For more information 

www.energystar.gov. 

Office of Air and Radiation

(6202A) EPA 430-F-04-024

July 2016

United States 

Environmental

Protection Agency

Recycled/Recyclable – Printed with Vegetable Oil Based Inks on Recycled Paper (Minimum 50% Post-consumer Content)
A DO-IT-YOURSELF GUIDE TO SEALING 

AND INSULATING WITH ENERGY STAR®

SEALING AIR LEAKS AND ADDING ATTIC INSULATION

CONTENTS

Locating Air Leaks

Getting Started

Sealing Attic Air Leaks

Additional Sources of Air Leaks

Sealing Basement Air Leaks

Adding Attic Insulation

1.2

1.4

1.6

2.1

3.1

4.1

Sealing and Insulating your home is 

one of the most cost-effective ways 

to make a home more comfortable 

and energy efficient—and you can 

do it yourself.

Use This Guide To:

1. Learn how to find and seal hidden 

attic and basement air leaks

2. Determine if your attic insulation 

is adequate, and learn how to 

add more

3. Make sure your improvements 

are done safely

4. Reduce energy bills and help 

protect the environment

When you see products or services with 

the ENERGY STAR® label, you know they 

meet strict energy efficiency guidelines 

set by the U.S. Environmental Protection 

Agency (EPA) and the U.S. Department 

of Energy (DOE). Since using less energy 

reduces greenhouse gas emissions and 

improves air quality, choosing ENERGY 

STAR is one way you can do your part to 

protect our planet for future generations.

For more information visit:

www.energystar.gov.

The U.S. EPA wishes to thank The Family 

Handyman Magazine for their contribution 

of photographs and content for this guide. 

Photos appear courtesy of The Family 

Handyman Magazine ©2001 except 

where otherwise noted.

1.1 CONTENTS
1.2 LOCATING AIR LEAKS

LOCATING AIR LEAKS

More than any other time of year, you notice your home’s air leaks in the winter. Most 

people call these air leaks “drafts.” You may feel these drafts around windows and 

doors and think these leaks are your major source of wasted energy. In most homes, 

however, the most significant air leaks are hidden in the attic and basement. These are 

the leaks that significantly raise your energy bill and make your house uncomfortable. In 

cold weather, warm air rises in your house, just like it does in a chimney. This air, which 

you have paid to heat, is just wasted as it rises up into your attic and sucks cold air in all 

around your home—around windows, doors, and through holes into the basement. The illustrations on Page 1.3 and 3.1 show warm air leaving (red arrows) the house through the 

attic and cold air being pulled into the house (blue arrows). Locating these leaks can be 

difficult because they are often hidden under your insulation. This guide will help you find 

these leaks and seal them with appropriate materials.

Behind Kneewalls

Attic Hatch

Wiring Holes

Plumbing Vent

Open Soffit (the box that hides 

recessed lights)

Recessed Light

Furnace Flue or Duct Chaseways 

(the hollow box or wall feature that 

hides ducts)

Basement Rim Joists (where the 

foundation meets the wood framing)

Windows and Doors

Common Household

Air Leaks Even if you have enough 

insulation in your attic, sealing 

attic air leaks will enhance the 

performance of your insulation 

and make for a much more 

comfortable home.

I

H

G

F

E

D

C

B

A

If you are not familiar with 

some of the terms in this guide, 

check our glossary inside the 

back cover.
1.3 LOCATING AIR LEAKS

Effects of Air Leaks

Heated inside air drawn into the attic

Cold outside air drawn into the house

I

H

G

F

E

D

B C

A
1.4 GETTING STARTED

GETTING STARTED

Attic air sealing and adding insulation 

are do-it-yourself projects if your attic is 

accessible and not too difficult to move 

around in. The projects recommended in 

this guide can usually be completed in a 

day or two and will provide benefits for 

years to come. However, if upon inspection 

of your attic you find any of the conditions 

listed to the left, we recommend you 

consider hiring a contractor to correct 

these problems before proceeding. 

For tips on hiring the right contractor, visit 

www.energystar.gov/homeimprovement.

