BUILDING TECHNOLOGIES PROGRAM

Energy Renovations

Insulation

A Guide for Contractors to Share 

with Homeowners

PREPARED BY

Pacific Northwest National Laboratory 

& Oak Ridge National Laboratory

May 2012

May 2012 • PNNL-20972

VOLUME 17. BUILDING AMERICA BEST PRACTICES SERIES

R

BUILDING AMERICA BEST PRACTICES SERIES

Energy Renovations

Volume 17: Insulation

A Guide for Contractors to Share with Homeowners

Prepared by

Pacific Northwest National Laboratory

Michael C. Baechler, Project Manager 

K. T. Adams, M. G. Hefty, and T. L. Gilbride

and 

Oak Ridge National Laboratory 

Pat M. Love

May 2012

Prepared for the 

U.S. Department of Energy Building America Program

PNNL-20972

Pacific Northwest National Laboratory

Richland, Washington 99352

Contract DE-AC05-76RLO 1830

This report was prepared as an account of work sponsored by an agency of the 

United States Government. Neither the United States Government nor any agency 

thereof, nor Battelle Memorial Institute, nor any of their employees, makes any 

warranty, express or implied, or assumes any legal liability or responsibility for the 

accuracy, completeness, or usefulness of any information, apparatus, product, or 

process disclosed, or represents that its use would not infringe privately owned rights. 

Reference herein to any specific commercial product, process, or service by trade 

name, trademark, manufacturer, or otherwise does not necessarily constitute or imply 

its endorsement, recommendation, or favoring by the United States Government or 

any agency thereof, or Battelle Memorial Institute. The views and opinions of authors 

expressed herein do not necessarily state or reflect those of the United States 

Government or any agency thereof.

Preface

The U.S. Department of Energy recognizes the enormous potential 

that exists for improving the energy efficiency, safety, and comfort of 

existing American homes. This series of Energy Renovation Guides 

describes approaches for homeowners and builders working on 

existing homes. 

This guide will help contractors and homeowners identify ways to 

make their homes more comfortable, more energy efficient, and 

healthier to live in. It also identifies the steps to take, with the help 

of a qualified home performance contractor, to increase their home’s 

insulation, ensure healthy levels of ventilation, and prevent moisture 

problems. Contractors can use this document to explain the value of 

these insulation measures to their customers. The references in this 

document provide further explanation of insulation techniques 

and technologies. 

Heating and cooling account for 50% to 70% of the energy used 

in the average American home (DOE 2008b). Heat gain or loss 

due to inadequate insulation is a leading cause of energy waste in 

most homes. Studies show that proper insulation and air sealing 

techniques can typically achieve whole-house energy savings of 10% 

to 20% over pre-retrofit energy usage (EPA 2011b). In older homes 

and homes with little or no insulation, savings may be much higher. 

These recommendations for improving insulation are based on the 

results of research and demonstration projects conducted by the U.S. 

Department of Energy’s Building America and Home Performance 

with ENERGY STAR, sponsored by the U.S. Environmental 

Protection Agency and DOE. Home Performance with ENERGY 

STAR offers a comprehensive, whole-house approach to improving 

the energy efficiency and comfort of existing homes and requires a 

test-in/test-out process. DOE’s Building America has worked with 

some of the nation’s leading building scientists and more than 600 

production builders on more than 42,100 new homes. Building 

America’s research applies building science to the goal of achieving 

efficient, comfortable, healthy, and durable homes. 

You can learn more about Building America 

and download additional copies of this 

document and others, including climate 

guides, best practices guides, research 

reports, and case studies, at 

www.buildingamerica.gov.

To see the current list of Building America 

research teams, go to www.eere.energy.

gov/buildings/building_america/

research_teams.html.

R

May 2012 i

i

ENERGY RENOVATIONS INSULATION
ii May 2012

ENERGY RENOVATIONS INSULATION
Contents

Preface.................................................................................................................... i

1.0 Introduction ...................................................................................................... 1

1.1 How to Use this Guide........................................................................................ 2

1.2 The Home Performance Energy Checkup................................................................. 2

1.3 When to Get a Home Energy Checkup .................................................................... 3

2.0 Adding Insulation during Remodeling Projects – 

When, Where, and How Much .......................................................................... 5

2.1 When and Where to Add Insulation ....................................................................... 5

2.2 How Much Insulation to Add ................................................................................ 7

2.3 The Bottom Line: Is Adding Insulation Worth the Cost? ............................................... 11

3.0 Types of Insulation.......................................................................................... 13

3.1 Insulation Table Summary Tables ......................................................................... 13

3.2 Vapor Retarders.............................................................................................. 18

4.0 Insulation—Safety and Health Issues ............................................................... 19

4.1 Health and Safety Steps: Do These Before You Insulate .............................................. 19

4.2 Insulation Products: Health and Safety Concerns ...................................................... 22

5.0 How to Add Insulation..................................................................................... 27

5.1 Insulating an Attic ........................................................................................... 29

5.1.1 Preparing to Insulate an Attic........................................................................ 29

5.1.2 Insulating a Vented Attic ............................................................................. 32

5.1.3 Insulating Unvented Attics ........................................................................... 37

5.2 Insulating Flat Roofs and Vaulted Ceilings .............................................................. 43

5.3 Insulating Exterior Walls................................................................................... 44

5.3.1 Stud-Framed Walls: When to Insulate ............................................................. 44

5.3.2 Stud-Framed Walls: Adding Interior Cavity Insulation ........................................... 47

5.3.3 Stud-Framed Walls: Adding Exterior Insulation .................................................. 50

5.3.4 Masonry Walls: When and Where to Insulate...................................................... 52

5.3.5 Masonry Walls: Adding Exterior Insulation......................................................... 53

5.3.6 Masonry Walls: Adding Interior Insulation ......................................................... 53

5.4 Insulating a Crawlspace..................................................................................... 55

5.4.1 Why Vents Should be Closed in Humid Climate Zones........................................... 57

5.4.2 Insulation for a Closed Crawlspace ................................................................. 57

5.4.3 How to Seal and Insulate a Crawlspace ............................................................ 58

5.4.4 Insulating a Crawlspace in Dry and Marine Climate Zones....................................... 61

May 2012 iii

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ENERGY RENOVATIONS INSULATION
5.5 Insulating Basements ....................................................................................... 62

5.5.1 Moisture Control and Air Sealing.................................................................... 63

5.5.2 Choosing the Best Approach for Insulating your Basement..................................... 63

5.5.3 Preparing to Insulate your Basement............................................................... 67

5.5.4 Installing Insulation on the Interior of Basement Walls........................................... 69

5.5.5 Installing Insulation on the Exterior of Basement Walls .......................................... 70

5.5.6 Installing Insulation on the Basement Ceiling...................................................... 71

5.5.7 Maintaining a Dry, Problem-free Basement ....................................................... 72

5.6 Insulating Concrete Floors ................................................................................. 72

5.6.1 Insulating the Surface of a Concrete Floor ........................................................ 73

5.6.3 Insulating the Perimeter of a Slab................................................................... 75

5.7 Insulating Ducts .............................................................................................. 77

References ..................................................................................................... 81

Photo Credits .................................................................................................. 85

Appendix A – 

How Insulation Works: Understanding Heat Flow and Air Pressure...................... A.1

Appendix B – 

Air Leakage, Moisture, and Ventilation: Why You Need a “Whole-House” Approach . . B.1

B.1. Air Leakage ................................................................................................... B.1

B.2. Moisture ...................................................................................................... B.3

B.3. Ventilation.................................................................................................... B.3

B.4 Vapor Retarders............................................................................................. B.5

Appendix C – 

Building America Energy Performance Briefs for Improving Existing Homes........ C.1

Air Sealing a Flue or Chimney Shaft....................................................................... C.3

Improving Recessed Lighting .............................................................................. C.5

Air Sealing Duct Boots and Duct Chases ................................................................. C.7

Preventing Ice Dams......................................................................................... C.9

Insulating Attic Kneewalls................................................................................... C.11

Installing a Radiant Barrier in the Attic................................................................... C.13

Insulating and Air Sealing Cantilevered Floors .......................................................... C.15

Air Sealing a Porch Wall.................................................................................... C.17

Insulating and Air Sealing Tubs ........................................................................... C.19

Air Sealing and Insulating Fireplace Enclosures......................................................... C.21

Insulating Pipes ............................................................................................ C.23

Insulating Hot Water Heaters. ............................................................................ C.25

Keeping Wind-Blown Rain Out of Soffits ............................................................... C.27

Installing Sidewall and Kick-out Diverter Flashing 

on Homes with Rigid Foam Insulation Sheathing...................................................... C.29

Installing Sidewall and Kick-out Diverter Flashing 

on Homes with Housewrap over OSB or Plywood Sheathing ......................................... C.31

iv May 2012

ENERGY RENOVATIONS INSULATION
1.0 Introduction

Your home may not be well insulated. The insulation may be too 

thin, uneven, or missing altogether. Cracks, leaks, or vents in 

walls, floors, ceilings, or roofs may allow air to flow through your 

insulation, reducing its effectiveness. Adding insulation and sealing 

air leaks can make your home more comfortable, increase its value, 

and cut your utility bills. 

This guide provides descriptions of the many insulation options 

available to homeowners, along with guidance on where, when, and 

how to install insulation throughout your house. The guide was 

developed by the U.S. Department of Energy’s Building America 

program, which works with building scientists and construction 

experts to identify effective, research-backed measures to save energy 

and improve the comfort of your home. 

This country has more than 128 million homes. Eighty percent of 

them were built prior to 1980, and the vast majority of these are 

poorly insulated. State adoption of residential energy codes didn’t 

become common until 1983, when the Model Energy Code for 

residential and commercial buildings was first issued (Halverson 

et al. 2009). Pre-1980 homes are responsible for a majority of the 

residential energy use in the country (DOE 2009d), and many homes 

built after 1980 can also have inadequate insulation. 

Inadequate or improperly installed insulation and poor air sealing 

make your home less energy efficient and less durable. Large swings 

in indoor temperature and humidity can result, causing wood to 

swell and shrink and paint to crack and peel. Your heating and air 

conditioning equipment undergoes more wear and tear because it 

has to operate more frequently and for longer periods. 

Attic insulation. In the attic below, batts 

were installed in a sloppy fashion and 

some of them have been moved out of 

place, leaving big gaps in the insulation 

layer (Photo Source: PNNL).

May 2012 1

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ENERGY RENOVATIONS INSULATION
Insulation and Air Sealing:

Air sealing and insulation work together 

to improve comfort and performance.

You may think that insulation is the first 

step in making your home comfortable and 

energy efficient. However, money spent on 

insulation can be wasted if you don’t first 

seal the holes and gaps in your ceilings, 

walls, and foundation. 

Insulation works by trapping a layer of 

warm, still air around your house. If air is 

allowed to flow through the insulation, from 

cracks or holes in the walls, the warm air 

is no longer trapped and the insulation is 

“robbed” of its R-value. 

Without air sealing, the air you pay to 

heat and cool escapes from your house. 

Incoming air can bring in moisture, dust, 

and air pollutants. A contractor trained in 

whole-house building science understands 

that air leaks should be identified and 

sealed before any insulation is added. 

For more information on how insulation 

and air sealing work, see Appendix A at 

the back of this guide.

For detailed information on air sealing 

an existing home, see the U.S. Department 

of Energy’s Air Sealing Guide at 

http://apps1.eere.energy.gov/buildings/

publications/pdfs/building_america/

ba_airsealing_report.pdf

An effective insulation project will put money back in your 

pocket. As energy prices continue to climb, the dollars you save 

will only increase. At the same time, the additional insulation will 

improve your comfort, increase your home’s value, and benefit the 

environment by reducing carbon dioxide emissions.

1.1 How to Use this Guide

FOR HOMEOWNERS. This guide will help you make sure that the 

best research-supported practices are used to improve your home’s 

insulation as part of an energy upgrade. The guide describes types 

of insulation and their R-values (the common measurement of 

insulation effectiveness), and explains insulation approaches for 

various parts of your house. It also provides valuable information 

about safety and health issues related to insulation. 

FOR CONTRACTORS. Share this guide with your customers so 

they can understand the building science process you will follow to 

improve insulation as part of an energy upgrade. This guide explains 

the research-backed, whole-house approach to improving comfort, 

durability, and energy efficiency. It explains the connections between 

insulation, air sealing, ventilation, and moisture, and clarifies the 

options of projects and materials. 

1.2 The Home Performance

Energy Checkup

Insulation upgrades can improve the energy efficiency, durability, 

and comfort of your home, and can save money in the long term. 

However, it is important to recognize that each component of a 

house interacts with the rest of the house. 

To ensure health and safety, your insulation options should be 

considered within a whole-house, systems-based approach advocated 

by the U.S. Department of Energy's Building America program and 

building scientists across the country. This whole-house approach, 

which is based on years of research in thousands of real homes, 

takes into account how one change in a home’s insulation can 

affect the energy efficiency, comfort, durability, and safety of 

the whole house.

To implement this whole-house approach and to confirm real 

energy-use improvements, Building America recommends that 

insulation upgrades start with a home performance energy checkup 

(also known as an assessment or audit). This whole-house checkup 

BUILDING TECHNOLOGIES PROGRAM

R

Retrofit Techniques & Technologies:

Air Sealing

A Guide for Contractors 

to Share with Homeowners

PREPARED BY

Pacific Northwest National Laboratory 

& Oak Ridge National Laboratory

April 12, 2010

April 12, 2010 • PNNL-19284

VOLUME 10. BUILDING AMERICA BEST PRACTICES SERIES

2 May 2012

ENERGY RENOVATIONS INSULATION
should be conducted by a contractor who is trained and certified in 

building science principles, such as those described in the following:

•	 DOE Guidelines for Home Energy Upgrade Professionals, 

www.eere.energy.gov/wip/retrofit_guidelines.html

•	 U.S. Environmental Protection Agency’s Healthy Indoor 

Environment Protocols for Home Energy Upgrades, 

www.epa.gov/iaq/homes/retrofits.html

•	 Home Performance with ENERGY STAR programs

•	 Building Performance Institute (BPI) standards

•	 State weatherization programs 

•	 Accredited college program recommendations.

The checkup consists of three steps: testing in, conducting the 

work, and testing out. In the test-in step, the contractor interviews 

homeowners about any concerns they have about their home, 

such as comfort complaints or high utility bills; conducts safety 

tests and tests for air leakage in the ducts and whole house; and 

visually inspects for insulation levels and signs of mold or moisture 

problems. The contractor uses energy software to analyze the results 

and gives this report to the homeowner, along with a prioritized 

list of recommendations. The homeowner works with the energy 

performance contractor or another qualified contractor to determine 

a scope of work and have the work completed. In the test-out 

step, the completed work is evaluated with safety tests and visual 

inspections. For more information on what you can learn from a 

home performance energy assessment and why it is a good idea to 

have one, visit the websites of Home Performance with ENERGY 

STAR or the Building Performance Institute.

It is impossible to overstress the importance of finding a contractor 

trained in building science. Don’t skimp on time or effort here. Your 

contractor will become your “expert” and will ultimately control 

the quality of the job, so find out as much as possible about all the 

candidates. Costs can vary widely, so consider the quality of the 

proposed work and materials.

1.3 When to Get a Home Energy Checkup

“My house is not comfortable.” Many homeowners decide to do a 

home energy assessment because their home is too cold, too hot, or 

too drafty. An assessment will identify solutions, such as air sealing, 

replacing HVAC equipment, and adding insulation.

How to find a certified 

energy contractor

An easy way to find a certified energy 

contractor is through a national or regional 

retrofit program. One such program 

is Home Performance with ENERGY 

STAR, a national program from the U.S. 

Environmental Protection Agency and the 

U.S. Department of Energy that is applied 

at the state level. Go to www.energystar.

gov and click on the link for Home 

Performance with ENERGY STAR. Next, 

click on the “locations” link for certified 

contractors in your state. You can also 

find local contractors who understand the 

whole-house approach through the Building 

Performance Institute, www.bpi.org, and the 

Residential Energy Services Network, 

www.resnet.us.

As part of the home performance energy 

checkup, your certified contractor will 

use a blower door test to measure wholehouse air leakage and determine places 

where insulation and air sealing are 

inadequate (Photo Source: PNNL).

See Appendix A and B for 

more building science basics.

May 2012 3

3

ENERGY RENOVATIONS INSULATION
Another motivator 

is decreasing energy 

bills. On average, 

home energy checkups can identify ways 

to reduce energy 

bills by 20% or more. 

You should obtain a 

home energy checkup 

when the roof needs 

to be replaced, when 

you want to make an addition or finish a basement or attic, or when 

you are planning major remodeling. Because work already has to be 

done and equipment fixed or purchased, this is an opportune time to 

get an energy checkup for your home. 

Profile

Poor insulation contributed to decay in hundreds of homes built on Native 

American reservations in the 1970s. The Yakama Nation Housing Authority 

teamed with Building America to design a retrofit package that included 

stripping out old sheetrock, insulation, roofing, windows, plumbing, 

appliances, and heating equipment; laying new R-19 batts in the attic; 

covering the batts and new mastic-sealed ducts with 12 inches of blown 

cellulose; covering exterior walls with rigid foam and new siding; installing 

R-30 fiberglass batt under-floor insulation; weather stripping attic and 

crawlspace hatches; and installing new heat pumps, windows, roofs, and 

roof ventilation. Together these changes cut energy use by 47% and greatly 

improved durability and comfort. (Source: DOE 2009b)

New Insulation Increases Durability

BEFORE AFTER

Without a professional energy 

checkup, you may miss existing health 

and safety problems, you may end 

up with poor indoor air quality, and 

your project may create dangerous 

problems with combustion appliances.

Do Not Proceed with 

Energy Upgrades if...

If your home has any of the conditions 

listed below, the problems must be 

corrected before adding insulation 

or proceeding with any home energy 

upgrades:

•	 moldy or rotted attic rafters or floor joists

•	 visible mold or mildew growth on

surfaces anywhere in the house including 

the basement or crawlspace

•	 damaged or wet insulation

•	 wood rot

•	 insect infestation

•	 leaking pipes

•	 liquid water entering the home or

crawlspace from improper irrigation 

practices, ground slope, rain runoff, 

or high groundwater tables

•	 kitchen, bathroom, or clothes dryer vents

that exhaust moist air directly into the 

attic space instead of outdoors

•	 an unvented kerosene heater or

gas fireplace

•	 a history of ice dams in the winter,

which can indicate serious air leaks

•	 elevated levels of carbon monoxide,

radon, or other indoor air pollutants

•	 knob-and-tube wiring (pre-1930), which

can be a fire hazard when in contact 

with insulation

•	 vermiculite insulation in the attic or walls,

which may contain asbestos. Asbestos is 

a serious health hazard. See Section 4.2.

4 May 2012

ENERGY RENOVATIONS INSULATION
2.0 Adding Insulation 

during Remodeling

Projects—When, 

Where, and How Much

Remodeling and renovation projects can create ideal opportunities 

for adding insulation. This chapter provides specific suggestions on 

when to add insulation, where to add insulation around your home, 

and how much insulation to add.

2.1 When and Where to Add Insulation

Adding insulation to attics is usually easy and cost-effective at 

any time, but replacing a roof creates an ideal time to do it. You 

will have access to all parts of the attic for air sealing as well as 

insulation. You will also have the opportunity to use highly effective 

exterior rigid insulation. 

You can add insulation to an unfinished basement at any time, 

as long as you carefully address moisture and ventilation issues. 

Moisture and ventilation strategies must also be part of a project 

to turn a basement or attic into living space. You can insulate the 

crawlspace at any time, adding underfloor insulation if you live in 

a dry or marine climate. If you live in a humid climate, Building 

America scientists recommend converting it to an unvented 

crawlspace and insulating its walls.

Replacing siding or drywall creates an ideal time to add 

insulation to walls. Adding insulation to walls at other times 

requires drilling holes into the wall and blowing in insulation, 

known as “drill and fill.” The repaired holes may be unsightly. 

However, remodeling can create opportunities to drill and fill 

without leaving evidence. New kitchen cabinets, for example, will 

hide the filled holes, as will new crown molding or chair railing. 

Insulating a basement. A basement can 

be turned into living space by air sealing 

and insulating the walls. In this basement, 

spray foam insulation does both jobs (Photo 

Source: Building Science Corporation).

May 2012 5

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ENERGY RENOVATIONS INSULATION
When replacing a bathroom tub or shower against an exterior wall, 

you should take the opportunity to air seal and add insulation to 

the wall. (See Appendix C for project details.) When you drill new 

holes to install plumbing or wiring, you may wish to use the holes 

for blowing in insulation before patching them. Even if you don’t 

choose to increase the wall insulation, make sure you air seal the 

holes around the pipes and wiring to avoid air leaks.

Replacing or repairing a chimney or adding insulation in an attic 

may be an opportunity to perform air sealing and to insulate gaps 

around the chimney. (See Appendix C for project details.) Replacing 

a fireplace may be another time to insulate. In some homes, fireplaces 

were built with no insulation in the wall behind them; this is the 

chance to add it. (See Appendix C.)

You may not wish to wait until remodeling or renovation creates an 

ideal opportunity to insulate. You can make energy and air-sealing 

improvements in your home any time you have problems with 

comfort, air quality, moisture, mold, or excessive energy bills, or 

if you want to take advantage of tax rebates and incentives. The 

figure below shows key places where properly installed and adequate 

insulation can solve energy, comfort, and durability problems.

Missing air barrier. This photo shows a 

bathtub and the batt insulation in the wall 

behind it. This tub was installed without 

a proper air barrier, such as cement fiber 

board or rigid foam, to cover the batt 

insulation. As a result, air can flow through 

the wall cavity, robbing the insulation of 

its heat-retaining properties and making 

the tub feel cold. If you are replacing your 

tub or shower, make sure your contractor 

insulates the wall behind it and covers 

it with sheathing to prevent drafts and 

convective air currents (Photo Source: 

PNNL).

Figure 2.1. Building America research has identified key areas where insulation 

can improve a home’s comfort, durability, and energy efficiency. (Source: 2008b)

Examples of Where to Insulate

1. In unfinished attic spaces, insulate between 

and over the floor joists to seal off living 

spaces below.

1A attic access door

2. In finished attic rooms with or without 

dormer, insulate...

2A between the studs of "knee" walls;

2B between the studs and rafters of 

exterior walls and roof;

2C ceilings with cold spaces above;

2D and extend insulation into joist space 

to reduce air flows.

3. Insulate all exterior walls, including...

3A walls between living spaces and unheated 

garages, shed roof, or storage areas;

3B foundation walls above ground level;

3C foundation walls in heated basements, 

full wall either interior or exterior.

4. Insulate floors above cold spaces, such as 

vented crawl spaces and unheated garages. 

Also insulate...

4A any portion of the floor in a room that 

is cantilevered beyond the exterior wall 

below;

4B slab floors built directly on the ground;

4C as an alternative to floor insulation, 

foundation walls of unvented crawl spaces;

4D extend insulation into joist space to reduce 

air flows.

5. Insulate band joists.

6. Caulk and seal around all windows and doors.

ORNL 96-5415R2/abh

6 May 2012

ENERGY RENOVATIONS INSULATION
2.2 How Much Insulation to Add

How much insulation you’ll need to add depends on how much 

insulation you currently have. As part of a home performance energy 

assessment, your contractor will:

•	 Identify the amount of insulation you have, what shape it’s in, and 

what your energy-efficiency goals are

•	 Recommend measures to address comfort, health, safety, air 

quality, and moisture issues

•	 Identify the most cost-effective improvements.

Before you call a home performance contractor, you may wish to 

do some preliminary estimates yourself. DOE and EPA offer three 

online tools that can help you assess your insulation needs.

THE ZIP-CODE INSULATION PROGRAM, developed by DOE’s 

Oak Ridge National Laboratory, can be found at www.ornl.

gov/~roofs/zip/ziphome.html. It will tell you the most cost-effective 

insulation levels for your house, based on its location. You enter 

your zip code, information about your house, and current costs 

of the fuel you use. The site will show you DOE’s recommended 

R-values for your climate. The ZIP-Code site’s cost-effectiveness 

recommendations are based on average local energy prices, regional 

average insulation costs, equipment efficiencies, climate factors, and 

energy savings for both the heating and cooling seasons.

HOME ENERGY SAVER (http://homeenergysaver.lbl.gov/

consumer/) computes a home's energy use based on models and 

data developed at DOE’s Lawrence Berkeley National Laboratory. 

Users can enter detailed information about their energy sources, 

appliances, heating and air conditioning equipment, location of duct 

work, and current insulation levels. On the basis of these, the site 

generates a list of energy-saving upgrade recommendations. It also 

projects the reduction in carbon emissions.

AIR SEAL AND INSULATE WITH ENERGY STAR provides links 

to information at www.energystar.gov/index.cfm?c=home_sealing.

hm_improvement_sealing. ENERGY STAR is a program of the U.S. 

Environmental Protection Agency and DOE. 

What is R-Value?

Insulation is rated in terms of its 

resistance to heat flow, called its R-value. 

The R-value of insulation depends on 

the type of material, its thickness, and 

its density. The higher the R-value, the 

more effective the insulation. R-values 

are usually given per inch of building 

material. Since R-values are cumulative, 

using thicker material or a combination 

of materials provides more resistance 

to heat flow.

Depth of insulation. When installing 

loose-fill insulation in an attic, your 

contractor should staple rulers in several 

places to ensure the insulation is deep 

enough and has been spread evenly. 

These rulers are also useful for measuring 

changes over time as insulation settles 

(Photo Source: PNNL).

May 2012 7

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ENERGY RENOVATIONS INSULATION
1

2 2

2 3

3

4

4

5 5

6

6

7

Marine (C)

Dry (B) Moist (A)

All of Alaska in Zone 7

except for the following

Boroughs in Zone 8:

Bethel

Dellingham

Fairbanks N. Star

Nome

North Slope

Northwest Arctic

Southeast Fairbanks

Wade Hampton

Yukon−Koyukuk

Zone 1 includes

Hawaii, Guam,

Puerto Rico,

and the Virgin Islands

Warm−Humid

Below White Line

Figure 2.2. IECC Climate Regions. Designated by the International Energy 

Conservation Code (IECC) (Figure Source: 2009 IECC; Briggs et al. 2003).

1

2 2

2 3

3

4

4

5 5

6

6

7

Marine (C)

Dry (B) Moist (A)

All of Alaska in Zone 7

except for the following

Boroughs in Zone 8:

Bethel

Dellingham

Fairbanks N. Star

Nome

North Slope

Northwest Arctic

Southeast Fairbanks

Wade Hampton

Yukon−Koyukuk

Zone 1 includes

Hawaii, Guam,

Puerto Rico,

and the Virgin Islands

Warm−Humid

Below White Line

1

2 2

2 3

3

4

5 5

6

6

7

Alaska in Zone 7

t for the following

ghs in Zone 8:

l

gham

anks N. Star

Slope

Northwest Arctic

Southeast Fairbanks

Wade Hampton

Yukon−Koyukuk

Zone 1 includes

Hawaii, Guam,

Puerto Rico,

and the Virgin Islands

Warm−Humid

Below White Line

1

2 2

2 3

3

4

4

5 5

6

6

7

e (C)

All of Alaska in Zone 7

except for the following

Boroughs in Zone 8:

Bethel

Dellingham

Fairbanks N. Star

Nome

North Slope

Northwest Arctic

Southeast Fairbanks

Wade Hampton

Yukon−Koyukuk

Zone 1 includes

Hawaii, Guam,

Puerto Rico,

and the Virgin Islands

Warm−Humid

Below White Line

Energy Codes

Check with your local building department 

to see which codes apply to your 

remodeling job. When you add insulation to 

an existing house, you typically do not have 

to meet code-required R values for new 

homes, unless you’re building an addition 

or finishing a basement or attic. However, 

the latest codes are good goals to aim for; 

reaching them will improve your home’s 

energy efficiency and increase its resale 

value. The requirements vary by climate 

zone, based on the International Energy 

Conservation Code (IECC)-designated 

climate zones shown on the map below. The 

insulation requirements for both the 2009 

and 2012 IECC are shown in Table 2.1.

Each state sets its own building energy 

efficiency requirements. Many states 

base their codes on the IECC. The code is 

updated every three years. Many states 

have adopted the 2009 IECC. The 2012 

IECC was published in June 2011 and is 

now available for adoption. For information 

about each states energy code, see the DOE 

site www.energycodes.gov/states/maps/

residentialStatus.stm. 

Figure 2.3. Adoption of IECC by State. As of Sept. 29, 2011 (Source: DOE BECP).

American Samoa

Guam

N. Mariana Islands

Puerto Rico* U.S. Virgin Islands

IECC 2003, equivalent or less energy efficient

IECC 2009, equivalent or more energy efficient

IECC 2012, equivalent or more energy efficient

IECC 2006, equivalent

No Statewide Code

KEY

10

9

4

32

1

*Adopted new code to be effective at a later date

8 May 2012

ENERGY RENOVATIONS INSULATION
Table 2.1. Minimum Insulation Levelsa for New Homes as Required by the 2009 and 2012 

International Energy Conservation Code. 

Climate 

Zone

Ceiling 

R-Value

Wood Frame Wall 

R-Valueb

Mass Wallc

R-Value

Floor

R-Valued

Basement 

Walle R-Value

Slab R-Valuef

and Depth

Crawlspaceg

Wall R-Value

2009 

IECC

2012 

IECC

2009 

IECC

2012 

IECC

2009 

IECC

2012 

IECC

2009 

IECC

2012 

IECC

2009 

IECC

2012 

IECC

2009 

IECC

2012 

IECC

2009 

IECC

2012 

IECC

1 30 30 13 13 3/4 3/4 13 13 0 0 0 0 0 0

2 30 38 13 13 4/6 4/6 13 13 0 0 0 0 0 0

3 30 38 13 20/13+5b,d 5/5 8/13 19 19 5/13h 5/13h 0 0 5/13 5/13

4 except

Marine

38 49 13 20/13+5b,d 5/10 8/13 19 19 10/13 10/13 10, 2 ft. 10, 2 ft. 10/13 10/13

5 and

Marine

38 49 20/13+5b,c 20/13+5b,d 13/17 13/17 30f 30f 10/13 15/19 10, 2 ft. 10, 2 ft. 10/13 15/19

6 49 49 20/13+5b,c 20+5/13+10b,d 15/19 15/20 30f 30f 15/19 15/19 10, 4 ft. 10, 4 ft. 10/13 15/19

7 and 8 49 49 21 20+5/13+10b,d 19/21 19/21 38f 38f 15/19 15/19 10, 4 ft. 10, 4 ft. 10/13 15/19

Source: 2009 and 2012 IECC Tables 402.1.1

a. R-values are minimums. When insulation is installed in a cavity which is less than the labeled design thickness of the insulation, the installed R-value of the 

insulation shall not be less than the R-value specified in the table

b. The first value is cavity insulation, the second value is continuous insulation or insulated siding, so “13+5” means R-13 cavity insulation plus R-5 continuous 

insulation or insulated siding. 

c. If structural sheathing covers 25 percent or less of the exterior, insulating sheathing is not required where structural sheathing is used. If structural sheathing covers 

more than 25 percent of exterior, structural sheathing shall be supplemented with insulated sheathing of at least R-2.

d. If structural sheathing covers 40% or less of the exterior, continuous insulation R-value shall be permitted to be reduced by no more than R-3 in the locations where 

structural sheathing is used – to maintain a consistent total sheathing thickness

e. The second R-value applies when more than half the insulation is on the interior of the mass wall.

f. Or insulation sufficient to fill the framing cavity, R-19 minimum.

g. “15/19” means R-15 continuous insulated sheathing on the interior or exterior of the home or R-19 cavity insulation at the interior of the basement wall. “15/19” shall 

be permitted to be met with R-13 cavity insulation on the interior of the basement wall plus R-5 continuous insulated sheathing on the interior or exterior of the 

home. “10/13” means R-10 continuous insulated sheathing on the interior or exterior of the home or R-13 cavity insulation at the interior of the basement wall.

h. Basement wall insulation is not required in warm-humid locations as defined by 2009 and 2012 Figure 301.1 and Table 301.1.

i. R-5 shall be added to the required slab edge R-values for heated slabs. Insulation depth shall be the depth of the footing or 2 feet, whichever is less in Zones 1 

through 3 for heated slabs.

Faced fiberglass batt Loose fiberglass insulation Vermiculite insulation 

insulation 

Unfaced fiberglass batt 

insulation

If you see: It is probably Total R-value

Loose fibers Light-weight yellow, pink, or white Fiberglass Depth (inches) x 2.5 = R-value

Dense gray or near-white, may have black specks Rock wool Depth (inches) x 2.8 = R-value

Small gray flat pieces or fibers (from newsprint) Cellulose Depth (inches) x 3.7 = R-value

Granules Light-weight gray, white Vermiculite or Perlite Depth (inches) x 2.7 = R-value

Batts Light-weight yellow, pink, or white Fiberglass Depth (inches) x 3.2 = R-value

(Source: DOE 2008)

Table 2.2. R-Values for Insulation Types Commonly found in Existing Homes

May 2012 9

9

ENERGY RENOVATIONS INSULATION
Existing Insulation Levels

Your energy contractor will check insulation levels in the attic, walls, 

and crawlspace or basement as part of a home energy assessment. 

You can get an idea of the R-value of existing insulation values 

yourself using the tips below. Table 2.2 will help you figure out what 

kind of insulation you have and what its R-value is.

LOOK IN YOUR ATTIC. Batt insulation that is faced with paper or 

foil will often have its R-value printed on the facing. If it’s not faced, 

use a ruler to measure the depth and refer to Table 2.2 to estimate 

the R-value. The quality of the installation has a significant impact 

on performance. If you have loose-fill insulation, look for places 

where it is thin or missing, especially at the edges of the attic. If you 

have batts, look for ones that are squished or pushed aside in places 

to allow for wiring or recessed lights. 

LOOK INTO YOUR WALLS. Your contractor will likely use an 

infrared camera that can show where heat is coming through the 

walls or ceilings, giving a clear picture of just where insulation 

is missing. You can check visually for wall insulation through an 

electrical outlet or switch plate. Turn off the power to the outlet, 

then remove the cover plate and use a flashlight to look into the 

crack around the outlet box. You can also use a crochet hook to 

see if you can retrieve some insulation (but be sure the power to 

the outlet is off). You should check separate outlets on the first 

and second floor, and in old and new parts of the house, because 

insulation in one wall doesn't necessarily mean that it’s in every wall. 

LOOK UNDER YOUR FLOORS. Look at the underside of the floor 

over a garage, basement, or crawlspace and measure the thickness 

of any insulation you find there. If the insulation is foam board or 

sprayed-on foam, use any visible label information or multiply the 

thickness in inches by 5 to estimate the R-value. If the insulation is 

fiberglass batt, multiply the thickness in inches by 3.2 to find out the 

R-value (or the R-value might be visible on a product label). R-value 

is greatly reduced when batts are pinched or drooping. Air can flow 

in convective loops between the sagging insulation and the floor 

above, robbing the insulation of its heat-trapping ability.

LOOK AT YOUR DUCTWORK. Don’t overlook another area in 

your home where energy can be saved—the ductwork of the heating 

and air-conditioning system. Ducts should be insulated if they run 

through unheated or uncooled spaces in your home, such as an attic or 

crawlspace. R-value may be printed on the existing duct insulation.

LOOK AT YOUR PIPES. Water pipes should be insulated if they 

run through unheated or uncooled spaces in your home. 

(Top) Inspect the attic. Check the evenness 

and depth of the insulation on your attic floor.

(Bottom) Check under the floor. Inspect 

the insulation of ducts, pipes, and the floors 

over a garage, basement, or crawlspace. 

In this crawlspace, the fiberglass batts are 

drooping slightly from the ceiling, reducing 

their R-value. The duct insulation needs 

new tape. In cold climates, the pipes should 

be insulated to prevent freezing. 

(Photo Source: PNNL)

10 May 2012

ENERGY RENOVATIONS INSULATION
The home energy assessment found 

52 recessed “can” lights that allowed 

conditioned air to escape into the attic. To 

stop the leaks, workers built air-tight boxes 

over each light. They also inspected the 

attic to close off other air leaks over ceiling 

soffits. They also closed off the vented 

crawlspace; sealed leaks around wiring, 

ducts, and plumbing pipes; and replaced 

old rusted ducts that were dumping 

conditioned air into the crawlspace. 

Sealing air leaks in the attic, crawlspace, 

and floor cut air leakage by 45%. These 

measures, combined with adding R-38 

attic insulation, cut the home’s energy bill 

in half (Photo Source: DOE).

2.3 The Bottom Line: 

Is Adding Insulation Worth the Cost?

The potential for savings is different for every house. Your financial 

decision about adding insulation will depend on your climate, 

budget, and how much you are likely to save on energy bills. If your 

insulation is already adequate, adding more insulation may not be 

the best investment. You may not save enough energy to recoup the 

cost of the insulation. However, if your home is poorly insulated or 

you have high heating and cooling bills, added insulation is likely 

to pay for itself over time. 

“Simple Payback”

The cost of the upgrade measures divided by the annual estimated 

savings will provide a “simple payback,” telling you how many years 

the measures will take to pay for themselves. If you have little or no 

insulation, especially in the attic, adding insulation is likely to pay 

for itself within a few years. For example, in a retrofit of a tri-level 

home built in eastern Washington in the 1970s, auditors found that 

air sealing and insulating the attic would cost an estimated $1,131. 

With a projected annual savings of $239 a year, the owners will 

recoup their investment in five years. After that, the $239 a year 

will be money in their pocket (DOE 2011f). For more on estimating 

insulation payback, see www.energysavers.gov/your_home/

insulation_airsealing/index.cfm/mytopic=11360.

Grants and Tax Credits 

Many local, state, and federal agencies offer grants and tax credits 

for energy-efficient home improvements. Check with your local 

utility or city, or check the DOE-sponsored Database of State 

Incentives for Renewables and Efficiency (www.dsireusa.org). 

Organized by state, this site is frequently updated and has a 

wealth of information regarding federal, state, local, and utility 

incentives and tax credits.

Profile

Source: DOE Building America, www.buildingamerica.gov

Air seal before insulating. This 1950s home 

in Pasadena needed better insulation. 

However, insulation would not have 

stopped the constant flow of air in and out 

of the house. Blower door testing showed 

air leakage of 13,523 cfm at 50 Pascals of 

pressure: 5,000 cfm is typical in an older 

home; 1,000 cfm is ideal (Photo Source: DOE).

Insulation and Air 

Sealing Create a Cool, 

Comfortable Home

May 2012 11

11

ENERGY RENOVATIONS INSULATION
12 May 2012

ENERGY RENOVATIONS INSULATION
pink = insulation 

blue = air barrier

3.0 Types of Insulation

Insulation is made of a variety of materials that have a high 

thermal resistance, which means resistance to heat flow. The unit 

of measure for a material’s thermal resistance is its R-value. The 

R-value of insulation depends on the type of material, its thickness, 

and its density. The higher the R-value, the greater its insulating 

effectiveness. 

