claims under private law are to be clarified (warranty periods, deficiencies in construction) or infringements under public law (building regulations, German energy conservation laws). In practice, three questions in particular arise: a) Does the shell of the building conform to the generally recognised rules of structural engineering and rules on energy conservation in terms of airtightness? (This question is often asked in an acceptance inspection focusing on quality assurance).

50

Typical applications of building practice b) Are the draughts or coldness which the occupant is complaining about verifiable and reproducible? In other words, is there a technical reason for them, or is it a matter of oversensitivity? (This question usually arises in disputes between landlord and tenant). c) If apartments cannot be heated properly: - Does the cause lie in the heating system (radiators too small)? - in the building shell (workmanship of air membrane, windows etc.)? - or in the design (arrangement of concrete columns, wide areas of glazing, open-plan floors etc.)? The subsidiary questions under c) often refer back to b) and are aimed at finding those who are responsible (planners, craftsmen etc.). This subject area is actually very complex. For that reason only the basic principles and the application of flow measuring techniques will be explained here. The requirement: the entire shell must be made airtight. This is taken to mean that, assuming the usual differences in pressure between the inside and the outside, no significant air flows will penetrate or escape through walls, ceilings, windows and doors. Air that escapes while the building is being heated results in loss of energy and condensation damage. Air that penetrates brings a perceptible draught and a layer of cold air on the floor (the trend towards airtight structures arose out of energy considerations). The fresh air required for hygiene should be provided through conscientious shock ventilation or even a ventilation system. Airtightness can only be determined for the building as a whole. The only measuring device suitable for the purpose is what is known as a BlowerDoor. It determines the leakage flow quantitatively at an artificially high pressure difference so that natural weather conditions have less of an effect on the reproducibility of the measurement. A certain level of leakage must of course be allowed for given the tolerances used in construction work. The question asked under a) above can normally be answered with the help of a BlowerDoor. The limit values required for such assessments have been laid down in law.

51

Typical applications of building practice

Fig. 21: Fitted BlowerDoor If question b) is to be answered, the places where the air comes in must be known. Here too, a BlowerDoor (see Fig. 21) is useful. It generates the vacuum required for a forced draught (something that only naturally occurs in very strong winds). The inlet points of the air can usually be localised fairly easily by hand: at sockets, underneath sills, flaps in the dividing wall, built-in radiators, roof windows, screed edge joints.

Fig. 22: Smoke pipe/air flow at a socket 52

Typical applications of building practice Once the inlets have been found, it needs to be assessed whether the draught can have an actual impact on the level of comfort. A superficial assessment can have massive financial consequences ( just think of the court cases concerning very high renovation costs). Several factors must be taken into consideration: The temperature of the incoming air The position of the leakage point (hall or corner of the lounge, by the bed or in the shower, height, distance from people) The geometry of the leakage point (slit, nozzle, perforation) The size/distribution of the leakage point(s) The amount of leakage, i.e. the volume flow. As yet there are not practicable means of determining the volume flow of a leak. The form of a leak in window frames or similar locations usually prevents measurement with flow funnels such as can be carried out at geometrically properly defined places (e.g. room air outlets of air-conditioning systems). In addition, the volume flows are too small to be identified as differences in a BlowerDoor measurement. All that can be done, then, is to measure the temperature and the flow velocity. Although these measurements supply an inadequate description, given the lack of alternatives they are applied in the majority of cases. Rule: Air flows have a negative effect on comfort when people are standing still nearby, or even unclothed (the draught from the push knob of the WC cistern is a classic example); critical distance from the throw is approx. 0.5 m the air comes in unbraked from the outside the draught exceeds a flow velocity of 2 .. 3 m/s (assuming a significant volume flow and a differential pressure of 50 pascal) the incoming air is cold and is not heated up as it passes through that part of the building (temperature on entry more than 10 K below the room temperature) a leakage place, if only isolated or even in nozzle form, is of a significant size (about the size of a thumb) a leakage place in the shape of a slit is of significant length (e.g. length of a window casement)

53

Typical applications of building practice the leakage place lets in large quantities of air, albeit it braked, spread out and warmed up (e.g. unplastered floating brick) the incoming air cools down large areas through flushing (e.g. panels in front of sanitary installations, bathtubs or ceiling lining) the air comes in at an outside wall exposed to the wind. The more these assessment criteria accumulate, the more critical the draught is for the comfort level. It does not generally matter whether the actual occupant feels uncomfortable! What does matter is whether an impairment of comfort is felt by the average occupant as described by the guidelines on comfort!14 Even if all the limit values are observed, there will always be some people who tend to complain, whether through greater sensitivity or simply attitude.