Get Your Bearings 

from Below 

A good way to start home sealing is to 

make a quick sketch of your home’s floor 

plan. This sketch will serve as a reference 

point once you get into the attic and will 

help you locate areas of leakage. In your 

sketch, make note of dropped soffits over 

kitchen cabinets or bath vanities, slanted 

ceilings over stairways, where walls 

(interior and exterior) meet the ceiling, and 

any other dropped-ceiling areas. These 

areas may have open stud cavities leading 

directly into the attic and can be huge 

sources of air leaks (see photos 1-3 on 

Pages 1.6 and 1.7).

You May Need a Contractor 

to Correct These Problems:

■ Wet or damp insulation indicating a 

leaky roof

■ Moldy or rotted attic rafters or floor 

joists indicating moisture problems

■ Kitchen, bathroom, and clothes 

dryer vents that exhaust moist air 

directly into the attic space instead 

of outdoors

■ A history of ice dams in the winter 

(an indication of serious air leaks)

■ Little or no attic ventilation (see Page 

4.2 – A Note About Attic Ventilation) 

■ Knob and tube wiring (pre-1930), 

which can be a fire hazard when in 

contact with insulation

■ If you have many unsealed and 

uninsulated recessed “can” lights, 

special care must be taken when 

insulating around these fixtures 

(See Page 2.2)
• Batt or roll of unfaced fiberglass insulation 

and large garbage bags (for stuffing open 

stud cavities behind kneewalls and in 

dropped soffits)

• Roll of reflective foil insulation or other blocking 

material such as drywall or pieces of rigid foam 

insulation to cover soffits, open walls, and 

larger holes

• Silicone or acrylic latex caulk & caulk gun for 

sealing small holes (1/4 inch or less)

• Several cans of expanding spray foam insulation 

for filling larger gaps (1/4 inch to 3 inches)

• Special high-temperature (heat-resistant) caulk 

to seal around flues and chimneys

• Roll of 14-inch wide aluminum flashing to keep 

insulation away from the flue pipe

• Retractable utility knife and sheet metal scissors

• Tape measure and staple gun (or hammer and 

nails) to hold covering materials in place

• Safety glasses, gloves, and dust mask 

 (for insulation work as well)

• Flashlight or portable safety light

• Boards to walk on, if needed

• Large bucket to haul materials

1.5 GETTING STARTED

■	 Have a Plan in Place

The key to any successful home 

improvement project is adequate 

planning. Gather all your tools and 

supplies before you begin to minimize trips 

in and out of the attic. Be sure that the 

work area is well-lit by using a drop light, 

and keep a flashlight handy.

■	 Prepare to Get Dirty

The entire process of sealing your attic 

will be made easier if you take the time 

and effort to wear the right gear. Wear 

knee pads to help prevent pain associated 

with crawling on attic joists. Additionally, 

a lightweight disposable coverall, gloves, 

and hat can keep itchy and irritating 

insulation off your skin.

■ Above All – Be Safe

Take precautions to avoid a dangerous 

working environment in the attic. During 

hot weather start working early, as attics 

heat up as the day moves on. Drink plenty 

of water and use an OSHA-approved 

particulate respirator or double-strap 

dust mask to prevent inhalation of 

hazardous substances. Also remember 

to watch your step. Walk on joists or 

truss chords, not exposed ceiling drywall 

or insulation. In addition, watch out for 

sharp nails sticking through the 

roof deck!

Tips For Working in the Attic

Materials Checklist for Sealing Attic Air Leaks
1.6 SEALING ATTIC AIR LEAKS

SEALING ATTIC AIR LEAKS

Plug the Big Holes First 

Don’t worry about finding and sealing all the little holes in your attic; your biggest savings 

will come from plugging the large ones. Once in the attic, refer to your sketch to locate 

the areas where leakage is likely to be greatest: where walls (inner and outer) meet the 

attic floor, dropped soffits (dropped-ceiling areas), and behind or under attic kneewalls. 

Look for dirty insulation—this indicates that air is moving through it. Dropped soffits may 

be filled or covered with insulation and hard to see. Push back the insulation and scoop it 

out of the soffits. You will place this insulation back over the soffit once the stud cavities 

have been plugged and the soffits covered (photos 1-3) (If you have recessed “can” lights 

in your open soffits, please read about them on Page 2.2 before proceeding).

1. CREATE STUFFED BAGS

Cut a 16 inch long piece from a batt of unfaced 

fiberglass insulation and fold it into the bottom 

of a 13-gallon plastic garbage bag.

