EPA_T0958_DIY_Guide 2006new.indd

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

Home Sealing is one of the most

cost-effective ways to make a

home more comfortable and

energy effi cient – and you can

do it yourself.

Use This Guide To:

1. Learn how to fi nd and seal hidden

attic and basement air leaks

2. Determine if your attic insulation

is adequate, and learn how to

add

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 effi ciency 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

or call

1.888.STAR.YES

(1.888.782.7937).

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

where otherwise noted.

1.1 CONTENTS

1.3 LOCATING AIR LEAKS

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 signifi cant air leaks are

hidden in the attic and basement. These are the leaks that signifi cantly 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 diffi cult because

they are often hidden under your insulation. This guide will help you fi nd these leaks and seal them

with appropriate materials.

Effects of Air Leaks

Heated inside air drawn into the attic

Cold outside air drawn into the house

Behind Kneewalls

Attic Hatch

Wiring Holes

Plumbing Vent

Open Soffi t (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.

If you are not familiar with
some of the terms in this guide,
check our glossary inside the
back cover.

•

Batt or roll of unfaced fi berglass insulation

and large garbage bags (for stuffi ng open

stud cavities behind kneewalls and in

dropped

soffi

ts)

•

Roll of refl ective foil insulation or other blocking

material such as drywall or pieces of rigid foam

insulation to cover soffi ts, 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 fi lling larger gaps (1/4 inch to 3 inches)

•

Special high-temperature (heat-resistant) caulk

to seal around fl ues and chimneys

•

Roll of 14-inch wide aluminum fl ashing to keep

insulation away from the fl ue 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

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 diffi cult to move

around in. The projects recommended in

this guide can usually be completed in a

day or two and will provide benefi ts for

years to come. However, if upon inspection

of your attic you fi nd 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 fl oor

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 soffi ts 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).

■

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 fl ashlight 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

You May Need a Contractor
to Correct These Problems:

■

Wet or damp insulation indicating a

leaky

roof

■

Moldy or rotted attic rafters or fl oor

joists indicating moisture problems

■

Kitchen, bathroom, and clothes

dryer vents that exhaust moist air

directly into the attic space instead

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 fi re 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 fi xtures

(See

Page

2.2)

1.7 SEALING ATTIC AIR LEAKS

1.6 SEALING ATTIC AIR LEAKS

SEALING ATTIC AIR LEAKS

Plug the Big Holes First

Don’t worry about fi nding 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 fl oor, dropped soffi ts (dropped-ceiling areas), and behind or under attic kneewalls.

Look for dirty insulation – this indicates that air is moving through it. Dropped soffi ts may

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

out of the soffi ts. You will place this insulation back over the soffi t once the stud cavities

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

in your open soffi ts, 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

fi berglass 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 fi t

tightly. Plug all open stud spaces, then cover the

soffi t (photo 3, Page 1.7 ).

3. COVER DROPPED SOFFITS

After removing insulation from a dropped soffi t, cut

a length of refl ective 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 fi berglass

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 fl oor 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 fl oor of the fi nished space (photo 4).

Caution: Some attics have vermiculite insulation, which may contain asbestos, a health
hazard. Vermiculite is a lightweight, pea-size, fl aky 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.

16” PIECE OF
FIBERGLASS

BATT

RECESSED
CAN LIGHT

DROPPED

SOFFIT

PLUGGED
STUD CATIVITY

RECESSED

CAN LIGHT

OPEN
STUD CAVITY

REFLECTIVE FOIL
INSULATION

DROPPED

SOFFIT

CAULK OR ADHESIVE

24” BATT
ROLLED INSIDE
GARBAGE BAG

OPEN JOIST

CAVITY

KNEEWALL

1.9 SEALING ATTIC AIR LEAKS

1.8 SEALING ATTIC AIR LEAKS

Furnace Flues Require Special Sealing Techniques

The opening around a furnace or water heater fl ue 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 fl ues (2 inches from masonry chimneys) to any combustible