Fig. 23: Hot-ball and hot-wire designs

14

54

Although comfort guidelines such as VDI 2080 and DIN 1946 for homes are not binding, the limits they lay down can be useful when it comes to assessing a domestic situation. The measurement points and heights defined in these standards are of particular interest.

Typical applications of building practice

Fig. 24: Measurement at a window joint The velocity of the incoming air is measured with anemometers. Vane anemometers such as those used in meteorology and on air-conditioning ducts are too insensitive and too much concerned with direction for the above applications. Only hot-wire or hot-ball anemometers can be used for assessments of comfort levels. In addition to the flow velocity, they also supply the second important parameter, the air temperature. The geometry of most leakage places cannot be clearly defined. Usually, for instance, it is unclear exactly where and at what distance the maximum velocity occurs. The probe should be moved around slowly until the highest display value is shown. In practice, however, it is hard to keep the display value constant since it is not possible to hold the probe in a constant position. For this reason the decimal places are rounded up or down to half figures. Direct contact with solid materials must be avoided. This causes the spherical head to cool down and give an incorrectly greater flow velocity. Nor should the front part of the probes be enclosed with the hand because this is where a thermal sensor for the comparative measurement is located. The conditions for measurement are important if the reading is to be interpreted correctly. The log must take this into consideration. 55

Typical applications of building practice Example of a log 23.08.2003, Schmidt apartment, leakage place 1 = lounge balcony door, closing joint at bottom Measurement at 50 pascal differential pressure, generated by BlowerDoor installed in lounge door Readings between 2.0 and 3.5 m/s, measured directly on the frame Joint length 70 cm Maximum reading in corner up to 4.2 m/s, measured at distance of approx. 2 cm Outside temperature 2 C, RT 20 C Throw subjectively perceptible by hand at an inlet temperature of 7 C approx. 10 cm Reading there still 0.7 m/s All other joints practically tight (readings below 1 m/s) Position in balcony niche facing south Nearest seating 1.5 m away Underfloor heating => No impairment of comfort expected => Remedy by adjusting height of door. In practice, slight leaks (e.g. on window frames) can usually be remedied by simple measures such as silicone sealant or readjustment. More serious phenomena, on the other hand, are normally the result of moisture barrier foils not having been properly sealed. With such major breaches of building regulations, the cause and the blame can generally be easily proven. In these cases extensive renovation work must be requested. Minor improvements would not bring any significant success. Moisture occurs where escaping warm air forms condensation in the roof layer structure or in frame profiles of windows. Moisture penetration is usually localised. In insulating material, an air humidity sensor can be used to prod for moisture in the fibre layer, the moisture barrier foil having previously been perforated. Air humidity readings approaching 100 % are a sure sign of free water, particularly in structures which are not well ventilated. An endoscope can also be introduced through the same hole to provide a visual check for drip formation and commercially available gripping pliers can be inserted to pick some insulating material. The biggest mental hurdle here is the destruction or dismantling of the lagging. 56

Typical applications of building practice Once this step has been decided on, it is best to cut generously into the moisture barrier foil so that you can reach the relevant places with your hand. Any absence of bonding along the sides of the course - or any other cause, for that matter - must be documented. When cutting into the course, a sufficiently wide margin should be left so that the cut can be closed up again afterwards using special adhesive tape.

3.3 Assessing moisture damage

3.3.1 The problem Many households have to combat moisture phenomena such as chalking paint, disintegrating plaster, salt efflorescence, mildew odours, rotting wood and mould, especially in cellars.