The “best” type of insulation for your home depends on where you 

plan to install it, the R-value recommended for your climate, and the 

cost of buying and installing the material. Some types of insulation 

require professional installation; others you can install yourself. 

3.1 Insulation Summary Tables

The tables that follow will help you choose the best insulation for 

your project. The tables provide information in three ways:

Table 3.1 provides information about forms of insulation, such as 

batts, loose-fill, spray-on, and rigid board. The table describes the 

advantages and disadvantages of each, the best applications for each 

form, and installation tips. 

Table 3.2 provides information about insulation materials, such as 

cellulose, fiberglass, and polystyrene. The table gives R-values for 

each material and describes its advantages and disadvantages. 

Some insulation materials are also vapor retarders. Vapor retarder 

requirements are defined and specified in the International 

Residential Code as shown in Section 3.2.

Get a Whole-House Energy 

Checkup First

Before beginning any 

insulation project, be 

sure to get a wholehouse energy checkup. 

This assessment will 

identify the most 

effective improvements 

for your home and 

help you avoid unintended consequences. 

Because your house is a system and all 

its components work together, adding 

insulation can affect how other components 

perform. Moisture management and 

ventilation, for example, are major issues 

to address in your insulation plans. See 

Appendix B for more information on 

moisture, air leakage, ventilation, and the 

whole-house approach of building science.

Costs

Table 3.2 shows the relative cost of many 

insulation types. DOE’s National Renewable 

Energy Laboratory has also prepared a 

database of costs of various home energyefficiency upgrades including insulation. 

This can be found at www.eere.energy.gov/

buildings/building_america/measures_

costs.html

May 2012 13

13

ENERGY RENOVATIONS INSULATION
Table 3.1. Forms of Insulation 

Form of 

insulation

Type of insulation 

material

Areas 

for use Advantages Disadvantages Installation

Batts and 

blankets

made in 

standard 

widths. Batts 

are precut. 

Blankets 

come in rolls. 

Flexible, woven 

fibers, made of: 

Fiberglass,

Mineral wool,

Cotton, or

Sheep’s wool

Open walls; 

attic floor and 

kneewalls; 

basement or 

crawlspace 

ceiling in dry 

climates only

Relatively easy to 

install. Available 

unfaced or with 

facings (kraft paper, 

foil-kraft paper, or 

vinyl) for air and/or 

vapor resistance. Batts 

with flame-resistant 

facing are available 

for basement walls in 

which the insulation will 

be left exposed.

Not air-tight. Careful 

installation is necessary 

to reduce air leaks around 

edges, which significantly 

reduce R-value. Subject 

to air movement around 

and through the batts. 

Hard to fit into irregular 

spaces. Loses R-value 

when compressed. Nesting 

material for rodents. 

Batts are hand-cut and 

trimmed to fit. The batt 

must fill the entire cavity 

without any gaps. Batts 

must not be folded, 

tucked-in, or pinched. Slit 

batts to fit around wiring 

and plumbing. Improper 

installation reduces 

effectiveness. Facing 

material should face the 

‘warm-in-winter’ side to 

resist condensation in walls. 

Blown-in, 

loose-fill

fiber

Small particles of:

Cellulose,

Fiberglass, or

Mineral wool

Attic floor, walls, 

vaulted ceilings

Inexpensive. The small 

particles conform to the 

space into which they 

are blown. Well suited 

for retrofits. Fills spaces 

behind and around 

obstacles, such as 

electrical boxes, wiring, 

plumbing, and nails. 

Typically requires a 

professional installer. 

Must be applied using an 

insulation blowing machine. 

Some types have high 

water absorption. Can have 

settlement problems if not 

installed properly. Dusty. 

For wall retrofits, requires 

drilling of wall sheathing to 

gain access to wall cavities.

Blown with a pneumatic 

hose into open attics, or 

blown through holes drilled 

into the framing cavities 

of existing walls, floors, 

or vaulted ceilings. Use 

baffles to keep fiber away 

from soffit vents in attics. 

Don’t cover recessed light 

fixtures unless the fixtures 

are ICAT rated. Insulation 

must be kept away from 

chimneys and metal flues.

Blown-in, 

dense-pack 

fiber

Small particles of:

Cellulose, or

Fiberglass

Walls, cathedral 

ceilings

Inexpensive. Conforms 

to the space into which 

it is blown. Fully fills 

spaces behind and 

around obstacles. Some 

air sealing ability.

For wall retrofits, requires 

drilling of wall sheathing 

to gain access to wall 

cavities. Walls must be 

well air-sealed and strong 

enough to accommodate 

added pressure.

Like loose-fill, except 

the fibers are blown at 

relatively high density into 

a wall or ceiling cavity to 

resist air infiltration. Note 

cautions above regarding 

attic vents and hot objects.

Sprayed-on 

fiber 

mixed with 

water and 

adhesives

Fibers mixed with 

wet adhesive:

Cellulose,

Fiberglass, or

Mineral wool

Basement walls; 

walls with siding 

removed

Conforms to the space 

into which it is blown. 

Fully fills spaces behind 

and around obstacles.

Typically requires a 

professional installer. 

Requires interior drywall to 

be removed to install and to 

allow drying.

Fibers are mixed with wet 

adhesive and sprayed into 

open wall cavities, then 

allowed to dry.

14 May 2012

ENERGY RENOVATIONS INSULATION
Form of 

insulation

Type of insulation 

material

Areas 

for use Advantages Disadvantages Installation

Sprayed-on 

foam

Polyurethane, 

Castor- or soybased polyurethane,

Cementitious 

The perimeter 

of vented attics; 

roof deck of 

cathedralized 

attics; vaulted 

ceilings; flat roofs; 

basement walls; 

walls with siding 

removed

Excellent air barrier; can 

eliminate the need for 

separate air-tightness 

detailing. Very resistant 

to moisture, especially 

when treated with 

sealant. Fills even 

the smallest cavities, 

including spaces around 

obstacles such as 

electrical boxes, wiring, 

plumbing, and nails.

Expensive. Installation 

requires a trained installer. 

Limited attic access may 

impede proper installation. 

Hydrofluorocarbons 

(potent greenhouse gases) 

usually used in production 

or application. Foam 

insulation can be damaged 

by sunlight and high 

temperature. It produces 

toxic smoke when burned. 

Blown through a 

membrane with air.

Requires special 

equipment. Sprayed into 

cavities, where it expands 

to fill all spaces. All types 

of foam insulation must 

be protected from direct 

sunlight. Must be covered 

with a fire barrier.

Rigid 

insulation

Molded and 

hardened 

fibers or foam: 

Polyisocyanurate 

Expanded 

polystyrene (EPS), 

Extruded 

polystyrene (XPS), 

or Polyurethane 

Fiberglass

Above rafters 

in cathedralized 

attic; vaulted 

ceilings or flat 

roofs; exterior 

walls under 

siding; basement 

and crawlspace 

walls; under 

concrete floors; 

slab perimeters

High R-value per inch 

of thickness. An air 

barrier and vapor 

retarder if seams are 

properly sealed. Blocks 

thermal bridging. When 

replacing siding, can 

add insulation to walls 

without removing 

interior drywall or 

drilling. 

Expensive. Does not 

conform to irregular 

surfaces. Requires careful 

installation to limit gaps 

and air leaks. Can be 

damaged by sunlight and 

high temperature. Produces 

toxic smoke when burned.

Attached directly to 

framing. Must be protected 

from direct sunlight. In 

basements, must be 

covered with an ignition 

barrier, such as wood 

paneling or 1⁄2-inch drywall. 

Exterior rigid 

foam blocks

Molded and 

hardened expanded 

polystyrene foam

Exterior walls 

under siding

When replacing siding, 

can add insulation to 

walls without removing 

interior dry wall or 

drilling. High R-value 

prevents condensation 

problems. Blocks 

thermal bridging. 

Due to thickness of foam 

blocks, adjustments of 

windows and doors may 

be required. Some types 

require the installer to cut 

utility chases. Must avoid 

contact with soil.

A steel starting track 

holds the first row of 

blocks. Subsequent rows 

are attached with plastic 

clips and attached to walls 

with furring strips. Can be 

covered with any siding.

Reflective 

Insulation

Aluminum foil with 

paper or foam 

backing

Vented attics in 

hot-dry and hothumid climates

Reduces solar heat 

gain. Can be combined 

with many types of 

insulation. Can be costeffective as a radiant 

barrier in attics in hot 

climates, especially if 

duct system is in attic. 

Radiant barriers not 

recommended for cold 

climates. Not for use in 

unvented attic. The more 

attic insulation, the less 

cost-effective the radiant 

barrier will be.

Requires an air space 

adjacent to the reflective 

surface. Stapled on the 

underside of rafters or on 

top of ceiling. To avoid 

moisture problems, do 

not install radiant barriers 

in contact with attic floor 

insulation. 

May 2012 15

15

ENERGY RENOVATIONS INSULATION
Table 3.2. Insulation Materials

Note: All R-values are approximate and for general comparison only (Source for R-values: DOE (DOE 2008b; Krigger and Dorsi 2009)

What is it? Product 

form

R-value 

per inch Advantages Disadvantages Relative Costs

Cellulose insulation

Recycled newsprint, 

finely shredded 

and chemically 

treated to resist fire, 

corrosion, fungal 

growth, and vermin. 

Loose-fill is most 

suitable for existing 

homes. 

Blown-in, 

loose-fill 

R-2.9 to 

R-3.4

Inexpensive. Contains at 

least 70% recycled paper. 

Commonly used for energy 

upgrades in existing homes. 

Requires chemical treatment with fire 

retardant. Cellulose must be kept away from 

chimneys and metal flues. Address mold 

issues before installing cellulose. Accidental 

wetting and high humidity can cause cellulose 

to absorb large quantities of water, reducing 

thermal resistance, draining fire retardant, and 

creating risk of mold and moisture damage to 

building components.

$

Blown-in, 

dense-pack

R-3.0 to 

R-3.4

$

Sprayed-on R-3.6 to 

R-3.8

$

Cementitious insulation

Magnesium oxide 

from sea water. 

Sprayed-on 

foam

R-3.9 Excellent air barrier. High 

fire and mold resistance. 

Non-toxic. Does not offgas 

any volatile chemicals. Does 

not shrink or settle. 

Expensive. Must be applied by a trained 

installer. Few installers trained in this specialty. 

Expands as it sets and can crack walls if 

installed incorrectly. Can be fragile or brittle 

if exposed to frequent vibration, reducing its 

performance.

Cotton insulation

Low-grade, recycled, 

or waste cotton. 

Borate treated 

for pest and fire 

resistance. 

Batts R-3.4 Nontoxic. Limited availability. Batts may not be sized 

for standard stud cavity widths. Difficult to 

cut. Absorbs moisture, does not insulate 

when wet. Water can carry away pest and fire 

retardant. 

$$$

Fiberglass

Glass spun into long 

fibers and woven. 

May contain 30% 

or more postconsumer recycled 

glass. Batts come 

with or without 

vapor-retarder 

facings such as kraft 

paper, foil-kraft 

paper, or vinyl.

Batts Standard 

density: 

R-2.9 to 

R-3.8

High 

density: 

R-3.7 to 

R-4.3

Batts are inexpensive. 

Excellent fire and moisture 

resistance. Resistant to mold 

and pests. R-value depends 

on density.

Installation requires protective measures 

to prevent skin and eye contact. Gaps 

between batts may allow air infiltration 

or condensation, reducing effectiveness. 

Batts are not an air barrier. Available with 

kraft paper, foil-kraft paper, or vinyl facings 

to act as a vapor retarder. Kraft paper 

facing is flammable. Some brands contain 

formaldehyde, a toxic gas.

$

Glass spun into long 

fibers and woven. 

May contain 30 

percent or more 

post-consumer 

recycled glass. 

Blown-in, 

loose fill

R-2.2 to 

R-2.7

Produces little dust during 

installation. Non-flammable.

Blown fiberglass: Many blowing machines 

over-fluff fiberglass in attics, reducing density 

and R-value. Blown-in fiberglass requires 

careful protective measures to prevent 

breathing of fibers and skin and eye contact. 

Must be fully enclosed to prevent entry of 

glass particles into living spaces.

$

Blown-in, 

dense-pack

R-3.6 to 

R-4.4

$

Rigid board R-2.2 to 

R-4.3

Excellent for soil contact. Rigid board can be expensive. $$

Mineral wool

Slag (a non-metallic 

by-product of 

steel-making) or 

rock, melted and 

spun into fibers.

Batts R-3.7 Non-combustible. Excellent 

sound insulation.

Absorbs water. Vapor permeable. For batts: 

Improper installation reduces effectiveness; 

loses R-value when compressed. May not be 

readily available.

$$

Loose-fill R-3.7

Sprayed-on R-3.7

16 May 2012

ENERGY RENOVATIONS INSULATION
What is it? Product 

form

R-value 

per inch Advantages Disadvantages Relative Costs

Polyisocyanurate 

A petroleum 

product. Can be 

partially soy-based.

Rigid foam 

board

R-5.6 to R-8;

R-7.1 to R-8.7 

with foil 

facing

Highest R-value per inch, 

which is valuable when 

space is limited. When 

faced with aluminum foil, 

foil facing protects surface, 

retains R-value, and serves 

as vapor retarder.

Expensive. Requires a fire barrier. Should not 

be used in contact with soil. Its closed cells 

contain low-conductivity gas. Over time, 

R-value decreases as some of the gas escapes 

and is replaced by air. Foil and plastic facings 

can help stabilize the R-value. 

$$$

Polystyrene – Expanded (EPS)

A petroleum 

product. Also known 

as bead board.

Rigid foam 

board

R-3 to R-4 The least expensive foam 

board. Comes in many 

densities and grades.

Absorbs some water. Not a vapor retarder. 

Requires a fire barrier. Melts at 200°F. 

$$$

Exterior and 

interior rigid 

foam block 

systems

R-10 to R-26 When replacing siding, 

provides high R-value for 

walls without drilling or 

removing interior dry wall. 

Can be covered by any type 

of siding. 

Polystyrene – Extruded (XPS)

A petroleum 

product.

Rigid foam 

board

R-5.0 High R-value per inch. 

Excellent moisture 

resistance. Good vapor 

retarder. Preferred material 

for soil contact or as rain 

shield.

Requires a fire barrier. Melts at 300°F. 

Requires a capillary break between soil and 

insulation. Hydrochlorofluorocarbon, a potent 

greenhouse gas, used in production.

$$$

Polyurethane

Petroleum or soy 

or castor-based 

product.

Rigid foam 

board

R-7 to R-9 Requires a fire barrier. $$$

Spray foam: 

closed-cell, 

mediumdensity

R-7 to R-9 Very resistant to moisture. 

Excellent air barrier; can 

eliminate the need for 

separate air-tightness 

detailing. Great adhesion. 

Closed-cell foam 

strengthens a structure. 

Closed-cell foam is a vapor 

retarder.

Expensive. Installation difficult. Requires a fire 

barrier. 

$$$$

Spray foam: 

Open-cell, 

low-density

R-3.5 to 

R-3.8

Not a vapor retarder. Is an 

air barrier

Expensive. Installation difficult. $$$$

Spray foam 

with castor 

or soy oil

R-values 

comparable 

to 100% polyurethane 

foam

Available in both open- and 

closed-cell types. 

Expensive. Installation difficult. Requires a fire 

barrier.

$$$$

Radiant barrier 

Aluminum foil with 

backing

N.A. Reduces attic temperatures. 

Cost-effective in hot 

climates.

Not recommended and not cost-effective for 

cold climates. May create moisture problems. 

Not for use in unvented attic. 

Sheep’s wool

Sheep’s wool and 

borate

Batts R-3.5 Borate-treated for pest, 

mold, and fire resistance. 

Maintains insulation 

effectiveness when moist.

Repeated wetting and drying can carry away 

the pest and fire retardant.

$$$

Loose-fill

May 2012 17

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ENERGY RENOVATIONS INSULATION
3.2 Vapor Retarders

Some forms of insulation also serve as vapor retarders. Water vapor 

can be a source of damage when it is trapped within a building 

assembly and cannot dry out. Most water vapor movement in and 

through buildings is via air. Warm air carries more water vapor than 

cold air. When warm air touches a cold surface, the water vapor it 

carries can condense, turning the vapor into its liquid form, where it 

can cause damage to structural components. Stopping air leaks by 

thoroughly air sealing the building envelope is an important step in 

limiting damage from water vapor. Water vapor can also be carried 

through building components by diffusion, driven by pressure and 

temperature differences. Vapor diffusion can be impeded by use of 

a vapor retarder. The 2009 International Residential Code (IRC) 

defines vapor retarders based on their permeability; the higher 

the perm rating, the more easily water vapor can pass through the 

material (see Vapor Retarder Definitions table). Some builders refer 

to Class 1 vapor retarders as vapor barriers but the code no longer 

uses the term vapor barrier. 

The 2009 IRC R601.3 specifies the use of Class I or II vapor 

retarders on the interior side of framed walls (between the insulation 

and the drywall) in IECC climate zones 4c, 5, 6, 7, and 8 (see IECC 

map page 10). However, per a change in the 2009 IRC from the 2006 

IRC, Class III vapor retarders (e.g, latex paint) are now permitted 

in all of these climate zones when the wall is constructed in a way 

that allows drying through the use of vented cladding (e.g., brick 

or lap siding with an air space behind it) or reduces the potential 

for condensation by the use of insulating rigid foam sheathing 

(see Class III Vapor Retarders table). Building America scientists 

caution that the recommendation to install a vapor barrier on the 

“warm-in-winter” side of the wall assemblies is difficult to apply in 

mixed climates or climates that are air conditioned in summer. They 

recommend that walls should be allowed to dry to the inside, the 

outside, or both sides and they don’t recommend the use of Class I 

vapor retarders in any but the coldest climates. 

In older homes Class 1 vapor retarders (like plastic sheeting) were 

often installed on the interior side of the walls in all climate zones. 

If the walls are very drafty, due to lack of insulation and air sealing, 

drying can still occur. When insulation and air sealing are added, 

consideration should be given to any existing vapor retarders to 

minimize the likelihood of condensation problems.

For more on vapor retarders see Appendix B.4, also Lstiburek 

2004b, d; 2006e.

Class III Vapor Retarders 

Permitted in Cold Climate 

Under Following Conditions

(Source: 2009 IRC Table R601.3.1)

Zone Class III vapor retarders 

permitted for:

Marine 

4

•	Vented cladding over OSB

•	Vented cladding over plywood

•	Vented cladding over fiberboard

•	Vented cladding over gypsum

•	Insulated sheathing with

R-value > R-2.5 over 2x4 wall

•	Insulated sheathing with

R-value > R-3.75 over 2x6 wall

5 • Vented cladding over OSB

• Vented cladding over plywood

• Vented cladding over fiberboard

• Vented cladding over gypsum

• Insulated sheathing with

R-value > R-5 over 2x4 wall 

• Insulated sheathing with 

R-value > R-7.5 over 2x6 wall

6 •	Vented cladding over fiberboard

•	Vented cladding over gypsum

•	Insulated sheathing with

R-value > R-7.5 over 2x4 wall

•	Insulated sheathing with

R-value > R-11.25 over 2x6 wall

7 & 8 • Insulated sheathing with

R-value > R-10 over 2x4 wall

•	 Insulated sheathing with

R-value > R-15 over 2x6 wall

Vapor Retarder Definitions

The 2009 IRC R601.3 gives the following 

definitions and examples for vapor 

retarder classes:

Class Definition Examples

I 0.1 perm 

or less

Sheet 

polyethylene, 

sheet metal, 

non-perforated 

aluminum foil

II Greater than 

0.1 perm to less 

than 1.0 perm

Kraft-faced 

fiberglass batts or 

low-perm paint

III Greater than 

1.0 perm to less 

than 10 perm

Latex or enamel 

paint

18 May 2012

ENERGY RENOVATIONS INSULATION
4.0 Insulation—Safety 

and Health Issues 

When you air seal and insulate your home, you need to address 

some issues of health and safety. This chapter describes these issues 

and provides steps you and your contractor should take before you 

begin your project.

4.1 Health and Safety Steps: 

Do These Before You Insulate

TEST COMBUSTION APPLIANCES. Air sealing and adding 

insulation can alter the pressure and movement of air inside a 

home. (See Appendix A for a short primer on heat flow and air 

pressure in homes.)

Air pressure imbalances can sometimes cause fireplaces, furnaces, 

stoves, water heaters, and other non-closed combustion appliances 

that burn fuel (such as wood and natural gas) to pull exhaust gases 

back into the house instead of letting them vent up the flue. This 

situation is known as backdrafting. Carbon monoxide, a toxic 

gas without odor and color, can backdraft into homes, causing 

illness and death. If a combustion appliance has a pilot light flame, 

backdrafting, air pressure imbalances, or mechanical problems can 

cause the pilot light to blow out. Worse, the flame can “roll out” of 

the appliance, causing a house fire.

Before work begins and again when the project is complete, your 

contractor should test chimneys and all combustion appliances to 

ensure they have proper draft and emit little or no carbon monoxide. 

To check the safety of any combustion appliances in the home, your 

contractor should conduct a worst-case depressurization test using 

blower door equipment.

Backdrafting risks. Before beginning 

air sealing and insulation work, your 

contractor should test any combustion 

appliances, like this atmospheric-vented 

gas water heater, to ensure proper draft. 

Negative air pressure inside a home 

can cause fireplaces and fuel-burning 

appliances to backdraft, pulling dangerous 

carbon monoxide into the home. Your 

contractor should perform the combustion 

safety tests again when your project is 

complete (Photo Source: PNNL).

May 2012 19

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ENERGY RENOVATIONS INSULATION
If at all possible, replace natural draft (“draft-hood-equipped”) 

combustion appliances with sealed-combustion, induced-draft, or 

power-vented appliances. Homes with combustion appliances should 

have carbon monoxide detectors that meet UL 2034.

VENTILATE WELL TO PREVENT AIR POLLUTION AND 

MOISTURE PROBLEMS. Many homes contain hazardous 

substances, such as cigarette smoke, cleaning chemicals, pesticides, 

and offgases from carpets, paints, finishes, and home electronics. 

Good ventilation and exhaust fans are essential before you air seal 

and add insulation. Otherwise, these pollutants will become more 

concentrated inside the home. 

Poor ventilation also allows water vapor from showering, cooking, 

and breathing to concentrate in the home. This can lead to problems 

with mold, mildew, dust mites, wood rot, and building damage.

Oftentimes, a mechanical ventilation system is needed to supply fresh 

air once a home is air-sealed. Your contractor should make sure your 

ventilation system does not create depressurized areas inside the 

home and make sure all duct work is properly sealed. 

REPLACE ACTIVE KNOB-AND-TUBE WIRING. For fire safety, 

active knob-and-tube wiring should be replaced before your 

contractor begins the insulation project. Insulation can cause the 

wiring to overheat, creating a fire risk. 

CHECK FOR RADON. If radon is present in the soil under 

your home, air sealing your basement or crawlspace can lead to 

increased concentrations indoors (Hale 2011; DOE 2010b). Radon 

causes cancer. It is a naturally occurring gas that comes from the 

radioactive breakdown of uranium in soil. It is odorless, tasteless 

and invisible. The gas typically moves up through the ground and 

into your home through air leaks and cracks. According to the EPA, 

there is no level of radon known to be safe (EPA 2011e).

Nearly 1 out of every 15 homes in the United States is estimated to 

have high radon levels (EPA 2011e). The level of radon in soil varies 

from area to area, but radon beneath any particular home can be 

high. The only way to know whether radon is accumulating in your 

home is to test for it. Low-cost "do-it-yourself" radon test kits are 

available in stores. 

Before air-sealing work begins, your contractor should check 

for radon. If found, do not proceed until the radon problem is 

addressed. This is especially important if your project includes 

air-sealing your crawlspace or basement.

Maintain air quality. (Top) Adequate 

ventilation can include simple measures 

like installing high-efficiency bath fans 

that are ducted to the outside. 

(Middle) A garage fan can help remove 

fumes from car exhaust and chemicals.

Knob and tube wiring. (Bottom) If a home 

energy checkup reveals that you have old 

knob-and-tube wiring anywhere in your 

house, don’t add insulation until the wiring 

has been replaced with new, insulated 

electrical wiring.

(Photo Source: PNNL)

20 May 2012

ENERGY RENOVATIONS INSULATION
If the radon level in your home is elevated, you must reduce it to 

protect your health. A qualified radon contractor can advise you 

on the best radon remediation system for your home. The most 

common method is soil suction, which draws the radon from below 

the home and vents it through a pipe to the roof. The particular soil 

suction technique depends on what type of foundation a home has. 

Costs vary. 

After your air sealing and insulation project is complete, test again 

for radon. 

Figure 4.1. Radon Potential in the U.S. by County. This map shows predicted average indoor radon levels by county. 

Be sure your home is tested because radon accumulation can vary from home to home (Figure Source: EPA 2011c).

More information on radon

Radon in homes causes an estimated 

20,000 lung cancer deaths each year 

(EPA 2011e). For more information, see 

www.epa.gov/radon/aboutus.html. 

The U.S. Environmental Protection Agency 

(EPA) designates zones as having high, 

moderate, or low potential levels of radon 

(Figure 4.1). 

The EPA recommends installing a radon 

control system if the level in your home 

exceeds 2 to 4 picocuries per liter (pCi/L) 

of air. The EPA requires radon control above 

4 pCi/L. For more testing information, see 

www.epa.gov/radon/pubs/citguide.html.

To find a qualified or state-certified 

radon contractor, check with your state 

radon office or see www.epa.gov/radon/

whereyoulive.html. 

Highest Potential 

Moderate Potential

Low Potential

Zone 1 counties have a predicted average indoor radon 

screening level greater than 4pCi/L (picocuries per liter)

Zone 2 counties have a predicted average indoor radon 

screening level between 2 and 4 pCi/L

Zone 3 counties have a predicted average indoor radon 

screening level less than 2 pCi/L

May 2012 21

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ENERGY RENOVATIONS INSULATION
4.2 Insulation Products: 

Health and Safety Concerns

Insulation work can pose safety challenges that are best left to 

professionals. Two older types of insulation are known health 

hazards – asbestos and urea-formaldehyde. Installing new insulation 

requires knowledge and skill. Your energy contractor will help you 

choose the right product and install it properly, ensuring the health 

of your home environment. 

Vermiculite Insulation and Asbestos 

Until 1980, asbestos was widely used in building materials such as 

ceiling and floor tiles. It was also used as insulation for furnaces, 

boilers, and water pipes. Asbestos is a naturally occurring mineral 

fiber that can cause lung disease and cancer.

Until 1990, an insulation product called vermiculite was widely used 

in homes, and much of it was contaminated with asbestos. Over 70% 

of the vermiculite sold in the United States came from a mine near 

Libby, Montana, which was found to have natural asbestos deposits. 

If you have vermiculite insulation in your attic or walls, you should 

assume that it contains asbestos and take steps to protect yourself 

and your family from exposure. If asbestos is damaged or disturbed, 

microscopic fibers become airborne and may be inhaled. The most 

dangerous asbestos fibers are too small to see. There is no known 

safe level of asbestos exposure. 

If you are planning an insulation project and suspect you have 

vermiculite insulation or another form of asbestos in your home, 

don't touch it. Disturbing the material releases fibers into the air. 

Don’t make openings in your walls to check for vermiculite.

If you have vermiculite insulation in your attic, avoid going into the 

attic. Warn any contractors doing work in your attic that they may 

be exposed to asbestos and must avoid disturbing the vermiculite.

The U.S. Environmental Protection Agency makes the following 

recommendations for homes that contain vermiculite:

•	 Leave the vermiculite insulation undisturbed in the attic or walls.

•	 Do not store boxes or other items in the attic.

•	 Keep children away from it.

•	 Do not attempt to remove the vermiculite yourself.

For more information 

on vermiculite insulation

www.epa.gov/asbestos/pubs/insulation.

html#What

For more information 

on asbestos

www.epa.gov/asbestos/

Vermiculite insulation. If you have 

vermiculite insulation in your attic or 

walls, you should assume that it contains 

asbestos and be careful to avoid exposure. 

Vermiculite was commonly used before 

1990 (Photo Source: EPA).

DETAIL

22 May 2012

ENERGY RENOVATIONS INSULATION
Urea-formaldehyde foam insulation.

If possible, leave this insulation 

undisturbed. Removal should be done 

by a hazard-abatement professional

(Photo Source: Nachi.org).

If your home improvement plans require disturbing vermiculite 

or asbestos, you must hire a professional asbestos contractor. The 

professional will have two options: repair or removal. Repair usually 

involves sealing or covering asbestos material; this option costs less 

than removal. Removal increases the risk of fiber release. Unless it 

is required by state or local regulations, it should be your last option 

in most situations. Your state health department can provide a list of 

contractors certified to perform this work.

Urea-Formaldehyde Foam Insulation 

Urea-formaldehyde foam was a popular insulation in the 1970s. It 

looks like an oozing liquid, although it is solid, dry, and crumbles 

easily. With age, it turns butterscotch in color. You may find it in 

basements, attics, crawlspaces, and unfinished closets.

Because it offgasses formaldehyde, urea-formaldehyde insulation 

can cause eye and lung irritation, headaches, and dizziness in 

some individuals. In the early 1980s, the U.S. Consumer Product 

Safety Commission (CPSC) banned its use in homes and schools. 

Formaldehyde itself, however, is still widely used to make resins for a 

variety of household items, including fiberglass insulation (see next 

section). In June 2011, the U.S. Department of Health and Human 

Services classified formaldehyde as a known human carcinogen. 

Their report concluded that individuals with “higher measures of 

exposure to formaldehyde” are at increased risk for certain types of 

rare cancers (NIH 2011).

Old urea-formaldehyde insulation is unlikely to cause problems. 

According to the CPSC, the release of formaldehyde decreases 

rapidly after the first few months and reaches background levels in a 

few years. However, sensitivity to formaldehyde varies from person 

to person, and unsealed foam may still release small amounts of the 

gas, especially when wet or hot. 

If you have exposed urea-formaldehyde foam in your home, you 

should consult a professional hazard abatement contractor about the 

best way to seal it off. If renovation work requires removal, it should 

be done by a hazard-abatement professional. Your state health 

department can provide a list of contractors certified to perform this 

work. Removal is expensive.

Fiberglass Insulation 

Fiberglass insulation irritates skin and lungs. Some people are more 

sensitive than others. The U.S. Department of Health and Human 

Services has concluded that certain glass fibers are “reasonably 

anticipated to be human carcinogens,” but this refers only to glass 

For more information 

on urea-formaldehyde 

foam insulation

www.cpsc.gov/cpscpub/pubs/725.pdf

www.epa.gov/iaq/formalde.

html#Levels%20in%20Homes

May 2012 23

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ENERGY RENOVATIONS INSULATION
fibers that are small enough to be inhaled, are highly durable, and 

remain in the lungs for long periods of time (NIH 2011). While 

fiberglass insulation is made up of larger fibers, some very small 

fibers may be present (NIH 2009). Cancer risk is generally tied to 

high levels of exposure. 

Formaldehyde, a toxic gas, may also be an issue. Formaldehyde-free 

fiberglass batts and blankets are available, but some brands are 

bound with resins that contain small amounts of formaldehyde. 

Care should be taken when installing fiberglass insulation near hot 

fixtures. Fiberglass itself is noncombustible, but the resin binders 

it contains are combustible, as are some of the facings commonly 

used on batts. Kraft-paper facing should not be placed in contact 

with a chimney, flue pipe, or recessed light fixture. See Appendix 

C for instructions on constructing barriers to keep insulation from 

contacting chimneys, flue pipes, and recessed light fixtures.

Care should also be taken when installing blown fiberglass insulation 

in attics where ducts are located. Ducts must be properly sealed to 

keep fibers from being drawn into air distribution systems and then 

circulated within the living space. 

To avoid moisture problems, be sure that blown insulation does 

not cover attic eave vents. If you are putting additional insulation 

on top of fiberglass batts, there should be no facing between the 

layers. Facing between the layers can act as a vapor retarder and 

create problems with moisture and mold. If you already have 

faced batts on your attic floor with the facing on top, do not put 

insulation over them.

Mineral Wool Insulation

As with fiberglass batts, formaldehyde-free mineral wool batts are 

available, but some batts are bound with resins that contain small 

amounts of formaldehyde, a toxic gas. 

Plastic Foam Insulations: Polyurethane, 

Polystyrene, and Polyisocyanurate

All plastic foam insulation, whether spray foam or rigid board, 

can pose a health risk if it burns. Plastic foam insulation ignites at 

high temperatures and emits a dense smoke containing toxic gases, 

including carbon monoxide. (Cementitious foam, in contrast, is fire 

resistant and non-toxic, but not as widely available.) Plastic foam 

insulation must be covered with a thermal barrier to retard the 

spread of fire. For interior walls, 1⁄2-inch gypsum board is sufficient. 

Fiberglass. Take care when handling 

fiberglass insulation, which can irritate 

skin and lungs. Keep kraft facing on batts 

away from hot fixtures. Install vent baffles 

to keep loose-fill insulation from blocking 

attic vents. Blocked vents can lead to 

problems with moisture, mold, and 

wood rot (Photo Source: PNNL).

See Appendix C for performance 

briefs on insulating and air 

sealing around

•	 Flue and chimney shafts

•	 Recessed light fixtures

•	 Duct boots and duct chases.

24 May 2012

ENERGY RENOVATIONS INSULATION
For contractors:

Installing polyurethane or other foam 

insulations can involve significant safety 

risks. Check safety protocols at:

The National Institute for Occupational 

Safety and Health (NIOSH), 

www.cdc.gov/niosh/construction/

The Occupational Safety and Health 

Administration (OSHA), www.osha.gov/

pls/oshaweb/owasrch.search_form?p_

doc_type=STANDARDS&p_toc_level=1&p_

keyvalue=Construction

Polyurethane foam insulation. Leave 

the installation of spray foam to trained 

professionals. Toxic gases emitted during 

application are hazardous to skin, eyes, 

and lungs (Photo Source: NAHB).

Metal flashing should be used to keep rigid foam insulation away 

from hot fixtures, such as chimney flues and non-insulation-contact 

rated recessed “can” lights. For instructions, see the Performance 

Briefs in Appendix C on chimney flues and recessed lights.

Polyurethane spray foam emits toxic gases during application. 

Inhalation and skin and eye contact are hazardous. The foam must 

be installed by trained professionals, in strict accordance with 

manufacturer recommendations and local building and fire codes. 

Your contractor should ensure good ventilation and use a respirator, 

goggles, face mask, and protective clothing. Some experts suggest 

that residents stay out of the home for as long as 24 hours after the 

application is completed.

Rigid polystyrene foam insulation contains styrene, which is on 

a list of products that are “reasonably anticipated to be human 

carcinogens.” According to the U.S. Department of Health and 

Human Services, workers are at risk who breathe indoor air that 

has styrene vapors from building materials, tobacco smoke, and 

other products (NIH 2011). 

Cellulose Insulation

Although it is treated with fire retardant, cellulose may smolder 

if temperatures become hot enough. For instructions on keeping 

cellulose away from chimney flues and recessed “can” lights, see 

the Performance Briefs in Appendix C.

Before installing cellulose insulation in an attic where ducts are 

located, be sure to have a contractor seal the ducts to keep fibers 

from being drawn into the air distribution system. (See Appendix 

C, Duct Sealing.) In vented attics, use baffles to keep cellulose 

insulation from covering the soffit vents. Blocked vents can lead to 

severe moisture problems. 

Safety and Health: The Bottom Line

Your house is a system, and every component in it works together. 

Changing one component, such as insulation, can dramatically 

affect how other components perform. Building America strongly 

recommends getting a whole-house energy checkup before you begin 

your insulation work. Your energy contractor will use the results to 

plan your project, choose appropriate products, and help you avoid 

unintended consequences that could affect your health and safety. 

Safety tests. A whole-house energy 

checkup that includes testing in and testing 

out of combustion equipment can help 

you achieve the most cost-effective energy 

efficiency gains while helping to ensure 

health and safety (Photo Source: PNNL).

May 2012 25

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ENERGY RENOVATIONS INSULATION
26 May 2012

ENERGY RENOVATIONS INSULATION
Air sealing. Cracks and gaps that allow 

air to move in and out of the home can be 

sealed with spray foam. Air sealing is an 

essential step before insulation is added 

(Photo Source: PNNL).

This chapter provides guidance in choosing the best strategies 

for insulating each part of your home. It describes best practices, 

explains issues that must be addressed, and identifies pitfalls to 

avoid. The recommendations are supported by real-world building 

science research conducted by Building America partners. 

This chapter provides guidance for insulating the following areas:

5.1 Attics 

5.2 Cathedral ceilings and flat roofs 

5.3 Exterior walls 

5.4 Crawlspaces 

5.5 Basements

5.6 Concrete floors.

To identify problem areas and prioritize projects, begin with a home 

energy assessment. Be sure to work with a contractor who has 

earned certification from a nationally recognized organization to 

perform energy upgrades (see Chapter 2).

Before you add insulation, air sealing your home to reduce air leakage 

is essential. Air leaks carry both moisture and heat, usually in the 

direction you don't want. Most insulation does not stop airflow.

Air flows through any available hole or crack in your home, leading to: 

•	 Energy loss. In a typical home, air leakage accounts for 25% to 40% 

of the energy produced by your heating and cooling equipment.

5.0 How to Add

Insulation 

More Information

Additional information on home energy 

upgrades and other building science 

information can be found in the Building 

America Best Practices guides produced 

by the U.S. Department of Energy and 

available for free download at

www.buildingamerica.gov.

May 2012 27

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ENERGY RENOVATIONS INSULATION
•	 Poor air quality. Air leaks allow dust, pollen, and mold spores to enter 

the house, contributing to health problems. 

•	 Mold and rot. If the moisture in air condenses on organic surfaces such 

as wood or paper-faced drywall, it can lead to mold and rot inside the 

walls and in other parts of the house.

•	 Discomfort. Air leaks can cause drafts and uneven temperatures in 

your home. 

Chimneys and the cracks around doors and windows are well-known 

trouble spots when it comes to air leakage, but other leaks can be more 

significant. Common air leakage spots are shown in Figure 5.1.

Air sealing is inexpensive and highly effective. For more information 

on air sealing, see Building America’s Air Sealing Guide at http://

apps1.eere.energy.gov/buildings/publications/pdfs/building_america/

ba_airsealing_report.pdf

Ventilate Right

When you have sealed air leaks, you may 

need to add mechanical ventilation to 

ensure that your home has a good source 

of fresh air. Replacing stale air with fresh 

air is essential for health and comfort. 

Poorly ventilated homes can accumulate 

chemicals, gases, and moisture.

Your contractor will use ASHRAE Standard 

62.2 or other industry guidelines to 

determine your home’s ventilation needs. 

Figure 5.1. Where to air seal. Building America research has identified 19 key 

areas where air sealing can improve a home’s energy efficiency, comfort, and 

durability. A certified home performance contractor can perform a home energy 

checkup to identify areas in your home that need air sealing (Figure Source: PNNL). 