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

aluminum fl ashing 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 fl ashing to fi t around the fl ue. For

round fl ues, cut half circles out of two pieces so

they overlap about 3 inches in the middle. Press

the fl ashing 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

CAVIT

HIGH-TEMP
CAULK

CLASS B
FURNACE FLUE

6. SEAL WITH SILICONE CAULK

Seal the gap between the fl ue and metal fl ashing

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 fl ue pipe. Cut enough aluminum from

the coil to wrap around the fl ue 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 fl ue 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 fl ashing and high-
temperature silicone caulk

Chimney

Masonry/Metal

Aluminum fl ashing and high-
temperature silicone caulk

Plumbing

Cast Iron or PVC

Expanding foam or caulk,
depending on size of gap

2” TABS

BENT OUT

SEALING ATTIC AIR LEAKS

Caution: Furnace fl ues (the
pipe that removes your furnace
exhaust) can be very hot.

1.11 SEALING ATTIC AIR LEAKS

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 fi nd evidence of these gaps. Look for areas where the insulation

is darkened (see photo 8). This is the result of fi ltering 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 fi nd

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

9. FILL HOLES WITH CAULK

Fill wiring and plumbing holes with expanding foam.

Caulk around electrical junction boxes, and fi ll

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

fi berglass insulation into the space to serve as a

backer for the expanding foam. Once the fi berglass

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

SEALING ATTIC AIR LEAKS

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 effi ciency of your heating and cooling system by 20% and greatly

increase air fl ow.

2.1 ADDITIONAL SOURCES OF AIR LEAKS

1.12 SEALING ATTIC AIR LEAKS

11. WEATHERSTRIP THE DOOR

Weatherstrip the attic access hatch or door. Cut 1x3

boards to fi t the perimeter of the opening and nail

them on with 6d fi nish 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 fi berglass 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

■

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 fl oor.

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 fi rst, 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 metal-

backed (foil) tape

•

Duct insulation material rated at

least

R-6

•

Zip ties to hold duct insulation

in place

•

Gloves, safety glasses, mask,

ashlight

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-fi red 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.

SEALING ATTIC AIR LEAKS

ADDITIONAL SOURCES OF AIR LEAKS

COMPRESSED
WEATHERSTRIP

3.1 SEALING BASEMENT 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-effi cient.

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 fl ow 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

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.

Caution: Keep all insulation 3 inches
from “can” lights, except those rated
IC (insulation contact). You can use
a piece of circular metal fl ashing or
wire mesh around the light as a dam
to keep the insulation away from the
light (see photo 2, Page 4.3).

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

fi xed in portions of the basement that are unfi nished. 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 fl oor 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).

■

Call a Professional to Properly Seal

Recessed lights can be sealed, but it is diffi cult

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 Air-

Tight) 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 qualifi ed recessed fi xtures

that reduce energy use as much as 75%. However,

it’s important to check that any fi xture selected

meets your light output expectations since fi xtures

come with widely varying wattage bulbs and

optics. Also, make sure fi xtures have an ICAT

rating to minimize heat loss.

■

Switch to More Effi cient Bulbs

When keeping existing recessed lights, you

can still reduce lighting energy use as much

as 75% by installing ENERGY STAR qualifi ed

compact fl uorescent light (CFL) bulbs. This

includes CFL bulbs specifi cally designed

for recessed lights with built-in refl ectors

matching the appearance of traditional

incandescent refl ector bulbs. As with new

fi xtures, it is important to make sure any

CFL bulb selected meets your light output

expectations. Also, check the packaging of

the CFL to ensure that it may be used in an

enclosed fi xture. However, switching to CFL

bulbs will not solve the air leakage problem.

SEALING BASEMENT AIR LEAKS

4.1 ADDING ATTIC INSULATION

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 fi ll gaps from 1/4 inch to about

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

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

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

furnace exhaust).

