Research Paper.pdf

A REVIEW ON VERNACULAR INSULATING MATERIALS OF BHUTAN Ngawang Dema 1, Roma Adhikari 2, Chimi 3 College of science and Technology, Royal University of Bhutan Email: [email protected] , [email protected] , [email protected]

Abstract The building industry contributes to maximum impact on the environment consuming a substantial amount of the world’s energy. Vernacular buildings have evolved with minimal effect on the environment and preserved the natural resources for future generations. This study is a comprehensive review on how vernacular materials are adapted to its climate and geography providing thermal comfort to its occupants. Vernacular architecture was divided into three archetype according to the climatic and geographical zones. A thorough review on each of these zones has been made through literature review and case studies and a comparative analysis has been done to determine and conclude that the vernacular materials are indeed the most suitable materials to provide thermal comfort in a building envelop. Keywords: vernacular materials, geographical zones, thermal properties, thermal comfort.

INTRODUCTION Globally, buildings consume approximately 40% of the

materials that are not only sustainable during the

world’s total energy annually in developed countries and 10-

construction but also during its operation and after

15% in developing countries.(Omer, 2008, Robertson , 1992)

demolition. Thermal insulation is a very crucial

.Most of this energy is being utilized in the building’s heating,

aspect of a building design to reduce energy

ventilating and air conditioning (HVAC) purposes (Omer,

consumption by heat gain and loss through

2008). Throughout a building’s life time (construction,

various fenestrations (openings) and poor thermal

operation and dismantling) it has a direct impact on the

conductivity of the building materials.

environment, through resource and energy consumptions. (Revuelta et al., 2010), therefore it is essential, we use

Bhutanese construction practices were an outcome of trial and

Traditional village farmhouses throughout the

error method which were influenced by the culture and

country, follow a common prototype, with little

traditions of the country (Dujardin, 1994). These vernacular

variations in use of material and construction

construction techniques evolved through time and were

techniques (DoWHR, 1993; Dujardin, 1994).

predominant till modernization started in the country.

While

In

adobe/

rammed

earth

construction

order to keep up with the advancement in the modern times,

technique is extensively used in western part of

Bhutan started adopting various construction materials and

Bhutan, stone is preferred in central and eastern

techniques which were actually designed considering the

Bhutan, whereas, bamboo mats covered with

warm climatic conditions of India. These techniques are

earth plaster is the material used in southern

inappropriate

Bhutan. (Nock, 1995; Herrle et al., 2014).

to

the

climatic

conditions

of

Bhutan,

deteriorating the construction quality and minimizing the application of thermal insulation techniques leading to poor thermal comfort for the occupants (DoWHR, 1993; Jentsh, et al., 2017).Over the decades the vernacular houses have progressed to endure the harsh climatic conditions, rugged terrain and culture. Builders were restricted to conventional technologies and locally available materials. They were responsible for promoting climate orientated passive building

Figure 1: Topographic map of Bhutan.

technologies for heating and cooling, at the same time

(Source: South Asian Floods)

enhancing the energy performance for the buildings. These buildings are an answer to sustainable technologies and with

Table 1: Climatic zones of Bhutan (Source:

the principle of “learning from the past” the research is carried

DANIDA, 2008)

out with emphasis on thermal insulating properties of

Region

Climate

Elevation

ation

vernacular materials found in the eastern, western and southern regions of Bhutan.

Southern

Subtropical,

100

foothills

high humidity,

1,500 m

2. CATEGORIZATION OF VERNACULAR ARCHITECTURAL REGIONS The geography, climate and the culture of a region determines

Precipit

to

5,500m

heavy rainfall Inner

Cool

Himalayas

hot

m

winters,

1,500

summers,

300 m

to

1,000 to 2,500

moderate

the type of construction material, techniques and architecture

2,500 to

mm

rainfall

(Zhai, 2010). The topographic map in figure one and table 1 shows that Bhutan is categorised by three distinct climatic regions: the alpine conditions of the High Himalayas to the North, the more temperate highland climate of the Inner Himalayas in the centre of the country and humid subtropical conditions to the South (Dujardin, 1994, Jentsch, 2017).

Higher

Alpine,

Himalayas

summers, cold winters

cool

3,000 7,550 m

to

500

to

1,000 m

3. CHARACTERISTICS OF THERMAL

3.2 ROOF MATERIAL

INSULATION TECHNOLOGIES IN

Bhutanese roofs are characterized by high

BUILDINGS COMPONENTS.

pitched roof with deep eve board and wide roof overhangs as a climatic response to heavy

3.1 BUILDING ENVELOP

snowfall in the Inner Himalayas and heavy

Generally, building envelop constructions can be

rainfall in the southern foothills (Chuki et al.,

categorised into massive and lightweight

2017). Commonly used roof materials in

structures and it differs according to the climatic

traditional dwellings consists of stone (slates),

regions. Figure 2 demonstrations the wall mass

wooden shingles and thatch as shown in figure

in each of the climatic zones. While Alpine and

3 and 4. Initially seasoned wooden shingles

Sub- Alpine regions require massive building

placed on the timber truss secured by stones

mass, sub-tropical regions require light weight

was used as roofing material in the inner and

structures. (Zhai & Previtali, 2010) The

higher Himalayas. However, slate roofing

temperate regions combine both massive and

replaced the wooden shingles due to its

light weight structures. It should be noted that

durability. In the southern foothills thatches

many vernacular dwellings observed combine

made up the roofing material.

massive walls with lightweight roofs, most frequently thatch roofs. As they were frequently observed in temperate and hot climates. They are commonly combined with loose infiltration to facilitate natural ventilation. Portable structures used by nomadic people such as tents, lean-tos, tepees and yurts also fall into this category Figure 3: Thatched Roof (source: Mr.