Fig. 25: Example of moisture damage

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Typical applications of building practice In the event of damage, the same typical questions keep needing to be asked: Is the damage old damage or acute damage? Where is the water coming from? How long does it take to dry out? How high is the probability of reoccurrence? The question Where is the water coming from in particular has many different aspects and raises further questions: Are any pipes leaking? (Since this is usually evident from the damage picture, refer to chapter 3.1 for how to proceed) Is the water ground water, moisture from the earth, percolating water, stratum water or just water temporarily blocked? If it is surface water or water from the soil, does it come from sewage or gutter pipes, stair gullies or leaky cisterns? Is water coming in from the outside, or is it being absorbed upwards from underneath ( rising moisture )? Is the water penetrating through a leaking contact joint (between the floor slab and the wall), through the wall itself or only through the sole plate, or when the ground is permeated? Does condensation also play a role? These questions can only be answered with in-depth knowledge of the usual methods of construction and sealing (and their possible failings); fundamental knowledge of soil and water load types; sufficient experience. Complicating factors are that there may be a combination of causes; water ingresses cannot usually be reproduced exactly; access is often difficult. Provided that you have the knowledge listed above, the following information should help you to narrow down possible causes using measuring techniques.

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Typical applications of building practice 3.3.2 The procedure The first step is to have details of how the damage arose explained. An external inspection is then carried out and all statements and observations are noted. Normally a suspicion as to the cause and the structural defects will already be starting to develop in this stage. The next action is to determine the moisture condition. This is done most easily and quickly by a pin-type conductivity measuring instrument. The pins of the measuring instrument are pressed into the plaster. The important thing here is to ensure a uniform depth of impression. If the pins are suspiciously easy to press in, it can be assumed that the plaster is highly fatigued and that the water has been having an effect for a long time. Additional measurements are carried out at several places in order to ascertain the wall height up to which noticeably high readings are obtained. In most cases, for instance, the measuring instrument will indicate the same level of moisture at 5, 10, 15 and 18 cm, but this will suddenly decrease from 20 cm. This height is then marked. A moisture horizon can then be drawn by combing the markings of several adjacent measuring columns . Normally the moisture horizon that is determined in this way corresponds to the visible moisture horizon (darkish colouring, flaking paint etc.). If the measured moisture horizon is lower than the visible one, it can be assumed that the wall is in the process of drying out. It is rare for the measured horizon to be above the visible one.

Moisture horizon

Fig. 26: Measurement points and moisture horizon 59

Typical applications of building practice To be able to assess whether the moisture is drying out or increasing, it is best to repeat the measurement in 2 weeks. The readings must of course be recorded. They can be noted down either in a log or directly on the plaster (unless renovation is to begin immediately). The measurement points remain visible due to the punctures. When measuring a second time, push the pins in immediately beside the old impressions, not into them. This measuring technique is not suitable in the case of severe salt efflorescence and wet wallpapers (or even aluminium-backed wallpapers). To get measurements that are at all reliable in such cases, the wallpaper should be stripped, the salt fluff brushed off and flaky plaster removed. It may be that the measurements are unusable anyway due to constant end-of-scale readings. There is then no other choice than to use the scatter field method. Because of their hardness, cement plaster or joint mortar often do not allow the pins to be pushed in far enough. Here too, the scatter field method is recommended. The scatter field method is based on a grid pattern. It is important to record the measuring grid and the orientation of the probe precisely in the log or directly on the wall. Several consecutive measurements should be performed at one and the same measurement point in order to determine the scatter. The substrate may be too uneven for reproducibility to be achieved! Wallpaper should always be removed. It has proved to be useful to scale the measuring instrument accordingly. This scaling must be recorded and reproducible. A good zero point can be obtained by holding the probe freely in the air and giving this situation a reading of 0 . The other extreme, 10 , can be obtained by holding the probe in a full bottle of mineral water. With such a scale gypsum plaster will then produce readings of between 1.0 (dry) and 6.0 (moist). Since the room climate and the weather also have an influence on the moisture of the plaster, every grid measurement should be accompanied by a comparative reading taken at a dry section of wall of the same material.