18 15 19

3

13

18

16

17

5 4

14

9

13

6

1

8

17

17

10

12

13 7

11

2

Air Leakage Trouble Spots 

Air Barrier and Thermal 

Barrier Alignment 

Attic Air Sealing 

Attic Kneewalls 

Shafts for Piping or Ducts 

Dropped Ceiling/Soffit 

Staircase Framing at Exterior Wall 

Porch-Wall Juncture 

Flue or Chimney Shaft 

Attic Hatch 

Recessed Lighting 

Ducts 

Whole-House Fan 

Exterior Wall Penetrations 

Fireplace Wall 

Garage/Living Space Walls 

Cantilevered Floor 

Rim Joists, Sill Plate, 

Foundation, Floor 

Windows & Doors 

Common Walls between 

Attached Dwelling Units

1

2

3

4

5

6

7

8

9

10

11

12

14

13

15

16

17

18

19

28 May 2012

ENERGY RENOVATIONS INSULATION
5.1 Insulating an Attic

The attic is the first place your contractor should insulate. Airsealing and adding insulation to an attic can do more than any 

other insulation project to increase comfort and cut energy bills. 

Most attic insulation projects can be done at any time.

When you decide to add insulation to an attic, your contractor 

will first do some essential preparation. Installation should begin 

only after these steps are completed. Be sure to hire a contractor 

certified in building science. A knowledgeable contractor will help 

you decide whether a vented or unvented attic is best for your home.

This section provides guidance on the following topics:

5.1.1. Preparing to insulate an attic: Safety, moisture control, 

and ventilation

5.1.2. Insulating a vented attic

5.1.3. Insulating an unvented attic.

5.1.1 Preparing to Insulate an Attic

Before adding insulation to your attic, your contractor must: 

•	 Address safety issues.

•	 Control moisture by air sealing the attic.

•	 Address ventilation issues.

The following is guidance for these three crucial steps.

Address Safety Issues

Resolving safety issues is the first essential step in preparing to 

insulate an attic. Do NOT proceed with air sealing or insulating if: 

•	 The house has a leaking roof. Fix it to prevent moisture problems.

•	 Active knob-and-tube wiring is found in the attic. For fire safety, 

the house must be rewired first.

•	 An exhaust fan is vented into the attic. Bathroom, kitchen, and 

clothes dryer fans must be vented to the outdoors. Otherwise, fans 

can blow moist air into the attic, where it may condense and cause 

mold and wood damage.

Profile

Improving the ducts 

means insulating, air 

sealing, and proper 

installation too

When insulating your attic, make sure 

your ductwork is also properly installed, 

sealed, and insulated. A home in 

California’s Central Valley had leaky ducts 

suspended from the attic framing. Droops 

and kinks in the flex ducts severely 

restricted air flow in the leaky ducts. 

The hanging ductwork was removed. New 

R-8 insulated ducts were laid on trusses, 

the joints were sealed with mastic. A 

duct blaster test with the new system 

showed leakage of just 5.1%. The builder, 

Grupe, also replaced the aged, oversized 

furnace and air conditioner with a highefficiency 2.5-ton furnace and 2.5-ton air 

conditioner that were almost half the size 

of the equipment they replaced. 

Grupe removed old R-30 blown fiberglass 

in the flat attic and sagging R-22 

fiberglass batts in the cathedral ceiling. 

They air sealed the ceiling and reinstalled 

the fiberglass, then added blown cellulose 

over it for R-49 attic insulation. The builder 

also replaced 14 leaky can lights with 

insulation contact-rated recessed lights. 

Whole house air leakage was cut by 55%. 

(Source: DOE 2009a)

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ENERGY RENOVATIONS INSULATION
•	 The house has an unvented kerosene heater or gas fireplace. For 

health and safety, it must be vented or removed before you can 

air seal and insulate the attic.

•	 The attic has vermiculite insulation. Don’t disturb it. It may 

contain asbestos. See the information on vermiculite insulation in 

Chapter 4 of this guide.

Control Moisture by Air Sealing the Attic 

Air sealing to prevent moisture problems is the second essential step 

in preparing to insulate an attic. If you choose to add insulation 

without air sealing the attic, you risk serious moisture problems. 

AIR LEAKS AND THE “STACK EFFECT” PUT MOISTURE IN 

THE ATTIC. Air carries both moisture and heat. Just as hot air 

moves up a chimney to escape through the hole above, warm air 

in your house rises and escapes into the attic through holes in the 

ceiling (Figure 5.3). This upward movement of air is called the 

“stack effect.” 

Because of the stack effect, some of the moisture in your home—from 

cooking, bathing, and breathing—ends up in your attic. When moist 

air meets an attic surface with a temperature below the dew point, 

the air deposits its moisture. If the moisture condenses on organic 

surfaces such as wood or paper-faced drywall, it can lead to mold and 

rot. For further details, see Appendix B, “Air Leakage, Moisture and 

Ventilation: Why You Need a Whole-House Approach.”

Figure 5.3. The stack effect. The warmer 

air inside the home is more buoyant than 

the outside air. Thus it wants to rise and 

will push its way out of any holes in the 

ceiling. The flow of air out of the top of the 

building draws in cold air through cracks in 

the floor and walls of the house. Air sealing 

the ceiling slows down this stack effect 

(Figure Source: EPA).

Figure 5.2. Ceiling holes. Homes are 

typically constructed with lots of holes in 

the ceiling for lights, pipes, vents, ducts, 

and chimneys. If the builder fails to air seal 

around these, air escaping through the 

gaps can carry moisture, possibly leading 

to mold and wood rot. These gaps must 

be air sealed before insulation is added 

to the attic (Figure Source: PNNL).

Plumbing 

Vent

Attic

Hatch

Chimney

Electric 

Box Exhaust Fan

Top of 

Partition

PLUMBING 

STACK VENT

BATHROOM

FAN VENT

ELECTRICAL 

OUTLET

DRYER VENT

RECESSED 

LIGHTS

ATTIC 

HATCH RECESSED

LIGHTS

CHASE

KITCHEN 

FAN VENT

OUTDOOR 

FAUCET CRAWL 

SPACE

Air leaking into the house

Air leaking out of the house

30 May 2012

ENERGY RENOVATIONS INSULATION
(Top) Spray foam insulation. Spray foam 

was used to simultaneously air seal and 

insulate this ventilated attic. Baffles 

installed in each rafter bay keep the 

insulation from blocking the soffit vents 

(Photo Source: WSU Energy Office).

(Bottom) Spray foam at roofline. Some 

homeowners choose to air seal and insulate 

the attic at the roofline, turning the attic 

into an unvented, conditioned space. As 

a result, HVAC equipment and stored 

items in the attic are protected from the 

temperature extremes typical of a vented 

attic (Photo Source: IBACOS).

INSULATION WITHOUT AIR SEALING CAN WORSEN 

MOISTURE PROBLEMS. The fiberglass and cellulose insulation 

typically used on an attic floor will not stop the stack effect. Air 

moves right through fiber insulation. This reduces its R-value. 

More importantly, it can make moisture problems worse. Airborne 

moisture can dampen the fiber insulation, increasing moisture risks. 

At the same time, the insulation reduces the heat entering the attic, 

leaving wood surfaces colder. Moisture is more likely to condense 

on cold surfaces, leading to mold and wood damage.

Air escaping to the attic through the stack effect also creates 

problems with temperature, air quality, and moisture throughout 

your home:

•	 Air you pay to heat is lost to the attic.

•	 Replacement air is sucked into your living space from the outdoors 

or from the basement or crawlspace. 

•	 The incoming air can carry pollutants such as dust and soil gases.

•	 Your home’s equipment has to work harder to warm or cool the 

incoming air. 

•	 The incoming air is often damp or humid. The moisture in the air 

may condense on cold surfaces in your crawlspace or basement 

and even inside your walls, leading to mold and wood damage.

AIR SEALING KEEPS INDOOR MOISTURE OUT OF THE 

ATTIC. Air sealing the attic floor stops the escape of air into the 

attic, reducing moisture problems and saving energy. Furthermore, 

stopping the flow of air into the attic means that outside air will 

not be pulled in to the rest of the house to replace it, avoiding the 

problems listed above. 

As your energy contractor knows, it takes knowledge and skill to 

effectively air seal an attic floor in an existing home. It can involve 

pulling insulation back to seal the top plates and wire penetrations, 

making covers for recessed lights, cutting sheet metal to fit around 

flues, and trying to squeeze into areas with limited access to apply 

sealant – all while kneeling on top of ceiling joists and taking care 

not to fall between them. Some crucial areas may be impossible to 

reach. The low roof pitch of many homes can create a space too 

tight to do the crucial sealing of the top plates at the eaves. For 

some homes, the solution is to convert the attic to a “cathedralized” 

design, air sealing and insulating at the roof along the sloped 

roofline. This option is discussed in Section 5.1.3.

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ENERGY RENOVATIONS INSULATION
Make a Decision about Ventilation

The third essential step before insulating an attic is to address 

ventilation. Before adding insulation, your attic must have either 

good ventilation or no ventilation. Both options will control 

moisture problems and attic temperatures:

•	 Good ventilation. Outdoor air moving through the attic helps make 

it cool and dry. 

• No ventilation. An unvented attic is warmer in winter, cooler in 

summer, and dry year-round.

The best attic type for your home depends on your climate, your 

roof design, your budget, and whether ductwork is in the attic. 

Both approaches have advantages and drawbacks, as described in 

the next sections.

5.1.2 Insulating a Vented Attic

It may seem odd to seal air leaks at the attic floor and then make sure 

plenty of air can enter through the attic vents. This combination, 

however, is the key to preventing moisture problems. The air sealing at 

the attic floor blocks the entry of moist air from the living space. The 

ventilation along the roofline cools the attic and allows humid air to 

escape. In winter, cold air entering through the soffit vents discourages 

condensation, since cold air carries much less moisture than warm air. 

In summer, hot, humid air escapes through the roof vents (Figure 5.4).

With good ventilation, air sealing, and insulation, a vented attic can 

help make your home comfortable, durable, and energy efficient.

Advantages and Drawbacks of Vented Attics

A Vented Attic has Advantages in terms of:

• Climate. A well-ventilated and insulated attic works well in any 

climate, provided the attic floor and attic entryway are air-tight.

• Cost. The least expensive types of insulation, loose-fill fiber and 

fiberglass batts, are good choices for insulating the floor of a 

vented attic.

A Vented Attic may have Drawbacks in terms of:

•	 Ductwork. Ductwork in a vented attic can increase energy bills 

and compromise air quality (see sidebar). 

•	 Roof design. If your home does not have a simple gable roof, good 

ventilation can be difficult to achieve. Because ventilation requires 

Figure 5.4. Vented attics. Good ventilation 

helps keep an attic cool and dry. In winter, 

cold winter air entering through the soffit 

vents discourages condensation, since cold 

air carries much less moisture than warm 

air. In summer, hot, humid air can escape 

through the roof vents.

Potential Problems with 

Ductwork in a Vented Attic 

Ductwork and energy bills. If you have 

ductwork in a vented attic, the ducts have 

to run through space that can be hotter 

than 100°F in the summer and well below 

freezing in the winter. Heating or cooling 

the air inside the ducts will cost more, 

especially if the ducts are leaky.

Ductwork and safety. If you have ducts in 

a vented attic and live in a cold climate, 

leaky heating ducts can cause snow on the 

roof to melt, leading to ice dam formation. 

Ice dams are dangerous because the icicles 

that form with them can fall on people. The 

water that accumulates can leak through 

the roof, rot out attic framing, and collect 

on your ceiling; and the ice and water 

buildup can collapse the roof.

Ductwork and air quality. If you have 

ductwork in a vented attic and live in a hot, 

humid climate, moisture can condense on 

the inside and outside of ducts transporting 

cooled air. If mold and mildew form, the 

spores will be circulated through the 

home. Your home’s air quality can also 

be compromised if leaky return ducts in a 

vented attic pull in dust and moist air.

What to do. Your contractor can minimize 

these problems by insulating and air 

sealing the ducts. Alternatively, you can 

convert your attic to an unvented design, or, 

if you are replacing your heating and cooling 

system, you can opt for a ductless heat pump. 

32 May 2012

ENERGY RENOVATIONS INSULATION
a direct path from the soffit to the ridge, complex roofs typically 

have ventilation problems. Features such as valleys, hips, skylights, 

and multiple dormers can make attics difficult to ventilate 

effectively and to air seal and insulate well at the ceiling level 

(Lstiburek 2006c). Conversion to an unvented attic may be called 

for if you have a complex roof design.

A Poorly Ventilated Attic may have Problems with:

•	 Ice dams. Warm air can collect in the attic when it is poorly 

ventilated and lacks air sealing at the floor. (See Appendix C for 

a performance brief on preventing ice dams.)

•	 Mold, mildew, and wood rot in winter. Moist air trapped in a poorly 

ventilated attic can condense on cold surfaces. 

• Mold and mildew in summer. In hot, humid climates, moisture in a 

poorly ventilated attic can condense on both the inside and outside 

of ducts that are transporting cooled air.

• Energy efficiency. In a home with a poorly ventilated attic, heat 

in summer and the stack effect in winter will require more heating 

and air conditioning, especially if ductwork is in the attic.

To Improve Ventilation, your Contractor Should:

•	 Make sure your home has adequate vent space at the soffits and 

roof. For details, see the sidebar titled “How much attic ventilation 

do you need?”

•	 Make sure the soffit vents are not clogged, painted over, or 

blocked by insulation.

•	 In hurricane-prone areas, install special soffit vents that keep 

out wind-blown rain (see performance brief in Appendix C.)

If these measures do not solve moisture problems, consider 

converting your attic to an unvented design.

Your Contractor Should NOT Install Powered 

Roof Ventilation

Building America scientists do not recommend installing a 

powered roof fan to improve attic ventilation, because:

•	 Powered roof fans consume more energy than they save.

•	 They increase the stack effect, which pulls hot, humid 

outside air into the home and can pull in pollutants from 

the basement or crawlspace. 

•	 They can cause backdrafting of fireplaces and unsealed 

gas- or oil-burning appliances (DOE 2000b; Katz 2011).

How much attic ventilation 

do you need? 

A rule of thumb is to have 1 square foot 

of net vent opening for every 150 square 

feet of insulated ceiling. The most effective 

ventilation system combines a continuous 

ridge vent along the peak of the roof with 

continuous soffit vents at the eaves, but 

few existing homes are built that way (DOE 

2000b). The vent area is typically divided 

50:50 between the soffits and ridge, but a 

Building America scientist recommends a 

larger vent area for the soffits—a ratio of 

about 60:40 (Lstiburek 2011a). 

Lstiburek also calls for more ventilation 

than codes typically require, especially 

in areas with snow. He recommends a 

minimum airspace under the roof sheathing 

of 2 inches, not the typical 1 inch, and 

recommends that every rafter or truss 

bay, not every third one, be ventilated 

(Lstiburek 2011b).

Ice dams. Ice dams occur when the outside 

air is below freezing but the roof surface 

is above freezing. The roof surface may be 

warmed by the sun, by leaky heating ducts 

in the attic, or by warm air leaking into the 

attic from the living space below. Icicles are 

a telltale sign that ice dams are forming on 

your roof. Snow melts on the roof and then 

refreezes along the roof’s edge, forming an 

icy buildup. As more snow melts, some will 

spill over and drip down the edge of the 

roof, forming icicles. The rest will collect 

behind the ice dam. The water in the ice 

dam may eventually back up between the 

roof shingles and into the attic, causing 

moisture damage. It can also pool on the 

roof until it causes the roof to collapse 

(Source: BSC).

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ENERGY RENOVATIONS INSULATION
How to Insulate a Vented Attic

Your contractor should begin insulating your vented attic only 

after the following steps are completed (for details, see Section 

5.1.1, above):

1. All safety issues are resolved.

2. The attic floor is thoroughly air-sealed.

3. Good ventilation is ensured. 

This section provides guidance for insulating a vented attic. It 

includes information on preparing to insulate, installing batt 

insulation, installing loose-fill insulation, and using spray foam to 

insulate the attic perimeter.

Appendix C provides performance briefs with instructions for air 

sealing and insulating specific areas of a vented attic, as listed below:

•	 Attic kneewalls

•	 Attic hatches, doors, and drop-down stairs

•	 Around recessed “can” lights

•	 Around chimneys or flue pipes

•	 Around ducts and duct shafts.

Preparing to Insulate a Vented Attic

Your first step is to decide on a type of insulation. Typical forms of 

insulation are: 

•	 Batts or blankets, most often made of fiberglass. Alternative 

materials include mineral wool, sheep’s wool, and cotton. 

•	 Loose-fill, blown-in fiber, typically cellulose or fiberglass. 

Loose-fill fiber insulation usually costs less than batts and provides 

better coverage, because it conforms to the space into which it 

is blown. The small fiber particles fill spaces behind and around 

obstacles, where it’s difficult to install batt insulation. See the tables in 

Chapter 3 for other advantages and drawbacks of the insulation types. 

You can choose to put different forms of insulation together. 

For example, your contractor can add blown insulation over batt 

insulation. Note that material of higher density (weight per unit 

volume) should not be placed on top of lower-density insulation that 

is easily compressed. Doing so will reduce its R-value. 

(Top) Loose-fill fiberglass. In this 

Connecticut home, blown fiberglass 

insulation completely covers the ceiling 

joists of the attic floor, insulating it to R-50 

(Photo Source: BSC).

(Bottom) Sloppy batt installation.

The wall between the hot attic space and 

an upstairs bedroom had thick fiberglass 

batts. However, instead of putting the 

batts in the stud cavities, the installer had 

attached them to the front of the studs, 

leaving a gap behind the batts for hot air 

to reach the wall. The bedroom was hot 

in summer, despite air conditioning 

(Photo Source: PNNL).

Air leakage around recessed light.

As shown in this image taken with an 

infrared camera, hot attic air can leak into 

a home around a recessed can light in 

summer. In winter, warm, conditioned air can 

be pulled out of the house and into the attic. 

34 May 2012

ENERGY RENOVATIONS INSULATION
Insulated attic kneewall. The kneewall 

in this vented attic has been properly air 

sealed and insulated. Rigid foam insulation 

was installed in the open cavities under 

the kneewall (top), and then the kneewall 

and attic floor were insulated (bottom). 

Another option would be to air seal 

and insulate along the underside of 

the roofline to the eaves. This could be 

accomplished by continuing the attic 

room ceiling insulation and drywall to the 

eaves or installing rigid foam above the 

kneewall to the eaves. This would provide 

conditioned storage space outside the 

attic room, and there would be no need to 

insulate the kneewall.

For either batt or blown insulation, your contractor will have two 

goals: to gain enough R-value and to achieve that R-value uniformly 

across the attic, leaving no place where insulation is missing or too 

shallow. Your contractor will begin with the following:

1. Look into your attic to see what kind of insulation you already 

have and measure its depth. (If you are doing this step yourself, 

a table in Chapter 2 will help you identify the insulation. If you 

think you have vermiculite insulation, don’t disturb it; it may 

contain asbestos. See Chapter 4.)

2. Use tables like those in Chapter 2 to estimate the R-value of the 

current insulation and determine how much insulation should be 

added to reach the recommended R-value for your climate zone.

3. Install vent baffles to ensure that outside air can move directly 

from the soffits to the ridge vents (Figure 5.5). 

Using Spray Foam to Insulate the Attic Perimeter

Uniform R-value across the attic floor is difficult to achieve. In a 

typical attic, the rafters meet the floor at a tight angle that allows for 

little insulation. As a result, recommended R-values often cannot be 

reached with fiber insulation at attic perimeters. 

To solve this problem, your contractor may suggest using spray foam 

to insulate around the perimeter. Spray foam has a high R-value per 

inch and also provides excellent air sealing. Before using this method, 

your contractor should make sure vent baffles are installed in each 

rafter bay. The baffles should extend to the outside edge of the top 

plate and maintain a 2-inch airspace under the sheathing. This will 

ensure adequate air flow from the soffit vents to the ridge vents.

Installing Batt Insulation

Faced or unfaced batts? Batt facings are vapor retarders; they should 

be used in some climates but not others. Your contractor should:

•	 Install faced batts in IECC Climate Zones 5 and 6, with the 

facing against the attic floor. Note: If you are putting additional 

insulation on top of fiberglass batts, there should be no facing 

between the layers. If you already have faced batts on your attic 

floor with the facing on top, do not put insulation over them. 

Facing between the layers can act as a vapor retarder and create 

problems with moisture and mold.

•	 Use unfaced batts in IECC Climate Zones 1 through 4. Building 

America scientists do NOT recommended installing vapor 

retarders in vented attics in these zones (Lstiburek 2006c). 

Spray foam at the roof eaves. Spray foam 

can provide both air sealing and insulation 

in the hard-to-reach areas at the roof 

eaves. Baffles keep the insulation from 

blocking the soffit vents.

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ENERGY RENOVATIONS INSULATION
If you have no existing insulation on the attic floor, your contractor should:

•	 Measure and cut the batts to fit perfectly in each cavity and extend 

to the very edge of the attic floor.

•	 Roll out the batts between the joists, making sure the batts are in 

full contact with all floor and cavity surfaces. Even small gaps add 

up to a large reduction in effective R-Value; they are like holes in 

a blanket. 

•	 Cut the batts carefully to fit around pipes, ducts and wires, without 

any pinching or compression.

•	 Place a second layer of insulation over the tops of the joists to 

reduce thermal bridging (heat loss through the wood). This second 

layer can be blown loose-fill insulation or a second layer of batts 

laid perpendicular to the joists.

If you already have existing insulation that has no gaps and that fills 

the cavities to the tops of the joists:

•	 Your contractor should place the new batts perpendicular to the 

old ones, covering the tops of the joists; or cover the joists or old 

batts with blown insulation. 

Installing Loose-Fill Insulation

Loose-fill fiber insulation is blown into the attic with a pneumatic 

hose. It is usually installed by a professional installer, who will:

•	 Install vent baffles to keep blown insulation out of the soffit vents.

•	 Staple rulers to floor joists in different parts of the attic to measure 

the depth of the insulation as it is blown in.

•	 Blow insulation across the entire attic floor, at an even depth.

•	 Blow enough insulation to achieve the manufacturer's recommended 

density. If the density is too low (known in the trade as “fluffing”), 

the insulation will settle excessively and have a lower R-value.

Radiant Barriers for Vented Attics

If you live in a hot-dry or hot-humid climate, it may be cost-effective 

to install a radiant barrier in your vented attic along with the 

insulation. A radiant barrier is basically aluminum foil that comes 

with a variety of backings. It reduces the amount of heat that moves 

from your roof to the attic floor. Radiant barriers are appropriate 

only for vented – not unvented – attics (Lstiburek 2010b). For 

instructions on installing radiant barriers, see Appendix C.

Figure 5.5. Baffles. Your contractor will 

install vent baffles to maintain a 2-inch 

continuous ventilation channel above the 

insulation. 

Radiant barrier. While it doesn’t add 

R-value, a radiant barrier can reduce 

cooling loads in hot climates by minimizing 

solar heat gain. A radiant barrier looks like 

aluminum foil and has a backing of bubble 

wrap, paper, or sheathing. They can be 

stapled to the underside of the roof rafters. 

Or, when reroofing, sheathing can be 

installed that comes with a radiant barrier 

layer adhered to it, as shown here (Photo 

Source: David Weekley Homes).

36 May 2012

ENERGY RENOVATIONS INSULATION
5.1.3 Insulating Unvented Attics

An unvented attic is air sealed and insulated at the sloped roofline 

instead of on the floor. When you convert your attic to an unvented 

design, it becomes indoor space, similar to a room with a 

cathedral ceiling.

Advantages and Drawbacks of Unvented, 

Insulated Attics

An Unvented, Insulated Attic has Advantages in terms of:

•	 Energy efficiency when ducts are in attic. An unvented attic is 

warmer in winter and cooler in summer. Ductwork that is not 

subject to extreme temperatures will last longer and be more 

efficient (DOE 2003). 

•	 Energy efficiency in hot climates. Homes with an unvented attic in 

the hot-dry or hot-humid climate zones typically use less energy 

(DOE 2003, Rudd et al. 1999).

•	 Avoiding moisture problems. Moist air will stay outside the attic, 

provided the attic ceiling is thoroughly air sealed. This is especially 

an advantage for homes in hot, humid climates with ductwork in 

the attic (Rudd et al. 1999).

•	 Roof design. An unvented attic can be a good solution for complex 

roofs that are hard to ventilate well.

•	 Space. An unvented attic can easily serve as living or storage space.

•	 Weather resistance. Roofs over unvented attics are less likely to be 

blown off in high winds. In wildfire zones, a house without soffit 

vents is less like to catch fire. In coastal areas, an unvented roof 

keeps out wind-driven rain, and metal pieces in the roof assembly 

are protected against salt spray and corrosion (Lstiburek 2006c).

An Unvented Attic has Drawbacks in terms of:

•	 Cost. In cold or humid climates, unvented attics should be 

insulated with rigid or spray foam insulation, which is much more 

expensive than fiberglass batts or blown fiber. However, it may be 

cost-effective to seal and insulate an attic along the roofline when you 

are reroofing or creating an attic room.

•	 Maintenance. If you install exterior rigid foam insulation, it may 

be harder to locate roof leaks or repair rotten roof sheathing. 

Damp roof sheathing may take longer to dry. 

May 2012 37

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ENERGY RENOVATIONS INSULATION
•	 Roof durability. The temperature of shingles over unvented attics 

is higher, reducing their durability. Homeowners can expect a 10% 

decrease in the service life of the roof (Lstiburek 2006c).

•	 Ice dams where snow is thick. An unvented attic increases the 

possibility of ice dams in areas with heavy snow loads (in excess of 

50 lb/ft2). When sealing and insulating an attic in these areas, your 

roofer can minimize the risk by creating a vented air space between 

the shingles and the rigid insulation (Lstiburek 2011b).

•	 Wider fascia. Rigid insulation above the roof deck results in a 

wider fascia board at the eave or top of the wall. 

Your contractor can determine whether your attic has adequate 

ventilation. If you can ventilate your attic well and it has no 

moisture problems, your best option may be to leave it vented. On 

the other hand, if your attic cannot be well ventilated and develops 

moisture problems, sealing and insuating it (converting it to an 

unvented design) may be your best option. The following sections 

provide guidance for insulating both types of attics.

How to Insulate an Unvented Attic

This section provides guidance for the following steps:

1. Deciding where and how to insulate.

2. Preparing the attic and closing the vents.

3. Installing insulation below the rafters.

4. Installing insulation above the rafters.

Deciding Where and How to Insulate

In the hot-dry climate zone, you can insulate an unvented attic along the 

underside of the roof deck by fastening netting to the rafters and filling 

the space between the netting and the roof deck with blown cellulose 

or fiberglass. However, in all other climates, insulating the underside 

of the roof deck with fiber insulation could lead to moisture problems 

(Straube and Grin 2010). To prevent condensation under the roof deck: 

•	 Use rigid foam insulation above the roof deck to keep its 

temperature above 45°F throughout the year. Rigid foam can be 

installed if you are reroofing your house (Figure 5.6). 

•	 Use spray foam insulation under the roof deck to keep interior 

moist air from contacting it. 

•	 Supplemental insulation can be installed with either approach 

when additional R-value is needed. 

Unvented attic. This attic has been sealed 

and insulated with spray foam insulation 

applied under the roof deck. This turns the 

attic into a conditioned space for HVAC 

equipment (Photo Source: W. Hawthorne).

Figure 5.6. Rigid insulation above Roof 

Deck. If you are reroofing your home, 

another way to insulate a sealed attic is 

with rigid insulation applied above the roof 

deck, as shown here (Source: BSC). 

Shingles

Roofing 

paper

Wood decking

Timber rafter or exposed joist

Rigid insulation in two or 

more layers with horizontal 

and vertical joints staggered

Nail base 

for shingles 

(plywood or 

OSB) screwed 

through rigid 

insulation to 

wood decking or 

timber rafters

Air barrier 

membrane

38 May 2012

ENERGY RENOVATIONS INSULATION
Preparing the Attic and Closing the Vents

Your contractor should complete the following preparatory steps:

•	 Resolve all safety issues (see Section 5.1.1).

•	 Have a local code official review your unvented attic design. Code 

requirements for unvented attics vary significantly across the country. 

2009 IRC R806.4 lists requirements for unvented attic assemblies.

•	 Remove the old floor insulation. This will allow the living space 

below to indirectly condition the attic. (It will also let workers see 

where they are stepping.) Loose-fill insulation can be vacuumed out 

by an insulation professional. Batts need to be removed by hand. If 

you choose to do this job yourself, wear a dust mask and gloves. 

•	 If there is a vapor retarder on the attic floor, it must be removed. 

Any moisture that builds up in an unvented attic needs to diffuse 

into the house below. Vapor retarders on the floors of unvented 

attics are prohibited under the 2009 IRC.

•	 Close off and seal all the openings that exist to ventilate your attic, 

including ridge vents, gable vents, and soffit vents. 

•	 Reroof the previously open areas.

•	 Seal all wood-to-wood joints in the framing.

•	 Remove or disable any attic fan. Take particular care, however, 

not to block, remove, or disable the kitchen or bathroom exhaust 

stacks or the exhaust vents for water heaters or furnaces, radon 

vent stacks, or plumbing stacks. 

Building America scientists provide the following cautions:

•	 Do not install sheet polyethylene as an air barrier at the underside 

of the roof deck because of the difficulty of making it perfectly 

airtight. Airborne moisture can become trapped behind it (Straube 

2006). Sheet polyethylene is a Class I vapor retarder and is 

prohibited in unvented attics under the 2009 IRC. See Appendix 

B.4 for important distinctions between classes of vapor retarders.

•	 Make sure plans do not include the installation of recessed “can” 

lights in the attic ceiling, even ones that are ICAT-rated. There 

will be no room for insulation above them, and energy will be lost 

through the void. Worse, they create a risk of moisture problems. 

Recessed lights can draw warm moist air through the ceiling and 

into the insulation, even when they are designed to be airtight. 

Track lighting is a good alternative.

Moldy fiberglass batts. The fiberglass 

insulation in this unvented cathedral ceiling 

absorbed moisture, leading to mold and 

wood damage. Building America scientists 

do not recommend using fiberglass or 

cellulose in a cathedral ceiling or flat roof, 

unless rigid or spray foam insulation is 

installed above the fiber to form an air and 

moisture barrier (Photo source: BSC).

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ENERGY RENOVATIONS INSULATION
Installing Insulation Under the Roof Deck 

of an Unvented Attic

If you live in the hot-dry climate zone, you can insulate under the 

roof deck with fiberglass batts or netted cellulose insulation. 

As noted previously, fiber insulation should not be placed in contact 

with the roof deck anywhere outside the hot-dry climate zone. 

Instead, spray foam insulation should be applied under the roof 

deck. Spray foam not only insulates but provides a tight air seal, 

protecting the roof deck from airborne vapor (Figure 5.7).

Two types of spray foam insulation are available, open-cell and 

closed-cell. Open-cell foam costs less than closed-cell foam, but has a 

lower R-value per inch. Both will provide a good air barrier. Closedcell spray foam is also a vapor retarder, an advantage in cold climates 

that require more protection from condensation. Open-cell foam is 

not a vapor retarder. (See vapor retarder discussion in Section 3.2 

and Appendix B.4.)

If you choose to insulate the entire ceiling cavity with spray foam, 

Building America scientists make the following research-based 

recommendations (Straube 2006):

•	 In IECC Climate Zones 1 through 3, open-cell foam can be used, 

provided interior humidity is not high (see IECC map Chapter 2). 

•	 In Zones 4 and 5, use closed-cell foam or open cell-foam with a 

spray-applied vapor retarding paint on the interior side (2009 IRC 

Section R806.4). 

•	 In Zones 6 and higher, closed-cell foam should be used. 

•	 All foam on the interior should be separated from lining space by a 

fire-rated material, such as 1⁄2-inch gypsum board.

Supplementing Spray Foam Insulation 

with Fiber Insulation

In cold climates, applying enough spray foam insulation on the 

underside of the roof deck to reach the recommended R-value may 

be expensive. To reduce costs, your contractor can add inexpensive 

fiberglass batts, netted fiberglass, or dense-pack cellulose on the attic 

side of the closed-cell foam.

If you choose to supplement closed-cell spray foam with fiber 

insulation, Building America scientists make the following researchbased recommendations (Straube and Grin 2010).

Attic room. This attic was insulated with 

spray foam at the roofline to provide 

additional conditioned living space in 

the home.

Roof cladding

Roof underlayment 3 inches closed-cell 

spray foam (R-19.5)

6 inches blown

fiberglass (R-21)

Figure 5.7. Closed-cell spray foam 

provides an air barrier to keep vapor 

from condensing on the underside of 

the unvented roof. The spray foam is 

supplemented with blown fiberglass 

between the spray foam and drywall for 

additional R-value (Figure Source: adapted 

from Straube and Grin 2010).

40 May 2012

ENERGY RENOVATIONS INSULATION
Low density spray foam insulation

Asphalt shingles

Roofing paper

Roof sheathing

Raised heel truss

Rigid foam or 

comparable as 

backdam

Soffit

Roof underlayment 

sealed to drip edge

Gypsum board with 

latex paint separating 

occupiable space from 

non-occupiable space

Non-occupiable 

space

•	 Zones 1 through 4: Install 3 inches of closed-cell spray foam plus 

fiber insulation.

•	 Zones 5 and 6: Install 4 inches of closed-cell spray foam plus fiber 

insulation. This approach can also be used in Zone 7, provided 

interior humidity is not high

•	 Zones 5 through 8 and Marine Zone 4 require a Class II vapor 

retarder in direct contact with the underside (the attic side) of the fiber 

(Building Energy Codes Resource Center 2011a). Options include 

latex-painted gypsum board or a kraft facing on fiberglass batts.

Installing Insulation above the Roof Deck 

of an Unvented Attic

Reroofing your house creates an opportunity to add insulation above 

the roof deck. Your roofer can install sheets of rigid foam insulation 

between the roof shingles and the roof plywood or OSB (Figures 5.6 

and 5.9). Alternatively, your roofer can install sheathing bonded with 

rigid foam or structural insulated panels designed for roofs. 

Your contractor will follow the manufacturer’s installation 

instructions. Building America scientists add the following researchbased cautions and recommendations.

•	 Your roofer must make the roof deck exceptionally airtight. This 

can be done by placing the rigid foam between two layers of 

OSB and covering the lower OSB layer with a continuous, lapped 

peel-and-stick membrane. 

•	 To prevent air leaks, seams and edges at the eaves must be 

carefully sealed.

•	 With wood shingles or shakes, a 1⁄4-inch air space must separate 

the shingles or shakes from the roofing felt over the structural 

sheathing (DOE 2007a; Lstiburek 2004c). 

•	 With asphalt roofing shingles in the hot-humid, mixed-humid, and 

marine climate zones, a Class II vapor retarder should be installed 

under the shingles for moisture control (Lstiburek 2004c).

•	 When using sheets of rigid foam, install two layers of rigid foam (e.g., 

two 3-inch layers instead of one 6-inch layer) and stagger the seams.

•	 Apply latex primer to the gypsum board ceiling to serve as a vapor 

retarder (Straube and Grin 2010) before painting or texturing. 

Air seal and insulate. Spray foam was 

combined with unfaced batt insulation 

in this garage ceiling to get the air 

sealing value of the spray foam and the 

added R-value of the less expensive 

batt insulation (Photo Source: BSC).

To identify your climate zone, 

see the map in Chapter 2.

Figure 5.8. Spray foam in an unvented attic.

In this configuration, low-density, open-cell 

spray foam is used to insulate an unvented 

attic. This configuration is appropriate for hot 

climate zones. For unvented attics in mixed 

climate zones, use closed-cell foam or opencell foam covered by a vapor retarder. In cold 

climates, vapor-retarding closed-cell spray 

foam should be used (Figure Source: Straube 

and Grin 2010).

May 2012 41

41

ENERGY RENOVATIONS INSULATION
Roofing

1x3 strapping

Gypsum board

Cardboard baffle

Aluminum 

trim details

Lapped peel & stick membrane as 

drainage plane

OSB sheathing

Lapped peel & stick 

membrane as air barrier

OSB sheathing

Netted and blown cellulose 

insulation (R-32)

Two 21⁄2-inch layers of 

polyisocyanurate rigid 

foam (R-32); joints offset 

vertically and horizontally

Supplementing Rigid Foam Insulation 

with Fiber Insulation

In cold climates, it may not be practical to install enough rigid foam 

insulation above the roof deck to achieve the recommended R-value. 

To supplement the rigid foam, spray foam insulation can be added 

under the roof deck. Alternatively, inexpensive fiberglass batts or 

netted cellulose can be installed under the roof deck. However, 

placing fiber insulation against the roof deck requires careful 

measures to reduce the risk of moisture problems. In addition to 

the recommendations above, Building America research shows the 

following must be done: 

•	 The rigid foam above the roof deck must provide a certain 

proportion of the overall R-value (Straube and Grin 2010). The 

proportion depends on your climate zone (Table 5.1). For example, 

if you are in Climate Zone 5, your contractor should install rigid 

foam of at least R-20. It can then be supplemented with enough 

fiber insulation to achieve the goal of R-38.

•	 In Climate Zones 5 through 8, a vapor retarder must be installed 

in direct contact with the fiber insulation (Building Energy Codes 

Resource Center 2011a).

Table 5.1. Insulation Proportions for Condensation Control

When combining rigid foam over the roof deck with fiber insulation under 

the roof deck, the two types of insulation must be in correct proportion. The 

proportion depends on your climate.

Climate Zone

Install rigid foam 

insulation over roof 

deck with an 

R-value of at least:

Add fiber insulation 

under roof deck to 

reach these Rvalues recommended 

by the IECC:

2B and 3B tile roof only 0 (none required) R-30

1, 2A, 2B, 3 R-5 R-30

4C R-10 R-30

4A, 4B R-15 R-38

5 R-20 R-38

6 R-25 R-49

7 R-30 R-49

Source: Straube and Grin 2010: 2009 IRC Unvented Attics Table 806.4 with IECC R-values

Figure 5.9. Unvented attic.

In this configuration for insulating an 

unvented attic, rigid foam insulation 

is sandwiched between two layers of 

OSB sheathing. The lower layer of OSB 

is covered with a lapped peel-and-stick 

membrane, which provides an air and 

moisture barrier at the roof line. The 

upper layer of OSB serves as the roof deck 

and supports the roofing material. This 

OSB layer is covered with peel and stick 

membrane, which serves as a drainage 

plane. Blown or batt insulation can be 

installed between the roof deck and the 

ceiling gypsum to provide additional 

R-value (Figure Source: Straube and 

Grin 2010).

42 May 2012

ENERGY RENOVATIONS INSULATION
Roof shingles

Roofing felt

Roof sheathing

11⁄2" air space

1" XPS foam

I-joist

Blown 

insulation

Gypsum board

Notes: Latex paint

• 11⁄2” vented air space

connected to soffit and ridge vents

• Gypsum board as air barrier

• Use care at recessed fixtures

• Latex paint as primary vapor retarder

5.2 Insulating Flat Roofs 

and Vaulted Ceilings

Insulating a flat roof or vaulted ceiling (also called a cathedral 

ceiling) is challenging. The narrow cavity above the ceiling makes 

it difficult to add enough insulation and the constrained air flow 

hinders moisture diffusion.