2. PLUG OPEN STUD CAVITIES

Fold the bag and stuff it into the open stud cavity.

Add more insulation to the bag if it doesn’t fit 

tightly. Plug all open stud spaces, then cover the 

soffit (photo 3, Page 1.7 ).

16” PIECE OF

FIBERGLASS

BATT

RECESSED

CAN LIGHT DROPPED

SOFFIT

PLUGGED

STUD CATIVITY

RECESSED

CAN LIGHT

OPEN

STUD CAVITY
1.7 SEALING ATTIC AIR LEAKS

3. COVER DROPPED SOFFITS

After removing insulation from a dropped soffit, cut 

a length of reflective foil or other blocking material 

(rigid foam board works well) a few inches longer 

than the opening to be covered. Apply a bead of 

caulk or adhesive around the opening. Seal the foil 

to the frame with the caulk/adhesive and staple or 

nail it in place, if needed.

4. SEAL BEHIND KNEEWALLS

Cut a 24 inch long piece from a batt of fiberglass 

insulation and place it at the bottom of a 13-gallon 

plastic garbage bag. Fold the bag over and stuff it 

into the open joist spaces under the wall (a piece of 

rigid foam board sealed with spray foam also works 

well for covering open joist cavities). Again, cover 

with insulation when you’re done.

If You Have a Finished Attic, Seal Behind the Kneewalls

Finished rooms built into attics often have open cavities in the floor framing under the 

side-walls or kneewalls. Even though insulation may be piled against or stuffed into these 

spaces, they can still leak air. Again, look for signs of dirty insulation to indicate air is 

moving through. You need to plug these cavities in order to stop air from traveling under 

the floor of the finished space (photo 4).

Caution: Some attics have vermiculite insulation, which may contain asbestos, a health 

hazard. Vermiculite is a lightweight, pea-size, flaky gray mineral. Don’t disturb vermiculite 

insulation unless you’ve had it tested by an approved lab to be sure it doesn’t contain 

asbestos. Contact your local health department for the name of an approved lab.

REFLECTIVE FOIL

INSULATION

DROPPED

SOFFIT

CAULK OR ADHESIVE

24” BATT

ROLLED INSIDE

GARBAGE BAG

OPEN JOIST

CAVITY

KNEEWALL
1.8 SEALING ATTIC AIR LEAKS

Furnace Flues Require Special Sealing Techniques 

The opening around a furnace or water heater flue or chimney can be a major source of 

warm air moving in the attic. Because the pipe gets hot, building codes usually require 

1 inch of clearance from metal flues (2 inches from masonry chimneys) to any combustible 

material, including insulation. Photos 5 and 6 show how to seal this gap with lightweight 

aluminum flashing and special high-temperature (heat-resistant) caulk. Before you push 

the insulation back into place, build a metal dam (photo 7) to keep it away from the pipe. 

Use the same technique for masonry chimneys.

5. CUT ALUMINUM FLASHING

Cut aluminum flashing to fit around the flue. For 

round flues, cut half circles out of two pieces so 

they overlap about 3 inches in the middle. Press 

the flashing metal into a bead of high-temperature 

caulk and staple or nail it into place. If there’s no 

wood, staple or nail it directly to the drywall, but 

be sure not to staple or nail through the drywall.

14” ALUMINUM

FLASHING

OPEN JOIST

CAVITY

HIGH-TEMP

CAULK

CLASS B

FURNACE FLUE

SEALING ATTIC AIR LEAKS

Caution: Furnace flues (the 

pipe that removes your furnace 

exhaust) can be very hot.
1.9 SEALING ATTIC AIR LEAKS

6. SEAL WITH SILICONE CAULK

Seal the gap between the flue and metal flashing 

with special high-temperature caulk. Don’t use 

spray foam.

7. FORM AN INSULATION DAM

Form an insulation dam to prevent insulation from 

contacting the flue pipe. Cut enough aluminum from 

the coil to wrap around the flue plus 6 inches. Cut 

slots 1 inch deep and a few inches apart along the 

top and bend the tabs in. Cut slots about 2 inches 

deep along the bottom and bend out the tabs. Wrap 

the dam around the flue and secure the bottom by 

stapling through the tabs. Now put insulation back 

right up against the dam.

