The average home has the equivalent
of a 2-ft.-square hole in
the ceiling that allows warm air
to leak out through the attic. That hole is
actually in the form of many smaller
cracks and gaps around lights, plumbing
pipe, chimneys, walls and other ceiling
penetrations. In dollars and cents, this
leakage accounts for anywhere from
one-quarter to one-third of your annual
heating bill! No small change.
Yet for less than $100 in caulk, foam
and other materials available at a hardware
store or home center, plus a day's
labor, you can plug most of those holes
and reduce your heating bill. In this article,
we'll tell you how to find those attic
"bypasses" and how to seal them.
FIGURE A Common attic air leak zones
Click Image to enlarge.
How to find the gaps
Before you crawl into your attic,
make a rough sketch of the floor
plan and the ceiling below the
attic. Sketch in the walls, the
chimney, the main plumbing
stack, ceiling electrical fixtures
and lower sections of ceiling
(soffits; Figure A). They all have
high leak potential, and your
sketch will help you find them
when you're in the attic.
To help generate actual leakage,
place a box fan in a window
so it blows air into the house.
Then close all other windows
and doors. Tape cardboard
around the fan to eliminate large
gaps. When you turn the fan on
high, you'll slightly pressurize
the house, just like an inflated
balloon. Then when you're in
the attic (with the hatch closed),
you can confirm a leaky area by
feeling the air coming through.
You may even spot the insulation
blowing in the breeze.
Another helpful sign is
dirty insulation (photo above).
Insulation fibers filter the
household air as it passes,
leaving a dirt stain that marks
the leaky area.
Now gather up the gap-sealing
materials we show in this story and suit up.
Attics are miserable places to
work in. Be sure to read the
following tips before you start.
Editor's note:
Tips for working
in the attic
I've made almost every mistake
you can make working
in the attic. I've sweated in
110-degree F conditions when
the roof sheathing felt like a
hot radiator, endured itchy skin
after working in short sleeves,
bumped my head many times
and inadvertently stepped
through a ceiling. To avoid
these goofs, do the following:
• Work when it's cool outdoors:
early morning or on
cloudy days in the summer.
• Wear an old long-sleeve
shirt, work pants and a hat
to protect your skin from
insulation irritation. Wash
the clothing or toss it when
you're done.
• Wear a double-strap
face mask or particulate
respirator.
• Use a couple of short 2x6s
or 3/4-in. plywood to kneel
on and hold your supplies.
• Pull a clamp-on light around
with you and carry a flashlight
as well.
• Collect all your materials
and tools and place them in
the attic before you climb
up. Ask a helper to remain
within shouting range in
case you
forget
something.
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.
1. Plug open stud and joist cavities
It's tempting to grab a can of expanding foam and squirt it into all the little holes you can
find. But your biggest savings will come from plugging the big holes. Look for them first.
Open stud cavities are the worst (Photo 1). Look for them around lowered areas of ceilings
(soffits) and where the ceiling height shifts, especially in split-level homes. Pull back insulation
to examine these areas, because the insulation itself doesn't stop the leaks. Plug them
with a plastic bag partially filled with insulation. The plastic bag stops the airflow (Photo 2).
The insulation makes the bag expand tightly to close off gaps.
Use the same method for open joist spaces under floors (Photo 3). You can't get to the
potentially leaky areas under floors, but you can plug the cavity where it leads into the attic.
Click Image to enlarge.
1. Cut a 16-in. length from a batt of unfaced fiberglass insulation and fold it into the
bottom of a 13-gallon plastic garbage bag.
2. Fold the bag over once and stuff it
into the open stud cavity. Make sure
there's enough insulation in the bag to
achieve a tight fit in the cavity.
3. Plug open joist spaces under side walls.
Cut a 24-in. length from a fiberglass
batt and roll it into a garbage bag. Fold the
bag over and stuff it into the joist cavity.
2. Cover open soffits
Builders often put a soffit where they want to put
cabinets or recessed light fixtures, and sometimes
they use soffits to contain heating ducts. Soffits have
a high potential for leakage, especially if they contain
recessed lights. Refer to your sketch and dig
around in the insulation if necessary to find them.
Reflective foil insulation, sometimes called "bubblepack"
insulation, works well as an air barrier for
soffits. It's flexible and only about 1/4 in. thick,
making it easy to cut with a scissors. The photo at
right shows how to install it. You have to clear insulation
from the surrounding wood to get the caulk
to stick. Then cover the foil with insulation when
you're finished. However, don't put insulation within
3 in. of recessed lights unless the fixture is IC
rated (for "insulation contact"). The rating will be
listed on a label inside the recessed can.