Insulating a flat roof or vaulted ceiling is generally done as part of a 

reroofing project or indoor remodeling project. Gaining access to the 

ceiling cavity requires removal of either the ceiling or the roof, and 

removal of any existing insulation. 

This section provides guidance for insulating a vented flat roof 

or vaulted ceiling. If you are insulating an unvented space, follow 

the instructions in Section 5.1.3, “How to Insulate an Unvented, 

‘Cathedralized’ Attic.” 

Insulating a Vented Flat Roof or Vaulted Ceiling

A vented flat roof or vaulted ceiling requires a continuous ventilation 

space under the roof sheathing to prevent moisture problems: 

•	 Vented flat roofs require a continuous 11⁄2-inch air space between 

the roof sheathing and the top of the insulation (Figure 5.10). This 

air space is the critical factor in controlling moisture accumulation 

in the sheathing. 

•	 Vaulted ceilings require the same continuous 11⁄2-inch air space 

from soffit vents to ridge vents. Note: This direct path for 

ventilation is possible only in a house with a rectangular plan, 

a simple gable roof, and no dormers. If this does not describe 

your house, effective moisture control requires conversion to an 

unvented design (Straube and Grin 2010). Follow the guidance in 

Section 5.1.3.

Building America scientists recommend insulating a vented flat 

roof or vaulted ceiling with moisture-resistant XPS (extruded 

polystyrene) rigid foam:

•	 Install 1-inch-thick pieces of XPS, leaving a 11⁄2-inch air space 

between the XPS and the roof sheathing. For additional R-value, 

add extra layers of XPS or supplement it with dense-pack cellulose 

in the space left between the XPS and the ceiling gypsum board, 

as shown in Figure 5.10. 

Figure 5.10. Vented flat roof. When 

insulating a vented flat roof or vented 

vaulted ceiling, a 11⁄2-inch air space is 

required over XPS foam insulation. The joist 

cavities below the rigid foam are filled with 

blown fiber insulation for additional R-value 

(Source: Straube and Grin 2010).

Figure 5.11. Vented cathedral ceiling.

Rigid insulation can be added to a vented 

cathedral ceiling to provide additional R-value. 

It is important to provide a continuous air 

barrier to prevent moisture-laden air from 

getting into the attic by taping at seams and 

sealing at the edges. A continuous air barrier 

is difficult to achieve if the ceiling contains 

recessed lighting fixtures or other ceiling 

penetrations (Source: Straube and Grin 2010).

Roof insulation

Insulation wind baffle

2 in. minimum space

Water protection

membrane (ice-dam 

protection where 

required)

Continuous

soffit vent

Vinyl or 

aluminum 

siding

Rigid insulation

(taped or 

sealed joints)

Cavity insulation

with vapor diffusion

retarder backing

Gypsum board

Caulking or sealant

Gypsum 

board

Rigid 

Insulation

(taped or 

sealed joints)

Continuous ridge

ventilation

May 2012 43

43

ENERGY RENOVATIONS INSULATION
Profile

Spray Foam Insulates 

Las Vegas Ceiling

The builder wanted to cut energy use 

and retain this 1963 Las Vegas home’s 

Mid Century Modern styling so he 

worked with Building America on a plan 

that included gutting walls, replacing 

windows, and taking off the old roof to 

expose cathedral ceiling cavities that were 

then filled with 8 inches of closed-cell 

spray foam. The foam was topped with 

OSB, water-proofing membrane, and two 

perpendicular layers of 1x3 wood spacers 

to allow venting under the “cool” white 

metal roof. These and other measures cut 

the ReVision home’s energy use 60%. 

•	 Make sure the ceiling gypsum board is thoroughly air sealed with 

caulk, mud, and tape, and then apply latex paint as a 

vapor retarder. 

Building America scientists do NOT recommend installing 

fiberglass or cellulose insulation in vented flat or vaulted ceilings 

without XPS rigid foam separating the fiber from the air space. 

Otherwise, air will blow through the fiber insulation, leading to 

mold and rot (Lstiburek 2010a).

Recessed “can” lights should never be installed in a vaulted ceiling 

or under a flat roof, even if they are ICAT-rated. There is no room 

for insulation above them, and energy will be lost through the void. 

Worse, they create a risk of moisture problems. Recessed lights can 

draw warm moist air through the ceiling and into the insulation, 

even when they are designed to be airtight. Any recessed lights 

already installed must be removed, and the holes carefully repaired 

and sealed. 

5.3 Insulating Exterior Walls

This section provides general guidance for most wall insulation 

projects. A knowledgeable contractor can help you choose the best 

insulation for your project and plan strategies to control moisture.

Decisions about wall insulation depend on whether your home has 

non-masonry stud-framed walls sided with wood, vinyl, aluminum, 

or fiber cement or masonry walls of brick, stone, or concrete.

5.3.1 Stud-Framed Walls: 

When to Insulate

Stud-framed walls with wood, vinyl, aluminum, or fiber cement 

siding can be insulated with a variety of products. Loose batts can 

be added to the interior of the walls within the stud cavities. Rigid 

foam insulation can be attached to the interior side of the walls or to 

the exterior, under the siding. Each approach has advantages 

and drawbacks.

Projects for insulating non-masonry, stud-framed walls fall into 

three categories: those you can do any time, those you can do when 

replacing your siding, and those you can do when a wall is gutted on 

the inside for a remodeling project. 

Closed-cell spray foam fills the rafter bays 

of the vented cathedral ceiling.

This 1963 Las Vegas home got new 

insulation, windows, and a new roof to 

cut energy use by 60%.

44 May 2012

ENERGY RENOVATIONS INSULATION
Adding Insulation at any Time

•	 “Drill and fill.” Your contractor will drill holes into each stud 

cavity from the interior or exterior and then blow in cellulose or 

loose fiberglass insulation. 

•	 Cantilever insulation. A cantilevered floor, such as a bump-out, 

bay window, or room over an open porch may not be air sealed 

and insulated. You can correct this at any time. For details, see the 

performance brief in Appendix C.

Adding Insulation when Replacing your Siding

•	 Exterior rigid insulation. Highly effective rigid foam insulation can 

be installed over the existing sheathing or in place of it. 

•	 Proprietary insulation systems. You can install rigid foam blocks 

under new siding, or replace your siding with insulated vinyl siding 

or a stucco-like exterior insulation finish system (EIFS). 

•	 “Drill and fill” through the sheathing. Holes can be drilled through 

the existing sheathing to blow dense-pack fiber insulation into the 

stud cavities. 

•	 Replacing exterior wall surfaces. If the siding project includes 

removal of the sheathing, the open wall cavities can be filled with 

batt, blown, or spray foam insulation. 

Adding Insulation when Remodeling

•	 Cavity insulation. If a wall is gutted, it will be inexpensive to 

fill the open wall cavities with fiberglass or cellulose insulation. 

Alternatively, you can fill the cavities with spray foam insulation 

or attach rigid foam insulation to the exposed studs. The foam 

products are much more expensive but provide superior air sealing 

and moisture resistance. 

•	 Bathroom remodeling. If your shower stall or bathtub is removed, 

you may find there is no insulation or air barrier in the exterior 

wall behind it. For details on air sealing and insulating this space, 

see Appendix C.

•	 Replacing a fireplace insert or rebuilding a chimney. You may find 

that the stove or fireplace was installed with no insulation or air 

barrier in the exterior wall behind it. For details on air sealing and 

insulating this space, see Appendix C.

Opportunity to insulate. The siding needed 

to be replaced in this major renovation of an 

uninsulated Sacramento home. Removing 

the siding created an opportunity to add 

rigid foam insulation to the exterior of the 

walls (Photo source: SMUD).

See Appendix C for 

performance briefs on

•	 Insulating cantilevers

•	 Air sealing and insulating behind

tubs and showers

•	 Air sealing and insulating around

fireplaces.

May 2012 45

45

ENERGY RENOVATIONS INSULATION
Profile

1953 Home Held a Rotten Surprise

After 25 years of improving the interior, the Massachusetts homeowners were ready 

to work on energy efficiency and exterior upgrades. Plans included exterior rigid 

foam insulation under new siding and a new roof, high-performance windows, and 

basement insulation. The National Grid Deep Energy Retrofit Pilot provided financial 

incentives, and Building Science Corporation, a Building America team member, 

provided technical support. 

The project came to a sudden stop when workers removed the existing vinyl siding 

and discovered rotting wood shingles beneath them. They removed the shingles 

and tar paper and found extensive water damage. Molded and rotten sections of the 

wood sheathing, wall studs, mud sill and a window header had to be torn out. 

The roof was the source of the problem. The home had been built with no roof 

overhangs, putting the roof gutters in the same plane as the walls. Whenever gutters 

leaked or overflowed, water coursed down the walls. Some of it seeped through the 

vinyl siding. Without an adequate air cavity and drainage plane between the vinyl 

and the wood shingles, the water penetrated the shingles and the tar paper and 

soaked into the wood framing. Melting water from ice dams also made its way 

into the walls. 

The water-damaged framing and sheathing were replaced, and the upgrade work 

continued. Workers wrapped the above-grade walls with house wrap, applied 

shingle-style over the wood sheathing, with seams and edges taped. A self-adhering 

roofing membrane was overlapped onto the house wrap to create a continuous air 

barrier. Two 2-inch layers of foil-faced polyisocyanurate rigid foam insulation were 

attached over the roof and walls. The owner commented that the house looked like a 

box wrapped in “a blanket of insulation.” 

Eave and rake overhangs were added before the new roof was installed – a major 

improvement in water management. In the sealed attic, the rafter bays were filled 

with spray foam insulation. Together with the rigid foam above, this created an 

R-60 roof. 

With batt insulation in the wall cavities and the rigid foam outside, the new wall 

assemblies are R-40. The upgrade served the homeowners by exposing the water 

damage. Now the home is durable as well as comfortable and energy-efficient.

Air barrier. The new wall assembly has foilfaced rigid foam sheathing, carefully taped 

to provide a continuous air barrier. Furring 

strips in front of the foam create an air 

space for proper drainage. 

Source: BSC 2011 

Exterior insulation. Workers installed a 

continuous air barrier on the above-grade 

portions of the house, including the roof, 

then wrapped it again with continuous 

layers of insulation.

Rotting wood. Hidden under the vinyl 

siding was the home’s original wood siding, 

which was moldy and rotten. A poorly 

designed wall assembly had allowed water 

to penetrate for years.

46 May 2012

ENERGY RENOVATIONS INSULATION
5.3.2 Stud-Framed Walls:

Adding Interior Cavity Insulation

The most common insulations used to fill wall cavities are fiberglass 

batts, loose-fill fiber (cellulose or fiberglass), and spray foam. 

Cavity insulation will improve your home’s energy efficiency, but it 

has limitations. The R-value attained with cavity insulation is limited 

by the depth of the stud cavities and by thermal bridging. Thermal 

bridging is the loss of heat through the wood studs, which can reduce 

the R-value of the wall assembly by 25% to 40% (Straube 2011). 

Every stud marks the absence of insulation.

This section provides guidance on the following approaches to 

adding insulation to non-masonry walls :

•	 Adding insulation to a closed wall with “drill and fill” 

•	 Adding fiber insulation to open wall cavities

•	 Adding spray foam insulation to open wall cavities

•	 Attaching rigid foam to the interior of a non-masonry wall.

Adding Insulation to a Closed Wall with “Drill and Fill” 

Your contractor will drill a series of 2-inch holes through either the 

exterior sheathing or interior wallboard, and then blow cellulose or 

fiberglass insulation into the stud cavities. For the exterior approach, 

small pieces of siding may need to be removed to expose the 

sheathing. The patched holes may be noticeable, unless covered with 

new siding or trim.

The density of the fiber in the walls determines the R-value achieved. 

Your contractor may use a “dense-pack” method, which offers a 

higher R-value. This method also reduces settling within the cavity 

and air leakage through the wall. However, the walls must be wellsealed and strong enough to accommodate added pressure.

“Drill and fill” is popular and time-proven. It should be done only by 

a trained professional, who will make sure the insulation completely 

fills the cavities, at the correct density. 

(Top) Dense-pack fiberglass. In this newly 

built home, dense-pack fiberglass is held 

in place with netting. This is a popular 

choice for retrofit insulation, blown into 

open cavities or installed using the drilland-fill method (Photo Source: 

Bob Ward Company).

(Bottom) Cellulose insulation. Made 

from recycled newspaper mixed with fire 

retardant, cellulose insulation is a popular 

wall insulation choice. Unlike batts, it easily 

conforms to the space and fits around 

obstacles, such as wiring and pipes. In this 

home, the cellulose has been blown dry 

into open wall cavities, where it is held in 

place with netting. It can also be mixed 

with adhesive and sprayed into open wall 

cavities or blown dry into closed cavities, 

using the drill and fill method (Photo 

source: G.W. Robinson).

May 2012 47

47

ENERGY RENOVATIONS INSULATION
Adding Fiber Insulation to Open Wall Cavities

Adding fiber insulation to stud cavities is the least expensive way 

to insulate a wall. Fiber insulation is most commonly available 

as fiberglass batts. Loose-fill insulation is also available, made of 

fiberglass or cellulose. For advantages and disadvantages of the 

various types of fiber insulation, see the tables in Chapter 3. 

Fiber insulation has a big drawback: it can hold moisture, which 

reduces its R-value and can lead to mold and wood rot. To control 

moisture in walls and keep fiber insulation dry, walls should be 

designed to shed water and to dry to the exterior; a continuous 

air barrier is also important. See Chapter 3 and Appendix B.4 for 

information on vapor retarders.

Adding Spray Foam Insulation to Open Wall Cavities

Stud cavities can be filled with polyurethane spray foam insulation. 

Spray foam has the advantage of being an excellent air barrier; 

it performs the jobs of air sealing and insulating in one step. 

When installed correctly, it protects the wall from condensation 

due to indoor moisture. However, using foam instead of fiber 

does not avoid the problems of thermal bridging at the studs and 

condensation of outdoor moisture. 

Because it is much more expensive than fiber insulation, 

homeowners are likely to choose spray foam insulation only in 

applications where a perfect air barrier is needed, such as the shared 

wall between living space and the garage. 

The amount of spray foam required depends on your climate zone. 

See the tables in Chapter 3 for more information on spray foam’s 

advantages and disadvantages. 

(Top) The Building America Chesapeake 

Habitat for Humanity case study 

demonstrates a solution for brick walls: 

installing rigid insulation between bricks 

and framing, air sealing, and filling the new 

cavity with batts (www.eere.energy.gov/ 

buildings/building_america/mixed_humid_ 

case_studies.html). 

(Middle/Bottom) The Building America 

SEER case study in New Jersey 

demonstrated the use of blownin and foamed insulation under the 

siding (http://apps1.eere.energy.gov/ 

buildings/publications/pdfs/building_ 

america/36474.pdf). 

seal the edges and gaps with foam, and then fill the new interior stud 

wall with R-19 batts. The existing gap between the double brick wall 

allowed for ventilation, so moisture did not penetrate to the foam. 

New Jersey 19th Century 

The Building America Strategies for Energy-Effi cient Remodeling 

2003 retrofit in rural New Jersey (Drumheller and Wiehagen 2004; 

http://apps1.eere.energy.gov/buildings/publications/pdfs/building_ 

america/36474.pdf) demonstrates solutions for a different set of 

issues. In this case, a 19th century home had uninsulated 2x4 walls, 

with wood siding and partial interior sheathing. However, the siding 

had deteriorated and needed to be replaced. The case study shows 

that based on the existing wall conditions, two wall cavity insulation 

choices were available—the use of blown-in insulation materials or 

foam-in-place insulation. Blown-in and foamed insulation materials 

provide more of an opportunity to completely fill irregular wall 

cavities and may be installed through small openings in the framing 

bay. They also are particularly adaptable to insulating wall sections 

that have coverings on both the exterior and interior of the framing 

members. Additional insulation on the exterior of the framing was 

also considered because the siding was being replaced. The Building 

America partners ultimately chose blown and foamed insulation in 

the wall cavity and sheet insulation under the siding. 

Another option for wood-clad buildings is the “drill-and-fi ll” 

method of opening 2-inch holes and injecting fiberglass or cellulose 

insulation into the cavity, resulting in an R-13 to R-21 insulated wall, 

depending on the cavity depth and type of insulation. 

8 February 28, 2011 

ENERGY PERFORMANCE TECHNIQUES AND TECHNOLOGIES PRESERVING HISTORIC HOMES

Windows 

The energy audit will have identified moisture and/or air leakage 

around windows and any other problems that exist with the current 

windows. Window treatments may include the following: 

• air sealing, flashing, and weatherstripping 

• repair and reconstruction 

• addition of storm windows 

• replacement with historically accurate replicas 

• replacement with wood windows of similar design (e.g., replacing 

double hung with double hung outfitted with similar material). 

Which option is best suited to the project depends on the results of 

the energy audit, climate, and the project objectives—preservation, 

rehabilitation, or restoration. Because of the highly visible nature 

of windows and their direct bearing on the historical integrity of 

the building, the NTHP promotes rehabilitating existing windows 

whenever possible. If there is water damage to the sills or around 

the window, evaluate whether the window needs resetting with an 

improved drainage plane. 

As noted earlier, it is important to first maximize the inherent 

potential of the house to be energy efficient. Existing awnings or 

shutters that provide appropriate shading, serve to ventilate the 

(Left) Drill-and-fill wall insulation on a 

house located in a Portland, Oregon historic 

district. Typically narrow strips of siding are 

removed before drilling, and sealed holes 

are hidden when siding is reinstalled. 

(Right) Blown-in insulation can be installed 

in walls from the interior. Care must be taken 

to match existing wall fi nish textures. 

The window may not be 

the problem, but the installation 

may be. The Building Science 

Corporation, in Building Science 

Digest-105: Understanding Drainage 

Planes (https://www.buildingscience. 

com/documents/digests/bsd-105-

understanding-drainage-planes/fi les/ 

bsd-105_understanding_drainage_ 

planes.pdf), provides a variety of 

window installation solutions for 

different wall types. 

February 28, 2011 19 

19 

(Top) “Drill and fill” from the interior. 

A 19th century New Jersey home 

undergoing a gut rehab had walls with 

irregular framing and no insulation. A 

worker blew cellulose insulation into holes 

drilled from the interior, completely filling 

the irregular spaces. On the exterior, 

insulated vinyl siding provided the air and 

moisture barrier (Photo Source: PNNL). 

(Bottom) “Drill and fill” from the exterior.

Workers drilled holes in the siding for 

blowing insulation into the walls of this 

home in a Portland, Oregon, historic 

district. The sealed holes will be hidden 

when the siding is repainted (Photo 

Source: PNNL).

(Left) Poorly installed batts. These fiberglass batts have reduced R-value 

because of the gaps and compressed areas (Photo Source: PNNL).

(Right) Properly installed batts. Fiberglass batt insulation should fill the entire 

cavity without any gaps, folds, tucks, or pinches (Photo Source: PNNL).

48 May 2012

ENERGY RENOVATIONS INSULATION
Attaching Rigid Foam to the Interior of a Non-Masonry Wall

Walls with wood, vinyl, aluminum, or fiber cement siding can be 

insulated on either the interior or exterior with rigid foam insulation. 

Rigid foam reduces thermal bridging and is a good air barrier when 

the panels are properly sealed. 

Appropriate types of foam board include polyisocyanurate, expanded 

polystyrene (EPS), and extruded polystyrene (XPS). The foam board 

should be unfaced. All foam requires an ignition barrier for fire 

safety. Before installing, check your local building and fire codes.

If the interior drywall is removed, rigid foam panels can be nailed or 

glued to exposed studs according to the manufacturer’s instructions. 

Fiber cavity insulation can be added for additional R-value. Edges 

and seams should be carefully sealed with caulk, tape, or spray 

foam. Complete the wall with 1⁄2-inch gypsum board, which provides 

the necessary ignition barrier. Do not cover the walls with vinyl 

wallpaper or any other Class I vapor retarder.

Insulating Lathe and Plaster Walls 

You can remove the lathe and plaster, then insulate the cavities with 

spray foam, cellulose, or dense-pack fiberglass, and put up sheetrock. 

Batts are not a good option because the framing cavities are seldom 

uniform in older houses. If you want to keep the lathe and plaster 

wall, the best way to insulate the walls is to add rigid insulation 

on the exterior of the walls. Otherwise, you should probably leave 

the walls uninsulated and just do airsealing. Drill-and-fill from the 

outside may damage the inside wall by breaking off the plaster 

“keys” behind the lathes. It may also create moisture problems. 

Furthermore, drill and fill should not be used if there is knob-and 

tube wiring in the wall. Adding insulation can push the wiring 

against the wood studs, creating a fire hazard. Drill and fill is not 

recommended from the inside because it can damage the plaster, it 

can disturb lead paint, and it will produce a lot of dust. 

The National Park Service, Technical Preservation Service, 

recommends against adding insulation to the walls in historic 

buildings: “ Adding blown-in insulation to historic wall assemblies 

may trap moisture within the wall and lead to accelerated and often 

hidden deterioration of the structure... as the wall is repaired. 

It is best to limit insulation to attics and basements where it can 

be installed with minimal damage to the historic building.” The 

Technical Preservation Service recommends adding wall insulation 

only “if walls are so deteriorated that complete replacement is 

required,” then “insulation can be properly installed.”

Interior rigid foam. To create an air barrier, 

seams of the rigid foam insulation were 

carefully sealed with spray foam (Photo 

Source: PNNL).

May 2012 49

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ENERGY RENOVATIONS INSULATION
5.3.3 Stud-Framed Walls:

Adding Exterior Insulation 

If you are replacing your siding, you have several options. This 

section provides guidance on the following approaches to insulating 

the exterior of a non-masonry wall: 

•	 Adding exterior rigid foam insulation

•	 Installing a proprietary wall insulation system (rigid foam blocks, 

an exterior insulation finish system, or insulated vinyl siding).

Adding Exterior Rigid Foam Insulation to a Non-masonry Wall

When replacing siding, it may be cost-effective to install exterior 

rigid foam insulation as part of your project. Rigid foam, also 

known as insulating sheathing, can be made of extruded polystyrene 

(XPS), expanded polystyrene (EPS), or polyisocyanurate. XPS is 

water-resistant and provides structural strength. EPS is the least 

expensive and the most vapor-permeable. Polyisocyanurate absorbs 

water, but it comes with a foil facing that can make a good drainage 

plane when well sealed. For further descriptions of each type of rigid 

foam insulation, see the tables in Chapter 3.

Advantages of insulating walls with exterior rigid foam:

•	 Properly installed, it will keep your exterior walls warm and dry, 

avoiding the risk of condensation, mold, and moisture damage. 

•	 It provides a high R-value for its thickness. 

•	 Because it covers the studs, it stops thermal bridging – the gain or 

loss of heat through the studs.

•	 It can be installed over the existing sheathing. Alternatively, XPS 

rigid foam can be used instead of wood sheathing. 

•	 You usually can stay in your home while the work is done, with 

no disruption to the interior.

Drawbacks of insulating walls with exterior rigid foam:

•	 It is expensive. 

•	 Doors and windows will need new flashing to integrate them with 

the rigid foam, which serves as a drainage plane. If the window 

frames are sealed improperly or to the wrong surface, water can get 

inside the wall cavities.

•	 Adding the foam may create a thicker wall assembly. If it does, the 

door and window jambs and sills may need to be extended. This 

can require removal and reinstallation of the windows and doors. 

Exterior rigid insulation. A complete 

renovation of this Massachusetts home 

included insulating the walls with exterior 

rigid insulation and interior cellulose 

(Photo Source: BSC).

See Appendix C for 

performance briefs on

Integrating sidewall and kick-out flashing 

with rigid foam exterior insulation.

50 May 2012

ENERGY RENOVATIONS INSULATION
Tips for installing rigid foam insulation. Rigid foam panels are 

available in several thicknesses, from 3⁄4 inch to 4 inches. To create 

a tighter air and moisture barrier, four inches of foam insulation 

can be attached in two 2-inch layers, with the joints offset both 

horizontally and vertically. Your contractor should attach the rigid 

foam with strong screws that extend from wood strapping on the 

outer surface, through the foam, and into the framing. The foam 

panels should fit together tightly. 

All edges and seams must be sealed to make an airtight, waterresistant assembly. Construction adhesive or silicone sealant can be 

used in outside corners and places where the foam meets the wall 

plates. Your contractor should apply housewrap tape over all seams 

and inside corners, and where the foam meets windows and doors.

Do not put vinyl wallpaper or oil or epoxy paint on the interior 

face of the wall. Follow local codes regarding fire protection and 

setback requirements.

Proprietary Wall Insulation Systems

There are several proprietary products for insulating exterior walls. 

Exterior rigid foam blocks. Several companies make rigid foam block 

insulation that is attached to sheathing with screws. The blocks 

are installed in courses, like a brick wall. The first course fits in a 

metal track attched to the wall. Clips are attached to the blocks or 

base plate to maintain a drainage and ventilation cavity. Properly 

installed, exterior foam blocks provide a high R-value and an 

effective air and moisture barrier. Siding is attached to the blocks. 

As with any exterior insulation approach, the thickness of the 

foam blocks can pose difficulties. The windows and doors must be 

properly flashed, and the door and window jambs and sills may need 

to be extended. This can require removal and reinstallation of the 

windows and doors.

Exterior insulation finish systems (EIFS). If you would like your new siding 

to look like stucco, your contractor may recommend using an exterior 

insulation finish system (EIFS). This approach provides a waterproof, 

insulated covering for all wall surfaces, including the attic gable end walls. 

For non-masonry walls, the existing siding must be removed. The 

sheathing should be fiberglass-faced gypsum board, which is moisture 

resistant. Insulating foam is attached directly to the sheathing 

(AWCI 1994). Wire or fiberglass mesh is attached over the foam. 

The assembly is covered with a proprietary finish. There are several 

brands available. Care must be taken with structural shear issues.

Exterior foam block insulation.

These blocks stack up like bricks. The 

insulation shown provides an R-value of 18 

(Photo Source: DOE).

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ENERGY RENOVATIONS INSULATION
Often called “synthetic stucco,” EIFS can be effective in most climate 

zones, depending on the thickness of the foam insulation. Although 

EIFS have been associated with moisture damage (Lstiburek 2007), 

Building America scientists have found that EIFS can be durable if 

drainage and water management details are constructed correctly. A 

continuous drainage plane and good flashing are required (Straube 

and Smegal 2009, Lstiburek 2004a).

As with any exterior insulation approach, the door and window 

jambs and sills may need to be extended. This can require removal 

and reinstallation of the windows.

Insulated vinyl siding. Insulated vinyl siding has rigid foam 

insulation permanently attached to the vinyl. The insulation, usually 

expanded polystyrene (EPS), provides some moisture protection 

along with R-value. For installation, your contractor will follow the 

product instructions.

5.3.4 Masonry Walls: 

When and Where to Insulate

A masonry wall may be solid; more typically, it is built with two or 

more rows (wythes) of brick, stone, or concrete that have a drainage 

and ventilation cavity between them. The cavity varies from about 

1 inch to 4 inches in width. The face of the second row serves as a 

drainage plane. 

When to Insulate a Masonry Wall

•	 When there are comfort problems or moisture issues.

•	 When structural problems in the masonry walls require new siding.

•	 When a major remodeling project allows for removal of plaster or 

drywall to expose the interior side of the brick, stone, or concrete. 

How to Insulate a Masonry Wall

Your choices for insulating masonry walls are limited and expensive. 

Exceptional care must be taken to prevent condensation, mold, and 

moisture damage when insulating masonry walls. Building America 

researchers have found that three approaches can be successful:

•	 exterior rigid foam 

•	 interior spray foam 

* interior rigid foam.

Insulated vinyl siding. Rigid foam 

insulation is permanently attached to 

the vinyl siding (Source: NAHB).

52 May 2012

ENERGY RENOVATIONS INSULATION
Building America researchers do NOT recommend the use of fiber 

insulation in direct contact with a masonry wall. Fiber insulation 

(fiberglass batts or cellulose) next to a masonry wall will absorb 

moisture, creating a risk of mold, mildew, and structural damage.

5.3.5 Masonry Walls: 

Adding Exterior Insulation

Both cavity and solid masonry walls can be insulated from the 

outside with rigid foam insulation. 

Rigid foam offers some advantages. Properly installed, it will 

keep your exterior walls warm and dry, avoiding the risks of 

condensation, mold, and moisture damage. You usually can stay in 

your home while the work is done, with no disruption to the interior.

However, the aesthetic value of an aged brick or stone wall will be 

lost when it is covered by the rigid foam and new siding. Additionally, 

rigid foam is expensive and, combined with the new siding, creates a 

thicker wall assembly. The door and window jambs and sills may need 

to be extended. This can require removal and reinstallation of the 

windows and doors. Building America scientists suggest combining 

window replacement with a siding and insulation project. The new 

window jambs can be sized to fit the new wall thickness (Ueno 2010).

Your contractor can attach rigid insulation to the existing masonry, 

using fasteners or glue recommended by the foam manufacturer. All 

edges and gaps must be sealed carefully. Stucco or an exterior insulation 

finish system (EIFS) should be installed over the rigid foam, leaving a 

drainage and ventilation space between the foam and the siding.

5.3.6 Masonry Walls: 

Adding Interior Insulation

For some homeowners, covering masonry walls with exterior insulation 

is unacceptable because of aesthetics or historic home requirements. 

In these cases, Building America researchers recommend applying 

spray foam insulation on the interior of the walls. While spray foam is 

expensive, it provides air sealing and good R-value. However, installing 

insulation on the interior has two major drawbacks: 

•	 Risk of moisture damage. Adding interior insulation to a masonry 

wall creates a serious risk of moisture damage. Bricks and other 

types of masonry readily absorb moisture from rain and humid 

air. Once interior insulation is in place, less warmth passes through 

the wall. The bricks, stone or concrete will be colder, increasing 

the amount of condensation and extending the time it takes to 

Exterior rigid foam. Rigid foam insulation 

is installed on the exterior of a new framed 

home in Georgia. The rigid foam takes 

the place of OSB wall sheathing (Photo 

Source: IBACOS).

May 2012 53

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ENERGY RENOVATIONS INSULATION
dry. This may lead to mold, mildew and rusting of embedded 

steel supports. Where winter temperatures go well below freezing, 

repeated freeze-thaw cycles can permanently damage the walls. 

•	 Loss of floor space. Insulation installed on the interior needs a new 

stud wall built in front of it to attach wallboard. The thicker wall 

will reduce a room’s square footage.

While loss of floor space is unavoidable, moisture risks can be 

minimized. This requires two strategies:

•	 First, minimize rain absorption. Reduce the amount of rainwater 

absorbed by the masonry in two key places: the bottom corners of 

windows and the wall at grade level. Adding projecting window 

sills and base drainage will do the most to reduce water absorption.

•	 Second, create an airtight wall. This is easiest to achieve with spray 

foam insulation. It creates a continuous air barrier to prevent the 

movement of moisture-laden air from the living space into the 

wall. If you are using rigid foam insulation, edges and seams must 

be carefully sealed.

Installing Interior Spray Foam Insulation on a Masonry Wall

Building America scientists have found spray foam to be both the 

most successful and practical approach to insulating the interior of 

both cavity and solid masonry walls (Straube 2007). Both high-density 

closed-cell and medium-density open-cell foam create excellent air 

barriers and eliminate the need for separate air sealing measures. 

Before applying the foam, Building America scientists recommend 

constructing a steel-stud wall 2 inches away from the masonry wall. 

(The space allows complete coverage of the wall and reduces thermal 

bridging.) The foam is then sprayed directly on the entire surface of 

the masonry at a thickness of 2 to 4 inches. 

Once the foam is in place, fiber insulation can be installed in the 

stud cavities for additional R-value. Drywall is then attached to the 

studs. Do not use vinyl wallpaper or any other kind of Class I vapor 

retarder on the inside face of the wall.

Installing Interior Rigid Foam Insulation on a Masonry Wall

Rigid foam can be used to insulate the interior of masonry walls. 

However, Building America researchers have found that rigorous 

attention to detail is required to avoid moisture problems. It is difficult 

to create a perfect air barrier and to get the rigid foam to adhere to the 

masonry at every point. Even small gaps will make the insulation less 

effective and create a spot for moisture to condense (Straube 2007).

(Bottom) Rigid foam insulation. As 

part of an energy-efficient retrofit, rigid 

foam insulation will be used to insulate a 

basement (Photo Source: PNNL).

(Top) Interior rigid foam insulation. Rigid 

foam has been installed on the interior 

basement walls of this new home in 

Pennsylvania. The ground has also been 

covered with rigid foam, in preparation 

for pouring the concrete floor slab (Photo 

Source: IBACOS).

54 May 2012

ENERGY RENOVATIONS INSULATION
Rigid insulation should be installed in amounts that permit indoor 

drying: Up to 2 inches of XPS or unfaced polyisocyanurate, or up 

to 4 inches of the more vapor-permeable EPS (Lstiburek 2006d; 

Straube 2007). 

Your contractor should take the following steps:

•	 Apply a liquid, highly vapor-permeable air and water barrier 

to the exterior of the masonry. This serves as an air barrier and 

keeps water from penetrating, yet allows the wall to dry in either 

direction. 

•	 Attach the rigid foam panels to the interior of the masonry with 

construction adhesive applied in a serpentine pattern. 

•	 Make sure the panels are fully in contact with the masonry wall, 

with no gaps. 

•	 When using two layers of foam, stagger the seams.

•	 Create airtight seals where the foam panels meet and where 

they join other materials. Use acrylic-latex caulk, foam 

sealant, or mastic.

5.4 Insulating a Crawlspace

Insulating your crawlspace can reduce your energy bills and make 

your home more comfortable. However, taking the wrong approach 

can create moisture and air quality risks. Your decisions about 

crawlspace insulation must take into account your climate (Figure 

5.12) and the radon level in your soil.

•	 HUMID climate zones: A vented crawlspace in a humid climate 

zone is vulnerable to serious moisture problems (Malkin-Weber et 

al. 2008). Adding insulation on the ceiling of a vented crawlspace 

will increase the risk of mold and wood rot (Lstiburek 2008b). If 

you live in a humid climate outside a flood-prone area, Building 

America scientists recommend closing the vents, air sealing 

the crawlspace walls and floor, and insulating the walls of the 

crawlspace.

• DRY climate zones: Both vented and closed crawlspaces can 

perform well in dry climate zones, where airborne moisture 

is seldom a problem (Hales 2011). In hot-dry zones, adding 

insulation to a crawlspace is unlikely to be cost-effective (Straube 

2011). In other dry zones, several insulation approaches are 

recommended, as discussed below. 

Wet masonry. Avoid insulation strategies 

that increase moisture retention in masonry 

walls. Wet masonry can develop mold and 

efflorescence, a chalky salt residue (Photo 

Source: PNNL).

May 2012 55

55

ENERGY RENOVATIONS INSULATION
•	 MARINE climate zones: Building America partners and other 

researchers have found that airborne moisture is seldom a problem 

in the marine climate zones of the western United States. Both 

vented and insulated closed crawlspaces can perform adequately 

(Hales 2011).

• RADON: In areas with high levels of radon in the soil, vented 

crawlspaces have the advantage of diluting the gas. Closed 

crawlspaces require a radon mitigation system, because radon can 

become concentrated (DOE 2010d). Although radon maps provide 

the historical and statistical probability of increased radon in your 

geographic area, the only way to know if you have high levels in 

your home is to test for radon.

Even where vented crawlspaces perform adequately, it can be an 

advantage to close and seal the crawlspace before insulating. Closed 

crawlspaces typically perform better than vented crawlspaces in 

terms of safety, health, comfort, durability, and energy consumption 

(Lstiburek 2006a). Where radon is not a problem, the U.S. 

Environmental Protection Agency (EPA) recommends closed 

crawlspaces for indoor air quality (EPA 2006). 

This section describes recommended approaches to crawlspace 

insulation for humid climates and for dry and marine climates. The 

research-based guidance, developed by Building America scientists, 

will help you insulate your crawlspace safely and effectively. Be sure 

to hire a contractor certified in building science. A knowledgeable 

contractor will help you choose the best approach for your home.

Climate is the crucial consideration in 

crawlspace decisions. In humid (moist) 

zones, vented crawlspaces can have 

moisture problems. Building America 

scientists recommend closing and 

sealing the crawlspace and insulating 

the crawspace walls. In dry and marine 

climates, either closed or vented 

crawlspaces can work well.

Warm-humid 

below white 

line Figure 5.12. IECC climate 

regions. Designated by 

the International Energy 

Conservation Code (IECC) 

(Figure Source: 2009 IECC; 

Briggs et al. 2003).

56 May 2012

ENERGY RENOVATIONS INSULATION
5.4.1 Why Crawlspace Vents Should be 

Closed in Humid Climate Zones

In humid climates outside of flood-prone areas, Building America 

scientists recommend closing the crawlspace vents before adding 

insulation. A vented crawlspace in a humid climate can compromise 

the structural integrity of a home and the health of the occupants 

(Advanced Energy 2011). Air entering through the vents can deposit 

moisture in the crawlspace, leading to mold and wood rot. The 

crawlspace air then gets pulled into the living space by the stack effect, 

bringing in moisture and any mold spores that have formed (see 

sidebar). Mold contributes to respiratory problems, such as asthma. 

A vented crawlspace insulated with batts or cellulose in the 

crawlspace ceiling has an even higher risk of moisture accumulation, 

mold, and wood rot. Fiberglass batts installed between the floor 

joists in a vented crawlspace are cool on the underside, and the 

exposed bottom edges of the floor joists are even cooler. If these 

temperatures are below the dew point, condensation will form. 

The damp batts will insulate poorly, mold can grow, and the damp, 

exposed floor joists can rot (Lstiburek 2008b). Cellulose insulation 

installed between the floor joists can develop the same problems. 

Done properly, closing the crawlspace will minimize or eliminate 

moisture risks (Lstiburek 2006a). Closing the crawlspace can also reduce 

the energy used for heating and air conditioning your home, especially 

if ducts and heating equipment are located in the crawlspace (Lstiburek 

2006a; Malkin-Weber et al. 2008). Savings can be reduced, however, if 

local conditions require supplying warm air to the crawlspace in winter 

or continuously running an exhaust fan (Hales 2011). 

Note: You must test for radon before closing a crawlspace. If radon 

levels are high, you must install an appropriate radon mitigation 

system before closing the crawlspace (see Chapter 4). Radon can 

become concentrated in a closed crawlspace.

5.4.2 Insulation for a Closed Crawlspace 

Building America researchers have found that rigid foam and spray 

foam insulation on the interior side of closed crawlspace walls can 

give good results in most areas. In cold climates, however, interior 

wall insulation can increase the wall’s vulnerability to thermal stress 

and freezing, and may increase the likelihood of condensation on 

sill plates, rim joists, and joist ends (DOE 2010d). Foam insulation 

installed on the exterior of crawlspace walls can solve these coldclimate problems, but the approach is usually impractical for existing 

homes. See Section 5.3.5 for information on exterior wall insulation. 