60

Pa

Typical applications of building practice Important! Measurements are distorted by: 1. Inhomogeneity in the substrate material 2. Measuring in corners or along edges

Fig. 27: Grid measurement on a wall

Direction of measurement

Ventilation grille Direction of measurement

Left wall

Right wall

Partition wall

Partition wall

Hairline crack

Shower pan

Shower pan

Bath tub

* hollow, lying

Fig. 28: Grid measurement analysis table with colour scales 61

Typical applications of building practice Grid measurements covering wide areas can easily produce more than 30 measurement points. It may then be helpful to use a spreadsheet software based e.g. on EXCEL for the purposes of recording and analysis. Worksheets can then be superimposed on each other in order to highlight the differences in colour. Drying-out areas can be shaded green, for instance, areas becoming more moist shaded red, and readings remaining the same indicated with yellow. The moisture pattern and drying-out process can then be seen at a glance (see Fig. 28). Readings that remain the same after initial drying out indicate that the wall has dried out as much as it can under actual building conditions. The optimal solution is to combine both measuring techniques, conductivity and the scatter field method. Drying-out and moistening processes are clear if they are reflected in the readings obtained through both methods. In addition to dividing into grids and repeat measurements, it is also possible to create a moisture profile both for height and in wall cross-sections. This is done using brush probes and the conductivity method. The assessment requires a sufficient number of holes to be drilled, with the brush probes being pushed in progressively. This allows the moisture distribution at different depths to be established. It can then be illustrated by colour coding in a table or diagram. This measurement can be repeated at a later date in order to pick up any trend over time. The holes must always be sealed tight between the measuring dates.

3.4 Assessing mould damage The assessment of mould damage is one of the most complex tasks to do with moisture and its measurement. Absolute care in applying the system, conscientious logging and plenty of experience are essential requirements for reliable reports. The consideration below is limited to aspects relating to the physics of construction. The health aspects of mould damage can only be assessed on an interdisciplinary basis, i.e. in conjunction with a structural biologist and a doctor. The cases in which this is required, however, are few and far between.15

15

62

For an initial assessment of whether the number of spores in the room is hazardous, leave a petri dish set open for 1 hour. The number of mildew patches that form is counted later and can also be analyzed by type.

Typical applications of building practice 3.4.1 Procedures in an inspection At this point it is again referred back to the information provided in chapter 2.3. Observation and questioning are invaluable sources of information without which no serious assessment can be made. In addition to the measurement, for instance, it is important to know: the occupation density of the flat, the lifestyles of the occupants, the number of house plants, weather phases, the direction the flat is facing, structural heat bridges, the timing of structural measures or incidents. Good preprinted log forms are highly recommended. They will ensure that the important things are not forgotten. If you do not want to produce them yourself, ready-made ones can be bought (from the author). The details that should be asked for and observed can be established in TESTO building moisture seminars and symposia for experts!

Fig. 29a: Extract from mould report, page 1 63

Typical applications of building practice

Fig. 29b: Extract from mould report, page 2 A first inspection can be carried out at any time of year. Should it prove to be the case, however, that mould is the result of condensation rather than moisture penetrating from the outside (broken pipes, faulty washing machine or the like), measurements can only be performed during cold parts of the year (i.e. when heating is switched on). The following sections explain how the measuring technique can be applied methodically.

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Typical applications of building practice 3.4.2 Short-term and long-term measurement The aim is to record the ventilation conditions of the apartment through measurement in as representative a way as possible. This means that the rooms must be measured when in a condition typical for the lifestyle of the occupants. In other words, the presence of the person doing the measuring should not have a significant impact on the moisture balance.