Click Image to enlarge.
With a scissors, cut a length of foil insulation about 6 in. longer
than the opening to be covered. Apply a bead of latex caulk around
the opening. Embed the foil in the caulk and staple it into place.
Recessed lights:
No easy
solution
Recessed lighting is a
great lighting technique,
but the cans are notorious
energy-wasters when put
into a ceiling with an attic
above. They usually leak,
and when hot, create a
strong heat draft into the
attic. If you find recessed
lights protruding into your
attic, take these steps:
• Replace incandescent
bulbs with cooler-operating
compact
fluorescent bulbs.
• Replace the old cans
with newer airtight
models. They're available
at home centers
and lighting stores for
$20 to $30 each.
3. Seal around flues
and chimneys
The opening around a furnace or water
heater flue is a major source of warm air leakage
into the attic. Because the pipe gets hot,
building codes require at least a 1-in. clearance
from combustible materials, including
insulation. For masonry chimneys, the minimum
clearance is 2 in. The trick then is to
block airflow with aluminum flashing and
high temperature caulk ($5 to $10). Photos 1
- 3 show you how. Before you push insulation
back into place, build a metal dam to maintain
the required minimum clearance.
Click Image to enlarge.
1. Cut aluminum flashing to fit around the
flue. For round flues, cut half circles out
of two pieces so they overlap about 3 in.
Press the flashing metal into a bead of latex
caulk and staple it to wood or drywall.
2. Seal the gap between the flue and metal
flashing with special high-temperature
silicone caulk. Don't use spray foam here.
3. Form a 16-in.-high dam to keep insulation from contacting the flue.
Cut enough aluminum to wrap around the flue plus 6 in. Cut 1-in.-
deep slots spaced every 2 in. along the top and bend the tabs in. Cut slots
about 2 in. deep along the bottom and bend the tabs out. Wrap the dam
around the flue and secure the bottom by stapling through the tabs.
WARNING: Insulation must be 1 in. from Class B flues.
4. Use foam or caulk
for small gaps
Now concentrate on the small stuff.
Actually it's best to keep your can or
expanding foam and caulk gun handy
and plug the obvious electrical cable
holes and fixture boxes as you move
around working on the bigger air leaks.
Make sure you get to the plumbing vent,
because the gap around it is usually large
(Photo 1). Use your sketch to help find
this and other features. Also look for the
2x4 top plates (framing) of interior walls
and follow them, keeping a sharp eye out
for electrical cable holes and dirty insulation,
which would indicate a gap or long
crack between drywall and a wood plate.
Seal these with caulk.
Work carefully with expanding
foam because it's super sticky and
almost impossible to get off your
clothes and skin. Wear disposable
gloves when working with it.
1. Stuff fiberglass batt insulation into
the space around the plumbing vent
pipe as a backer for the expanding foam.
Then follow the directions on the can
to fill the space around the pipe.
2. Fill wiring and plumbing
holes with expanding foam.
Caulk around electrical junction
boxes and plug holes in the box
with caulk.
5. Weatherstrip hatches and doors
When you're done sealing the attic bypasses, push the insulation back into place with an old
broom handle or a stick as you back out of the attic. Then finish up by sealing the access hatch
with self-sticking foam weatherstrip (Photo 1). You may have to add new wood stops to provide
a better surface for the weatherstrip and enough room for hook-and-eye fasteners (Photo
2). Position the screw eyes so that you slightly compress the weatherstrip when you latch the
hatch. Use a similar procedure if you have a hinged door that leads to the attic.
1. Weatherstrip the attic access hatch or
door. Cut 1x3 stops and nail them on
with 6d finish nails. Apply self-adhesive foam
weatherstrip to the top edge of the stop.
2. Attach hook-and-eye fasteners to the
door and stops. Position the eyes so
that the weatherstrip is compressed when
you latch the hooks.
Check for
backdrafting
If you do a good job, you'll
quickly notice the results.
Your home will feel less
drafty and more snug.
Your heating system will
run less too. But whenever
you tighten your home,
there's less air turnover
and a greater risk of carbon
monoxide poisoning
from a poorly adjusted furnace,
gas water heater or
other combustion appliances.
Test your CO alarm
to make sure it's working
or install one if you don't
have one already. And ask
the furnace pro to check
your furnace and water
heater for backdrafting at
the next regular service
interval. (See "Prevent Carbon Monoxide Poisoning", October 2001.)