Crawlspace vents create 

moisture risks in humid climates

Crawlspace vents are supposed to prevent 

moisture problems. The assumption has 

been that fresh air will enter through a vent 

on one side, and stale air with moisture and 

contaminants will be pushed out the other. 

Unfortunately, cross-ventilation doesn’t 

work well in crawlspaces; air is more likely 

to be pulled up into the living space by the 

stack effect. Studies by Building America 

research partners have found that 40% to 

50% of the air in a typical home has been 

in the crawlspace at one time (Dastur and 

Davis 2005; DOE 2011a). 

Structural risks. In humid climates, air 

entering through the vents carries water 

vapor. The vapor will condense on the 

cooler surfaces of the floor joists and 

foundation walls if their temperatures are 

below the dew point. If framing stays moist, 

mold and wood rot will develop. Moist 

wood also attracts termites and carpenter 

ants. The floor above a crawlspace ceiling 

can also be damaged by airborne moisture. 

Hardwood floors can buckle and warp. 

If a floor is covered with vinyl, mold may 

develop underneath it. 

Health risks. A home is likely to have 

high mold counts inside the living space 

when the crawlspace has high moisture 

levels (Malkin-Weber et al. 2008). Mold 

contributes to respiratory problems, such 

as asthma.

Air conditioning can increase moisture 

risks. In an air-conditioned home where 

ducts are in a vented crawlspace, airborne 

moisture can condense on the duct 

surfaces, both inside and out, possibly 

leading to mold. Subflooring around floor 

registers in the crawlspace ceiling can 

become cold and damp and may develop 

mold (Lstiburek 2008b).

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ENERGY RENOVATIONS INSULATION
Spray foam insulation.Two types of spray foam can be used to 

insulate the interior side of a crawlspace wall—open-cell and closedcell. Open-cell foam costs less than closed-cell foam, but has a lower 

R-value per inch. Both will provide a good air barrier and enough 

vapor permeability to allow moisture in the walls to evaporate to 

the inside (open-cell foam is more permeable than closed-cell). 

Recommended amounts for crawlspace walls include:

•	 3 inches of closed-cell, medium-density spray foam

•	 Ten inches of open-cell, low-density spray foam (BSC 2009b). 

Rigid foam insulation. Two types of rigid foam can be used to 

insulate the interior side of a crawlspace wall:

•	 Up to 2 inches of unfaced extruded polystyrene rigid foam (XPS)

•	 4 inches of unfaced expanded polystyrene (EPS) (BSC 2009b).

Fiber insulation (fiberglass batts or cellulose) should not be used 

against a crawlspace wall. Fiber insulation collects and holds 

moisture (Yost and Lstiburek 2002). 

5.4.3 How to Seal and Insulate 

a Crawlspace

Moisture Control

Creating a dry, closed crawlspace requires careful preparation. 

Moisture control is crucial:

Air sealing is the primary defense against condensation. Your 

contractor must create a tight air barrier to prevent the entry of 

airborne moisture. Simply closing the vents without performing air 

sealing is likely to make moisture levels higher and may cause damage. 

A ground vapor retarder must be installed to prevent evaporation of 

ground moisture into the closed crawlspace. The IRC requires a Class 1 

vapor retarder that is overlapped at the edges, taped, and sealed to walls. 

Conditioned air must circulate in the crawlspace for the space to 

remain dry (see the 2009 IRC R408.3 requirements listed in the 

sidebar on page 59). Your certified home performance contractor 

can advise you on the best system for your house.

Insulation for unvented crawlspaces. 

(Top) Rigid foam was used to insulate this 

unvented crawlspace (Photo Source: WSU 

Energy Office).

(Bottom) This unvented crawlspace was 

insulated with rigid foam on the walls and 

spray foam at the rim joist (Photo Source: 

W. Hawthorne).

58 May 2012

ENERGY RENOVATIONS INSULATION
Steps to Close and Insulate a Crawlspace 

Be sure to hire a contractor certified in building science 

(see Chapter 1) to ensure that all technical and safety issues are 

addressed. Your contractor should do the following:

1. PLAN:

•	 Check with the local building department. Some areas do 

not permit closed crawlspaces. However, the International 

Residential Code (IRC) allows unvented crawlspaces as long as 

the ground is covered with a properly installed vapor retarder, 

the perimeter walls are insulated, and the crawlspace has a 

drying mechanism. This can include passive air exchange with 

the living space, a dehumidifier, or a power vent to the outdoors.

•	 Many builders have gotten permission by showing their code 

officials that the crawlspace will be a conditioned space, like a 

miniature basement. 

•	 Check with local pest control officials on ways to ensure access 

for termite inspections.

•	 Plan access once the crawlspace is closed. Plan for an access 

door inside the home, through the subfloor, or an airtight, 

insulated door in the perimeter wall. 

2. TEST FOR RADON:

•	 Low-cost do-it-yourself kits are widely available (see sidebar, 

next page). If radon is a concern, a radon mitigation system 

must be installed before proceeding any further.

3. PROTECT THE CRAWLSPACE FROM WATER SOURCES:

•	 Make sure the yard and pavement slope away from the crawlspace.

•	 When the crawlspace ground level is below the surrounding grade, 

crawlspaces should have perimeter drainage, just like a basement.

•	 Monitor for water intrusion after the work is complete.

4. ADDRESS EXISTING MOISTURE DAMAGE:

•	 Remove any existing insulation.

•	 Replace rotting wood.

•	 Clean the walls.

IRC Code for Closed 

Crawlspaces

A closed crawlspace is permitted under the 

2009 and 2012 International Residential 

Code (R408.3) if all of the following 

conditions are met:

1. Exposed earth is covered with a 

continuous Class I vapor retarder. Joints 

of the vapor retarder shall overlap by 6 

inches (152 mm) and shall be sealed or 

taped. The edges of the vapor retarder 

shall extend at least 6 inches (152 mm) up 

the stem wall and shall be attached and 

sealed to the stem wall or insulation; and

2. One of the following is provided for the 

under-floor space:

2.1. Continuously operated mechanical 

exhaust ventilation at a rate equal 

to 1 cubic foot per minute (0.47 L/s) 

for each 50 square feet (4.7m2) of 

crawlspace floor area, including an 

air pathway to the common area 

(such as a duct or transfer grille), 

and perimeter walls insulated in 

accordance with Section N1103.2.1 

of this code;

2.2. Conditioned air supply sized to 

deliver at a rate equal to 1 cubic foot 

per minute (0.47 L/s) for each 50 

square feet (4.7 m2) of under-floor 

area, including a return air pathway 

to the common area (such as a duct 

or transfer grille), and perimeter 

walls insulated in accordance with 

Section N1102.2 of this code;

2.3. Plenum in existing structures 

complying with Section M1601.5, 

if under-floor space is used as 

a plenum. 

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ENERGY RENOVATIONS INSULATION
5. ADDRESS COMBUSTION EQUIPMENT ISSUES:

•	 If oil or gas furnaces or water heaters are located in the 

crawlspace, they should be sealed-combustion units equipped 

with a powered combustion system. Natural draft combustion 

appliances are more likely to backdraft in a closed crawlspace 

due to power venting of the space or the stack effect. 

6. AIR SEAL THE CRAWLSPACE: 

•	 Carefully seal all holes and cracks in the subfloor over the 

crawlspace. 

•	 Seal all air leaks through the exterior wall, including the rim joist. 

•	 Make sure any ductwork is sealed with mastic, not ordinary duct 

tape. (See the performance brief on ducts in Appendix C.)

7. PROVIDE CONDITIONED AIR:

•	 Allow passive air exchange between the closed crawlspace and 

the living space by installing floor registers or transfer grilles. If 

humidity in the crawlspace is still a concern:

	 	 • Install supply ducts if the home is air conditioned. 

	 	 • If it is not air conditioned, install a small dehumidifier. 

•	 Where soil gases are a problem, install a durable fan to 

exhaust air continuously from the crawlspace to the outside 

(Lstiburek 2006b).

8. PROTECT AGAINST GROUND MOISTURE:

•	 Cover the ground with a polyethylene liner at least 6 millimeters 

thick, sealed at the seams and sealed to the crawlspace walls to 

the height of the exterior grade and fastened to the wall with 

pressure-treated furring strips. 

9. CLOSE THE VENTS 

•	 Insert cinder blocks or foam plugs and seal with mastic.

10. INSTALL INSULATION

•	 Make sure the surface is completely dry.

•	 Install according to the manufacturer’s instructions. 

•	 Cover all types of foam with an ignition barrier for fire safety, 

such as 1⁄2-inch gypsum board. Spray foam can be painted with 

ignition barrier paint.

•	 Insulate the access door and make it airtight. 

Radon in Crawlspaces

For your health’s sake, you must check 

for radon before deciding to close a 

crawlspace. Radon is a naturally occurring 

gas that causes lung cancer. Odorless and 

invisible, it is produced by the radioactive 

breakdown of trace uranium in soil. 

(See Chapter 4, “Safety and Health.”) 

Researchers have found that closing a 

crawlspace can concentrate radon to 

unacceptable levels. Based on these 

findings, researchers concluded that closed 

crawlspaces in high radon areas should be 

vented with an active, fan-powered radon 

mitigation system, with the fan installed in 

the attic. The fan must be well maintained 

and operate at all times (Hales 2011; 

DOE 2010d).

In many parts of the country, radon levels 

are low enough that closing a crawlspace is 

unlikely to cause problems. However, radon 

beneath any particular home can be high; 

the only way to know is to test. 

Low-cost, do-it-yourself radon test kits 

are available in stores. If tests indicate a 

radon level of 2 or more picocuries per 

liter of air, you must install an appropriate 

radon mitigation system. Be sure to hire 

a qualified radon contractor. With the 

system installed, then you can close the 

crawlspace. Perform a radon test again 

after the work is done. To find a qualified 

or state-certified radon contractor in your 

area, check with your state radon office or 

see www.epa.gov/radon/whereyoulive.html. 

For information on 

crawlspace exhaust fans 

“Details for Mechanically Vented 

Crawlspaces - Code Notes,” at 

http://resourcecenter.pnl.gov/cocoon/morf/

ResourceCenter/article//131

60 May 2012

ENERGY RENOVATIONS INSULATION
Figure 5.13. Foil-faced insulation in 

crawlspace. Foil-faced insulation can be 

added to the underside of floor joists in 

a vented crawlspace. The rigid insulation 

keeps floor joists warm and the foil 

facing is a Class I vapor retarder that 

keeps crawlspace air from condensing on 

the floor joists as long as the foil-faced 

insulation is taped at all seams with foil 

tape. Any type of floor covering will work 

with this insulation and it will work in any 

climate zone (Source: Lstiburek 2008b).

11. TEST AND CHECK

•	 Test again for radon. Even if previous tests showed no elevated 

radon levels, you should test again for your health and 

safety. Sealing and insulating a crawlspace can increase the 

concentration of radon.

•	 Make sure the polyethylene ground cover has no tears or holes.

•	 Consider installing a wireless humidity sensor, paired with an 

alarm inside the home (Advanced Energy 2011). 

5.4.4 Insulating a Crawlspace 

in Dry and Marine Climate Zones

Your Choice: Vented or Unvented

Research indicates that both closed and vented crawlspaces are 

acceptable in the dry and marine climates of the western United 

States. A closed crawlspace can have advantages in terms of energy 

efficiency and improved air quality, especially if ducts are located 

in the crawlspace. It also provides protection against freezing pipes. 

On the other hand, keeping the crawlspace vented may be the best 

option for your home. Closing a crawlspace costs money. In a 

high-radon area, a closed crawlspace requires the installation of a 

radon-mitigation system (see sidebar on previous page). 

A home performance contractor who is certified in building science 

can identify the approach that will best increase your comfort, 

improve air quality, and reduce energy bills. 

How to Insulate a Vented Crawlspace in Dry 

and Marine Climates

If you choose to keep your crawlspace vented, your contractor 

will install insulation on the crawlspace ceiling. Several products 

can be used:

•	 Unfaced batts can be installed between the floor joists, in contact 

with the floor above. Make sure there is no airspace between the 

insulation and the crawlspace ceiling (DOE 2010d). Support 

the insulation with rigid foam board, mechanical fasteners, or 

inexpensive landscape cloth so it will not fall out of the joist spaces 

in the years to come. Avoid pinching or compressing the batts; 

this reduces their R-value.

Carpet

Carpet pad

Floor sheathing 

(OSB or plywood)

Closed cell (2 lb/ft3 density) spray foam

Figure 5.14. Spray foam insulation in 

crawlspace. Spray foam insulation will 

create an air barrier on the ceiling of a 

vented crawlspace, keeping the floor 

above it warm and dry. The foam should 

completely encase the floor framing. 

A minimum of 3 inches of high-density 

closed-cell foam should provide an 

adequate vapor retarder for any floor 

type including vinyl, in any climate zone. 

If using low-density foam or a thinner 

layer of high-density floam, avoid vinyl 

flooring (Source: Lstiburek 2008b).

Any type of flooring/floor finish

Floor sheathing (OSB or plywood)

Airspace

Foil-face isocyanurate Cavity insulation

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ENERGY RENOVATIONS INSULATION
•	 Rigid insulation can be attached to the underside of the floor 

trusses, with the seams carefully sealed. For additional R-value, 

loose-fill insulation can be blown into the space above. 

•	 Cellulose insulation can be installed with netting for support. 

Before work begins, your contractor should:

•	 Test for radon. If the radon level is high, install a mitigation 

system before proceeding further. 

•	 Air seal the crawlspace ceiling. Plug leaks in the rim joists and 

air seal all plumbing, electrical, and duct penetrations. For 

details, see Building America’s Air Sealing Guide at http://apps1.

eere.energy.gov/buildings/publications/pdfs/building_america/

ba_airsealing_report.pdf.

•	 Air seal and insulate pipes and ducts to protect against heat loss 

and freezing (see Appendix C for instructions). 

•	 If the crawlspace opens to the house, insulate and air seal the 

crawlspace access cover. 

5.5 Insulating Basements

Insulating your basement—when done properly—will increase your 

comfort, save energy, improve your home’s air quality, and make 

your home more durable (DOE 2002). However, a dry basement 

requires careful moisture control and air sealing before insulation is 

added. Be sure to hire a contractor certified in building science. A 

knowledgeable contractor will make moisture control and air sealing 

the first priority. 

Your basement may already be damp, cold, and musty. According 

to Building America researchers, the best remedy is air sealing and 

expertly installing foam insulation on your basement walls. You will 

need to supply heating and air conditioning to your basement. In dry 

climates, insulation can be installed on the basement ceiling instead, 

as long as you don’t use your basement as living space.

This section provides guidance for achieving a dry, energy-efficient 

basement, with steps for:

5.5.1. Moisture Control and Air Sealing

5.5.2. Choosing the Best Approach for Insulating your Basement

5.5.3. Preparing to Insulate

5.5.4. Insulating Basement Walls on the Interior

(Top) Poor insulation. Here batt insulation 

is no longer attached and is falling away 

from the floor above. To be effective, batt 

insulation must be in full contact with the 

crawlspace ceiling, and a vapor retarder 

of 6-mil visquene should fully cover the 

crawlspace ground (Photo Source: PNNL).

(Middle) Good insulation. This photo 

shows a vented crawlspace with batt 

insulation that is properly fastened to be 

in full contact with the subfloor above.

(Bottom) In hot-humid and/or coastal 

climates where a pier foundation is 

used, spray foam can be applied to the 

underside of the subfloor to both insulate 

and air seal it. 

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ENERGY RENOVATIONS INSULATION
5.5.5. Insulating Basement Walls on the Exterior

5.5.6. Insulating Basement Ceilings

5.5.7. Maintaining a Dry, Problem-Free Basement.

5.5.1 Moisture Control and Air Sealing

Contact with cold earth makes basements vulnerable to moisture, 

mold, and rot. Adding insulation to a basement with existing moisture 

problems will only make them worse. Moisture control is crucial.

Moisture in basements comes from two sources:

• Water intrusion. Rainwater, groundwater, and water from your 

sprinklers can wick through the walls or up from the footings. 

• Condensation. Condensation can occur when air comes into contact 

with cold surfaces. Since basements are mostly below ground level, 

they are chilled by the surrounding earth. The moisture in basement 

air will condense on the walls and floor joists if those surfaces are 

below the dew point temperature. The wood framing and any batt 

insulation and gypsum board can stay chronically damp. 

The first step in controlling moisture is to evaluate its presence in 

your basement. If at times you can see moisture on the walls or if 

water sometimes drains from the walls onto the floor, you have a 

serious problem. Your contractor must install an interior drainage 

system before taking any other steps. 

The next step is to fix any sources of water intrusion and perform 

air sealing. Air sealing is a crucial defense against condensation, 

because it keeps moist air away from cold basement surfaces. Your 

final step in moisture control will be to add insulation. Insulation 

will further reduce condensation by raising basement temperatures. 

5.5.2 Choosing the Best Approach

for Insulating your Basement

This section provides guidance on where to insulate and how to 

choose an insulation product for your basement.

Where to Insulate: Walls or Ceiling? 

Your first step is to determine whether to insulate the walls or ceiling 

of your basement. Factors include your climate and how you want 

to use your basement:

Recognize the signs of 

basement moisture problems: 

•	 Foundation cracks that leak 

•	 Standing water that doesn’t drain 

•	 Damp walls or floor 

•	 White, chalky stains (called

efflorescence) on walls and floors

•	 Mildew or visible mold

•	 Wet, decaying wood

•	 Condensation on windows, pipes,

and other fixtures 

•	 Damp insulation

•	 Moisture-damaged finishes 

•	 Musty or damp carpets 

•	 Stuffy, damp smells 

•	 High humidity.

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ENERGY RENOVATIONS INSULATION
Insulate the ceiling. You can choose to insulate the ceiling and leave 

the basement unheated only when ALL of the following are true: 

•	 You live in a dry climate, and

•	 you find no evidence of moisture, and

•	 you don’t use your basement as living space.

Insulate the walls. You should insulate the basement walls and supply 

heating and air conditioning when any ONE of the following is true: 

•	 You want to use your basement as living space, or

•	 you live in a humid climate zone, or

•	 your basement shows evidence of moisture.

Basement Ceilings: Choosing Insulation

Spray foam, rigid foam, and fiber insulation can all be used to 

insulate basement ceilings. Spray foam has the advantage of 

providing air sealing and insulation in one step. Fiberglass batts 

are much less expensive than foam, and will perform well in a dry 

climate as long as the ceiling is air sealed. Section 5.5.6 provides 

guidance for insulating a basement ceiling.

Basement Walls: Choosing Insulation 

Your goal is a basement with dry, warm walls. This requires 

strategies to keep moisture out of the walls. However, it is inevitable 

that walls will get wet sometime, and the walls must be able to dry 

out. Moisture cannot dry to the exterior where the walls are below 

grade. Therefore, insulated basement walls must have these features:

•	 To discourage condensation, the walls need an air barrier to keep 

moist interior air from reaching the foundation. The walls need to 

be kept warmer than the dew point of the air. 

•	 To prevent moisture retention, insulated walls must be able to dry to 

the interior. The insulation must not retain water and the wall must 

not have a Class I vapor retarder on the interior. Vapor retarders 

to be avoided include foil, plastic, vinyl wallpaper, and oil, alkyd, 

and epoxy paint (Lstiburek 2006b). Foil-faced polyisocyanurate 

may be an exception; see the discussion below, under “Basement 

Walls: Spray Foam or Rigid Foam Insulation.” Do not use 

fiberglass batts or cellulose insulation; they hold water.

•	 To reduce moisture wicked up by the foundation, leave a 1⁄2- to 

3⁄4-inch gap between the gypsum wallboard and the concrete floor. 

Basement ceiling insulation. Unfaced 

fiberglass batts are installed in the ceiling 

of this basement in Portland, Oregon 

(Photo Source: PNNL).

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ENERGY RENOVATIONS INSULATION
With these factors in mind, Building America scientists provide the 

following appraisal of the three ways to insulate basement walls:

1. Unacceptable: Putting fiberglass insulation in framing cavities and 

covering it with a Class I vapor retarder, such as plastic sheeting.

2. Recommended: Installing rigid or spray foam insulation on the 

interior of the walls.

3. Recommended when feasible: Installing rigid insulation on the 

exterior of the walls. 

Note: Although a Class I vapor retarder should NOT be used on 

the interior side of a basement wall, a Class II or III vapor retarder 

may be called for. See Section 3.2 and Appendix B.4 for details on 

vapor retarders.

Basement Walls: Interior or Exterior Insulation?

Most homeowners will choose to insulate their walls on the interior 

because exterior rigid foam insulation is difficult and expensive 

to install on the foundation of an existing home. Nonetheless, the 

exterior approach has some advantages:

•	 Exterior foundation insulation provides better moisture 

control than interior insulation, according to Building America 

researchers (DOE 2011a). 

•	 It discourages condensation by warming the foundation walls, 

and any moisture in the walls can easily dry to the interior of 

the basement. 

•	 It protects the foundation from the risk of freeze-thaw cycles that 

can occur in very cold regions. 

Exterior rigid insulation also has some disadvantages:

•	 It must be protected from moisture while being installed. 

•	 It can become an “insect highway” for termites to reach the wood 

framing. Many Southern states prohibit its use.

•	 Exterior insulation requires excavating around the foundation to 

a depth of at least 2 feet (up to 8 feet in very cold climates). This 

is cost-effective only if your project includes installing a perimeter 

drainage system. 

Section 5.5.4 provides guidance for installing interior basement wall 

insulation. Section 5.5.5 provides guidance for the exterior approach.

Basement wall insulation. In this 

Pennsylvania basement, rigid XPS foam 

insulation is attached directly to the 

concrete basement walls with spray 

foam. Rim joists are insulated with spray 

foam. Frame walls will be built to finish 

the basement (Photo Source: Asdal 

Construction).

Fiberglass batts with plastic 

sheeting: Refuse to use in a 

basement wall

The most common approach to basement 

insulation can damage your home. Many 

builders construct interior stud framing 

in the basement, install fiberglass batts, 

and cover it all with sheet polyethylene. 

According to Building America researchers 

and other scientists, this approach can 

cause serious problems with mold, odor, 

and decay (Yost and Lstiburek 2002; Fugler 

2002; Ellringer 2002). Cellulose insulation 

covered by polyethylene can cause the 

same problems.

Inevitably, outdoor moisture will come 

in contact with insulation. Water seeps 

through the porous foundation, and moist 

air condenses on the cold foundation 

wall behind the insulation. Fiberglass and 

cellulose insulation can trap and hold 

large amounts of water. The wet insulation 

cannot dry, because the polyethylene 

traps the moisture. This puts your home at 

risk for mold, wood rot, and termites, and 

creates an unhealthy environment for you 

and your family.

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ENERGY RENOVATIONS INSULATION
Basement Walls: Spray Foam or Rigid Foam?

Building America scientists recommend foam insulation for 

basement walls. There are two forms of foam insulation: rigid foam 

and spray foam. Rigid foam can be used as exterior insulation. Both 

forms can be used on the interior. Also available are proprietary 

foam board insulation systems.

Properly installed, foam insulation minimizes moisture problems:

•	 Most foam insulation will not absorb or retain water that seeps 

through the foundation walls or slab. 

•	 It has enough vapor permeability to allow moisture in the wall to 

diffuse to the basement interior. 

•	 Spray foam is an excellent air barrier, keeping moist indoor air 

away from the foundation walls. Rigid foam is a good air barrier 

when its seams are well sealed. 

Spray Foam Insulation

When choosing spray foam insulation, consider the following 

characteristics:

•	 Closed-cell spray foam, available in medium- or high-density. 

Closed-cell foam is both an excellent air barrier and a good vapor 

retarder. It provides the best moisture control of all interior 

foundation insulations (Smegal and Straube 2010). 

•	 Open-cell spray foam, which has low density, is an excellent air 

barrier but not a good vapor retarder. It costs less than closed-cell 

foam but must be applied much more thickly to attain the same 

R-value. The thicker walls will decrease the useful interior space.

Rigid Foam Insulation

When choosing rigid foam insulation, consider the following 

characteristics:

•	 EPS (expanded polystyrene) is the least expensive rigid foam but 

is not a good vapor retarder. 

•	 XPS (extruded polystyrene) has a high R-value per inch and is 

a good vapor retarder. XPS is a better choice than EPS where 

moisture is an issue.

•	 Both EPS and XPS should be installed in amounts that permit 

indoor drying—up to 4 inches of unfaced EPS (R-15), or up to 

2 inches of unfaced XPS (R-10) (Lstiburek 2006d).

Insulated rim joist. Stop air leakage 

through the rim (or band) joist at the top 

of the basement wall with spray foam 

(shown) or with rigid foam cut to fit in 

the cavities and sealed around the edges. 

When insulating the entire basement is 

too expensive, just sealing and insulating 

the rim joists will save energy and improve 

comfort (Photo source: DOE).

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ENERGY RENOVATIONS INSULATION
Warm, humid, less 

dense air rises 

to top of room 

and is drawn in 

through cracks 

and openings

Convection loops 

form when cool 

air falls and warm 

air rises.

Condensation on 

cold surfaces

Cool air is more 

dense so falls

Cooled and dried 

air pushed out the 

bottom opening

Wood floor beams

Cold Outside

Warm Inside

Figure 5.15. Air leakage behind framed 

basement walls. Air leakage in an 

insulated basement allows moisture to 

condense behind insulation, reducing the 

effectiveness of the insulation and leading 

to mold (Source: BSC).

•	 Polyisocyanurate has a high R-value per inch. It is usually faced 

with aluminum foil to protect its surface. Foil is a Class I vapor 

retarder, and Building America scientists strongly advise against 

putting Class I vapor retarders in basement walls. However, foilfaced polyisocyanurate may be an exception. An excellent air barrier, 

it may be successful as interior basement insulation as long as edges 

and seams are well sealed and the foam is completely adhered to the 

foundation wall, with no gaps (Straube and Smegal 2009).

Whichever product you choose, plan to install enough foam to meet 

the recommended R-value for your climate. (See Section 2.2, “How 

much insulation do you need?”)

Proprietary Rigid Foam Board Systems 

You might want to consider a foam board insulation system. 

Specialty foam board systems can be more effective and faster to 

install than ordinary rigid foam panels (Krigger and Dorsi 2009). 

The system boards have fastening strips embedded in their surface, 

and some have built-in chases for wiring. The boards are installed 

using a foam-compatible adhesive and mechanical fasteners.

5.5.3 Preparing to Insulate your Basement

A successful project depends on careful preparation. Your contractor 

should perform the following steps, as needed:

Address Moisture and Mold

• Address water intrusion. Make sure rain and groundwater drain 

away from the foundation. Make sure no sprinklers spray the 

foundation or wet the ground next to it. Fix plumbing leaks. If 

you can't remove the source of water, don't insulate.

• Address interior drainage. If at times you can see moisture on 

the basement walls, or if water sometimes drains from the walls 

onto the floor, you should install an interior drain system before 

insulating your basement. Serious problems may require a sump 

pump, excavating and waterproofing exterior foundation walls, and 

installing drains outside. Your certified contractor can advise you 

on the best approach.

• Address mold. If you have mold, your contractor may advise you 

to gut the walls to expose the foundation. The moisture-damaged 

wood, damp insulation, and wallboard must all be removed. 

Save nothing! Mold spores are hard to kill and, if given enough 

moisture, can become a problem later. After the foundation is 

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ENERGY RENOVATIONS INSULATION
exposed, clean it thoroughly. The U.S. Environmental Protection 

Agency recommends using detergent and water (EPA 2010a) 

and recommends against using chlorine bleach or other biocides, 

because they can be health hazards themselves (EPA 2010b). 

Remove all the dust and dirt; these are food sources for mold. 

• Dry and waterproof. The foundation should be thoroughly dry 

before your work begins. This is a good time to put a damproof 

coating on the foundation exterior (Lstiburek 2006b).

Air Seal

• Air seal the attic floor. Oddly enough, air sealing your attic floor will 

help reduce moisture problems in your basement (and your whole 

house). This is because of the stack effect, in which air rises inside 

a home the way it does in a chimney. If air can escape into the attic, 

replacement air will be pulled into your basement from outside. In 

most climates, the incoming air carries moisture. Air sealing the 

attic floor will stop the escape of air into the attic. This reduces the 

stack effect, so less moist air will be pulled into your basement.

•	 Air seal the basement ceiling. All holes and cracks in the basement 

ceiling should be sealed. If the subfloor plywood panels are 

accessible, those seams should be sealed as well.

• Seal the foundation. Seal air leaks where the sill plate meets the 

foundation. Check the foundation for cracks and holes and seal them.

• Seal Ductwork. Make sure any ductwork in the basement is sealed 

with mastic. 

Seal and Insulate the Rim Joists

•	 Also called a band joist, the rim joist is the horizontal beam 

that rests on the sill plate, a 2 x 6 that sits horizontally on top of 

the foundation wall. Air can leak through multiple seams and 

holes where the rim joist meets the wall, the sill plate, and the 

subfloor. The rim joist should be air sealed and insulated to the 

same R-value as the walls. The best moisture control is achieved 

by filling the cavities where the floor joists meet the rim joist 

with spray foam insulation. Rigid fiberglass or rigid foam are 

also options, using caulk or spray foam to seal the edges (Saturn 

2011; Yost and Lstiburek 2002). Rim joist air sealing is especially 

important at bump-out areas such as bay windows that extend 

beyond the foundation. Note: Do NOT install fiberglass batts in 

the rim joist cavities without air sealing first.

Spray foam was used in the rim joists 

and rigid foam was used on the inside 

walls of this basement remodel near 

Pittsburgh, Pennsylvania (Photo Source: 

Asdal Construction).

For additional information 

on Air Sealing 

Building America’s Air Sealing Guide at 

http://apps1.eere.energy.gov/buildings/

publications/pdfs/building_america/

ba_airsealing_report.pdf.)

Tape

Rim Joist

Seal outside if it can 

be done without 

interfering with drainage

Housewrap Drywall

Bottom Plate Caulk

Sill Plate

Subfloor

Floor Joist

Sill gasket Foundation Wall

Ground

Rigid Foam

Caulk or Spray Foam

Figure 5.16. Insulating rim joists. Insulate 

and air seal the rim joist with closed-cell 

spray foam or pieces of rigid foam that are 

cut to fit each joist bay and sealed in place 

along all edges with caulk or spray foam.

68 May 2012

ENERGY RENOVATIONS INSULATION
Final Steps

• Check for radon. If a test shows that radon is a concern, your 

contractor will need to install a radon mitigation system before 

proceeding any further. Radon causes lung cancer. For more 

information, see Chapter 4, “Safety and Health.” When the 

insulation project is complete, your contractor should check 

for radon again, since radon can become concentrated once the 

basement is air-sealed.

• Insulate the basement floor, if that will be of value in your climate. 

See Chapter 5.6, “Insulating Concrete Floors.”

5.5.4 Installing Insulation on 

the Interior of Basement Walls

Spray Foam Insulation

After preparing the basement as described above, your contractor 

should perform the following steps to install spray foam:

•	 Apply the foam directly to the foundation walls, thickly enough to 

reach the recommended R-value for your climate. 

•	 Cover the foam with an ignition-barrier paint if you do not intend 

to cover the walls with framing and gypsum, which serves as an 

ignition barrier.

Alternatively, steel-stud framing can be embedded in the foam. Your 

contractor should:

•	 First construct a steel-stud wall 2 inches away from the foundation. 

(The space allows complete foam coverage of the wall and reduces 

thermal bridging.) 

•	 Spray the foam directly on the entire surface of the masonry at a 

thickness of 2 to 4 inches. 

•	 Attach 1⁄2-inch unfaced gypsum board to the stud wall as an 

ignition barrier for fire safety. The gypsum board should be at least 

1⁄2-inch off the floor. It can be covered with latex paint.

Interior Rigid Foam Insulation 

After preparing the basement as described in Section 5.5.3, your 

contractor should perform the following steps to install rigid 

foam insulation:

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ENERGY RENOVATIONS INSULATION
•	 Attach the foam panels to the interior of the foundation walls with 

construction adhesive applied in a serpentine pattern. 

•	 Make sure the panels are fully in contact with the foundation wall, 

with no gaps. 

•	 When using two layers of foam, stagger the seams.

•	 Create airtight seals where the panels meet and where they join 

other materials. Use acrylic-latex caulk, foam sealant, or mastic 

(Straube 2007).

If the rigid foam provides enough R-value, your contractor should:

•	 Attach wood furring strips to the foam to create an airspace and/

or a nailer for the wall finish material.

•	 Attach 1⁄2-inch unfaced gypsum board to the furring strips, keeping 

the gypsum board at least 1⁄2-inch off the floor. It can be covered 

with latex paint.

If you need more R-value than the rigid foam provides, your 

contractor should:

•	 Construct stud framing of metal or wood, attached to the foam 

panels. Wood should not touch the concrete floor.

•	 Fill the stud cavities with unfaced fiberglass batts, damp spray 

cellulose, or spray fiberglass (Smegal and Straube 2010). 

•	 Attach 1⁄2-inch unfaced gypsum board to the framing, keeping 

the gypsum board at least 1⁄2-inch off the floor. It can be covered 

with latex paint.

5.5.5 Installing Insulation on 

the Exterior of Basement Walls

Where termites are a threat, exterior foundation foam insulation 

is not recommended. The insulation can become a “highway” for 

termites to reach wood framing. Boric acid can be added to foam 

insulation to discourage termites, but the chemical is likely to leach 

out over time (Krigger and Dorsi 2009). Check with local pest control 

officials before planning to install exterior foundation insulation. 

Either rigid fiberglass or XPS foam insulation can be used on the 

exterior of basement walls. To install the insulation, your contractor 

should take the following steps:

Exterior insulation. At this new home, in 

Pittsburgh, workers install rigid insulation 

on the foundation and exterior walls. Rigid 

foam insulation can be installed on the 

walls of existing homes when the siding is 

removed. Insulating the foundation of an 

existing home is more difficult; it requires 

digging a trench down to the frost line 

(Photo Source: IBACOS).

Termites can tunnel through exterior foam 

insulation and make it a “highway” to reach 

wood framing. Where termites are a threat, 

check with local pest control officials 

before using exterior foam insulation.

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ENERGY RENOVATIONS INSULATION
•	 Locate any utility lines.

•	 Excavate around the foundation to a depth of at least 2 feet. In 

cold climates, go down to the frost line.

•	 Damp-proof the foundation. 

•	 Install a protective shield, such as metal flashing, between the 

top of the foundation wall and the sill plate to keep water from 

wicking into the foundation. It also serves as a termite shield.

•	 Install enough insulation to meet the recommended R-value for 

your climate, following the manufacturer’s instructions.

•	 Protect foam insulation from ultraviolet light, moisture, and 

mechanical damage during installation and afterwards. 

Proprietary Rigid Foam Board Systems 

Several companies make specialty foam board systems for exterior 

basement insulation. While they can be more effective and faster 

to install than ordinary foam panels, they still require excavation, 

special coverings, and flashing measures. 

5.5.6 Installing Insulation on 

the Basement Ceiling

Insulating the ceiling of your basement instead of the walls is 

recommended only when ALL of the following are true:

•	 You live in a dry climate, and

•	 you see no evidence of moisture in your basement, and 

•	 you do not use your basement as living space.

Before beginning your insulation project, your contractor should 

complete the following steps:

•	 Replace any knob-and-tube wiring on the basement ceiling. It can 

overheat, creating a fire risk when covered with insulation.

•	 Make sure the basement has adequate ventilation. 

•	 Make sure any pipes and ducts in the basement are well insulated 

against freezing and heat loss. Your basement will be colder when 

the ceiling is insulated. (Appendix C provides information on 

insulating ducts and hot water heaters.)

Basement ceiling insulation. When this 

home was remodeled for energy efficiency, 

the basement ceiling was extensively air 

sealed and then insulated with unfaced 

batts (Photo Source: PNNL).

See Appendix C for 

performance briefs on

•	 Air sealing ducts

•	 Insulating hot water heaters.

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ENERGY RENOVATIONS INSULATION
•	 Air seal the basement ceiling to prevent soil gases, dust, and 

pollutants from moving up and into your home. Plug leaks in 

the rim joists and seal all plumbing, electrical, service, and duct 

penetrations. For details, see Appendix C. See also Building 

America’s Air Sealing Guide at http://apps1.eere.energy.gov/buildings/

publications/pdfs/building_america/ba_airsealing_report.pdf

You have several insulation choices for your basement ceiling: 

•	 Spray foam can be applied, achieving air sealing and insulation 

in one step. 

•	 Rigid insulation or netting can be attached to the underside of 

the floor trusses. The space should be filled with blown fiberglass 

or cellulose. 

•	 Unfaced batt insulation can be installed between the floor joists.

To install batt insulation, your contractor should do the following:

•	 Install the unfaced batts in full contact with the joists and the 

floor above.

•	 Seal all seams carefully. 

•	 Support the insulation with mechanical fasteners or inexpensive 

landscape cloth. 

•	 Check to be sure there is no airspace between the insulation 

and the floor. 

•	 Weather-strip the basement door. 

5.5.7 Maintaining a Dry, 

Problem-free Basement 

When your project is complete, you should take the following steps 

to ensure a healthy environment:

•	 Test again for radon. Radon levels can rise when the basement is 

air-sealed.

•	 Avoid using vinyl flooring or vinyl wallpaper in the basement. 

These are Class I vapor retarders and create a risk of mold.

•	 Use only latex paint, not oil, alkyd, or epoxy paint, which can hold 

moisture inside the wall.

•	 Keep storage items on shelves, off the floor, and allow for air 

circulation between the items and the wall. 

Profile

Design Challenge: 

Converting a Cold, 

Wet Basement into 

Useable Space

Building Science Corporation (BSC), 

a Building America research partner, 

helped launch the National Grid Deep 

Energy Retrofit Pilot in 2010. The first 

project involved the renovation of a 

Cape Cod-style home in Belchertown, 

Massachusetts, built in 1760.

One challenge was the cold, damp 

basement. It often contained standing—

and sometime flowing—water. With advice 

from BSC, the homeowners worked with 

the builders to transform the basement 

into dry space for storage. They dug 

trenches in the basement, installed 

drainage piping, and laid down several 

cubic yards of gravel. They covered 

the gravel with sheet polyethylene to 

control vapor and block the entry of 

soil gases. The conversion to a dry, 

temperate basement was completed 

with an insulated concrete slab over the 

polyethylene sheet and the addition 

of spray foam insulation on the 

foundation walls.

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ENERGY RENOVATIONS INSULATION
Finally, you should monitor your basement to make sure it stays dry:

•	 Measure your basement’s relative humidity in both winter and 

summer. According to the U.S. Environmental Protection Agency, 

the ideal humidity is 30% to 50%. Higher humidity can promote 

dust mites and mold (EPA 2010a).

•	 Install a dehumidifier if your basement’s humidity exceeds 60%. 