How should you proceed? Ideally, visits will be unannounced; If they have to be announced in advance, note whether ventilation was provided specially for your visit; Close the front door behind you immediately; Start measuring at once, before the air humidity is altered by your presence. Remember the time the probes need to acclimatise, though. Measurement should be performed on every visit in order to gain an impression of the situation at that moment in time. However, only long-term measurements, which should take place over at least 2 and preferably 3 weeks, are really conclusive, especially when it comes to legal disputes. Untypical occasions should be avoided, e.g. Christmas, holidays, when visitors are staying. If it is only an assessment of the ventilation and average air humidity that is required, the measurement can be carried out in November, a period of increased mould occurrence. If, however, heat bridges are also to be recorded, the measurement must be performed during a period of frost lasting for several days. Of course, the planning is dependent on the weather.

3.4.3 Measuring location When measuring with handheld devices, it is no great problem to measure in several rooms. There are significant temperature and moisture differences between bathrooms, kitchens, lounges and bedrooms, and these differences can be crucial. Long-term recording is only carried out in rooms under attack from mould because the normal user does not have an unlimited number of data loggers. In most cases the bedroom is the critical room. 1 or 2 loggers should always be located here.

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Typical applications of building practice If I want to establish whether there is a risk of condensation in a corner or on the floor, I have to measure at exactly these points. In the case of mould, the positioning of the probe in the room is obvious as it marks condensation by visual means only. Any moisture penetration from the outside must be ruled out. A further interesting question is whether the occupants keep to specifications or average values for air humidity. Recommended values for air humidity and air temperature always relate to a height of about 1.40m in the centre of the room. This is taken from the comfort standards referred to in chapter 1.1.2. If the actual is to be compared with the target , it is therefore essential to measure in the centre of the room. This applies for both one-off and constant measurements. A centre of the room can be taken to mean any place that is further than 50 cm from the wall. Poorly ventilated niches or similar locations should not be taken into account. The following side constraints must be borne in mind when positioning the air probes: Positioning probes on or even in cabinets or cupboards delays the recording of measurements because of the temperature inertia of that piece of furniture and the restricted circulation of air. However, the readings that are obtained can still be used to form mean values. Temperature and humidity peaks and ventilation phases are not recognised, though. Heat or moisture sources nearby distort the result. Probes should not be attached to lamps or near computers, radiators, dog baskets, aquariums or the like. No sunlight should fall on the sensor at any time of day. If the measurement is for diagnostic purposes, the device should be located in as inconspicuous a place as possible. If the measurement is for indicative/informative purposes, the sensor can remain visible.

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Typical applications of building practice 3.4.4 Recommended programming for loggers used to record room climate Measuring instruments for long-term recording are also called data loggers. They may be programmed to your requirements, e.g. with regard to measuring limits, clock rates, number of readings, start and end of measurement. The programming, and especially the analysis, are demonstrated thoroughly in TESTO s 2-day seminars. Measurement should start when the instrument is put in position. Since experience has shown that occupants tend to make more effort at ventilation in the first couple of days and then fall back into old habits, measurement can also start 2 or 3 days later. The end of measurement should be when the instrument is collected. To avoid any distortion of the mean values that can be determined using the software, it must be ensured that no data not relating to the apartment (e.g. on a long journey back or in the office) are recorded after the actual measurement period. The advantage of an open-ended measurement period is that the device can be left in place for a little longer, e.g. to wait for a frosty period. The clock rate depends on the particular problem. If only the average air humidity prevailing in the apartment is of interest, hourly measurement is always enough. If ventilation periods (times when the window is open) are to be recorded, a clock rate of 2 minutes is recommended. If only the periods when the window is open are to be recorded, the air sensor can be located immediately beside the window. The differences in the readings will then be larger and more sudden. The measurement limits are set to reflect the living conditions, e.g. in the temperature range of 0 to 30 C or the humidity range of 20 to 85 % RH. The choice of sensor will also depend on the particular task. If heat bridges are to be assessed, or the hours of operation of the radiator, sensors for recording surface temperature are located in the coldest corner or on the radiator.