BUILDING MASS IN WALLS

Dhrubaraj Sharma)

100% 80% 60% 40% 20% 0% high altitude

temperate massive

humid subtropical

light

Figure 2: Observed wall mass in percentage Figure

4:

Wooden

(source: Yankee blog)

Shingles

Roof

3.3 WINDOWS AND DOORS

4. THERMAL PERFORMANCE

Bhutanese dwellings comprise of minimal

OF TRADITIONAL DWELLINGS

windows in the building façade. These windows were small and fabricated out of timber. The shutters were made of wooden panels reducing

4.1

TRADITONAL

RAMMED

EARTH

BUILDING IN WESTERN BHUTAN

the solar gains and minimizing daylight. In

Traditional houses constructed of mud maintain a cool

central and western parts of Bhutan, the main

interior temperature than the exterior air temperature in

façade of the building consists of elaborate bay

early summer, retaining an adequate natural cooling

windows called Rabels as shown in figure 5.

effect when outside daytime temperature is unpleasantly

While the windows in the southern foothills are

warm. While the summer heat tends to heat the building

orientated in such a way that they keep out

mass, natural ventilation enables sufficient cooling

direct sunlight as displayed in figure 6. Buffer

during the nights. Due to the heat storage effect in the

spaces such as verandas are placed in the

building envelop, indoor temperature tends to be above

southern façade in order to allow cross

the outdoor temperature in early fall. In late spring, due

ventilation, cooling the spaces while providing

to the same time lag the temperature of the structure falls

thermal comfort to the occupants.

below outside air temperature, and hence windows have to open to admit the sunlight for heating to avoid extra heating. The dotted line in graph below represents the approximate seasonable temperature lag in building interiors that results from using materials that have a high capacity to store heat in the western area. (Watson and Bertaud, 1976)

Figure 5: Traditional house in western Bhutan (Paro) Source: Bhutan nun’s foundation

Figure 7: Graph representing seasonable temperature Figure 6: traditional house in southern bhutan ( samtse) Source : ( Purna kumar, panoramro google maps

lag (Watson and Bertaud, 1976)

The design of protected courtyard spaces is an

The timber rammer is one ended, with a thin handle

obvious response to the severe wind condition. By

and a heavy round timber end. (Jaquin, 2011)

creating outside courtyards that benefit from direct and reflected radiation, with south-facing walls and windows devised to maximize direct solar heat gain in winter, the artificial heating requirement of the house can be minimized as shown in figure 8. In contrast, the construction of recent buildings have used concrete blocks as wall construction, which does not offer either the thermal capacity of resistance to create comfort without a greatly increased reliance

Figure 9: Rammed earth construction with put

upon artificial heating. (Watson and Bertaud, 1976;

logs in Punakha. Source: (Jenin Bhutan)

DoWHR, 1993).

4.1.2MUD AS INSULATING MATERIAL The thermal performance of rammed earth is measured in a number of different ways. Houben & Guillaud (1994) claims that for rammed earth the thermal storage is around 1830 J/m3 C. According to Standards Australia (2002), a 300mm thick rammed earth wall has an R value ( thermal resistance) between 0.35-0.70 m2 K. Minke (2000) claims that the U-values( thermal transmittance) for

Figure 8: courtyard in central Bhutan. Source: (Art Photo Travel)

a 300mm thick rammed earth can be as much as 1.92.0 W/m2 K. Rammed earth, is a dense material,

4.1.1 RAMMED EARTH CONSTRUCTION

has poor insulating properties.

The rammed earth construction in Bhutan uses the

4.1.3 Case study on Rammed Earth dwelling

characteristic ‘putlog’ holes (figure 9) used to support formwork, and the wall is vertical, rather than tapered towards the head. The formwork here is supported on timbers running through the center of the wall, leaving putlog holes. The forms are supported using a solid timber piece over the top of the formwork box, fixed to the head of vertical timbers, which have wedges driven between them to keep the formwork boards apart.

In a research conducted by Mark F. Jentsch, Christoph Kulle, Tobias Bode, Toni Pauer, Andrea Osburg, Tenzin, Karma Namgyel, Karma Euthra, Jamyang Dukjey, Karma Tenzin, (2017) a comprehensive

field

study

on

the

energy

performance of a traditional farmhouse and seven other building types were carried out.