Look for models with an ENERGY STAR seal. The dehumidifier 

should be plumbed directly to a condensate drain (Lstiburek 2006b).

5.6 Insulating Concrete Floors

Insulating a concrete floor can do more than reduce heat loss. Done 

properly, it can help solve moisture problems, making your home 

healthier, more comfortable, and more durable. 

Concrete floors don’t always need insulation. In hot climates, a 

cool floor is an advantage in summer. In other climates, however, 

the concrete floor of a basement or a home with a slab-on-grade 

foundation may be cold and uncomfortable in winter. Moisture 

may collect on the floor, creating an inviting place for mold and 

dust mites and leading to structural damage in the long term. The 

moisture can come from two sources: 

• CONDENSATION. Moist indoor air can condense when it 

contacts cold concrete, making your carpet damp and musty. If 

you have a vinyl floor over concrete, it may be hiding mold.

•	 GROUND MOISTURE. Moisture in the ground may be wicking 

up through the concrete if there is no polyethylene vapor retarder 

under the slab. The floor may appear to be dry, but only because 

ground moisture passing through the slab is diffusing into the air. 

Your concrete floor may also be wasting your energy dollars. 

Although little heat is lost through the floor of a deep basement, as 

much as 20% of a home’s heat may be lost through a ground-level 

slab (DOE 2000c).

The subsections below provide guidance on two approaches to 

insulating a concrete floor:

•	 insulating the surface of a concrete floor

•	 insulating the exterior perimeter of a ground-level slab.

Be sure to hire a contractor certified in building science. A 

knowledgeable contractor can help you determine the best approach 

for your home, and expert installation is the key to a good outcome.

Figure 5.17. Insulating concrete floors.

If your existing concrete floor is dry and 

in good repair, an epoxy coating can be 

brushed onto the concrete. XPS insulation 

can then be installed directly over the 

surface (Figure Source: BSC).

Top-side epoxy coating

Extruded polystyrene; 

unfaced, no polypropylene 

or foil facing

1x4 furring 

(16" o.c.)

concrete slab

Plywood subfloor

Vapor semi-permeable assembly allows 

moisture to pass in a slow, controlled manner

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ENERGY RENOVATIONS INSULATION
Figure 5.18. Vapor pressure equalization.

“An airspace is provided over the top 

of a wet concrete slab. This airspace is 

bounded by a vapor impermeable chamber 

(outward evaporation is not possible) 

and equilibrates with the slab. The vapor 

pressure in the airspace tracks the vapor 

pressure in the slab and stasis is achieved.”

(Quote and Figure Source: Lstiburek 2008a)

5.6.1 Insulating the Surface 

of a Concrete Floor 

Your contractor should take the following steps to insulate the 

surface of your concrete floor:

Prepare to Insulate

•	 Make sure adequate clearance will remain between the new floor 

and ceiling per local code (for example, 7.5 feet). Adding insulation 

and installing a new floor over the existing concrete will raise the 

height of the floor. 

•	 Make sure any interior drainage system works well or install one 

if needed.

•	 Fix any sources of water intrusion. Make sure rain and groundwater 

drain away from the foundation. Make sure no sprinklers spray the 

foundation or wet the ground next to it. Fix plumbing leaks. If you 

can’t remove all sources of water, don’t insulate. 

•	 Make sure the floor is clean and fix any problems in the concrete 

such as cracks, spalls, and water problems.

Control Moisture if the Concrete Appears Wet

Use one of the following moisture control measures when the 

concrete is visibly wet or where chalk-like salts (called efflorescence) 

are visible:

•	 Install a drainage mat directly over the concrete. A drainage mat 

works by moving water laterally to the interior drainage system. 

•	 Alternatively, install a dimpled plastic sheet membrane, using 

cement to attach it to the concrete (see Figure 5.18). A dimpled 

membrane provides an air space over the wet concrete slab. The 

vapor pressure in the air space equalizes the vapor pressure in the 

slab. As a result, the concrete will not wick water up to the surface 

(Lstiburek 2008a).

Seal the Concrete if it Appears Dry

•	 Use an epoxy coating or chemical sealant (Figure 5.11). Any 

moisture wicked up by the concrete will pass through the floor and 

diffuse into the interior of the home in a slow, controlled manner 

without inviting mold growth. 

Vapor pressure on top of slab 

and under slab equalizes, thereby 

stopping capillary transfer of water 

and soluable mineral salts (moisture 

content in air space and under slab 

remains the same; i.e. “wet).

Damp ground (no capillary 

break, no polyethylene 

ground cover)

Existing slab

Dimpled plastic sheet 

membrane (air tight 

and gas tight)

Carpet or wood floor 

(avoid vinyl flooring as vinyl 

flooring does not breathe)

3⁄4" plywood, narrow edges 

“biscuit” joined

Rigid insulation (extruded 

polystyrene — unfaced, no 

polypropylene or foil facers)

Air space

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ENERGY RENOVATIONS INSULATION
Install Insulation 

•	 Place extruded polystyrene rigid foam insulation (XPS) directly 

over epoxy-covered concrete, drainage mat, or dimpled membrane. 

•	 Seal the joints between the foam panels with tape. Seal the edges 

along the walls with spray foam.

•	 Since XPS is a vapor retarder, there is no need to install another 

vapor retarder. 

Install the New Floor

•	 Float a subfloor, using pressure-grooved sleepers or tongue-andgroove plywood.

Finish the Floor 

•	 Install carpet or wood flooring to finish the floor.

•	 Do not install vinyl flooring. It will trap moisture, leading to mold 

and mildew.

Finish the Room

•	 Trim the bottom of any doors leading into the room to match the 

new floor height.

•	 Adjust the steps leading into the space, as raising the floor can 

create an unequal step on stairs.

5.6.3 Insulating the Perimeter of a Slab

A ground-level slab can be insulated on the perimeter instead of 

its surface or subsurface. The approach is effective because slabs 

primarily lose heat outward and through the edge of the slab. The 

concrete floor absorbs heat from inside the home and transfers it to 

the foundation wall, where it escapes outside. 

Slab perimeter insulation is not appropriate for every climate zone. 

Building America scientists make the following recommendations 

(DOE 2004a):

• HOT-DRY: Slabs in this climate do not require insulation.

• MIXED-DRY: In the absence of insulation below or above the slab 

surface, slabs in this climate should be insulated at the perimeter 

with borate-treated rigid foam or rigid fiberglass.

Moisture control. A dimpled plastic 

membrane can be placed over the existing 

concrete and under the the XPS to keep 

your concrete floor from wicking ground 

water into your home (Photo source: BSC).

To identify your climate zone,

see the map in Chapter 2.

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• HOT-HUMID: Slabs in this climate are generally not insulated, 

even at the perimeter, because of mild winters and code restrictions 

on below-grade use of rigid foam insulation.

• MIXED HUMID: In the absence of insulation below or above 

the slab surface, slabs in this climate should be insulated at the 

perimeter with borate-treated rigid foam or rigid fiberglass, unless 

prohibited by local code due to termite concerns.

•	 COLD OR VERY COLD: Insulating the surface of the slab is a 

more effective choice in these climates. When that is not feasible, 

perimeter insulation can be valuable.

To identify your climate zone, see the IECC map in Chapter 2.

Slab Perimeter Insulation: Advantages and Drawbacks

Where recommended, insulating the exterior edge of the slab can 

reduce winter heating bills by 10% to 20% (DOE 2011e). It can 

also reduce moisture problems, since a warmer slab is less prone 

to condensation.

On the other hand, several factors may make slab perimeter 

insulation unfeasible for your home. It is expensive. To install the 

insulation, your contractor will need to dig a trench around your 

house to the depth of the frost line. A driveway, sidewalk, or trees 

may be in the way. Where termites are a risk, your local building 

codes may not allow you to insulate the slab perimeter with rigid 

foam. Termites can tunnel through foam to reach wood framing. 

Rigid fiberglass is an alternative. 

To insulate the perimeter of your concrete slab, your contractor 

should take the following steps:

Prepare to Insulate

•	 Review the plans with pest control officials as well as building officials.

•	 Check that the lot is graded properly so that rain and groundwater 

don't run into the foundation. Make sure the sprinklers don’t spray 

the foundation or wet the ground next to it. 

•	 Install a perimeter drainage system if needed or check that an 

existing system is working well. 

•	 Check for radon, which causes cancer. If the radon level is 

elevated, you will need to install an appropriate radon mitigation 

system. (See Chapter 4, Safety and Health.)

Figure 5.20. Slab perimeter insulation.

Use rigid fiberglass insulation or boratetreated rigid foam approved for 

below-grade use (Source: DOE).

Figure 5.19. Heat loss. Concrete slabs 

primarily lose heat outward and through 

the edge of the slab. In cold climates, 

insulating the slab perimeter can reduce 

heating bills by 10% to 20% (Source: DOE).

slab

heat 

loss

Slab Flashing

Protection board

Rigid insulation

76 May 2012

ENERGY RENOVATIONS INSULATION
Dig a Trench and Waterproof

•	 Dig a trench around the house to the depth prescribed by your 

local building codes. In areas where the ground freezes, the 

minimum depth will be the frost line. 

•	 Clean the foundation and allow it to dry.

•	 Apply a waterproof coating.

Install Insulation

•	 Use rigid fiberglass insulation or borate-treated rigid foam 

approved for below-grade use. Foam insulation must be protected 

from ultraviolet light, moisture, and mechanical damage during 

installation and afterwards. 

•	 Install flashing or protective board over the insulation.

•	 Install insulation directly against the slab’s exterior edges, 

extending it from the top of the slab to the depth of the frost line. 

Local building codes may require a termite inspection gap between 

the sill plate and the top of the insulation.

•	 Follow the manufacturer’s instructions for attaching the insulation.

•	 Air seal all edges. The insulation should be continuous and airtight.

•	 Air-seal the interface between the foundation and the exterior wall.

Install a Protective Membrane

•	 Encapsulate or cover the exterior face of the insulation with a 

protective membrane, such as rubberized roofing material or 

an ice-dam protection membrane. This will serve as a capillary 

break to reduce the wicking of water from the foundation. This 

membrane can also serve as a termite shield.

 Cover Above-grade Insulation

•	 Cover the portion of the insulation exposed to the outside air with a 

stucco coating, pressure-treated wood, brick, or aluminum flashing. 

Finish and Test

•	 Replace the dirt around the perimeter. 

•	 Check again for radon, since insulation can lead to concentrated 

radon levels inside the home. 

Once the project is complete, be sure to inspect your home regularly 

for termite infestation. 

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5.7 Insulating Ducts

As much as 40% of the energy used to heat and cool your home 

can be lost by leaky, poorly insulated ducts that run through 

unconditioned parts of your home, such as the attic or crawlspace 

(LBNL 2001). This can add hundreds of dollars a year to your 

heating and cooling bills (DOE 2009). Your heating and cooling 

equipment has to work harder, and some rooms may be colder in 

winter because of heat loss through conduction along the ducts and 

from air leaks at seams and joints, such as where branches meet a 

trunk line, where the ducts meet the registers, and where the ducts are 

connected to the furnace or air conditioner. About half of typical 

energy loss from ducts is due to air leaks (LBNL 2001). Even ducts 

in conditioned space can have lose energy through uninsulated 

ducts and air leaks that waste conditioned air and cause pressure 

imbalances between rooms and inadequate air flow to parts of the 

home. Ducts should be airtight and insulated not only for comfort 

and energy savings but to prevent condensation and mold. Mold can 

grow on moisture and dirt collecting inside ducts, and the air moving 

through the ducts will distribute the spores through the home.

Ducts in older homes are usually made from sheet metal and may 

or may not have added insulation. Newer homes often have ducts 

made of fiberglass duct board or flexible plastic, both of which 

have built-in insulation. If your ducts are already insulated, adding 

insulation is recommended if the R-value is less than 4.2 (LBNL 

2003). The International Energy Conservation Code recommends 

that supply ducts in attics be insulated to a minimum of R-8 and 

other ducts be insulated to a minimum of R-6, although it does not 

have a minimum requirement for ducts that are completely within 

the building’s thermal envelope (2009 IECC 403.2.1). Supply ducts 

in conditioned space should be insulated to avoid condensation on 

the inside of the duct in summer and the outside in winter. Exhaust 

ducts going through cold spaces in the winter should also be 

insulated to avoid condensation inside (Rudd 2009).

Before insulation is added, the ducts should be tested for air leaks. Air 

leaks are tested with a duct test, which is often done as part of a wholehouse energy checkup or audit (see Chapter 2). The IECC recommends 

total duct leakage of less than or equal to 12 cfm per 100 ft2 of 

conditioned floor area when tested at 25 Pascals (2009 IECC 403.2.2). 

Because ducts are often concealed in walls, ceiling, attics, and 

basements, repairing them can be difficult. Get a qualified 

professional to seal and insulate them. In addition to the duct blaster 

test, the contractor should visually inspect the duct system, evaluate 

the system’s supply and return air balance, and check air flow at each 

register. Adjustments such as larger return ducts may be needed.

(Top) Mastic is a thick, gooey substance 

that is painted onto seams and joints. 

Duct seams and joints should be sealed 

with mastic or approved metal tape, 

not duct tape (Photo Source: FSEC).

(Bottom) Ducts should be inspected to 

make sure they aren’t crushed, sagging, 

leaking, or disconnected, a surprisingly 

common finding during duct inspections 

(Photo Source: BSC).

78 May 2012

ENERGY RENOVATIONS INSULATION
The contractor will replace damaged ducts, reconnect disconnected 

ducts with mechanical fasteners, and straighten and tighten 

flexible ducts that are tangled, crushed, kinked, or sagging due to 

unnecessary length or lack of adequate hanging straps. Leaks and 

joints should be sealed with a long-lasting material such as mastic, 

a gooey substance that is “painted” on to seams and reinforced with 

wire mesh tape if needed (Rudd 2009). Butyl tape, foil tape, or other 

heat-approved tapes with the Underwriters Laboratories logo can 

also work well if the area to be taped is cleaned of surface dust and 

dirt first. Plastic or cloth duct tape should not be used because it 

dries, cracks, and quickly loses its bond. Pressure- or heat-sensitive 

aluminum foil tape is recommended if a joint needs to be accessible 

for future maintenance. The contractor will use caulk to seal all 

registers and grills tightly to the ducts. 

Once the ducts are sealed, they should be covered with fiberglass 

duct insulation that has a foil or vinyl facing on the exterior to keep 

the insulation dry. If you already have duct insulation that is wet, 

smelly, or visibly moldy, it should be removed and replaced by a 

qualified heating and cooling system contractor. If your ducts were 

made with a fiberglass duct liner, cleaning will not prevent re-growth. 

The material must be replaced (EPA 2011).

The ducts should be wrapped with foil- or vinyl-faced fiberglass 

duct insulation, with the vapor retarder facing out. The insulation 

should cover the duct completely. The facings should overlap where 

sections of insulation meet and they should be tightly sealed with 

fiberglass tape, applied carefully to avoid compressing the insulation. 

Compressed insulation loses R-value. The end of each piece of tape 

should point downward; tape pointing upward will eventually fall 

(Krigger and Dorsi 2009). Metal fasteners may also be added.

Upon completion of the work, your contractor will evaluate air 

flow and conduct a combustion safety test to be sure there is no 

backdrafting of gas- or oil-burning appliances.

When you insulate ducts in an unconditioned basement or 

crawlspace, that space will be colder. Water pipes and drains 

located there may freeze and burst if you live in a cold climate. 

Consider insulating the basement walls or closing and insulating 

the crawlspace. Both projects can have significant benefits for your 

health, comfort, and energy savings. If your renovation project 

includes replacing the furnace and ducts, consider installing a highefficiency, sealed-combustion furnace and insulated ducts within the 

thermal envelope of the home. You may also want to consider going 

ductless with ductless heat pumps.

All ducts should be laid straight and 

adequately supported. Flex ducts should 

be stretched tightly; loose, sagging ducts 

can greatly restrict air flow (Photo Source: 

PNNL).

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80 May 2012

ENERGY RENOVATIONS INSULATION
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by Building Science Corporation for the U.S. Department of Energy. www.buildingscience.com/documents/reports/rr-1006-bahigh-r-roofs-case-study-analysis

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Building Science Corporation for the U.S. Department of Energy. www.buildingscience.com/documents/reports/rr-0903-buildingamerica-special-research-project-high-r-walls

Straube, John, Jonathan Smegal and John Smith. 2010. Moisture-Safe Unvented Wood Roof Systems, RR-1001, Building Science 

Corporation. www.buildingscience.com/documents/reports/rr-1001-moisture-safe-unvented-wood-roof-systems

Straube, John. 2006. Wood Pitched Roof Construction, BSD-115, Building Science Corporation. www.buildingscience.com/documents/

digests/bsd-115-wood-pitched-roof-construction?topic=doctypes/digests

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Photo Credits

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U.S. Department of Energy. 2010g. Case Study: Nelson Construction. 

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(Not online yet.)

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Residential Buildings for DOE. Accessed 9-12-11. 

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www.epa.gov/asbestos/pubs/insulation.html#What Volume 12. 

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Insulation reduces the movement of heat between your 

home and the outside, keeping the interior cool in summer 

and warm in winter. Understanding insulation means 

understanding heat flow and air pressure.

Heat Flow

Heat tends to flow from a warm space to a cool space. 

Your walls, ceilings and floors form a “thermal envelope” 

around the air in your home. In the winter, heat from inside 

the thermal envelope moves to any area that’s cooler—the 

outdoors and the unheated parts of your house. In the 

summer, heat flows into the cooler interior of your home. 

The larger the temperature difference between the inside 

and the outside, the faster the heat will move.

Heat moves in and out of your house through a number of areas: 

construction joints and seams, penetrations in your walls for pipes 

and wires, cracks around doors and windows, and your attic access 

opening. Heat also moves directly through walls, floors, ceilings, 

and windows. All materials, including wood, metal, and glass, allow 

some measure of heat to pass through them. Insulation is made of 

materials that have a high resistance to heat flow.

Heat is transferred in three ways: conduction, convection, and 

radiation (Figure A.1). 

CONDUCTION. Conduction is the movement of heat through a 

solid material. For example, the heat from a stove moves through a 

saucepan to its contents. In a building, heat flows from the warmer 

side of a wall to its cooler side. A material’s resistance to conduction 

is called its R-value. The more resistant a material is to allowing heat 

to flow through it, the higher its R-value. 

Figure A.1. Heat is transferred through 

conduction, convection, and radiation 

(Source: PNNL).

Appendix A

How Insulation Works: 

Understanding Heat Flow and Air Pressure

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ENERGY RENOVATIONS INSULATION
Most of a home’s heat is typically lost through conduction. 

Lumber, which provides the frame for your home’s thermal 

envelope, is not very good at resisting heat flow. It conducts some 

heat and has an R-value of about R-1. The best way to slow down 

conduction is to insulate. 

CONVECTION. Convection is the movement of heat through air (as 

well as through liquids and other gases). In simple terms, warm air 

becomes buoyant and rises to the top of a structure. Cold air sinks. 

The most effective strategy for stemming convective heat loss is to 

reduce the amount of air that flows through cracks and holes in the 

walls, ceilings, and floors. Filling the wall cavities with insulation and 

sealing the air leaks will eliminate cold spots in walls. Insulating and 

air-sealing floors and ceilings will also reduce the amount of warm 

air being lost to the attic and the amount of cold air coming into the 

thermal envelope from the crawlspace or basement. 

RADIANT ENERGY. On a sunny day, you’ll feel warmer sitting in 

the sun than in the shade, although there is little difference in air 

temperature. The warmth you’re feeling is radiation, which flows 

through space in the form of waves. These waves have two types: 

solar radiation, which is radiant energy from the sun, and infrared 

radiation, which is radiant energy reflected back from the earth into 

space. Radiation heats anything solid that absorbs its energy.

Radiant heat has an impact on indoor comfort. Radiant heat 

from a sun-heated window can make you feel warmer than the air 

temperature suggests. Radiant heat also affects your home’s energy 

efficiency. During the day, sunshine warms your house. At night, your 

house can radiate heat to a clear night sky. The resulting cooling can 

lead to condensation in your attic or the underside of your roof if the 

temperature inside your attic drops below the dew point.

Roof overhangs, window awnings, and tree shading help reduce 

radiation from the sun to your home. In hot-dry and hot-humid 

climates, you can reduce heat gain by installing a radiant barrier 

in an unsealed attic (see Appendix C). In cold climates, however, 

radiant barriers are seldom cost-effective. Homeowners in hot 

climates can also benefit from re-roofing with light-colored material. 

Light-colored roofs keep a building cooler by reflecting the sun’s 

heat away from the building. In cold climates, however, light-colored 

roofs are not recommended; they can increase energy use by 

reducing the sun’s ability to heat the home in winter.

Heat flow. An infrared camera shows 

thermal bridging—heat moving through 

the wood framing into the home by 

conduction (Photo Source: DOE).

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ENERGY RENOVATIONS INSULATION
Air Pressure

Another factor in energy efficiency is air pressure.

You may recall that air moves naturally from areas with higher 

pressure to areas with lower pressure. For example, air in an inflated 

balloon is under pressure. Poke a hole in the balloon and the air will 

flow out quickly. The larger the pressure difference between the air in 

the balloon and the outside air, the faster the air will move. Positive 

pressure refers to an enclosure with higher air pressure than the area 

around it, like an inflated balloon. Negative pressure refers to an 

enclosure with lower air pressure than the area around it. A vacuum 

cleaner works because air moves from the higher-pressure room into 

the lower-pressure canister.

In your home, differences in air pressure affect the flow of heat and 

moisture. For example, your bathroom fan sucks out air, putting 

the room under negative pressure. Air from other parts of the house 

rushes into the bathroom.

Factors that change air pressure in homes are temperature, height, 

ventilation fans, furnace blowers, chimneys, and the wind.

TEMPERATURE. During the winter, warm indoor air rises, creating 

positive pressure at the top of your house. This positively pressured, 

warmer air naturally flows out of your living space to where the air is 

cooler and has lower pressure. It exits to the attic through air leaks, 

gaps in your existing insulation, penetrations in the walls and ceiling, 

and the attic access door. 

This movement of warm air to the top of the house creates lower 

air pressure at the bottom of the house. This negative pressure pulls 

cold outside air into the lower part of the house through air leaks, 

insulation gaps, penetrations in the walls and floor, and crawlspace 

vents. 

This air movement from bottom to top is called the stack effect. 

The greater the difference in temperature between the inside and the 

outside, the greater the stack effect. Insulating and sealing air leaks 

in the attic can dramatically reduce the stack effect and the resulting 

heat loss.

BUILDING HEIGHT. The force of the stack effect also depends on 

the height of a building. The taller your house, the more pressure 

difference there will be between the bottom and the top.

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ENERGY RENOVATIONS INSULATION
VENTILATION FANS AND FURNACE BLOWERS. A fan or 

furnace blower that forces air into the home creates positive pressure, 

which will push air out of the top of the house. On the other hand, 

negative pressure is created by the exhaust fans for your kitchen, 

bathroom, and clothes dryer. “Make-up air” will be pulled in 

through air leaks, insulation gaps, penetrations, and leaky ducts. 

CHIMNEYS. The stack effect naturally moves air up a chimney, 

reducing air pressure in the lower part of the home. However, if the 

negative pressure inside a house becomes too great, it can pull air 

down the chimney and into the house—a dangerous situation called 

backdrafting.

WIND. Wind creates positive pressure on the side of your house 

facing the wind, and negative pressure on the side away from 

the wind. These pressures push and pull air through leaks and 

penetrations in your home’s thermal envelope.

What Makes Insulation Effective

Insulation works by slowing the movement of heat, whether by 

conduction, convection, radiation, or differences in air pressure. The 

more heat flow resistance your insulation provides, the lower your 

heating and cooling costs will be. The heat resistance of insulation is 

called its R-value. The higher a material’s R-value, the better it is at 

stopping heat transfer. 

Different kinds of insulation address the different ways heat travels. 

In general, insulation and its essential accompaniment, air sealing, 

work by:

•	 Forming an air barrier – reducing the movement of interior or 

exterior air moving through your home’s thermal envelope. 

•	 Hindering heat transfer – trapping air in millions of tiny pockets.

•	 Minimizing thermal bridges – reducing the conduction of heat 

through concrete, wood, and metal.

•	 Retarding vapor – reducing the movement of moisture through 

the building envelope.

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ENERGY RENOVATIONS INSULATION
Appendix B

Air Leakage, Moisture, and Ventilation: 

Why You Need a “Whole-House” Approach

Discomfort, moisture, and big energy bills are symptoms that a 

home needs thermal improvements. The following symptoms occur 

because of the links between temperature, air quality, and moisture. 

Simply adding insulation will not solve these problems; it may even 

create new ones. Making the entire home comfortable, safe, durable 

and energy-efficient requires a whole-house approach to control the 

flow of heat, air, and moisture.

Winter Symptoms

•	 drafts 

•	 cold floors 

•	 uneven temperatures from room to room or floor to floor 

•	 walls that are cold to the touch 

•	 condensation on windows, walls, or ceiling surfaces

•	 visible mold or mildew growth on any surface

•	 water-damaged finishes or water stains 

•	 cracked or missing caulking

•	 ice dams or icicles 

•	 high heating bills.

Summer Symptoms

•	 warm or muggy inside air

•	 visible mold or mildew growth on any surface 

•	 condensation on windows, walls, or ceiling surface 

•	 uneven temperatures from room to room or floor to floor

•	 mold growth in the basement

•	 high energy bills for air conditioning. 

Building science. When performing 

energy upgrades on an existing house, 

it’s important to take a whole-house 

approach that addresses the interactions 

of heat flow, air flow, and moisture 

management (Photo Source: PNNL).

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ENERGY RENOVATIONS INSULATION
B.1. Air Leakage

Air leaks carry both moisture and heat, usually in the direction you 

don't want. Air movement accounts for more than 98% of all water 

vapor movement in building cavities (DOE 2011). Air naturally 

moves from a high pressure area to a lower one—generally through 

any available hole or crack in the thermal envelope (see Appendix A).

Air leakage can create significant problems. If the moisture in air 

condenses on organic surfaces such as wood or paper-faced drywall, 

it can lead to mold and rot inside the walls and in other parts of the 

house. Air leaks allow dust, pollen, and mold spores to enter the 

house, contributing to health problems. In a typical home, air leakage 

accounts for 25% to 40% of the energy used for heating and cooling.

Air leaks are a problem within a house as well as between the 

house and the outside. Building scientists talk about your home’s 

“thermal envelope”—the floors, ceilings, walls, windows, and 

doors that surround the space in which you live, keeping it warm in 

winter and cool in summer. Parts of the house may be outside the 

thermal envelope—an unfinished attic or basement, a crawlspace 

or garage. Air is leaked between your home’s thermal envelope and 

unconditioned parts of the house.

Chimneys and the cracks around doors and windows are well-known 

trouble spots when it comes to air leakage. But often the leaks 

between the thermal envelope and other parts of the house are much 

greater. Air leaks through: 

•	 ceilings

•	 floors above an unconditioned basement, garage, or vented 

crawlspace

•	 leaky ducts

•	 plumbing and electrical wiring penetrations

•	 gaps around electrical outlets, switch boxes, and recessed lights

•	 gaps behind recessed cabinets and false ceilings, such as kitchen 

or bathroom soffits

•	 gaps around attic access hatches and pull-down stairs

•	 duct chases

•	 furnace flues

•	 walls behind bath tubs and shower stalls 

•	 walls between the living space and the garage

•	 basement rim joists—where the foundation meets the wood framing

Air leaks. There are numerous spots where 

air can leak into or out of a house, wasting 

energy and risking problems with moisture 

and air quality.

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ENERGY RENOVATIONS INSULATION
•	 cantilevered floors

•	 attic kneewalls 

•	 any openings or cracks where two walls meet, where the wall 

meets the ceiling, or near interior door frames.

Most insulation does not stop airflow. Before you add insulation, 

sealing a home to reduce air leakage is essential. It is inexpensive 

and highly effective. 

Appendix C provides Performance Briefs on air sealing and 

insulating many of the leakage sites listed above. For additional 

information on air sealing, see Building America’s Air Sealing 

Guide at http://apps1.eere.energy.gov/buildings/publications/pdfs/

building_america/ba_airsealing_report.pdf

B.2. Moisture 

Done right, adding insulation and air sealing can cure moisture problems. 

One reason moisture problems develop is because of differences 

in surface temperatures. You may recall that warm air is able to 

carry more moisture than cool air. When air meets a cold surface, it 

cools. If its temperature drops below the dew point, the air deposits 

moisture on the cold surface. This is why inefficient windows 

or poorly insulated walls may have condensation in wintertime. 

Moisture buildup in walls can lead to mold and mildew, wood rot, 

and subsequent structural and health problems.

Moisture can also be deposited in walls during the summer. In 

an air-conditioned home, warm air comes in through leaks in the 

thermal envelope. As that air enters a wall assembly, it hits the back 

of the interior wall, which has been cooled by air conditioning. If 

the air temperature drops below the dew point, the air will deposit 

moisture inside the wall cavity. 

Insulation itself can cause moisture problems. When you insulate a wall, 

you change the temperature inside it. A surface inside the wall can be 

much colder in the winter than it was before you insulated. Without 

proper moisture control, this surface could become a place where water 

vapor traveling through the wall condenses and leads to trouble. The 

same thing can happen in the attic or in a crawlspace or basement. 

However, with careful design, insulation and air sealing can prevent 

condensation and keep your walls, attic, and basement or crawlspace 

drier than they were before. A contractor certified in building science 

principles (see Chapter 1) can advise you on this. 

Building codes in some areas require the use of vapor retarders to 

help control moisture. For information, see Section B.4 below.

May 2012 B.3

B.3

ENERGY RENOVATIONS INSULATION
Dew Point

The dew point is the temperature at which 

water vapor starts to condense. Above the 

dew point temperature, moisture stays in 

the air. At or below the dew point, moisture 

leaves the air and condenses on a cool 

surface, like the glass for your iced tea.

B.3. Ventilation

When you perform air sealing, you must ensure that your home 

will be well ventilated. Replacing stale air with fresh air is essential 

for health and comfort. Poorly ventilated homes can accumulate 

chemicals, gases, mold, dust, and moisture. You and your family 

generate moisture every time you cook, shower, and do laundry. Just 

by breathing and perspiring, a typical family adds about 3 gallons of 

water per day to their indoor air (DOE 2008).

Most homes rely on random air leakage to supply fresh air and 

prevent the buildup of stale inside air. But, as noted above, these 

uncontrolled leaks cause their own problems.

To provide proper ventilation, your contractor may recommend 

adding ventilation fans, also known as a mechanical ventilation 

system. There are several options. Spot ventilation—using exhaust 

fans in the kitchen and bathroom, removes water vapor and pollutants 

from specific locations in the home, but does not supply fresh air. 

Supply-side ventilation delivers fresh air but brings in moisture and 

hot or cold air from outside. This fresh air usually comes from an 

intake connected to the return side of your air handler, using the 

central heating system’s fan and ducts to distribute the air. If you 

don’t have a central heating system, a dedicated fan can be attached to 

a fresh air intake to draw in outside air. Balanced ventilation systems, 

such as air-to-air exchangers, heat-recovery ventilators, and energy 

recovery ventilators, supply and exhaust equal amounts of air to the 

house. The outgoing air tempers the incoming air, saving heat and 

energy. Your contractor can help you determine which approach is 

most appropriate for your specific climate, house design, and budget. 

The Whole-House Approach

Improving the thermal envelope, like any 

renovation, requires careful planning. 

The interactions of all of your home’s 

components, including its ventilation, 

must be taken into account to maximize 

performance and avoid unintended 

consequences. This “whole-house” 

approach recognizes that changes in one 

component can dramatically change how 

other components perform. 

More Information 

For more information on heat and 

energy recovery ventilators, see the U.S. 

Department of Energy’s Energy Saver 

site: www.energysavers.gov/your_home/

insulation_airsealing/index.cfm/

mytopic=11900

Table B.1. Pros and Cons of Various Mechanical Ventilation Systems 

(Adapted from Rudd, A. 2011. “Local Exhaust and Whole House Ventilation Strategies,” prepared by BSC for DOE Building America)

Ventilation Type Pros Cons

Exhaust Only

(air is exhausted from 

the house with a fan)

•	 Inexpensive

•	 Easy to install

•	 Simple method for spot ventilation

•	 Removes heated or cooled air

•	 Makeup air is from random sources

•	 May create negative pressure in house, causing backdrafting

Supply Only

(air is supplied into the 

house with a fan)

•	 Does not interfere with combustion appliances

•	 Creates positive pressure in house, inhibiting

the entry of pollutants 

•	 Delivers fresh air to important locations

•	 Brings in moisture and hot or cold air from outside

•	 Does not remove indoor air pollutants at their source

•	 Air circulation can feel drafty

•	 Furnace fan runs more often unless fan has an ECM

(variable-speed motor)

Balanced Air 

Exchange System

(heat and energy 

recovery ventilators)

•	 No combustion impact

•	 Can be regulated to optimize performance

•	 Provides equal supply and exhaust air

•	 Recovers up to 80% of the energy in air

exchanged, significantly reducing energy cost

•	 With installation, may cost between $700 and $2,000

•	 More complicated design considerations

•	 Can overventilate if building is not tight

B.4 May 2012

ENERGY RENOVATIONS INSULATION
B.4 Vapor Retarders

Vapor retarders are often installed to impede the movement of 

water vapor through walls and other building materials. A number 

of materials are used as vapor retarders; they vary in performance. 

Building scientists use a unit of measure called “perms” to denote a 

material’s permeability to vapor. The higher the perm number, the 

more easily vapor can pass through the material.

The recommended placement of vapor retarders depends on climate. 

Moist air generally moves from warmer places to colder ones. Where 

homes are heated much of the year, vapor retarders are typically 

placed on the interior side of insulation to keep out moisture carried 

by warm indoor air. Where homes are air-conditioned much of 

the year, vapor retarders are typically placed on the exterior side 

of insulation to keep out moisture carried by warm outdoor air. A 

vapor retarder should not be placed on both sides of the insulation. 

Any moisture that reaches the insulation must be able to diffuse 

either to the interior or the exterior.

Presently, research into the usefulness of vapor retarders is 

inconclusive. Evidence shows they sometimes trap moisture inside 

walls by hindering evaporation (Lstiburek 2004). The following 

precautions may help:

SHEET POLYETHYLENE. Avoid using sheet polyethylene and other 

Class I vapor retarders, except in the very cold and subarctic climates. 

Class I vapor retarders are materials with extremely low permeability, 

and are commonly called vapor barriers. Building America scientists 

warn that the use of Class I vapor retarders can cause serious moisture 

problems in humid climates. Class I vapor retarders include foil and 

sheet metal as well as plastics such as polyethylene, and have a perm 

rating of less than 0.1. The 2009 IRC does not require a Class 1 vapor 

retarder in any climate zone. In the very cold and subarctic climates, 

however, they can be of value (Lstiburek 2006).

VAPOR RETARDERS IN COLD CLIMATES. Local building 

codes may require a vapor retarder on the interior, warm-in-winter 

side of insulation. You should not consider using a Class I vapor 

retarder unless the house has a vapor-permeable air barrier such as 

housewrap on the exterior of the sheathing. Otherwise, moisture 

in the wall will not be able to evaporate to the outdoors. If a home 

is air-conditioned in summer, Building America scientists do NOT 

recommend installing a Class I vapor retarder on the interior side 

of a wall assembly. Moisture coming from outside can condense on 

the wall’s cool interior surface, leading to mold and wood rot. Where 

a vapor retarder is desired or required in conjunction with cavity 

insulation, a good choice is paper-faced batt insulation or gypsum 

wallboard with latex paint (Lstiburek 2006).

Vapor retarders and mold. Vapor barriers 

like this polyethylene sheet can trap 

moisture in walls. The damp fiber insulation 

in this wall developed mold and odors 

(Source: BSC).

Class I vapor retarders, 

a.k.a. vapor barriers

Frequently a distinction is made between 

vapor barriers and vapor retarders. 

Vapor barriers are formally called Class 

I vapor retarders. They have extremely 

low permeability and include sheet 

polyethylene and other plastics, foil, 

and metal sheathing. 

Building America scientists do NOT 

recommend using polyethylene or other 

Class I vapor retarders in humid climates 

because they can trap moisture inside walls 

and other building assemblies. A Class II or 

III vapor retarder should be used whenever 

possible; they provide protection against 

moisture but still permit wet materials 

to dry. Class II includes kraft facing on 

fiberglass batts, and Class III includes 

latex paints.

May 2012 B.5

B.5

ENERGY RENOVATIONS INSULATION
VAPOR RETARDERS IN HOT CLIMATES. Local building codes 

may require a vapor retarder on the exterior side of insulation. If 

you choose a Class 1 vapor retarder such as foil-faced sheathing, 

your contractor must make sure moisture can evaporate to the 

indoors. When using any kind of vapor retarder on the exterior of 

the insulation, avoid filling the walls with faced insulation batts; 

the facings can trap moisture in the walls. Vinyl wallpaper or other 

“nonbreathable” wall coverings will also trap moisture. Remove them.

VAPOR RETARDERS IN MIXED CLIMATES. The location of a 

vapor barrier or retarder is problematic in mixed climates, which are 

cold in winter and hot in summer. Since moist air generally moves 

from warmer places to colder ones, moisture needs to diffuse to the 

exterior in winter and the interior in summer. A vapor retarder will 

prevent one or the other, depending on where it is located. Building 

America scientists suggest that it may be better to have a vapor-open 

assembly in mixed climates (Lstiburek 2004). Local building codes, 

however, may require a vapor retarder.

Vapor Retarder Definitions

The 2009 IRC R601.3.2 gives the following definitions and examples for vapor 

retarder classes:

Class Definition Examples

I 0.1 perm or less Sheet polyethylene, sheet metal, 

non-perforated aluminum foil

II Greater than 0.1 perm to 

less than 1.0 perm

Kraft-faced fiberglass batts or 

low-perm paint

III Greater than 1.0 perm to 

less than 10 perm

Latex or enamel paint

Perm Ratings of Common Sheathing Materials

Material Permeability

Plywood sheathing More than 1.0 perm

OSB More than 1.0 perm

Exterior gypsum More than 1.0 perm

Fiberboard sheathing More than 1.0 perm

Extruded polystyrene foam sheathing 1 inch 1.0 perm or less

Film-faced extruded polystyrene 0.5 inch thick 

with perforated facing

More than 1.0 perm

Nonperforated foil-faced rigid insulation Less than 0.1 perm

Polypropylene-faced rigid insulation Less than 0.1 perm

Three-coat, hard-coat stucco over 2 layers of Type D 

asphalt-saturated Kraft paper and OSB

Less than 1.0 perm

Source: Lstiburek 2006. 