Identifying Attic Pipes

HIGH-TEMP 

CAULK

INSULATION DAM

1” TABS

RENT IN

STAPLE

DOWN

FLUES/VENTS/PIPES: MADE OUT OF: SEAL AROUND WITH:

Furnace/Water Heater Galanized Metal Aluminum flashing and hightemperature silicone caulk

Chimney Masonry/Metal Aluminum flashing and hightemperature silicone caulk

Plumbing Cast Iron or PVC Expanding foam or caulk, 

depending on size of gap

2” TABS

BENT OUT
1.10 SEALING ATTIC AIR LEAKS

Foam or Caulk Small Gaps in Your Attic 

Even though most of the gaps spilling warm air into your attic are buried under insulation, 

you might be able to find evidence of these gaps. Look for areas where the insulation 

is darkened (see photo 8). This is the result of filtering dusty air from the house. In cold 

weather, you may also see frosty areas in the insulation caused by warm, moist air 

condensing and then freezing as it hits the cold attic air. In warmer weather, you’ll find 

water staining in these same areas. Although the insulation is dirty, it is still okay to use. 

There’s no need to remove and replace. After sealing the areas, just push the insulation 

back into place. If you have blown insulation, a small rake can be helpful to level it 

back into place. 

8. FIND ATTIC BYPASSES

Check for gaps in your attic that facilitate air 

movement by checking for dirty insulation. Seal the 

gaps with caulk or expanding foam. When complete 

and dry, push the insulation back into place.

DIRTY INSULATION

DUST FROM

LEAKING AIR

SEALING ATTIC AIR LEAKS
1.11 SEALING ATTIC AIR LEAKS

9. FILL HOLES WITH CAULK

Fill wiring and plumbing holes with expanding foam. 

Caulk around electrical junction boxes, and fill 

holes in box with caulk.

10. STUFF GAPS WITH INSULATION

If the space around your plumbing pipe is wider 

than 3 inches, you may need to stuff some 

fiberglass insulation into the space to serve as a 

backer for the expanding foam. Once the fiberglass 

insulation is in place, follow the directions on the 

can to foam the space around the pipe.

ELECTRICAL BOX

EXPANDING FOAM

PLUMBING

VENT

GAP AROUND

PLUMBING VENT

Seal Small Gaps 

Use expanding foam or caulk to seal the openings around plumbing vent pipes and 

electrical wires (see photos 9 and 10). Be sure to wear gloves and be careful not to get 

expanding foam on your clothes, as the foam is very sticky and nearly impossible to 

remove once it sets. When the foam or caulk is dry, cover the area again with insulation. 

CAULK

OPENINGS

SPRAY FOAM

IN HOLES
1.12 SEALING ATTIC AIR LEAKS

11. WEATHERSTRIP THE DOOR

Weatherstrip the attic access hatch or door. Cut 

1x3 boards to fit the perimeter of the opening and 

nail them on with 6d finish nails. Apply self-adhesive 

foam weatherstrip tape to the top edge of the stop.

12. ATTACH FASTENERS

Attach hook-and-eye fasteners to the attic door and 

stops. Position the eyes so that the weatherstrip is 

compressed when you latch the hooks.

HOOK-AND-EYE

LATCH

HATCH 

DOOR

Complete the Job by Sealing the Attic Hatch or Door 

Finish up by sealing the access hatch with self-sticking weather stripping (photos 11 and 

12). If your hatch rests directly on the moldings, add 2-1/2 inch wide stops around the 

opening. The stops provide a wider surface for attaching the weatherstrip and a space 

to mount hook-and-eye fasteners. Position the screw eyes so the weatherstrip is slightly 

compressed when the hooks are latched. Cut a piece of fiberglass or rigid foam board 

insulation the same size as the attic hatch and nail or glue it to the back of the hatch. 

If you have pull-down attic stairs or an attic door, these should be sealed in a similar 

manner: weatherstrip the edges and put a piece of rigid foam board insulation on the back 

of the door. Treat the attic door like a door to the outside. Pre-made insulated attic stair 

covers are also available from local home improvement centers or on the Web.