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Typical applications of building practice

Fig. 30: Mounting of a lamina sensor

3.4.5 Narrowing down the causes It takes experience and analytical thinking to interpret the measuring results. The following questions in particular must be answered: In the case of excess air humidity: Where is it coming from? From the occupants (presence, showers, drying clothes etc.), from house plants etc.? Why is the humidity increasing? Is the room not ventilated often enough? Only with the window in a tilted position? No through-ventilation? Does the rhythm of life make it more difficult to have regular ventilation periods? Why is the condensation occurring? Are the walls as cool as can be expected from an intact building fabric, or much colder? Would condensation occur even if the building was well insulated, because the air humidity is extremely high? The last block of questions is extremely important for legal cases, especially with regard to the rectification of defects, reductions in rent, the assumption of court costs, rights of termination etc. The problem of heat bridges will be examined in more detail in the next chapter. 68

Typical applications of building practice The key question: Is it the case that 1. given conscientious ventilation and heating (such as is appropriate and reasonable for homes) and 2. given the usual winter weather (such as is typical for this region), the building component is indisputably taking several days or even longer to cool down, and in such a way that the temperature of the surface of the building component comes to within less than 3 K of the dew point temperature?

An assessment of this question demands the extensive measuring and recording of the frequency and duration of the ventilation periods (or the functional capability of a ventilation system); the type of window ventilation (tilting or swivelling, through-ventilation or individual aeration); the average air humidity and air temperature in the centre of the room; the operating times and temperature of radiator(s); the influence of furniture on the additional cooling of wall surfaces behind them; the (inside) surface temperature of the critical building component zones; the air temperature outside; the (outside) surface temperature of the critical building component zones (only on east, west or south-facing sides, as the effect of sunlight there can lead to heating up to above the air temperature). This measuring task cannot be performed using one single data logger. That is why two or three loggers are used instead. Of course, these will have to be synchronised first and calibrated in exactly the same way. The measuring curves can be combined in the software.

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Typical applications of building practice 3.5 Assessing heat bridges

3.5.1 The problem and its importance In the case of mould damage, the standard question can be summed as follows: Who is at fault? Is it the occupants, with their ventilation habits? Or is it the landlord/vendor, with the deficient building fabric of the building? For these questions to be answered, heat bridges must be recorded and evaluated.

3.5.2 Types of heat bridge Heat bridges are taken to mean places in the building fabric which become particularly cold under winter conditions. Every wall and every floor has areas which are colder than the rest of the surface. These are normally edge and corner areas. This is where better heat dissipation from the inside to the outside takes place, with 2 results: The temperature on the outside of the building component rises, greater heat is given off into the environment and energy losses increase heating costs. The temperature on the inside of the building component falls, the cold surface tends to form mould and condensation and the comfort level is diminished.

Different types of heat bridge must be distinguished: dimension-related heat bridges: these are places at which the building component has thinner dimensions, e.g. radiator niches, roller blind cases with only thin cover plates. material-related heat bridges: these are places at which an unsuitable building material (i.e. that dissipates heat well) was used, e.g. steel girders, concrete columns, brick noggings of former window openings, gaps in masonry filled in with concrete.16 geometry-related heat bridges: these are places which have a cooling rib form in the widest sense, i.e. their outer surface is larger than their inner surface. Where this is the case, the heat radiated to the outside exceeds the heat absorbed from the room, e.g. on cantilever plates, fascias, window lintels and embrasures and eaves. Essentially, every corner of a house is a geometric heat bridge! 16

70

Strictly speaking, these even include all brickwork joints, as thermography demonstrates. However, these are irrelevant in practice.

Typical applications of building practice Geometry and material-related heat bridges usually occur in combination. Where parts jut out, they are normally made from steel or reinforced concrete!

Fig. 31: Geometric heat bridge under attack from mould

Fig. 32: Geometric heat bridge, 2-dimensional (schematic diagram)

71

Typical applications of building practice In practice, the critical heat bridges are: cantilever plates on balconies (especially if they are not thermally isolated); projecting concrete roofs underground garage ceilings with only screed insulation, but no insulating layer on the garage side (see Fig. 33); concrete post and lintel constructions with brick-lined compartments.