References

Lstiburek, Joseph. 2004. Insulations, Sheathings 

and Vapor Retarders. RR-0412, Building 

Science Corporation. www.buildingscience.

com/documents/reports/rr-0412-insulationssheathings-and-vapor-retarders

Listiburek, Joseph. 2006. Understanding Vapor 

Barriers, BSD-106, Building Science Corporation. 

www.buildingscience.com/documents/digests/

bsd-106-understanding-vapor-barriers

U.S. Department of Energy. 2008. Insulation 

Fact Sheet. DOE/CE-0180. www.ornl.gov/sci/

roofs+walls/insulation/ins_01.html 

U.S. Department of Energy. 2011. Energy Savers: 

How Moisture Moves through a Home.

www.energysavers.gov/your_home/insulation_

airsealing/index.cfm/mytopic=11760

B.6 May 2012

ENERGY RENOVATIONS INSULATION
The Performance Briefs provide step-by-step instructions that your 

contractor can follow when implementing the following upgrades:

1. Air Sealing a Flue or Chimney Shaft

2. Improving Recessed Lighting 

3. Air Sealing Duct Boots and Duct Chases 

4. Preventing Ice Dams 

5. Insulating Attic Kneewalls 

6. Installing a Radiant Barrier in the Attic

7. Insulating and Air Sealing Cantilevered Floors –

8. Air Sealing a Porch Wall 

9. Insulating and Air Sealing Tubs

10. Air Sealing and Insulating Fireplace Enclosures 

11. Insulating Pipes

12. Insulating Hot Water Heaters

13. Keeping Wind-blown Rain Out of Soffits

14. Installing Sidewall and Kick-out Diverter Flashing 

On Homes with Rigid Foam Insulation Sheathing 

15. Installing Sidewall and Kick-out Diverter Flashing 

On Homes with Housewrap over OSB or Plywood Sheathing

Appendix C

Building America Energy Performance 

Briefs for Improving Existing Homes

May 2012 C.1

ENERGY RENOVATIONS INSULATION

 How to Air Seal a Masonry Chimney Chase

Durability & Health

Use the right air sealing products and 

techniques to keep flammable materials 

from touching hot flues. If combustion 

appliances are present in the home, 

always conduct combustion safety 

testing before and after any air sealing 

measure.

There are often gaps around chimneys and furnace and water heater 

flues that allow conditioned air to flow up into the attic. Insulation 

should not come in contact with a hot chimney or flue. The steps below 

show you how to safely block the air gaps around masonry chimneys 

and flue pipes and then construct an insulation dam to allow insulation 

to be placed around the chimney or flue pipe while maintaining a 3-inch 

clearance for fire safety. With metal chimneys and vent pipes, you can 

use sheet metal to form an insulation dam and air block, installed level 

with the bottom of the framing (see Option 1 next page) or on top of 

the framing (see Option 2).

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Air Sealing a Flue 

or Chimney Shaft

R

BUILDING AMERICA

ENERGy PERFORMANCE BRIEF

When to Do This 

When you want to add insulation 

in the attic. 

You can make a sheet metal or gypsum 

board dam to keep insulation from 

touching hot metal or masonry chimneys 

and flues (Source: EPA 2008a).

Remove any insulation around the chimney. Caulk seams of framing and 

add a wide bead of fire-resistant caulk to the top of the framing around the 

chimney. 

Cut the sheet metal to fit around the chimney. Fasten to the framing with 

nails or screws. Seal to the chimney with fire-resistant caulk. 

Build a gypsum or sheet metal dam to keep insulation at least 3 inches 

from the chimney on all sides. Make dam 4 inches higher than the finished 

insulation level. 

Replace any old insulation and add additional insulation to desired height 

(Source: Lstiburek 2010). 

1

2

3

4

Chimney

Insulation

Insulation

Fireresistant 

caulk Sheet metal

Gypsum 

board dam

 
How to Air Seal a Metal Chimney or Flue Vent Pipe – Option 1 – Air Seal at Bottom of Framing

Option 2 – Air Seal at Top of Framing

Pull insulation away from metal chimney pipe. 

Cut two pieces of sheet metal to cover the chase opening. Allow 1 inch of overlap. Fasten the sheet metal to the framing and 

seal all edges and seams with fire-rated caulk.

Use sheet metal to make a shield that will wrap around the pipe with a 3-inch clearance. Fold tabs at top and every other tab at 

bottom in to maintain a 3-inch clearance. With tabs folded, shield should be 4 inches taller than finished insulation level. 

Replace insulation.

Add more insulation to desired height. Insulation should cover rafters (Source: Lstiburek 2010).

PNNL-SA-82686 September 2011

2009 IECC/2009 IRC

Code Requirement for New 

Construction and Additions

Shafts, penetrations – Duct shafts, utility 

penetrations, knee walls and flue shafts 

opening to exterior or unconditioned space 

are sealed.

References

DOE. 2010. Building America Best Practices 

Series, Volume 10: Retrofit Techniques and 

Technologies: Air Sealing, PNNL-19284, U.S. 

Department of Energy. www1.eere.energy.gov/ 

buildings/building_america/publications.htm.

EPA. 2008a. A Do-It-Yourself Guide to 

Sealing and Insulating with ENERGY STAR. 

U.S. Environmental Protection Agency, www.

energystar. gov/index.cfm?c=diy.diy_index

EPA. 2008b. “Indoor Air Quality and Attics.” U.S. 

Environmental Protection Agency, www.epa.gov/

iaq/homes/hip-attic.html

Lstiburek, Joseph. 2010. Guide to Attic Air 

Sealing. Prepared for U.S. Department of Energy 

by Building Science Corporation. http://www.

buildingscience.com/documents/guides-andmanuals/gm-attic-air-sealing-guide.

Pull insulation away from metal 

chimney pipe. 

Cut two pieces of framing lumber 

equal in height to the ceiling joists. 

Fasten cross pieces to joists keeping at 

least 3 inches of clearance to the pipe. 

Caulk wood blocking to framing. 

Cut two pieces of sheet metal or 

aluminum flashing to fit around the 

chimney pipe with 1 inch of overlap. 

Fasten the sheet metal to the framing 

and seal all edges and seams with 

fire-rated caulk. 

Use sheet metal to make a shield 

that will wrap around the pipe with 

a 3-inch clearance. Fold in tabs at 

top and every other tab at bottom to 

maintain a 3-inch clearance. With tabs 

folded, shield should be 4 inches taller 

than finished insulation level. 

Replace insulation and cover with 

additional insulation to desired height. 

Insulation should cover rafters (Source: 

Lstiburek 2010).

Metal 

chimney pipe

Chimney 

chase 

framing

Sheet 

metal

Metal 

collar

Fireresistant 

caulk

1

1

2

3

3

4

5

4

Insulation

Fireresistant 

caulk

Wood 

blocking

Insulation

2

5

Aluminum 

flashing

Fire-resistant 

caulk

Chimney 

chase 

framing

Metal 

chimney pipe

Old 

insulation

New 

insulation

BUILDING AMERICA ENERGy PERFORMANCE BRIEF

2
 

Durability & Health

Non-airtight recessed can fixtures can 

draw heated air into the attic in winter, 

carrying moisture that can condense in 

a cool attic. They can also allow hot attic 

air into the home in summer, pulling dust 

and insulation particles into the home. 

If combustion appliances are present in 

the home, always conduct combustion 

safety testing before and after any air 

sealing measure.

Do not let insulation come in contact 

with non-IC rated fixtures, due to the 

risk of fire. 

Recessed downlights (also called can lights or high-hats) are the most 

popular lighting fixture installed in U.S. homes today. Unfortunately 

they can be a significant source of energy loss. Older model recessed can 

fixtures are energy intensive in three ways. If they are not approved for 

insulation contact, insulation has to be kept at least 3 inches from the 

fixture, leaving a square foot or more of uninsulated ceiling space. When 

the lights are turned on, the tube-shaped light fixtures heat up, and 

work like a chimney to pull conditioned air out of the living space into 

the attic, which is a waste of energy and can cause moisture problems 

in the attic. Many existing recessed can lights have incandescent bulbs 

that use 3 to 5 times the electricity of fluorescents and add to airconditioning loads. 

The best method for dealing with an old, non-airtight recessed can light 

is to replace the whole fixture with an insulation contact-rated, airtight 

(ICAT) fixture. Caulk around the fixture under the trim ring to ensure 

air tightness and install an ENERGY STAR-rated compact fluorescent 

or LED bulb that is designed for recessed can lights. Insulation can 

safely be laid on top of these ICAT-rated fixtures. Insulation-contact 

rated lights are indicated by an “IC” at the end of the model number. 

Another option might be to remove the can fixture, patch the ceiling, 

and install a surface-mounted fixture.

If the homeowner does not want to replace their non-ICAT rated 

recessed can lights, you can make the lights airtight by covering them 

from the attic side with a box made of rigid foil-faced foam or drywall. 

The box should be large enough to allow 3 inches of clearance on all 

sides of the fixture. It should be sealed in place to the ceiling drywall 

with spray foam, and covered with attic insulation.

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Improving Recessed 

Lighting

R

BUILDING AMERICA

ENERGy PERfORMANCE BRIEf

When to Do This 

When remodeling includes replacing 

ceiling fixtures or painting ceilings, or 

when adding insulation to the attic. 

Recommend that homeowner replace 

incandescent bulbs with compact 

fluorescents any time.
Studies Show Old, recessed can 

lights are like a hole in the ceiling, 

only worse. Leaky recessed cans with 

incandescent bulbs can pull 3 to 5 

times as much air as a hole in the 

ceiling the same size, thanks to the 

“stack effect.” The heat inside the can 

pulls air from the house up through the 

holes in the can into the attic (Source: 

McCullough and Gordon 2002).

Replace old, leaky 

recessed can fixtures 

with insulated, 

airtight recessed 

light fixtures. 

AIR TIGHTNESS 

LABEL

Airtight wire 

connection from 

junction box

Airtight

can

Decorative

cover Caulk

around fixture 

under the trim ring.

PNNL-SA-82688 September 2011

How to Insulate and Air Seal Non-insulation Contactrated, Non-airtight Recessed Can Lights.

References

McCullough, Jeff J. and Kelly L. Gordon 2002. 

“High Hats, Swiss Cheese, and Fluorescent 

Lighting” Proceedings of the 2002 ACEEE 

Summer Study, prepared by Pacific Northwest 

National Laboratory. www.aceee.org/conf/

bldindex.htm 

EPA. 2007. “A Do-it-Yourself Guide to Sealing 

and Insulating with ENERGY STAR ®” U.S. 

Environmental Protection Agency. http://

www.energystar.gov/ia/partners/publications/

pubdocs/DIY_Guide_May_2008.pdf

Lstiburek, Joseph. 2010. Guide to Attic Air 

Sealing. Prepared for U.S. Department of Energy 

by Building Science Corporation. http://www.

buildingscience.com/documents/guides-andmanuals/gm-attic-air-sealing-guide.

2009 IECC/2009 IRC

Code Requirement for New

Construction and Additions

Recessed lighting – Recessed light fixtures 

are airtight, IC rated, and sealed to drywall. 

Exception: fixtures in conditioned space. 

This infrared camera image 

shows summertime attic heat 

leaking into the home around a 

leaky recessed can light. 

Holes in the top of the recessed can 

encourage the stack effect, pulling 

conditioned air up into the attic.

Non-insulation contact-rated cans mean 

no insulation can touch the can, which 

allows heat transfer around the can. Air 

leaks around the rim add to heat loss.

Incandescent lamps use 3 to 5 times 

more energy than a compact fluorescent, 

don’t last as long, and generate heat that 

adds to air-conditioning bills. 

Pull back any insulation around the fixture. 

Caulk where the ceiling gypsum board meets 

the rafter on each side of the fixture.

Cut gypsum board or foil-faced rigid foam 

insulation to form a box. Seal box seams with 

metal tape or mastic. 

Seal the box to the ceiling dry wall and 

rafters with caulk or spray foam.

Replace insulation and add insulation to 

cover the sides of the box (Source: Adapted 

from Lstiburek 2010).

No insulation

Caulk

Seams of gypsum 

board box taped

Caulk

1

2

3

4

5

Existing 

insulation

Figure Source: PNNL

for More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

BUILDING AMERICA ENERGy PERfORMANCE BRIEf
 

Seal with

sheet metal Seal and insulate 

and high-temp dropped sot 

caulk Seal

chases

Caulk

electrical 

fixtures to 

drywall Seal HVAC 

penetrations 

Seal electrical 

penetrations 

Seal

bottom Seal plumbing 

penetrations plate

Any place where holes are made in the ceiling can become a venue for 

heated and cooled air to escape into the attic (as shown in the figure 

below). Air sealing around duct boots, duct chases, and ducts in shafts 

and building cavities is especially important because of the potentially 

large air leaks that can be present. You should inspect these areas and 

close the gaps with caulk, spray foam, and blocking material (pieces of 

rigid foam, plywood, or oriented strand board cut to fit and sealed in 

place with spray foam). Furnace flues may require high-temperaturerated sealing materials. Duct boots are subject to high air flow and the 

joints should be checked for air tightness. They can be sealed with spray 

foam or caulk. All duct joints and seams should be sealed with mastic, 

or approved metal tape, or flex duct fasteners. Studies show cloth-backed 

duct tape fails within months; it should not be used to seal ducts.

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Air Sealing Duct Boots 

and Duct Chases

R

BUILDING AMERICA

ENERGy PERfORMANCE BRIEf

Use caulk and spray foam to stop air leaks around heat registers, 

ducts shafts, pipes, electrical fixtures, and outlets (Source: DOE 2000).

When to Do This 

When adding attic insulation, sealing 

ducts, or replacing HVAC or ducts.

Durability & Health

HVAC, plumbing, and wiring chases 

can bring conditioned air into attics, 

causing energy loss and leading to 

condensation and mold problems. If 

combustion appliances are present in 

the home, always conduct combustion 

safety testing before and after any air 

sealing measure.

2009 IECC/2009 IRC

Code Requirement for New 

Construction and Additions

Shafts, penetrations – Duct shafts, utility 

penetrations, knee walls and flue shafts 

opening to exterior or unconditioned space 

are sealed. 
Pull back insulation to expose the 

chase and framing area. Add wood 

framing cross pieces in attic rafter 

bays if needed. Measure and cut an 

air blocking material like plywood, 

rigid foam, or drywall into strips to 

be fastened to framing in step 3.

Seal all framing joints around the 

chase with sealant. Lay a generous 

continuous bead of sealant along 

the top edge of the chase framing.

Place the blocking material on 

the framing leaving a 1⁄4-inch gap 

between the rigid duct and the 

material. Fasten in place with nails 

or screws. Seal the material to the 

duct with sealant. Also seal any 

joints in the blocking material. 

Replace the original insulation and 

add additional insulation. 

(Source: Adapted from Lstiburek 2010).

Pull back insulation to expose the 

duct boot.

PNNL-SA-82687 August 2011

How to Air Seal a Rigid Duct Chase

References

DOE. 2000. Air Sealing Fact Sheet, Prepared 

for the U.S. Department of Energy by 

Southface Energy Institute and Oak Ridge 

National Laboratory. http://apps1.eere.

energy.gov/buildings/publications/pdfs/

building_america/26446.pdf

EPA. 2008. A Do-It-Yourself Guide to Sealing and 

Insulating with ENERGY STAR. U.S. Environmental 

Protection Agency, www.energystar.gov/index.

cfm?c=diy.diy_index 

EPA. 2008. Indoor Air Quality and Attics. U.S. 

Environmental Protection Agency. www.epa.gov/

iaq/homes/hip-attic.html

Lstiburek, Joseph. 2010. Guide to Attic Air 

Sealing. Prepared for U.S. Department of 

Energy by Building Science Corporation. 

www.buildingscience.com/documents/

primers/guide-to-attic-air-sealing-withdetails/?searchterm=air%20sealing

Pull back 

insulation.

Add wood 

framing if 

needed.

Apply a continuous 

bead of sealant

Fasten plywood, 

OSB, gypsum board, 

or duct board to framing

Replace 

insulation

Pull back insulation to expose the 

chase and the framing area. Add 

wood framing pieces between rafters 

if needed. Measure and cut an air 

blocking material like plywood, rigid 

foam, or drywall to cover the chase 

opening. Cut the material into two 

halves and then cut half circles to 

encompass the flex duct.

Seal all framing joints around the 

chase with sealant. Lay a generous 

continuous bead of sealant along the 

top edge of the chase framing. 

Place the blocking material on the 

framing and in contact with the duct. 

Fasten with nails or screws. Seal the 

material to the duct with sealant. 

Also seal the joints in the material. 

Replace the original insulation and 

add more insulation if needed. 

(Source: Adapted from Lstiburek 2010).

1

2

3

1

2

3

Apply a 

continuous 

bead of 

sealant

Duct

Pull back insulation. Add 

wood framing if needed. 

Apply a 

continuous 

bead of sealant

Fasten 

plywood, 

OSB, 

gypsum 

board or 

duct board 

to framing Replace insulation

Continuous 

bead of 

sealant

How to Seal a Duct Boot 

to the Ceiling

Add wood blocking

Chase framing; 

open to below

Chase 

opening; 

open to 

below

1

2

Replace insulation. 

(Source: Adapted from Lstiburek 2010).

3

Spray foam to 

cover ceiling 

boot penetration

Caulk with a 

continuous bead 

of sealant

How to Air Seal a Flex Duct Chase

Seal all sides of the duct boot 

to the gypsum board with spray 

foam or caulk. Apply mastic to 

all duct seams and joints.

-ORDuct

for More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

BUILDING AMERICA ENERGy PERfORMANCE BRIEf

2
 

Durability & Health

Icicles can fall on people causing 

injuries. Ice dams can allow water to 

back up and enter the attic under roof 

shingles, causing structural damage 

and mold. Excessive water and ice 

accumulation can cause roofs to 

collapse.

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Preventing Ice Dams

R

BUILDING AMERICA

ENERGy PERfORMANCE BRIEf

When to Do This 

Whenever ice dams are occurring. 

1

2

3

How to Prevent Ice Dams in Vented Attics 

Construct an airtight 

ceiling plane. Limit 

the number of holes 

through the ceiling and 

air seal every one. 

Insulate well, especially 

over the top plates, use 

raised heel trusses or 

spray foam from under 

baffle to ceiling deck 

to get full insulation 

coverage. 

Vent the underside of the roof deck, with vent screens at every rafter bay and 

a 2-inch airspace under the sheathing where ground snow loads are greater 

than 30 lb/ft2 (Source: Lstiburek 2011).

Icicles indicate ice dams are forming 

(Photo Source: PNNL).

Ice dams can form when the roof deck temperature is above freezing and 

the air is below freezing. Melted snow eventually reaches the colder edge 

of the roof where it refreezes, creating an ice dam that collects more water 

and ice. The ice dam 

is often not visible 

under the snow except 

for the telltale icicles, 

which indicate melting 

is occurring somewhere 

on the roof (Source: 

Lstiburek 2011).

Continuous ridge 

ventilation

Attic Ventilation

Roof insulation

Insulation wind baffle

2" minimum spacing

Water 

protection 

membrane

Continuous 

soffit vent

Caulking or sealant

Consider increasing depth 

of insulation by using 

deeper trusses or oversized 

(longer) trusses

Thin ice slab under snow

Snow

Melt water running 

under thin ice slab

Melt water 

running down 

underside of 

Ice dam sheathing

Ice

Icicles
How to Prevent Ice Dams in Unvented Attics

How to Prevent Ice Dams in Unvented Attics in HighSnow-Load Areas

PNNL-SA-83160 September 2011

2009 and 2012 IRC 

R905.2.7.1

Code Requirement for New 

Construction and Additions

Ice Barrier – In areas where there has 

been a history of ice forming along the 

eaves causing a backup of water ... an ice 

barrier that consists of at least two layers 

of underlayment cemented together or a 

self-adhering polymer modified bitumen 

sheet shall be used in place of normal 

underlayment and extend from the lowest 

edges of all roof surfaces to a point at least 

24 inches inside the exterior wall line of 

the building.

References

DOE. 2010. Building America Best Practices 

Series, Volume 12. 40% Whole-House Energy 

Savings in the Cold and Very Cold Climates, 

PNNL-20139, U.S. Department of Energy. www1.

eere.energy.gov/buildings/building_america/

publications.htm.

Lstiburek, Joseph. 2011. Dam Ice Dam, Insight 

046, Feb. 2011, Building Science Corporation, 

www.buildingscience.com/documents/insights/

bsi-046-dam-ice-dam/

Roof sheathing

Roof sheathing

Vented space

Vented 

fascia Timber rafter or 

exposed joist

Wood decking

Air barrier membrane

Spray foam 

air seal

Roofing membrane

Shingles

Roofing paper

Cover roof sheathing with a fully adhered air barrier membrane. 

Install two layers (to R-50 or greater) of rigid insulation over air barrier; stagger the seams. 

Note, there is no vented space under the roof cladding to compensate for the insulation 

value of the snow layer. This roof should be used where the ground snow load is less 

than 50 lb/ft2

. With ground snow loads greater than 50 lb/ft2, provide a ventilation 

space under the roof cladding as shown below (Source: Lstiburek 2011).

1

2

for More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

Shingles Roofing paper

Wood decking

Timber rafter or exposed joist

Minimum, R-50 rigid insulation in two 

or more layers with horizontal and 

vertical joints staggered

Nail base for shingles (plywood or OSB)

screwed through rigid insulation to wood 

decking or timber rafters

Air barrier membrane

R-60 rigid insulation

 (horizontal and vertical 

joints staggered)

In regions with snow loads greater than 50 lb/ft2

, the snow can provide enough 

thermal resistance to allow the roof cladding to be above freezing even when the 

air temperature is below freezing (one foot of snow = R-10 to R-15). To prevent ice 

damming with an unvented attic in these conditions, construct a “vented over-roof” 

over the top of the “unvented compact roof” (Source: Lstiburek 2011).

BUILDING AMERICA ENERGy PERfORMANCE BRIEf

2
 

Kneewalls, the sidewalls of finished rooms in attics, are often left 

uninsulated, and open cavities between the floor joists beneath the kneewall 

are often a big source of air leakage. Kneewalls can also occur where a 

room with a cathedral ceiling is adjacent to a room with a standard height 

ceiling; the wall separating the two spaces is often uninsulated on the attic 

side. Your contractor can insulate these walls by filling the wall stud cavity 

with fiberglass batt insulation, blown fiberglass or cellulose, or spray foam 

(see Figure 1). The R-value of kneewall insulation should equal or exceed 

the code requirement for exterior walls for your climate zone.

Another option is to continue the insulation along the roof line to the 

attic floor with either rigid foam or cavity insulation covered with rigid 

foam or sheet goods (see Figure 2). This ceiling covering is air sealed to 

attic flooring to form an air-sealed enclosed space, which insulates the 

kneewall and provides insulated attic storage space.

Doors cut into kneewalls should also be insulated and airsealed by 

attaching rigid foam to the attic side of the door, and using a latch that 

pulls the door tightly to a weather-stripped frame. Closets or drawers cut 

into the kneewalls should also be insulated (see Figure 3).

Seal

Attic living

space Hardboard

Desired

ventilation

Option 1

Seal air barrier at edges

Seal

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Insulating Attic Kneewalls

R

When to Do This 

•	 Any time you have access to existing

attic kneewalls. 2			

•	 When you are adding insulation to

the attic. 3				

•	 When you are adding an addition to

your attic.

BUILDING AMERICA

ENERGy PERfORMANCE BRIEf

Durability & Health

Uninsulated walls provide cold surfaces 

for warm, humid indoor air to condense, 

encouraging mold growth. When warm 

indoor air gets into a cold attic through 

leaks in the home’s thermal envelope, it 

can condense on rafters and other solid 

surfaces, encouraging mold growth. In 

a cold climate in winter conditions, heat 

escaping into the attic can warm the roof 

deck encouraging ice dam formation.

3. Attic Kneewalls

Air barrier is installed at the insulated boundary 

(kneewall transition or roof, as appropriate).

Kneewalls, the sidewalls of finished rooms in attics, are often leaky 

and uninsulated. Your contractor can insulate and air seal these 

walls in one step by covering them from the attic side with sealed 

rigid foam insulation. Your contractor can plug the open cavities 

between joists beneath the kneewall with plastic bags filled with 

insulation or with pieces of rigid foam. Another option is to apply 

rigid foam to the underside of the rafters along the sloped roof line 

and air seal at the top of the kneewall and the top of the sidewall, 

which provides the benefit of both insulating the kneewall and 

providing insulated attic storage space. 

Doors cut into kneewalls should also be insulated and airsealed by 

attaching rigid foam to the attic side of the door, and using a latch 

that pulls the door tightly to a weather-stripped frame. 

When To Do This

Any time you have access to kneewalls.

Durability & Health

If warm moist air gets into a cold attic 

through leaks in the home’s thermal

envelope, it can condense on rafters and

other solid surfaces, which may lead to 

water damage and mold growth.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Ceiling/attic

Attic access (except unvented attic),

kneewall door, or drop down stair 

is sealed.

More Information 

•	 Building America Best Practices

•	 Iowa Energy Center 2008

•	 Lstiburek 2010

•	 U.S. Department of Energy 2000a

•	 U.S. Environmental Protection

Agency		2008a

•	 U.S. Environmental Protection

Agency		2008b

•	 U.S. Environmental Protection

Agency		2008c

Seal

Attic living

space Hardboard

Desired

ventilation

Option 1 Option 2

Seal air barrier at edges

Seal

Drawers

Drawers

Figure 3.1. Insulate and air

seal the kneewall itself, as 

shown, or along the roof line 

(Source: DOE 2000a).

Figure 3.2.		Air seal floor joist

cavities under kneewalls by

filling cavities with fiberglass

batts that are rolled and stuffed 

in plastic bags (as shown here)

or use rigid foam, OSB, or other

air barrier board cut to fit and 

sealed at edges with caulk.

Figure 3.3.		Build an airtight,

insulated box around any

drawers or closets built into 

attic knee walls that extend into

RETROFiT TECHNiQuES AND TECHNOLOGiES AIR SEALING

Figure 1. Insulate and air seal the kneewall (Source: DOE 2000).

Figure 2. Continue the insulation along the roof line to the roof edge. Cover with a

sheet good that is caulked where it meets the wood floor sheathing, which is extended

to the outside wall.

Figure 3. Build an airtight, insulated box around any drawers or closets built into attic

kneewalls that extend into uninsulated attic space. Insulate along the air barrier (shown

in yellow on drawing) or along the roof line with rigid foam.

3. Attic Kneewalls

Air barrier is installed at the insulated bou

(kneewall transition or roof, as appropriate

Kneewalls, the sidewalls of finished rooms in atti

and uninsulated. Your contractor can insulate an

walls in one step by covering them from the attic 

rigid foam insulation. Your contractor can plug t

between joists beneath the kneewall with plastic 

insulation or with pieces of rigid foam. Another 

rigid foam to the underside of the rafters along t

and air seal at the top of the kneewall and the to

which provides the benefit of both insulating the 

providing insulated attic storage space. 

Doors cut into kneewalls should also be insulate

attaching rigid foam to the attic side of the door, 

that pulls the door tightly to a weather-stripped f

Attic living

space 

Desired

ventilation

Option 1 

Seal air barrier at edges

Seal

Insulated Box

Drawers

Drawers

Figure 3

seal the 

shown, o

(Source: 

Figure 3

cavities 

filling ca

batts tha

in plastic 

or use ri

air barrie

sealed a

Figure 3

insulated 

drawers 

attic kne

uninsula

along air 

yellow o

line with 

Iowa Ene

RE

Figure 1 Figure 2 Figure 3

This attic

kneewall has

been thoroughly

insulated.
for More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

PNNL-SA-78652 March 2011

Stuff cavities with roll of fiberglass batt 

and cover with spray foam to edges

Add insulating sheathing to kneewall framing

Add additional insulation

Replace insulation in cavity

Kneewall framing

Insulation pulled back to expose cavity

If any subfloor, cut back to expose open cavity

Open cavity

Seal edges with a continuous bead of caulk 

or foam sealant

Insert solid wood blocking or rigid foam board in 

floor cavity openings

—OR—

Replace insulation in wall cavity

2009 IECC 

Code Requirements for New 

Construction and Additions

2009 IECC 402.2.3: Access doors from 

conditioned spaces to unconditioned 

spaces (e.g., attics and crawl spaces) shall 

be weather stripped and insulated to a 

level equivalent to the insulation on the 

surrounding surfaces.

2009 IECC 402.4.1: The building thermal 

envelope shall be durably sealed to limit 

infiltration.... The following shall be caulked, 

gasketed, weather stripped, or otherwise 

sealed with an air barrier material, suitable 

film, or solid material: 1. All joints, seams, and 

penetrations... 6. Knee walls... 10. Attic access 

openings... 12. Other sources of infiltration.

References

U.S. Department of Energy. 2010. Building 

America Best Practices Series, Volume 10: 

Retrofit Techniques and Technologies: Air 

Sealing, PNNL-19284, www1.eere.energy.gov/

buildings/building_america/publications.htm

Lstiburek, Joseph. 2010. Guide to Attic Air 

Sealing. Prepared for U.S. Department of

Energy by Building Science Corporation.

www.buildingscience.com/documents/

primers/guide-to-attic-air-sealing-withdetails/?searchterm=air%20sealing

U.S. Department of Energy. 2000. Air Sealing 

Fact Sheet, Prepared by Southface Energy

Institute and Oak Ridge National Laboratory.

http://www.toolbase.org/Home-Building-Topics/

Remodeling/air-sealing

U.S. Environmental Protection Agency. 2008.

ENERGY STAR Qualified Homes Thermal 

Bypass Checklist Guide. www.energystar.gov/

ia/partners/bldrs_lenders_raters/downloads/

TBC_Guide_062507.pdf

U.S. Environmental Protection Agency. 2008.

“Indoor Air Quality and Attics.”

www.epa.gov/iaq/homes/hip-attic.html

Figure 4. Air seal floor joist cavities under

kneewalls by filling the cavities with rigid foam

insulation, OSB, or another rigid material that is

cut to fit and sealed at the edges with caulk (as

shown here and below). Another option is to

block the joist cavity with fiberglass batts that

are rolled and stuffed in plastic bags or covered

with spray foam.

(Source: Lstiburek 2010)

To stop air leakage from the open cavities between the floor joists under 

the kneewall, these cavities are stuffed with unfaced batt insulation that 

is rolled and covered with spray foam (see Figure 4). Or rigid foam (or 

another air barrier material like gypsum board or OSB) can be cut to fit 

each joist space and sealed in place with caulk or spray foam (see “How 

to” below).

How to Insulate and Air Seal floor Joist Cavities 

Under Kneewalls

BUILDING AMERICA ENERGy PERfORMANCE BRIEf
 

In hot climates, the sun’s heat can push roof surface temperatures over 

160°F. The roof’s heat can radiate to the attic insulation and heat up 

the ceiling and living space below. This heat transfer can be reduced 

significantly by a radiant barrier, a foil-faced material installed under the 

roof that stops the transfer of heat. 

If your home is in a hot-dry or hot-humid climate and has a roof that 

receives direct sunlight in summer, adding a radiant barrier can be 

cost-effective. Studies show that radiant barriers can cut cooling costs 

between 8% and 12% in hot climates (Melody 2005). However, radiant 

barriers are seldom cost-effective in marine climates, which have moderate 

temperatures, or in cold climates, where thick attic insulation already 

minimizes heat transfer. To estimate the benefit for your attic, see the U.S. 

Department of Energy’s savings calculator at http://www.ornl.gov/sci/ees/

etsd/btric/RadiantBarrier/rb_calc.shtml 

Building America scientists recommend two types of radiant barriers for 

existing homes. If a re-roofing project includes replacement of the roof 

deck, you can choose OSB sheathing with a foil underside. Your roofer 

should install it with the foil side facing down. If you are not replacing 

your roof deck, perforated radiant barrier sheeting can be attached to the 

truss chords or rafters in one of the two ways described below. 

The radiant barrier material comes in rolls with a variety of tear-resistant 

backings. Products have foil on one or both sides; double-sided foil may 

offer little advantage over single-sided products. Be sure to buy a perforated 

product; it is less likely to trap vapor and cause moisture problems.

The effectiveness of a radiant barrier depends on proper installation, so 

it's best to use a certified installer. Your contractor should NOT install 

a radiant barrier in contact with attic floor insulation. Moisture will be 

trapped under the barrier, creating a risk of mold and wood rot. 

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Installing a Radiant 

Barrier in the Attic

R

BUILDING AMERICA

ENERGy PERfORMANCE BRIEf

In hot climates, radiant barriers can cut 

cooling costs 8% to 12%. In this house, a 

flexible radiant barrier material was draped 

over the rafters before installation of the 

roof deck. The material also can be stapled 

to rafters from the underside (Photo 

Source: Universal Forest Products).

When to Do This

When replacing the roof; any time you 

want to reduce energy bills and heat 

gain from the attic.

Climate Essentials

Hot-dry and Hot-humid climates: 

 reduces air conditioning costs.

Cold and Marine climates: 

 seldom cost-effective. 
This approach can be used only when the roof deck is being replaced.

Drape the material over the rafters, shiny side down.

Let the material droop 

between rafters to create a 

3-inch space between the 

material and the roof deck. 

Staple the material to the 

top of the rafters to keep it in 

place. 

Follow the installation 

guidelines below. 

PNNL-SA-83945 October 2011

References

Melody, Ingrid. 2005. (FSEC) Radiant Barriers: A 

Question and Answer Primer. http://www.fsec.ucf.

edu/en/publications/html/FSEC-EN-15/

Southface Energy Institute. 2004. Home Energy 

Projects. http://www.southface.org/ez/media/

homeenergyprojects.pdf

U.S. Department of Energy. 2011. Energy Savers: 

Radiant Barriers. http://www.energysavers.gov/

your_home/insulation_airsealing/index.cfm/

mytopic=11680

U.S. Department of Energy. Accessed 9-8-11. 

Radiant Barrier Fact Sheet: Installation Options. 

Prepared by Oak Ridge National Laboratory. 

http://www.ornl.gov/sci/ees/etsd/btric 

RadiantBarrier/rb4a.shtml

for More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

Staple the radiant barrier 

material, shiny side down, to 

the bottom of the rafters.

Follow the installation 

guidelines below.

How to install a radiant barrier: option a

How to install a radiant barrier: option b

2009 IECC

Code Requirement for New 

Construction and Additions

The IECC has no code requirements for 

radiant barriers, but products should meet 

ASTM Standard C1313. Installing a radiant 

barrier does not change the amount of attic 

insulation required to meet codes. 

In California, a radiant barrier can be one 

component of meeting the prescriptive 

requirements for cool roofs under Title 24, 

Section 152(f).

• Leave a 11⁄2-inch airspace between the radiant barrier material and the roof 

deck. 

• Leave a minimum gap of 6 inches (measured horizontally) between 

sections of material at the roof peak. 

• Keep the material at least 3 inches above the insulation on the attic floor.

• Do not cover any vents.

• Cut and patch around obstructions, maintaining a 3-inch distance from any 

hot surface, such as a chimney, furnace, or flue pipe. 

• Overlap the seams by 2 inches. The seams do not need to be sealed.

• Cover the gable ends of the attic as well as the roof deck. 

installation GUidelines

Durability & Health

A radiant barrier increases occupant 

comfort by cutting the amount of 

heat entering a home through the 

attic. It increases the durability of 

the air conditioner by reducing the 

cooling load.

1

2

1

2

3

4

To prevent moisture 

problems when 

installing a radiant 

barrier, leave 

adequate gaps 

for air flow above, 

below, and behind 

the barrier material.

BUILDING AMERICA ENERGy PERfORMANCE BRIEf
 

A cantilevered floor is a floor that sticks out past the foundation or 

supporting wall below. It may be a first- or second-story bump-out, a 

bay window, or a room over an open porch. 

In older homes, cantilevered floors often lack proper air sealing and 

insulation. Floor joist bays that extend from the house out under the 

cantilevered floor are often left open by the builder, allowing outside air 

to flow through the home and conditioned air to escape.

If you have cantilevered floors in your home, you should make sure they 

have been properly air sealed and insulated. If you have a basement, you 

may be able to check a first-floor cantilever by peering into joist bays, if 

they are accessible. Otherwise, you will need to remove the exterior soffit 

covering under the cantilevered floor to view the area between the floor 

joists. Sometimes cantilevered floors are insulated but not air sealed. 

Air barriers must be in place to stop air from blowing through the 

insulation, which renders the insulation ineffective.

Blocking material (rigid foam, OSB, plywood, or drywall) should be 

installed across any open floor joist bays to form an air barrier between 

the cantilever and the rest of the house. Plywood subflooring above 

the cantilever should be caulked at the edges and seams. The cantilever 

floor cavity must be filled with insulation that completely touches the 

underside of the floor. Insulating foam sheathing can be installed on the 

underside of the cantilever.

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Insulating and Air Sealing 

Cantilevered Floors

R

BUILDING AMERICA

ENERGy PERFORMANCE BRIEF

If the cantilevered floor over this porch 

isn’t properly air sealed and insulated, the 

room above will feel cold and drafty in the 

wintertime (Photo Source: Pine Mountain 

Builders).

When to Do This 

When heat loss at cantilevered floors is 

causing comfort or moisture problems. 

When re-siding the home.

Durability & Health

When cantilevered floors are not 

properly air sealed and insulated, floor 

and exterior wall surfaces can be cold. 

Warm indoor air can condense on 

these cold surfaces causing moisture 

problems.

Some contractors use the “drill and fill” method to insulate a 

cantilevered floor, by drilling through the bottom covering and 

blowing in cellulose or fiberglass insulation, then patching the 

holes as shown in this photo. This method does not address 

air flow, because the contractor doesn't open up the cantilever 

flooring to see if joist cavities have been blocked off between 

the house and the cantilever. Insulation works by trapping dead 

air. If the air is moving, the insulation doesn’t insulate, it just 

filters the flowing air (Photo Source: PNNL).
PNNL-SA-83947 October 2011

2009 IECC

Table 402.4.2 and 2012 IECC 

Table R402.4.1.1

Floors (including above-garage and 

cantilevered floors): Insulation is installed to 

maintain permanent contact with underside 

of subfloor decking. Air barrier is installed at 

any exposed edge of insulation. 

References

Natural Resources Canada. 2009. How to Insulate 

Inside the Basement, http://oee.nrcan.gc.ca/

residential/personal/new-home-improvement/

choosing/insulation-sealing/basement/khiinbasement.cfm?attr=4#top

Advanced Energy. 2002. Cantilevers, Technical 

Bulletin F2, http://www.advancedenergy.org/

buildings/knowledge_library/framing/cantilevers.

pdf

ENERGY STAR. 2008. Thermal Bypass 

Checklist Guide. http://www.energystar.gov/

ia/partners/bldrs_lenders_raters/downloads/

TBC_Guide_062507.pdf

How to Air Seal and Insulate a Cantilevered Floor

For More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

Remove the exterior sheathing and any existing 

insulation. 

Create an air barrier between the house and 

the cantilever by cutting a rectangle of rigid 

foam to fit into each floor joist bay cavity. Make 

a backstop for the foam by tacking furring 

strips to the joists at plane with the foundation 

or house wall.

Insert rigid foam pieces into each joist bay, nail 

in place and caulk to air seal all four edges.