NEW WOOD STOPS

EXISTING MOLDING

SELF-ADHESIVE FOAM

WEATHERSTRIP

SEALING ATTIC AIR LEAKS

COMPRESSED 

WEATHERSTRIP
If Your Heating and Cooling Ducts Are in Your Attic, 

Seal Them While in the Attic 

Leaky and poorly-insulated ducts (especially in attics) severely compromise the 

performance of your heating and cooling equipment. Sealing and insulating your ducts 

can increase the efficiency of your heating and cooling system by 20% and greatly 

increase air flow.

2.1 ADDITIONAL SOURCES OF AIR LEAKS

■	 Check the duct connections for leaks 

by turning on your heating and cooling 

system fan and feeling for leaks—seal the 

joints with mastic or foil tape (household 

duct tape should not be used).

■	 Pay special attention to all the duct 

penetrations going through the attic floor. 

Seal these with foam.

■ Ducts should also be insulated—if your 

 ducts are uninsulated or poorly insulated

(i.e., you see gaps or torn insulation), seal 

them first, then add insulation to keep the air 

in your ducts at your desired temperature 

as it moves through the system. Use duct 

insulation material rated at least R-6.

Materials Checklist 

for Attic Duct Sealing

• Duct sealant (mastic) or metalbacked (foil) tape

• Duct insulation material rated at 

least R-6

• Zip ties to hold duct insulation 

 in place

• Gloves, safety glasses, mask, 

flashlight

NOTE: Duct sealant, also known as duct mastic, 

is a paste which is more durable than foil duct 

tape. It is available at home improvement centers. 

Traditional grey duct tape fails quickly and 

should not be used.

Caution: Check for Carbon Monoxide to keep your house safe. After making energy 

improvements that result in a tighter house, there can be an increased opportunity for CO 

to build up if your gas-burning appliances are not venting properly. Have your heating and 

cooling technician check your combustion appliances (gas- or oil-fired furnace, water heater, 

and dryer) for proper venting. For additional information on Indoor Air Quality (IAQ) issues 

related to homes such as combustion safety, indoor air contaminants, and proper ventilation, 

visit www.epa.gov/iaq/homes/hip-front.html.

ADDITIONAL SOURCES OF AIR LEAKS
2.2 ADDITIONAL SOURCES OF AIR LEAKS

Recessed “Can” Lights: Big Source of Air Leaks, 

But No Easy Solution 

Recessed “can” lights (also called high-hats or recessed downlights) look great, but 

when they protrude into your attic space, they can make your home less energy-efficient. 

These recessed lights in a one-story house or in the ceiling of a second-story create 

open holes into your attic that allow unwanted heat flow between conditioned and 

unconditioned spaces. In the summer, hot attic air can make the rooms warmer, and in 

the winter can lights draw warm air up into your attic. Both the warm air leakage and the 

heat from the lights can cause problems. In cold climates, the heat melts snow on the 

roof and forms ice dams (water re-freezes at the roof edge). This is more likely to happen 

if the “can” light is close to the roof deck. Recessed “can” lights in bathrooms also cause 

problems when warm, moist air leaks into the attic and causes moisture damage. Here 

are some suggestions for improving the recessed can lights in your attic:

ADDITIONAL SOURCES OF AIR LEAKS

Caution: Keep all insulation 3 inches 

from “can” lights, except those rated 

IC (insulation contact). You can use 

a piece of circular metal flashing or 

wire mesh around the light as a dam 

to keep the insulation away from the 

light (see photo 2, Page 4.3).

■ Call a Professional to Properly Seal

Recessed lights can be sealed, but it is difficult 

and can create a hazard if not done properly with 

non-combustible materials. Since any old-style 

lights need adequate air space around them to 

vent the heat they create, it’s best to consult with 

a professional before sealing them. Also, see 

“Caution” below. Alternatively, recessed lights 

can be replaced with ICAT (Insulated Ceiling AirTight) rated lights, which insulation can touch and 

are sealed to reduce air leaks.

■ When Replacing or Adding, Buy 

ENERGY STAR with ICAT

Look for ENERGY STAR certified recessed fixtures 

that reduce energy use as much as 90%. However, 

it’s important to check that any fixture selected 

meets your light output expectations since fixtures 

come with widely varying wattage bulbs and 

optics. Also, make sure fixtures have an ICAT 

rating to minimize heat loss.

