Insulation101

Residential Insulation Michael J. Currie GrotonLocal.org 10 October 2007

Why we insulate?

To slow the transfer of heat -Heat is the form of energy exchanged between objects of different temperatures!

Outline     

Building Envelope R-values Insulation Types Insulation Case Study Other insights  Health Factors  Installation  Tax incentives

 Discussion

Building Envelope -- the “skin” of your structure The building envelope consists of all the surfaces that separate the controlled space from the uncontrolled space.  Primary envelope is the exterior of your home  Secondary envelope is a controlled space that bisects an uncontrolled space -- ductwork in attic, pipes in basement, refridgerator, hot water heater

 Thermal bridges are lossy pathways across the envelope

To maximize efficiency of the home, all envelopes must be properly insulated.

R-values  Industry measurement of the resistivity to heat flow, inverse of thermal conductivity (U)

R = 1/U  Higher R-values (more insulation) prevent heat flow Material

R-value

Outside Air Film

0.2

Siding Wood Bevel

0.8

1/2” Plywood Sheathing

0.6

Fiberglass Batt

11.0

1/2” Drywall

0.5

Inside Air Film

0.7

Total Wall

13.8

R = R1 + R2 + R3 + … Units: ft2 .°F.hr/BTU

R-values cont’d

1 "Heat = (THOT # TCOLD ) Area R Factor

Energy Usage

R-value

Amount of energy you must supply per hour

Temp Difference Area

This is the basis for your insulation strategy!

!

Example - Your front door 1 "Heat = (THOT # TCOLD ) Area R 1 170 = 3.7 BTU/hr

(65 " 25)

21 (3’ x 7’)

Annual heat loss is equivalent to 5 gallons of fuel oil. (1 gallon fuel oil = 140,000 BTU)

!

!

!

Recommended R-values 38

38 49 38 25 11 to 22 30 Band Joist

19

10 11

Types of Insulation

R per inch 3.1 2.1 2.2 - 3.7

4-6.5

various Source: DOE Insulation Factsheet

R-value caveats  Insulation manufacturers measure R-values in a lab, not in the real world…  “Center of Cavity” -- only insulation, no structure,WYSIWYG  Clear Wall -- wall w/ minimal studs  Whole Wall -- wall w/ windows, corners, etc.

For a 2x6 wall w/ R-19 batts and studs 24” o.c. Center of Cavity

Clear Wall

Whole Wall

21.6

16.4

13.7

2/3

Source: Oak Ridge National Labs

Extreme Cold Air and Moisture degrade R-value performance of batt and loose fill insulation

Moisture -7.5% per 1% moisture Extreme Cold

Heating and cooling days 



Degree day captures the average temperature below the typical heating set-point of 65° F Example: 10° F average temperature gives 55 degree days

 Heating Days 6000 degree days

 Cooling Days 500 degree days 1400 1200 1000 800 2005

600

2006

400 200 0 Jan

Mar

May

Jun

Aug

Oct

Nov

-200

In New England, heating dominates energy consumption

Residential Case Study 

Built: 1978

  

Living Space: 2400 sq ft. Perimeter: 156 ft. Energy Usage: 800 gallons fuel oil and 20 kWh per day-(100 million BTU during the heating season)



Construction: 2x4, R-11 batts R-19 in cathedral ceiling Single/Double Pane Windows No basement insulation

What are the available options?

Upgrading Windows Type

R-value

BTU/year/ sq ft.

Case study savings

Single Pane

1.0

144000

-

Single Pane w/ storm

2.0

72000

$16.88 per window

Double Pane, low e

3.0

48000

$5.63 per window

Triple Pane

4.0

36000

Payback time is 50 to 200+ years! - Very bad news Assumes: Fuel Oil is $2.50

Insulating Basement  8’ below ground level temperature is 50 - 55° F during the winter. The equivalent number of degrees days during the heating season is 1800. For 1300 square feet of floor (R-value = 1.6), the heating load is equivalent to 300 gallons of fuel oil ($750). The actual value is higher if the basement has drafts, i.e. the underground temperature is higher.  How to insulate?  Do not use fiberglass if the area is moist. Your investment will be ruined.  Ceiling -- basement is unheated, attacks the problem at the source.  Walls -- basement is heated, fairly dry.  Always insulate band joist R30

External Foam under clapboarding  Can you economically add foam over siding, if you intend to change siding? Material

Old Rvalue

New Rvalue

Outside Air Film

0.2

0.2

Siding Wood Bevel

-

0.8

1” Rigid Insulation

-

5

Air Pocket

-

1.0

Siding Wood Bevel

0.8

0.8

1/2” Plywood Sheathing

0.6

0.6

Fiberglass Batt

11.0

11.0

1/2” Drywall

0.5

0.5

Inside Air Film

0.7

0.7

Total Wall

13.8

20.6

 Case Study: 1500 sq. ft. of siding -- savings of 53 gallons of fuel oil or $115 per year.  Not economical if you need to change any aspect of window detail, most likely over 10 year pay back time!

Case Study Conclusions  Basement Insulation would be a sure bet. Large possible savings, with easy access on the inside.  Replacement windows and insulation under new clapboarding are not cost effective.  Other options:  For windows: R-5 insert into windows at night would yield $5 per window per year.  Two other elements of the heat loss equation  Reduce square footage -- only heat required rooms  Reduce setpoint -- 7 degree setback for overnight saves 11% across whole structure during the heating season  Can be achieved with programmable thermostats

Other Factors  Health Factors  Vermiculite fill may contain asbestos  70% of vermiculite mined from contaminated mine in Libby, MT

 Fiberglass insulation is a skin and airway irritant, and can contain carcinogens, formaldehyde allergens  Wet insulation supports mold growth

 Installation  Improper installation may degrade whole wall r-value  Fiberglass should not be compressed, voids behind junction boxes should be insulated, area around door/window frames

 Vapor barrier products must have vapor barrier facing high moisture area.

 Tax Incentives  Energy Policy Act of 2005 -- credit of 10% up to $500 for the cost of qualifying energy efficiency purchases, i.e. insulation and appliances

Discussion