Caulk the subfloor to the floor joists at the 

perimeter of the cantilevered floor and at any 

seams in the subfloor. Seal any wiring or piping 

holes through perimeter joists or subfloor with 

caulk or spray foam. 

Install unfaced batt insulation in each floor joist 

bay. Use a thickness that will completely fill the 

cavity; it must be in contact with the top and 

bottom air barrier (i.e., the subfloor and rigid 

sheathing below) with no compressions or 

voids. Alternatively, spray foam each cavity with 

open- or closed-cell spray foam to the desired 

R-value. 

Cover bottom of cantilever area with rigid foam 

insulation. Caulk the rigid foam to the joists at 

the edges. Tape foam at seams. 

Cover rigid foam with siding or with 3/8-inch 

exterior plywood that is pressure-treated, 

painted, or primed on all exposed sides. 

If you have plumbing pipes in the cantilevered 

floor (not recommended) and live in a cold or 

very cold climate, ensure adequate insulation 

on the exterior side of pipes to prevent freezing 

pipes. One option is to box in the pipes with a 

rigid foam box that is caulked to the subfloor to 

allow warmth from the house to reach the pipes. 

1

2

3

4

5

6

7

8

These floor joist bays have 

been properly air sealed with 

caulked rigid foam insulation. 

Left: This cantilevered floor (viewed from 

the inside) does not yet have air sealing or 

insulation installed (Photo source: Energy 

Services Group).

Right: Blocking material has been installed 

in the cantilever on this home and 

insulation is now being installed (Photo 

Source: MaGrann Associates).

Plywood

Rigid foam

BUILDING AMERICA ENERGy PERFORMANCE BRIEF
 

In homes with a covered porch, the wall area hidden behind the porch 

ceiling may have been left open, with no air barrier and sometimes no 

insulation. These open areas can allow air to flow through cracks in 

the porch ceiling and into the home. This is especially problematic if 

you have a two-story house with balloon-framed walls because the joist 

cavity between the floors will be connected to this porch attic. This can 

occur even if batt insulation has been installed. If the wall sheathing is 

missing, air can flow through the insulation, robbing it of its thermal 

insulating properties.

One Building America research team led by Steven Winter Associates, 

investigated high-energy bill complaints at a 360-unit affordable housing 

development and found nearly twice the expected air leakage. Infrared 

scanning revealed an air leakage path on an exterior second-story wall 

above a front porch. They discovered that the wall between the porch 

and the attic had been insulated with unfaced fiberglass batts, but wall 

board had never been installed. The insulation was dirty from years 

of windwashing as wind carried dust up through the perforated porch 

ceiling, through the insulation, and into the wall above. Crews used rigid 

foam to cover and air seal the open wall area. Blower door tests showed 

the change reduced overall envelope leakage by 200 CFM50. The fix cost 

only $267 per unit and resulted in savings of $200 per year per unit, for a 

payback of less than two years.

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Air Sealing a Porch Wall

R

BUILDING AMERICA

ENERGy PERfORMANCE BRIEf

The house wall separating the porch attic 

from the rest of the house was correctly air 

sealed in this new home to prevent air from 

flowing into the home and causing heat loss.

When to Do This 

Any time, if porch wall is accessible, 

either from the attic or from the porch.

Durability & Health

If the air barrier is missing, flowing 

air can carry cold air in; moisture can 

condense on cold surfaces causing 

mold. When the wall 

connecting the 

porch to the 

house is properly 

blocked and 

air sealed with 

OSB, dry wall, 

or rigid foam, a 

significant source 

of air and heat 

loss is removed.
PNNL-SA-83944 October 2011

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Air barrier and thermal barrier

• Exterior thermal envelope insulation for 

framed walls is installed in substantial 

contact and continuous alignment with 

building envelope air barrier.

• Breaks or joints in the air barrier are filled 

or repaired.

• Air-permeable insulation is inside of 

an air barrier.

References

DOE. 2010. Air Sealing. Prepared by Pacific 

Northwest National Laboratory for the U.S. 

Department of Energy, www.buildingamerica.gov.

Moriarta, Courtney. 2008. “Fixing Air Leakage in 

Connecticut Town Houses,” Home Energy Magazine 

July/Aug 2008, p 28-30, www.swinter.com/news/

documents/FixingAirLeakage.pdf& 

EPA. 2008. ENERGY STAR Qualified Homes Thermal 

Bypass Checklist Guide. U.S. Environmental 

Protection Agency, www.energystar.gov/ia/

partners/bldrs_lenders_raters/downloads/

TBC_Guide_062507.pdf 

How to Air Seal a Porch Wall

for More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

Access the wall area through the porch 

roof or house attic.

Install insulation in the wall cavity, if none 

is present. If the porch wall adjoins living 

space, the batt insulation can be aligned 

with the existing drywall on the house 

side, before installing the air barrier on the 

porch side as described below. If the porch 

wall adjoins attic space and no air barrier 

is present, install an air barrier on the attic 

side, then install the insulation. Alternately, 

the air barrier can be installed on the 

porch side as described below and spray 

foam can be applied from the attic side. 

Apply a thick bead of caulk to framing 

that will be covered. 

Cut wall sheathing to fit the open space 

(wall sheathing rigid foam insulation, 

oriented strand board, or plywood). Nail or 

screw sheathing in place.

Caulk or spray foam around edges. If there 

are seams in the sheathing, seal them with 

caulk or tape.

Replace the porch ceiling covering.

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Building America researchers were called to investigate high heating bills at an 

affordable housing project in Connecticut. Infrared camera imagery revealed high 

heat loss on a second-story wall above a location where a porch extended from 

the first-story exterior wall. Researchers opened up the perforated vinyl porch 

ceiling to find that there was no air barrier covering the batt insulation. Air could 

flow through the insulation robbing it of its heating value. An air barrier of rigid 

foam board was put in place with spray foam (Source: Moriarta 2008).

2

BUILDING AMERICA ENERGy PERfORMANCE BRIEf

3

Unfaced 

batt 

Caulk insulaton

5

Rigid foam
 

When removing your old tub or shower during a bathroom remodel, 

you may discover that your tub was inserted directly into an open 

building cavity with no drywall behind it to block air movement and 

no insulation to prevent heat loss. This causes drafts and cold tubs, and 

allows moisture from the bathroom to escape into the walls and attic, 

inviting mold growth. 

Prior to installing your new tub or shower, have your building 

contractor fill the exterior wall with insulation and install an air 

barrier of cement backer board, rigid foam insulation, or non-paperfaced drywall. Any type of insulation may be installed as long as it 

completely fills the void and will be in full contact with the air barrier. 

While the old tub or shower is removed, inspect the building cavity for 

water damage or mold. If you find moldy wood or drywall, call a mold 

remediation specialist. Be sure to locate the cause of the problem and 

repair it before installing insulation. 

To guard against future moisture issues, the exterior wall behind a tub 

or shower should be designed to dry. Except in severely cold climates, 

(IECC Climate Zones 6 or higher), Building America scientists do not 

recommend the installation of vapor retarders in the exterior bathroom 

wall, nor should moisture-resistant gypsum board (green board) be used 

in any climate as backing for tile. Use cement backer-board instead.

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Insulating & 

Air Sealing Tubs

R

BUILDING AMERICA

ENERGy PERfORMANCE BRIEf

When to Do This 

When removing your tub or shower 

during a bathroom remodel.

Durability & Health

Air sealing and insulating the exterior 

wall behind a bathroom tub will 

minimize cold drafts. It will also prevent 

warm, moist bathroom air from 

escaping into the walls and attic, where 

it can lead to mold. 

This tub was installed 

without a proper air 

barrier, such as cement 

backer board or rigid 

foam, to cover the batt 

insulation. The batt’s 

paper facing doesn’t 

form a continuous air 

barrier so air can flow 

through the wall cavity. 

This robs the insulation of 

its heat-retaining properties and makes the 

tub feel cold.
Fill the entire wall 

cavity with insulation 

to the R-value 

required by local code 

or higher. 

Install 2x4 blocking 

between the wall 

studs if needed to 

support the air barrier. 

To form an air barrier: 

Apply a thick bead of 

caulk to the surface 

of exposed studs and 

wood blocking and 

caulk bottom plate 

to subfloor. Nail or 

screw cement board, paperless gypsum board, Thermo-Ply, or other thin 

barrier material to the studs. 

Seal seams and any holes made through the air barrier material with 

caulk or foam.

Install the new tub.

Block holes around the tub drain with sheet goods 

and spray foam. 

Finish the walls by installing fiberglass wall panels or tiling the surface. 

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PNNL-SA-83946 October 2011

References

Building Science Corporation. 2009. Info-407: Air 

Barriers—Tub, Shower and Fireplace Enclosures. 

http://www.buildingscience.com/documents/

information-sheets/air-barriers-tub-shower-andfireplace-enclosures

Consortium for Advanced Residential Buildings 

(CARB). 2010. High Performance Building Details: 

Insulation and Air Sealing II. Prepared by Steven 

Winter Associates. http://carb-swa.com/articles/

homepage/Air_Sealing2.pdf

Southface Energy Institute. 2009. Residential 

Energy Code Field Guide. http://www.southface.

org/default-interior/Documents/ms-field-guideres.pdf

U.S. Department of Energy. Accessed 9/20/11. 

Bathroom Remodeling: Strategies for Energy 

Efficiency. http://www.toolbase.org/PDF/

DesignGuides/MDL_%205_%20Bathroom.pdf

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How to Insulate and Air Seal Behind a Tub or Shower:

for More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

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2009 IECC/2009 IRC

Code Requirement for New 

Construction and Additions

2009 IECC 402.4.2: Shower/Tub on exterior 

wall: Showers and tubs on exterior walls 

have insulation and an air barrier separating 

them from the exterior wall.

2009 IECC 402.4.1: The building thermal 

envelope shall be durably sealed to limit 

infiltration... The following shall be caulked, 

gasketed, weatherstripped, or otherwise 

sealed with an air barrier material, suitable 

film or solid material: 1. All joints, seams and 

penetrations...8. Behind tubs and showers 

on exterior walls...12. Other sources of 

infiltration.

BUILDING AMERICA ENERGy PERfORMANCE BRIEf
 

Air that you’ve paid to heat or cool escapes from your home through gaps 

and holes, increasing your energy bills. Fireplace enclosures are common 

sources of air leakage that, unfortunately, are hidden from view and 

difficult to access for air sealing. The logical time to access and seal this 

area is when you remove the fireplace and replace it with a more efficient 

heating system. 

When your fireplace is removed, you may see an open building cavity 

with no insulation, sheathing, or evidence of air sealing. The following 

instructions provide simple guidance for correcting this problem. Doing 

it properly will save energy, increase your comfort, and reduce the load on 

your heating and air conditioning systems.

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Air Sealing and Insulating 

Fireplace Enclosures

R

BUILDING AMERICA

ENERGy PERFORMANCE BRIEF

Fireplaces are often installed against open framing without a proper 

air barrier or insulation. The arrow points to the framed exterior 

wall where insulation and an air barrier should be installed (Source: 

EnergyLogic).

When to Do This 

When replacing or adding a fireplace.

Durability & Health

An open wall behind an unsealed 

fireplace encourages drafts and 

pressure imbalances and could provide 

access for pests. If you are installing a 

new fireplace insert, Building America 

recommends a sealed insert with its 

own combustion air intake. Install 

carbon monoxide detectors in all 

homes that use gas or wood fireplaces.

2009 IECC/2009 IRC

Code Requirement for New 

Construction and Additions

Insulate walls in accordance with 

the requirements of the 2009 IECC Table 

402.1.1. Air seal in accordance 

with the requirements of the 2009 

IECC Section 402.4.
PNNL-SA-83153 September 2011

References

BSC. 2009. Air Barriers–Tub, Shower, and Fireplace 

Enclosures for All Climates. Information Sheet 

407. Prepared by Building Science Corporation 

for the U.S. Department of Energy’s Building 

America Program. Accessed 9/28/11. http://apps1.

eere.energy.gov/buildings/publications/pdfs/

building_america/tub_fireplace_enclosure.pdf

Steven Winter Associates. 2010. High Performance 

Building Details: Insulation and Air Sealing II. 

Prepared for U.S. Department of Energy’s Building 

America Program. http://apps1.eere.energy.gov/

buildings/publications/pdfs/building_america/

air_sealing2.pdf%20

DOE. 2010. Building America Best Practices 

Series, Volume 10, Retrofit Techniques and 

Technologies—Air Sealing: A Guide for Contractors 

to Share with Homeowners, p. 26. Prepared by the 

Pacific Northwest National Laboratory and Oak 

Ridge National Laboratory for the U.S. Department 

of Energy's Building America Program. http://

apps1.eere.energy.gov/buildings/publications/pdfs/

building_america/ba_airsealing_report.pdf

ENERGY STAR. 2008. Energy Star Qualified Homes: 

Thermal Bypass Checklist, Version 2.1. http://www.

energystar.gov/ia/partners/bldrs_lenders_raters/

downloads/TBC_Guide_062507.pdf

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How to Insulate and Air Seal the Wall Behind 

your Fireplace

For More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

The diagrams shown here represent a common design for fireplace 

enclosures within the framed space of an exterior wall. If the 

design of your fireplace enclosure differs, you should be able to 

adapt these basic instructions to your setting. 

Remove the old fireplace box.

Apply insulation (batt or spray foam) within the framing of the wall up to 

the ceiling/roof line. 

Install a thin structural sheathing material (e.g., drywall, plywood, 

rigid insulation, lightweight steel or aluminum sheeting) over the new 

insulation. Use heat-resistant tape to seal all the seams and joints.

Tape the sheathing to the enclosure 

opening on both the sides and the top of 

the fireplace enclosure. 

When the new fireplace insert and 

chimney are installed, seal the enclosure 

by placing a sheet metal firestop around 

the chimney pipe where it enters the 

chimney shaft.

Seal the joints and seams of the firestop 

with an approved high-temperature 

sealant.

Side view of fireplace enclosure 

(Source: Adapted from Building 

Science Corporation 2011)

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3

4 4 4 4

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Overhead view 

of fireplace 

enclosure (Source: 

Adapted from 

Building Science 

Corporation 2011)

Building AmericA energy PerformAnce Brief
 

Wire, tape, or clamp the insulation 

to the pipe every 1 to 2 feet to keep 

the sleeve from moving. 

Use caulk or foam to seal the holes 

where pipes penetrate walls.

Tubular pipe sleeves are made from flexible polyethylene or neoprene 

foam, and come with a precut split seam that makes them easy to install 

by slipping them over the pipe and sealing. There are different diameters 

of sleeves available to accommodate the varying sizes of your pipes, so 

measure your pipes before purchasing. Carefully match the pipe sleeve’s 

Durability & Health inside diameter to the pipe’s outside diameter to ensure a snug fit.

Insulating your water pipes reduces 

heat loss during water circulation, keeps 

pipes from sweating, and protects them 

from freezing during winter. 

Insulating your hot and cold water pipes is inexpensive, easy to do, and 

will allow you to lower the temperature on your hot water heater by 2 to 

4°F, saving you money (DOE 2011b). Begin by insulating the first 3 feet 

of pipes leading both into and out of your hot water heater; and then 

continue with any hot or cold water pipes that are accessible. Be sure to 

include pipes under your kitchen and bathroom cabinets, as well as those 

in a basement, crawlspace, attic, or garage. The insulation should be 

continuous, covering all sections of exposed pipes and fittings.

Pipe insulation is available in three forms: Tubular pipe sleeves, spiral 

insulation wrap, and fiberglass batts that can be taped around the pipes. 

If properly installed, all three can be effective. 

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Insulating Plumbing Pipes

R

BUILDING AMERICA

ENERGy PERfORMANCE BRIEf

When to Do This 

Any time.

Tubular pipe sleeves 

come with a precut 

seam, making them 

easy to wrap around 

your pipes and seal 

(Source: DOE).

How to Insulate Pipes Using Tubular Sleeves:

Cut the pipe sleeve to length and wrap 

it around the pipe, making sure there 

are no gaps between sleeves.

Remove the paper strips covering the 

self-sealing, pre-glued seam and press 

the edges together, with the seam side 

facing down on the pipe.

Tape the seams with acrylic or 

aluminum foil tape to increase 

durability. If using more than one 

sleeve, tape the seam where the two 

sleeves meet. 

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Insulating hot water pipes under kitchen 

and bathroom sinks and wherever else 

you have access to them is an easy way to 

save energy.
PNNL-SA-83948 September2011

2009 IECC

Code Requirement for New 

Construction and Additions

2009 IECC 403.4: All circulating service hot 

water piping shall be insulated to at least R-2.

2012 IECC R403.4.2: Insulation for hot 

water pipe with a minimum thermal 

resistance of R-3 shall be applied to ... 

[most circumstances]. 2012 IECC R403.3: 

Mechanical system piping capable of 

carrying fluids above 105°F or below 55°F 

shall be insulated to a minimum of R-3.

References

U.S. Department of Energy. Accessed 10/7/2011. 

Heat Distribution Systems. http://www.

energysavers.gov/your_home/space_heating_

cooling/index.cfm/mytopic=12580

U.S. Department of Energy. Accessed 9/30/2011. 

Insulate Hot Water Pipes for Energy Savings. 

http://www.energysavers.gov/your_home/water_

heating/index.cfm/mytopic=13060

U.S. Department of Energy. 2006. Energy 

Tips-Steam: Insulate Steam Distribution and 

Condensate Return Lines. http://www1.eere.energy.

gov/industry/bestpractices/pdfs/39306.pdf

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How to Insulate Pipes Using Spiral Wrap 

or fiberglass Batts:

for More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

Spiral insulation wrap can be made of fiberglass, foil, or polyethylene 

foam. Simply unroll the material and wrap it around your hot and cold 

water pipes. When working with fiberglass insulation, you may need to 

wrap your pipes in plastic after insulating to keep the fiberglass from 

absorbing moisture and reducing its R-value. Most hardware stores 

carry fiberglass insulation plastic, or you can purchase a fiberglass 

insulation that already has a moisture barrier attached to it. Be sure to 

wear gloves, goggles, and a dust mask when installing fiberglass.

Secure the end of the spiral wrap or fiberglass batt on the 

pipe with tape. 

Wrap the insulation around the pipe in a spiral fashion, overlapping each 

successive layer by a 1⁄2-inch for tape or half the width of the batt insulation. 

Wrap batts as loosely as possible, as compressing them will reduce their R-value.

If using fiberglass insulation without a moisture barrier, 

wrap plastic around the insulated pipe and seal with tape 

to keep the insulation from getting wet.

Wire, tape, or clamp the insulation (and plastic covering) 

to the pipe every 1 to 2 feet to keep the insulation from 

moving. 

Use caulk or foam to seal the holes where pipes penetrate walls.

If your house has a hydronic (steam or hot water) heating system, you can 

reduce unwanted heat loss by as much as 90% by insulating your steam 

distribution and return pipes (DOE 2006). Any surface over 120°F should 

be insulated, including boiler surfaces, steam and condensate return piping, 

and fittings. Use 1-inch-thick, heavy-density, resin-bonded fiberglass 

sleeves approved for steam or hot water heating systems, since other forms 

of insulation can melt. Seal and secure the fiberglass insulation sleeves with 

high-temperature tape. There are also removable insulation jackets that can 

be installed on elbows, tees, or other pipe fittings. 

How to Insulate Steam Pipes:

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It is easy to install highdensity fiberglass steam pipe 

insulation. Just wrap it around 

your hydronic pipes and seal 

(Source: National Institute of 

Building Sciences).

Pre-split along center

Self-sealing lap

Measure the length of the pipe you are insulating and 

cut the fiberglass sleeve to match.

Open the pre-cut fiberglass sleeve by pulling on the 

release strip.

Fit the sleeve around the pipe and align the selfsealing lap over the sleeve.

Seal by rubbing firmly on the adhesive strip to seal 

the lap to the sleeve.

Wrap high-temperature tape around the pipe where 

two sleeves meet to minimize gaps in the insulation. 

BUILDING AMERICA ENERGy PERfORMANCE BRIEf

2
 

Water heating can account for 14% to 25% of the energy consumed in 

your home. Insulating your hot water heater is an easy and affordable 

way to reduce your water heating costs by 4% to 9%. Unless your water 

heater is already insulated to R-24 or was manufactured since 2004, you 

should add insulation. If you don't know your water heater’s R-value, 

touch it. A tank that's warm to the touch needs additional insulation 

(DOE 2011b). 

You can purchase pre-cut insulation jackets or blankets. Insulation 

jackets are designed to fit specific models of water heaters and simply 

slide on, while insulation blankets come in a single size and must be cut 

to fit your specific unit. Choose one with an insulating value of at least 

R-8. Some utilities sell them at low prices, offer rebates, and even install 

them at low or no cost. Your insulation kit will include insulation, belts, 

and tape. If directions are included, read and follow those.

When insulating your water heater, avoid setting your thermostat above 

130°F. Higher temperatures can overheat the wires once the tank is 

insulated. For safety, never block any controls or valves and leave the 

thermostat access panel uncovered. 

Electric and gas water heaters 

require different approaches 

to insulation. Gas and oil-fired 

water heaters are more difficult 

to insulate than electric water 

heaters. Their installation may 

be best handled by a qualified 

plumbing or heating contractor. 

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Insulating Hot Water Heaters

R

BUILDING AMERICA

ENERGy PERfORMANCE BRIEf

When to Do This

When you have a water heater produced 

before 2004 or manufactured with less 

than R-24 insulation.

Durability & Health

Insulating a water heater extends 

the life of the appliance by reducing 

demand. 

For safety, electric and gas water 

heaters require different approaches to 

insulation (Source: DOE). %LECTRIC 'AS

#UT
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(EATTRAP
7

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Cut the tank top insulation to fit around the piping on the top of the tank. 

Place it over the tank and tape the cut sections closed.

Fold the corners of the tank top insulation down and tape to the sides of the 

tank with heat-resistant tape.

Position the insulating blanket around the circumference of the tank. For ease 

of installation, position the blanket so that the ends do not come together 

over the access panels in the side of the tank. (Some tanks have only one 

access panel.)

Secure the blanket in place with the belts provided. Position the belts so they 

do not go over the access panels. Belts should fit snugly over the blanket but 

not compress it more than 15% to 20% of its thickness. 

Locate the four corners of the access panel(s). Make an x-shaped cut in the 

insulating blanket from corner to corner of each access panel.

Fold the triangular flaps produced by the cuts underneath the insulating 

blanket. Repeat steps 5 and 6 for the rating/instruction plate.

If you are moving the water heater, you can place a piece of rigid foam 

insulation under the tank to reduce heat loss into the floor.

Replace or add seismic strapping as required by local code.

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PNNL-SA-83885 October 2011

References

DOE. 2011a. U.S. Department of Energy. Accessed 

10/3/2011. Installing an Insulation Blanket on 

an Electric Storage Water Heater. http://www.

energysavers.gov/your_home/water_heating/

index.cfm/mytopic=13080

DOE. 2011b. U.S. Department of Energy. Accessed 

10/3/2011. Insulate Your Water Heater Tank 

for Energy Savings. http://www.energysavers.

gov/your_home/water_heating/index.cfm/

mytopic=13070

How to insulate eleCtRiC wateR HeateRs

for More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

How to insulate Gas- oR oil-fiRed wateR HeateRs

2009 IECC

Code Requirement for New 

Construction and Additions

No minimum level of external insulation is 

prescribed in the 2009 or 2012 IECC or IRC. 

Per 2009 IRC PC2801.7, in Seismic Design 

Categories D0, D1, and D2, water heaters 

should be anchored to the wall with straps 

across the upper third and lower third of 

the tank to prevent tipping.

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Steps 1-2 Steps 3-4 Step 5 Step 6

drain valve

pilot light 

and burner

thermostat

gas valve

insulation

flue

pressure 

temperaturerelief valve

Wrap the insulation blanket around the sides 

of the tank, cut to size, and tape in place. 

To allow intake air for combustion, do not 

insulate below the drain valve. 

Cut any excess insulation from the bottom of 

the tank. 

Cut insulation away from the pressuretemperature relief valve, thermostat, gas 

valve, pilot light, and burner area. For fire 

safety, make sure the insulation can not drop 

in front of these areas.

Never insulate the top of a gas water heater. 

Insulating this area can result in improper 

venting and a possible fire hazard. 

Do not install insulation underneath gas or 

oil-fired water heaters, where flammable 

liquids may leak.

BUILDING AMERICA ENERGy PERfORMANCE BRIEf
Durability & Health

Rain entry into attic soffit vents during 

high winds can cause structural damage 

and mold.

In hurricane-prone and high-wind coastal regions, the typical soffit 

design for homes is susceptible to water intrusion from direct wind 

pressure, suction on the lee-ward side of the house, and surface 

tension that draws in water sheeting off the roof that clings to the 

fascia and soffit. 

The soffit detail for vented attics shown here discourages water draining 

off the roof from coming into the soffit vent openings. The improved 

eave design has a fascia that is extended one inch below the soffit to form 

a drip-edge to defeat the rain water’s surface tension. The soffit vent 

has recessed perforations rather than vents that stick down. Additional 

blocking is also installed to strengthen the soffit. 

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Keeping Wind-Blown Rain 

Out of Soffits

R

BUILDING AMERICA

ENERGy PERfORMANCE BRIEf

When to Do This 

When wind-blown rain intrusion is a 

problem. When replacing a roof.

Wind-blown rain can enter attics through 

soffit vents during storms.

Typical soffits have a fascia that is level 

with the bottom of the vent panel and vent 

perforations that face downward allowing rain 

water dripping down the fascia to be blown or 

drawn into the vent openings.

Aluminum wrap over 2x4 fascia

Continuously perforated 

vinyl soffit

Textured cement finish to top 

of concrete wall
PNNL-SA-83158 September2011

2009 and 2012 IRC R806.1

Code Requirement for New 

Construction and Additions

Ventilation Required. Enclosed attics ... shall 

have cross ventilation for each separate 

space by ventilating opening protected 

against the entrance of rain or snow.

References

DOE. 2011. Building America Best Practices Series, 

Volume 15: 40% Whole-House Energy Savings 

in the Hot-Humid Climate, PNNL-20768, U.S. 

Department of Energy. www1.eere.energy.gov/

buildings/building_america/publications.htm.

Zoeller, William. 2006. “Designing and Building 

Hurricane-Resistant Homes,” prepared by 

Steven Winter Associates, published in Home 

Energy Magazine, Fall 2006, www.carb-swa.

com/articles/in%20the%20news/HomeEnergy_

Designing%20and%20Building%20Hurricane%20

Resistant%20Homes.pdf.)

The fascia was redesigned 

to extend 1 inch below the 

soffit to form a drip edge, 

directing water down and 

away from the house. 

Perforated soffit board 

product with recessed 

rather than surface 

openings was installed 

to limit water intrusion 

while encouraging greater 

air circulation and faster 

drying within the eave 

assembly. 

Replace the roof fascia with a fascia that extends one inch further.

Wrap aluminum flashing over front of fascia and extend under and up 

inside surface of fascia.

Install additional blocking behind fascia.

Replace the soffit vent board with soffit vent panels with recessed 

perforations. 

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How to Prepare a Rain-Resistant Soffit

for More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

Aluminum wrap over 2x6 fascia

Vinyl soffit with recessed 

perforations

Textured cement finish to top 

of concrete wall

BUILDING AMERICA ENERGy PERfORMANCE BRIEf

2
Deluging rains can pour thousands of gallons of water onto a home’s roof 

in a single storm. In fact, 1 inch of rain can deposit 1,240 gallons of water 

on a 2,000-square foot roof. In house designs where roofs intersect walls, 

much of this water is channeled along the wall to a gutter. In big storm 

events the water can often overflow the gutter and stream down the walls. 

Diverters are sometime fashioned on site in an attempt to direct this water 

into the gutters. If undersized, these diverters are not very helpful. If not 

properly integrated with the existing housewrap and cladding, they can 

allow water to penetrate behind cladding and weather-resistant barriers. 

The result can be significant damage to wall sheathing, framing, and 

insulation and mold inside the house. While older wood siding would show 

evidence of this water intrusion by peeling paint, new wall claddings like 

fiber cement, vinyl siding and brick veneer can mask the evidence for years.

Proper flashing that is correctly integrated with housewrap and cladding 

along roof-wall intersections and kick-out diverters that are seamless and 

adequately sized to direct flowing water into the rain gutters are important 

tools to keep the wall cladding from being saturated by flowing water.

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Installing Sidewall and 

Kick-out Diverter Flashing

On Homes with Rigid Foam Insulation Sheathing

R

When to Do This 

When wall-roof intersections lack 

flashing or properly sized kick-out 

diverters.

BUILDING AMERICA ENERGy 

PERFORMANCE BRIEF

Durability & Health

Untreated water intrusion into wall 

cavities can quickly lead to material 

damage and mold. If left untreated for 

too long, structural damage can result.

(left) Improvised deflectors that are improperly integrated into the wall flashing and 

gutter are rarely sized to handle the volume of water that can run off the roof in a large 

downpour and they may contribute to water entry into the wall. To keep the water out, 

flashing should be integrated with the house wrap, siding, and shingles or roof tiles 

(center) and the diverter should be seamless and adequately sized to direct all of the 

water volume away from the wall and into the gutter (right). 

(Source: Steve Easley) (Sources: DryFlekt Products, Inc.) (Source: DryFlekt Products, Inc.)

Improper flashing can allow rain water into 

walls, causing significant damage (Source: 

DryFlekt Products, Inc.).

Installing Sidewall and Kick-out Diverter Flashing on Homes 

with Rigid Foam Insulation Sheathing

 
Apply drip edge and roof underlayment over roof 

deck and continue lapping up the sidewall and over 

the water-resistive barrier (in this case rigid foam 

insulation) a minimum of 7 inches.

• Install shingle starter strip at roof eave in 

accordance with roofing manufacturer’s 

instructions.

• Place seamless, one-piece, non-corrosive kick-out 

diverter flashing as the first piece of step flashing.

• Slide kick-out diverter up roof plane until the 

starter trough stops at the shingle starter strip. 

Diverter must be flat on the roof and flush to the 

sidewall.

Fasten and seal diverter to the roof deck and starter 

strip. (Do not fasten to the sidewall.)

Place first shingle and next section of sidewall 

flashing over up-slope edge of diverter, lapping 

a minimum of 4” over diverter. (Sidewall flashing 

height requirement should be determined by 

design professional and local building codes.

Install remaining sidewall flashing, appropriate 

counter flashing and shingles in accordance with 

manufacturer’s instructions.

Apply self adhesive flashing over top of wall 

flashing, diverter and rigid foam insulation.

Apply construction tape over the self-adhered 

flashing. 

Apply siding over rigid foam insulation.

For More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

PNNL-SA-83157 September 2011

How to Install Sidewall Flashing and Kick-out Diverters 

- On Homes with Rigid Foam Insulation Sheathing

Water runoff from rain storms can 

run along roof-wall intersections 

and spill over gutters to flow down 

exterior walls. If flashing is lacking 

or inadequate, this water runoff can 

get inside the wall and cause serious 

damage. Anywhere roof sections 

adjoin wall sections, sidewall flashing 

should be used to keep water from 

entering the walls and kick-out 

diverters should be used to direct the 

rain water into rain gutters where it 

can be carried down and away from 

the structure. The kick-out flashing 

should be seamless and sized as shown 

in the photos at right to manage large 

volumes of water run-off associated 

with torrential rains from a variety of 

roof pitches, with an expected service 

life to avoid premature failures. (Photo 

source: DryFlekt Products, Inc.)

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2009 and 2012 IRC R703.8

Code Requirement for New 

Construction and Additions

Approved corrosion-resistant flashing shall 

be applied shingle-fashion in a manner to 

prevent entry of water into the wall cavity 

or penetration of water to the building 

structural framing components.... flashings 

shall be installed at all of the following 

locations: ...6. At wall and roof intersections. 

R903.2.1 Locations. Flashings shall be 

installed at wall and roof intersections.... A 

flashing shall be installed to divert the water 

away from where the eave of a sloped roof 

intersects a vertical sidewall.

Reference

DOE. 2011. Building America Best Practices Series, 

Volume 15: 40% Whole-House Energy Savings 

in the Hot-Humid Climate, PNNL-20768, U.S. 

Department of Energy. www1.eere.energy.gov/

buildings/building_america/publications.htm.

BUILDING AMERICA ENERGy PERFORMANCE BRIEF

2
Deluging rains can pour thousands of gallons of water onto a home’s roof 

in a single storm. In fact, 1 inch of rain can deposit 1,240 gallons of water 

on a 2,000-square foot roof. In house designs where roofs intersect walls, 

much of this water is channeled along the wall to a gutter. In big storm 

events the water can often overflow the gutter and stream down the walls. 

Diverters are sometime fashioned on site in an attempt to direct this water 

into the gutters. If undersized, these diverters are not very helpful. If not 

properly integrated with the existing housewrap and cladding, they can 

allow water to penetrate behind cladding and weather-resistant barriers. The 

result can be significant damage to wall sheathing, framing, and insulation 

and mold inside the house. While older wood siding would show evidence of 

this water intrusion by peeling paint, new wall claddings like fiber cement, 

vinyl siding and brick veneer can mask the evidence for years.

Proper flashing that is correctly integrated with housewrap and cladding 

along roof-wall intersections and kick-out diverters that are seamless and 

adequately sized to direct flowing water into the rain gutters are important 

tools to keep the wall cladding from being saturated by flowing water.

BUILDING TECHNOLOGIES PROGRAM

Improving Existing Homes:

Installing Sidewall and 

Kick-out Diverter Flashing 

On Homes with Housewrap over OSB 

or Plywood Sheathing

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When to Do This 

When wall-roof intersections lack 

flashing or properly sized kick-out 

diverters.

BUILDING AMERICA

ENERGy PERFORMANCE BRIEF

Durability & Health

Untreated water intrusion into wall 

cavities can quickly lead to material 

damage and mold. If left untreated for 

too long, structural damage can result.

(left) Improvised deflectors that are improperly integrated into the wall flashing and 

gutter are rarely sized to handle the volume of water that can run off the roof in a large 

downpour and they may contribute to water entry into the wall. To keep the water out, 

flashing should be integrated with the house wrap, siding, and shingles or roof tiles 

(center) and the diverter should be seamless and adequately sized to direct all of the 

water volume away from the wall and into the gutter (right). 

Improper flashing can allow rain water into 

walls, causing significant damage (Source: 

DryFlekt Products, Inc).

(Source: Steve Easley ) (Sources: DryFlekt Products, Inc.) (Source: DryFlekt Products, Inc.)

Installing Sidewall and Kick-out Diverter Flashing 

on Homes with Housewrap over OSB or Plywood Sheathing

 
Apply drip edge and roof underlayment over roof 

deck. Continue lapping up the sidewall and over the 

weather-resistive barrier (in this case housewrap) a 

minimum of 6 inches.

Install shingle starter strip at roof eave in 

accordance with roofing manufacturer’s 

instructions.

• Place seamless one piece non-corrosive kick-out 

diverter as the first piece of step flashing. 

• Slide kick-out diverter up roof plane until the 

starter trough stops at the shingle starter strip. 

Diverter must be flat on the roof and flush to the 

sidewall.

• Fasten and seal diverter to the roof deck and 

starter strip. (Do not fasten to the sidewall.)

Place first shingle and next section of sidewall 

flashing over up-slope edge of diverter, lapping 

a minimum of 4 inches over diverter. (Sidewall 

flashing height requirement should be determined 

by design professional and local building codes.)

Install remaining sidewall flashing, appropriate 

counter flashing, and shingles in accordance with 

manufacturer’s instructions.

Apply self-adhesive flashing over top of wall 

flashing and diverter and housewrap.

Install house wrap. Cut the house wrap to fit over 

the self-adhesive flashing and sidewall flashing.

Apply siding over house wrap.

For More Information

www.buildingamerica.gov 

EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

eere.energy.gov/informationcenter

PNNL-SA-83154 September 2011

How to Install Sidewall Flashing and Kick-out 

Diverters - On Homes with Housewrap over OSB or 

Plywood Sheathing

2009 and 2012 IRC R703.8

Code Requirement for New 

Construction and Additions

Approved corrosion-resistant flashing shall 

be applied shingle-fashion in a manner to 

prevent entry of water into the wall cavity 

or penetration of water to the building 

structural framing components.... flashings 

shall be installed at all of the following 

locations: ...6. At wall and roof intersections. 

R903.2.1 Locations. Flashings shall be 

installed at wall and roof intersections.... A 

flashing shall be installed to divert the water 

away from where the eave of a sloped roof 

intersects a vertical sidewall.

Water runoff from rain storms can 

run along roof-wall intersections 

and spill over gutters to flow down 

exterior walls. If flashing is lacking 

or inadequate, this water runoff can 

get inside the wall and cause serious 

damage. Anywhere roof sections 

adjoin wall sections, sidewall flashing 

should be used to keep water from 

entering the walls and kick-out 

diverters should be used to direct the 

rain water into rain gutters where it 

can be carried down and away from 

the structure. The kick-out flashing 

should be seamless and sized as shown 

in the photos at right to manage large 

volumes of water run-off associated 

with torrential rains from a variety of 

roof pitches, with an expected service 

life to avoid premature failures. (Photo 

source: DryFlekt Products, Inc.)

2

3

4

5

6

Reference

DOE. 2011. Building America Best Practices Series, 

Volume 15: 40% Whole-House Energy Savings 

in the Hot-Humid Climate, PNNL-20768, U.S. 

Department of Energy. www1.eere.energy.gov/

buildings/building_america/publications.htm.

1

BUILDING AMERICA ENERGy PERFORMANCE BRIEF

2
 
eere.energy.gov

For information on Building America visit www.buildingamerica.gov. The website 

contains expanded case studies, technical reports, and best practices guides.

PNNL-20972 • May 2012 

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 10% post consumer waste.

Building America Program

Building America Program • 1-877-EERE-INFO (1-877-337-3463)

Office of Building Technologies, EE-2J • U.S. Department of Energy •

1000 Independence Avenue, S.W. • Washington, D.C. 20585-0121 •

www.buildingamerica.gov

National Renewable Energy Laboratory

www.nrel.gov

Oak Ridge National Laboratory

www.ornl.gov

Pacific Northwest National Laboratory

www.pnnl.gov

Produced for the U.S. Department of Energy (DOE) by Pacific Northwest National Laboratory, 

Under Contract DE-AC05-76RLO 1830.

Research and 

Development of Buildings

Our nation’s buildings consume 

more energy than any other sector 

of the U.S. economy, including 

transportation and industry. 

Fortunately, the opportunities to 

reduce building energy use—and 

the associated environmental 

impacts—are significant.

DOE’s Building Technologies 

Program works to improve the 

energy efficiency of our nation’s 

buildings through innovative new 

technologies and better building 

practices. The program focuses 

on two key areas:

•	 Emerging Technologies

Research and development of 

the next generation of energyefficient components, materials, 

and equipment

•	 Technology Integration of new

technologies with innovative 

building methods to optimize 

building performance and savings

Visit our Web sites at:

www.buildingamerica.gov

www.energystar.gov

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