■ Switch to More Efficient Bulbs

When keeping existing recessed lights, 

you can still reduce lighting energy use by 

installing ENERGY STAR certified light bulbs. 

These bulbs include compact fluorescent light 

(CFL) bulbs and light–emitting diodes (LED) and 

use about 70-90% less energy than traditional 

bulbs, last 15-25 times longer, and produce 70-

90% less heat. Be sure the bulb you select is 

specifically designed for recessed lights with 

built-in reflectors matching the appearance 

of traditional incandescent reflector bulbs. 

Also, check the packaging to ensure that it 

may be used in an enclosed fixture. However, 

switching to ENERGY STAR certified bulbs will 

not solve the air leakage problem. 
2

3

1

3.1 SEALING BASEMENT AIR LEAKS

Stopping the Chimney Effect 

Outside air drawn in through basement leaks 

is exacerbated by the chimney effect created 

by leaks in the attic. As hot air generated 

by the furnace rises up through the house 

➊ and into the attic through leaks ➋, cold 

outside air gets drawn in through basement 

leaks to replace the displaced air ➌. This 

makes a home feel drafty and contributes 

to higher energy bills. After sealing attic air 

leaks, complete the job by sealing basement 

leaks, to stop the chimney effect.

Locating Basement Air Leaks 

A common area of air leakage in the basement is along the top of the basement wall 

where cement or block comes in contact with the wood frame. These leaks can easily be 

fixed in portions of the basement that are unfinished. Since the top of the wall is above 

ground, outside air can be drawn in through cracks and gaps where the house framing 

sits on top of the foundation. This perimeter framing is called the rim (or band) joist. In the 

basement, the above floor joists end at the rim joist creating multiple cavities along the 

length of the wall, and many opportunities for leakage (see illustration on Page 3.2). 

SEALING BASEMENT AIR LEAKS
3.2 SEALING BASEMENT AIR LEAKS

Seal All Gaps and Cracks around Rim Joists 

Though you may not be able to see cracks in the rim joist cavities, it is best to seal up 

the top and bottom of the inside of the cavity. Also, rim joist air sealing is especially 

important at bump out areas such as bay windows that hang off the foundation. These 

areas provide greater opportunities for air leakage and heat loss. Caulk is best for sealing 

gaps or cracks that are 1/4 inch or less. Use spray foam to fill gaps from 1/4 inch to about 

3 inches. We also recommend you seal penetrations that go through the basement ceiling 

to the floor above. Generally, these are holes for wires, water supply pipes, water drain 

pipes, the plumbing vent stack (for venting sewer gases), and the furnace flue (for venting 

furnace exhaust).

Caution: When sealing the furnace 

flue (which will be encased in a 

metal sleeve) use high-temperature 

caulk. Run a bead of hightemperature caulk around the pipe 

sleeve and around the metal frame.

Materials Checklist for 

Basement Sealing

• Silicone or acrylic latex caulk and caulk gun

• Expanding spray foam

Areas to Foam or Caulk

Along the gap between the sill 

plate and the foundation

At the bottom and top of the rim 

joist on each end of the house

All electrical, water, or gas 

penetrations and any venting 

ducts that pass to the outside

C

B

A

ILLUSTRATION BY DALE HOFFMEYER

RIM JOIST

SUB FLOOR

SILL PLATE

FOUNDATION

FLOOR

JOIST

LONG RIM JOIST

SEALING BASEMENT AIR LEAKS

C

B A
4.1 ADDING ATTIC INSULATION

What About Insulating the Rim Joist?

After air sealing the rim joist area it is relatively easy to insulate each cavity with rigid 

foam insulation or fiberglass batts. If using batts, just cut the insulation to fit and place 

against the rim joist without compression, gaps, or voids. If using rigid, foam into place. 

This could also be done in conjunction with finishing the basement, when you would 

insulate the basement walls floor-to-ceiling. Attic and basement air sealing will go 

a long way to improve your comfort because your house will no longer act like an 

open chimney. 

Do I Have Enough?