Cooling down

Heat dissipation

Fig. 33: Underground garage ceiling with heat flow

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Typical applications of building practice 3.5.3 Recording heat bridges How can heat bridges be quantified? There are three possible ways: 1. If it is a standard heat bridge, then values that have already been calculated in a heat bridge atlas can be referred to. A large number of standard solutions have been worked out for wooden constructions and sand-lime brick structures. These are no longer critical in practice because they have already been optimised. The situation with old buildings, though, rarely or never fits in with such standardisation. It is also difficult to record the situation for an old building in any case (crosssections, apparent densities, lambda values) or to identify whether it corresponds to a standard situation. 2. The critical cross-section of the building component is recorded and the materials used are determined. These findings are then used to prepare a CAD model by which the cooling can be determined by computer. The difficulty here is computing not just for 2 dimensions, but at greater expense for 3 dimensions. There are heat bridge programs which can do this, but calculations and CAD conversion take several hours to organise. There is also the issue of what inaccuracies there will be. This is because simulations use material data which likewise have tolerances and do not necessarily correspond to the material as it was actually consumed in the building (the material controls and product quality for old buildings cannot be compared with the situation as it is today!).

Destructive analysis

Computer simulation

Care must also be taken to ensure that the correct inside and outside air temperatures are included in the calculations. Should standard values for the outside temperature be assumed? Or realistic values for the particular region? What inside temperature should be applied? Those that are used in DIN 4108 or the actual temperature, which depends on the position of furniture, the arrangement of radiators, intake temperatures, floorcoverings etc.? Finally, there is the question: does a stationary calculation come sufficiently close to real life, or should non-stationary calculations, i.e. with day/night fluctuations, be performed?

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Typical applications of building practice Given the complexity of the issues, the author tends towards the following solution: 3. Measurement on the living object. Here the surface temperatures as they occur under typical winter weather conditions are recorded. The main advantage: There is no need to survey and analyze the building components. Determining the cross-sections and building materials is actually normally destructive (core drilling, removal of bricks)! It also avoids the discrepancy that occurs between the standard situation and the actual regional or local climatic situation. What use is it if standard conditions say that no condensation occurs, if it does actually occur in practice?

Measurement under ideal conditions

The main disadvantage: It is essential to find a suitable measuring period in which a) the living situation is typical, and b) the weather is typical for the winter. The extent to which a measurement carried out in warmer weather can be extrapolated down to colder weather would be an interesting subject for a thesis or student research project!

Author: Martin Giebeler 74

Assessment of the heat bridge, however quantitatively it is described, is another whole area of debate. Standards offer insufficient means for assessing heat bridges in old buildings in particular. Only recently, in DIN 4108, have heat bridges even been described. The status of standards does not always coincide with common practice, which is of course of considerable importance when establishing the generally recognised rules of the art . The assessment of heat bridges is thus a typical task for an expert inspector and goes beyond the scope of this guide. Whether one ultimately prefers simulation or measurement, it is important always to be clear about the lack of precision. It is not proper to assign cause and guilt on the basis of decimal places or half a degree Celsius if the underlying assumptions or boundary conditions can only be described roughly . In practice, unfortunately, disputes about heat bridges always come down to a matter of just a few degrees Celsius! This does not of course mean there is no point in calculating and measuring. If building experts do not measure, the level of uncertainty will be all the greater, helping no one. Being aware of our limits should encourage us to carry out all investigations and measurements using suitable equipment and the requisite degree of care!

Reference to other field guides 4. Reference to other field guides For measuring air flows and surface temperatures and for requirements relating to heating, we recommend the other user guides from this series: Ambient Air Measurement for Practical Users

Ambient Air Measurement for Practical Users °C

% RH

td

g/kg

hPa

m/s

m3/h ppm CO ppm CO2

tes to

tes to

.14 45

mA

063 8

tes

to

tes

to

tes to

rpm

a edición 21st edition revisada

mV

75

Reference to other field guides

Manual for Infrared Measuring Technology

Manual for Infrared Measuring Technology °C

76

Reference to other field guides

Heating Measurement Technology

Practical Handbook

Heating Measurement Technology

Full of useful information

°C

O2

CO

NO

NO2

NOx

λ/qA

Efficiency

3rd Edition

77

General

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