Caution: When sealing the furnace
fl ue (which will be encased in a
metal sleeve) use high-temperature
caulk. Run a bead of high-
temperature 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

ILLUSTRATION BY DALE HOFFMEYER

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 fi berglass batts. If using batts, just cut the insulation to fi t 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 fi nishing the basement, when you would

insulate the basement walls fl oor-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 fl oor joists (i.e., you can easily see your joists), you should

add more. If you cannot see any of the fl oor 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 effi ciency of your home.

How Much Should I Add?

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

to resist heat fl ow. 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.

RIM JOIST

SUB FLOOR

SILL PLATE

FOUNDATION

FLOOR
JOIST

LONG RIM JOIST

SEALING BASEMENT AIR LEAKS

ADDING ATTIC INSULATION

4.3 ADDING ATTIC INSULATION

4.2 ADDING ATTIC INSULATION

A Note about Natural
Attic Ventilation

At fi rst 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-effi cient home. Here’s why: in the

winter, allowing a natural fl ow 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 fl ow 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 fl ow of air at the eaves. NEVER COVER

ATTIC SOFFIT VENTS WITH INSULATION – use rafter

vents and soffi t vents to maintain airfl ow (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 (soffi t and gable)

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

has blocked soffi t 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 unfi nished 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 fl ow.

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 fi ll on top of fi berglass

batts or blankets, and vice-versa. If you

use fi berglass over loose fi ll, make sure

the fi berglass batt has no paper or foil

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

choose to add loose fi ll, 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

fi ll insulation.

Photo courtesy of Green Fiber

1. LAY FIBERGLASS ROLLS

Layer fi berglass 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 fi xtures or vents.

Doing the Job

Laying fi berglass 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 fi rst (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 fi xtures or soffi t vents. Keep all insulation at least 3 inches

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

fi ll insulation, use sheet metal to create barriers around the openings. If using fi berglass,

wire mesh can be used to create a barrier.

ADDING ATTIC INSULATION

4.5 ADDING ATTIC INSULATION

4.4 ADDING ATTIC INSULATION

3. PLACE RAFTER VENTS

Place rafter vents in between the rafters where

the ceiling meets the fl oor.

4. ADD INSULATION

Add insulation around the rafter vent and out to

the edge of the attic fl oor.

Installing Rafter Vents

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

rafter vents (also called insulation baffl es). Complete coverage of the attic fl oor along

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

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

move into the attic at the soffi ts 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 fl oor. 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

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

being blown into the soffi t (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

RAFTER VENT

SOFFIT VENT

RIDGE VENT

NOTE: Gable vent not
shown in this diagram.

Attic Air Flow

The outside air fl ows through the soffi t,
along the rafter vent and out through
the gable or ridge vent.

GLOSSARY

ENERGY STAR

– ENERGY STAR is a government-backed

program helping businesses and individuals protect the

environment through superior energy effi ciency. To learn

more about the wide variety of energy-effi cient ENERGY STAR

products and processes visit

http://www.energystar.gov.

ENERGY STAR Home Sealing

– A process recommended by

the ENERGY STAR Program for improving the envelope of

a home to make it more comfortable and energy-effi cient.

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 fl ow

of heat in or out of a building structure.

Joist

– A beam used to support fl oors 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 soffi t into the attic

through the space between the attic rafters. This vent allows

air to correctly fl ow past insulation into the attic space (See

Pages 4.4 or 4.5).

Recessed “Can” Light

– A metal light fi xture (or can) that is

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

leaks when installed in the upper fl oor 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 fl at on top of a concrete or

masonry foundation or wall that supports a fl oor or ceiling joist

(See Page 3.2).

Soffi t

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

especially the underside of a stair or roof overhang (See

Page 4.5).

Soffi t Vent

– A screened vent in a house soffi t that allows air

to fl ow 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).

ADDING ATTIC INSULATION

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.