No matter what kind of insulation you currently have in your attic, one quick way to 

determine if you need more is to look across the span of your attic. If your insulation is 

just level with or below your floor joists (i.e., you can easily see your joists), you should 

add more. If you cannot see any of the floor joists because the insulation is well above 

them, you probably have enough and adding more may not be cost-effective. It is 

important that the insulation be evenly distributed with no low spots; sometimes there 

is enough insulation in the middle of the attic and very little along the eaves. To see how 

to add insulation out to the eaves, see Installing Rafter Vents (on Page 4.4). If your attic 

insulation covers your joists and is distributed evenly, you probably have enough.

Now that you’ve air-sealed your attic and basement, check your attic insulation levels 

and add more if necessary. The attic is the easiest place to add insulation to improve your 

comfort and the energy efficiency of your home. 

How Much Should I Add? 

Insulation levels are specified by R-Value. R-Value is a measure of insulation’s ability 

to resist heat flow. The higher the R-Value, the better the thermal performance of the 

insulation. The recommended level for most attics is to insulate to R-38 or about 

10 to 14 inches, depending on insulation type.

ADDING ATTIC INSULATION
4.2 ADDING ATTIC INSULATION

A Note about Natural 

Attic Ventilation

At first it may seem odd to add insulation for warmth 

and then purposely allow cold air to enter the attic 

through vents, but this combination is the key to a 

durable and energy-efficient home. Here’s why: in the 

winter, allowing a natural flow of outdoor air to ventilate 

the attic helps keep it cold, which reduces the potential 

for ice damming (snow that melts off a roof from an 

attic that is too warm and then re-freezes at the gutters, 

causing an ice dam that can damage the roof). Proper 

insulation and air sealing also keeps attics cold in 

winter by blocking the entry of heat and moist air from 

below. In the summer, natural air flow in a well-vented 

attic moves super-heated air out of the attic, protecting 

roof shingles and removing moisture. The insulation will 

resist heat transfer into the house. The most common 

mistake homeowners make when installing insulation 

is to block the flow of air at the eaves. NEVER COVER 

ATTIC SOFFIT VENTS WITH INSULATION—use rafter 

vents and soffit vents to maintain airflow (See Pages 4.4 

and 4.5).

A Note about Attic Fans

Attic fans are intended to cool hot attics by drawing 

in cooler outside air from attic vents (soffit and gable) 

and pushing hot air to the outside. However, if your attic 

has blocked soffit vents and is not well-sealed from the 

rest of the house, attic fans will suck cool conditioned 

air up out of the house and into the attic. This will 

use more energy and make your air conditioner work 

harder, which will increase your summer utility bill. 

You don’t want your unfinished attic cooled by your air 

conditioner. To prevent this, follow the air sealing and 

insulation strategies in this guide and make sure the 

attic is well-ventilated using passive vents and natural 

air flow.

Add the Right Kind 

of Insulation 

When adding additional insulation, you do 

not have to use the same type of insulation 

that currently exists in your attic. You 

can add loose fill on top of fiberglass 

batts or blankets, and vice-versa. If you 

use fiberglass over loose fill, make sure 

the fiberglass batt has no paper or foil 

backing; it needs to be “unfaced.” If you 

choose to add loose fill, it may be wise 

to hire a professional, as the application 

requires the use of a blowing machine, 

although some home improvement stores 

offer rentals of this machine. 

Use a blowing machine to blow in loose 

fill insulation.

Photo courtesy of Green Fiber

ADDING ATTIC INSULATION
4.3 ADDING ATTIC INSULATION

1. LAY FIBERGLASS ROLLS

Layer fiberglass roll insulation perpendicular 

to the joists.

Photo courtesy North American Insulation

Manufacturers Association

2. CREATE A BARRIER

Use sheet metal or wire mesh to help create a 

barrier around fixtures or vents.

Doing the Job 

Laying fiberglass rolls is easiest for a DIY job. If you have any type of insulation between 

the rafters, install the second layer over and perpendicular to the first (again, the second 

layer of roll insulation should be unfaced– with no vapor retarder). This will help cover 

the tops of the joists and reduce heat loss or gain through the frame. Also, when laying 

down additional insulation, work from the perimeter toward the attic opening. Never lay 

insulation over recessed light fixtures or soffit vents. Keep all insulation at least 3 inches 

away from “can” lights, unless they are rated IC (Insulated Ceiling). If you are using loose 

fill insulation, use sheet metal to create barriers around the openings. If using fiberglass, 

wire mesh can be used to create a barrier.
4.4 ADDING ATTIC INSULATION

3. PLACE RAFTER VENTS

Place rafter vents in between the rafters where

the ceiling meets the floor.