Located in the inner Himalayas, the building mass of the farmhouse (figure 10) is made up of massive rammed earth of 77cm thick walls (figure 12) with timber framed rabsel. Ceilings were made of timber with mud plaster, and wooden flooring. The thermal conductance of a wall orientated north was conducted for the duration of 3 nights in indoor climate and it was noted that the indoor climate was dependent on temperature and humidity. The airtightness test could not be conducted due to missing window panes and large cracks in rammed earth wall.

Figure 11: Graphs showing internal and external temperature along with absolute and relative humidity. Figure 10: Farmhouse in Western Bhutan The graphs shown in figure 11 illustrate the variation in indoor and outdoor temperature and humidity and response of building envelop to these variations. While there is huge variations in the outdoor temperature and humidity, the indoor conditions are maintained almost constant. Figure 12:77 cm Rammed earth.

It was inferred that rammed earth walls typically

durable. The propelling monuments of our

have a gross dry density of 1800 to 2200 kg/m3

fortresses are an example of its longevity. Due

(Schroeder, 2013, Jentsch et al., 2017). Therefore,

to the lack of information on the thermal

it was assumed that the rammed earth wall

conductivity of stone in Bhutan, the following

investigated in Bhutan had a gross dry density of

data has been inferred in order to analyse the

2000 kg/m3 for which DIN 4108–4:2013 specifies

thermal performance the material.

a thermal conductivity of 1.1 W/m2 K. It was concluded that the traditional rammed earth walls have a thermal transmittance i.e, U value of 1.11.2 W/m2 K, which is better than contemporary wall with brick as a infill material which has 1.25 -1.45. W/m2 K. It was also found that rammed earth walls lacked air tightness due to the presence of untreated wall surfaces which tend to incur big cracks. Therefore it can be assessed that rammed earth construction has high potential in thermal insulation if the drawbacks are taken care of during the construction phase itself. 4.2 STONE MASONRY IN EASTERN BHUTAN.

Nienhuys (2012) in his research carried out in the Himalayan region, concluded that Stone masonry are poorly insulated and extra heat is lost from poor window designs. Providing thick wall surfaces increases the insulation value of the building. The thermal properties of stone masonry can be improved by combining stone with various other modern insulating materials such as foam and introducing cavities in between masonry walls. Another research conducted in College of Science and Technology, Bhutan by Tshewang Lhendup, Pravakar Pradhan, Tandin Wangchuk and Yeshi Choden (2017) enhanced the need for

Most traditional houses in the eastern regions

thermal insulation techniques in Bhutan and

are built of massive unreinforced stone

testified that thermal insulation should have a

masonry. Random rubble, dressed and semi-

low thermal conductivity, often less than

dressed stone masonry with mud mortar are

0.1W/mK and high heat conductance. It was

commonly found in these regions (figure 14).

found out that a stone having density of 500

Stones masonry farmhouses have double wythe

kg/m3 had Heat conductance of 1.15 kJ/h.mK

(figure 13) stone bearing walls, and timber

with Specific heat capacity of 1 kJ/kgK. Stone

floors and roof support systems. The masonry

has better thermal conductance than concrete

walls are vulnerable to seasonal changes

blocks which has thermal conductance of only

leading the mud mortars to crack and weaken

1.04 kJ/h.mK.

the structures. However if proper construction quality is maintained, these structures can withstand the harsh climatic weathers are

average which is above the human comfort level; as a result, the interior of the house is heated at night to temperatures above the outdoor ambient. (Watson and Bertaud, 1976). Adobe has low thermal conductivity and high heat capacity enabling earthen building thermal stability compared with concrete building. The research on a house entirely constructed out of Figure 13: Stone masonry wall Source : neinhays 2012

soil, sand, cow dung and other materials that are not energy intensive found out that approximately 370 GJ of energy can be saved per year. The energy payback time for adobe house was found out to be 1.54 yrs. Mitigation of carbon dioxide was reduced by 101 tonnes per yr. (Revuelta et al.,2010). It was also found out that thatch (reed) having a density of 500 kg/m3 has a heat conductance of 1.15 kJ/ h.mK with a specific heat capacity of 1

Figure 14: Stone masonry structures in Merak. Source: Yankee Blog

KJ/ kgK which is similar to thermal properties of stone. On the other hand mud blocks of density

4.3 ADOBE IN SOUTHERN BHUTAN

1731 kg /m3 has a heat conductance of 2.7 kJ/

Climatic design in tropical lowland areas of

h.mK and specific heat capacity of 0.88 KJ/ kgK,

Bhutan requires light weight structures with low

( lhendup et al., 2017) proving to be ideal for use

thermal capacity and maximum provision for

in hot humid regions to keep the heat gain at a

ventilation during all parts of the year, with

minimum and optimizing the thermal comfort.

particular attention to protection against winddriven rain. This basic prototype can be found in the region (figure 15) Masonry structures that are presently used, provide the discomfort of overheating. In a hot-humid zone, the temperature variation between night and day is small; the temperature of masonry approaches a seasonal Figure 15: Typical rural house in Lowland Bhutan. Source : ( Dhrubaraj Sharma)

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