4. ADD INSULATION

Add insulation around the rafter vent and out to 

the edge of the attic floor.

Installing Rafter Vents 

To completely cover your attic floor with insulation out to the eaves you need to install 

rafter vents (also called insulation baffles). Complete coverage of the attic floor along 

with sealing air leaks will ensure you get the best performance from your insulation. 

Rafter vents ensure the soffit vents are clear and there is a channel for outside air to 

move into the attic at the soffits and out through the gable or ridge vent (see Attic Air 

Flow graphic on Page 4.5).

To install the rafter vents, staple them directly to the roof decking. Rafter vents come 

in 4-foot lengths and 14-1/2 and 22-1/2 inch widths for different rafter spacings. 

Rafter vents should be placed in your attic ceiling in between the rafters at the point 

where your attic ceiling meets your attic floor. Once they are in place, you can then 

place the batts or blankets, or blow insulation, right out to the very edge of the attic 

floor. Note: Blown insulation may require an additional block to prevent insulation from 

being blown into the soffit (see Page 4.5). A piece of rigid foam board placed on the outer 

edge of the top plate works very well for this.

Photo courtesy of Doug Anderson Photo courtesy of Doug Anderson

ADDING ATTIC INSULATION
4.5 ADDING ATTIC INSULATION

RAFTER VENT

SOFFIT VENT

RIDGE VENT

NOTE: Gable vent not 

shown in this diagram.

A

B

C

Attic Air Flow 

The outside air flows through the soffit, 

along the rafter vent and out through 

the gable or ridge vent. A

B

C

ILLUSTRATION ©FAMILY HANDYMAN MAGAZINE

GLOSSARY

ENERGY STAR – ENERGY STAR is a government-backed 

program helping businesses and individuals protect the 

environment through superior energy efficiency. To learn 

more about the wide variety of energy-efficient ENERGY STAR

products and processes visit http://www.energystar.gov. 

Seal and Insulate with ENERGY STAR – A process 

recommended by the ENERGY STAR Program for improving 

the envelope of a home to make it more comfortable and 

energy-efficient. The process includes sealing air leaks and 

adding insulation where cost-effective.

Air Duct – A hollow conduit or tube (square or round) that 

circulates air from a forced-air heating and/or cooling system 

to a room (supply duct) or returns air back to the main system 

from a room (return duct). 

Air Leak – A hole, crack, or gap where air can leak in or 

out of a house. Air leaks can make a home feel drafty or 

uncomfortable and waste energy (See Page 1.3).

Gable Vent – A screened vent installed at or near the peak of 

a roof gable that allows warm attic air to escape.

Insulation – A material that is designed to slow down the flow 

of heat in or out of a building structure.

Joist – A beam used to support floors or roofs (See Page 3.2).

Kneewall – A short wall in a room with a sloped ceiling. It is 

usually formed when the room ceiling follows the roof line of 

a house (See Page 1.3).

Rafter Vent – A vent leading from the soffit into the attic 

through the space between the attic rafters. This vent allows 

air to correctly flow past insulation into the attic space (See 

Pages 4.4 or 4.5).

Recessed “Can” Light – A metal light fixture (or can) that is 

in-set into the ceiling. These fixtures can be a big source of air 

leaks when installed in the upper floor of a home (See Pages 

1.6 and 4.3).

Ridge Vent – A screened vent installed along the top ridge of a 

roof that allows warm attic air to escape (See Page 4.5).

Sill Plate – A wood plank that lays flat on top of a concrete or 

masonry foundation or wall that supports a floor or ceiling joist 

(See Page 3.2).

Soffit – The underside of a building overhang, beam, or arch, 

especially the underside of a stair or roof overhang (See 

Page 4.5).

Soffit Vent – A screened vent in a house soffit that allows air 

to flow into the attic or the space below the roof sheathing. 

This helps keep the attic cool in the summer and allows 

moisture in the attic to evaporate (See Page 4.5).

For additional information on Indoor Air Quality (IAQ) issues related to homes such as combustion safety, 

indoor air contaminants, and proper ventilation, visit: http://www.epa.gov/iaq/homes/hip-front.html.