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Chances are, your ceiling has the equivalent of a 2-ft.-square hole that’s acting like a chimney, drafting expensive heated air into your attic and sucking cold air in around your windows and doors. You can’t see the hole because it’s the sum of many smaller openings. These gaps around plumbing pipes, light fixtures, chimneys and other attic bypasses are hidden under your insulation.
For less than $100 in materials and a day’s labor, you can save lots of money on heating every year by sealing these holes. We’ll show you where to find the bypasses in your attic and simple techniques for plugging and sealing them.
Sure, it’s dusty, dirty work, but it’s the quickest,
cheapest way to save money on your energy bills
You’ll find everything you need at a full-service hardware store, home center or lumberyard. If you can’t find the reflective foil insulation (image #3 below), substitute drywall or pieces cut from 4 x 8-ft. sheets of rigid foil-faced insulation. Fitting rigid material requires more precise measuring, but the result is the same.
1. Get your bearings from below
Before you crawl into the attic, make a quick sketch of the floor plan. Make note of dropped soffits over kitchen cabinets or bath vanities, slanted ceilings over stairways, and any other dropped-ceiling areas. These areas usually have open stud cavities leading directly into the attic that are huge sources of air leaks (#1 - 3). Locate the main plumbing stack, furnace flue or chimney and note this on your sketch for a reference point once you get into the attic.
___ A: Common attic air Leaks
2. Pressurize your house
Before you crawl into the attic, place a box fan in a window so it’s blowing air into the house and close all the remaining windows and doors. Tape cardboard around the fan to cover large gaps. When you turn the fan on high, the house will be pressurized, like an inflated bal loon. and just as you can feel the air from a leaky bal loon, you’ll be able to confirm leaks in the attic by feeling the draft with your hand. You may even be able to locate bypasses visually by looking for insulation being blown about. Close the attic access door or hatch behind you to maximize the effect.
Gather your supplies and suit up. Attics are miserable places to work. Be sure to read the tips on below before you start.
3. Plug the big holes first
It’s tempting to grab a can of expanding foam and squirt it into all the little holes, but your biggest savings will come from plugging the large holes. Find the plumbing stack or flue for a reference point. Then use your sketch to locate the soffits, stairwells or other dropped-ceiling areas. You’ll probably have to dig around in the insulation to uncover them. Soffits may be filled with insulation or covered with cardboard or fiberglass batts. Push back the insulation and scoop it out of the soffits. Now plug the open stud spaces (Images 1 and 2) and seal the top of the cavities with reflective foil (# 3). Cover the area with insulation again when you’re done.
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. Cut a 16-in.-long piece from a batt of unfaced fiberglass
insulation and fold it at 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 form a tight
fit in the cavity.
3. 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 in place.
4 Stuffed bags seal joist spaces too
Heated rooms built into attics often have open cavities in the floor framing under the walls. Even though insulation may be piled against or stuffed into these spaces, they can still leak air. Image 4 shows how to stuff these spaces with the same type of garbage-bag plug we used to seal stud cavities.
4. plug all open joist spaces under insulated side
walls. Cut a 24-in.-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 joist space under the wall.
The opening around a furnace or water heater flue is a major source of warm air into the attic (Image 5. Furnace flues require special techniques
Because the pipe gets hot, building codes require 1 in. of clearance from Class B flues (2 in. from masonry chimneys) to any combustible material, including insulation. Images 5 and 6 show how to seal this gap with lightweight aluminum flashing and special high-temperature silicone caulk ($12 per tube). Before you push the insulation back into place, build a metal dam (Image 7) to keep it away from the pipe. Use this same technique for masonry chimneys.
5. Cut aluminum flashing to fit around the flue. For
round flues like ours, cut half circles out of two pieces so they overlap
about 3 in. in the middle. Press the flashing metal into a bead of
latex caulk and staple it into place. If there’s no wood, staple it
right to the drywall.
6. SEAL the gap between the flue and metal flashing
with special high-temperature silicone caulk. Don’t use spray foam
here.
7. 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 in. Cut slots 1 in. deep and a few inches apart
along the top and bend the tabs in. Cut slots about 2 in. deep along
the bottom and bend out the tabs. Wrap the dam around the flue and secure the bottom by stapling through the tabs.Warning: Insulation
must be kept 1 in. away from class B flues.
6. Use foam and caulk to seal small holes
Seal openings around plumbing vents and electrical wires with expanding foam (images 8 and 9). Be careful, though; this stuff is super sticky and almost impossible to get off your clothes and skin. Wear disposable gloves and eye protection. Seal around electrical boxes with caulk (image 9).
8. STUFF a small piece of fiberglass ball 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 with expanding foam insulation.
9 FILL wiring and plumbing holes with expanding foam. Caulk
around electrical junction boxes and fill holes in the box with caulk.
TIP: Telltale signs— finding attic bypasses:
Even though most of the gaps spilling warm air into your attic are buried
in insulation, you’ll still see evidence of the escaping air. While in
your attic, look for areas where the insulation is darkened (see image),
a result of filtering dusty air from the house. In cold weather you may
see frosty areas in the insulation caused by warm, moist air condensing and freezing as it hits the cold attic air. In warmer weather, you’ll
find water staining in these same areas. If you pressurize the house
with a window fan (see “Pressurize your house” elsewhere on this site),
you may be able to feel the leaks with your hand as the air finds its
way into the attic.
Materials checklist:
- Roll of reflective foil insulation
- Bundle or roll of unfaced fiberglass batt insulation
- Acrylic latex caulk
- Special high-temperature silicone caulk
- Roll of 14-in.-wide aluminum flashing
- Roll of 13-gallon plastic garbage bags
- Can of expanding spray foam insulation
Tips for working in the attic:
- Start in the morning when it’s cool. Pick a cool, cloudy day if possible. Don’t spend more than 15 or 20 minutes in a hot attic.
- Wear a lightweight disposable coverall (available in paint departments), gloves and a hat to keep itchy insulation off your clothes and skin.
- Always wear a double-strap dust mask or an OSHA approved particulate respirator.
- Wear knee pads if you have them. Crawling around on joists gets painful. Use scraps of plywood to kneel on and as a platform for your supplies.
- Buy a rough-service light-bulb ($2.50) and a clamp-on light ($6), both available at hardware stores. Have a flashlight handy just in case.
- Minimize trips in and out of the attic by collecting all of your tools and supplies and placing them in the attic before you go up.
- Look out where you step. You must walk on ceiling joists or truss chords and carry a small piece of ply wood to work from. Don’t step on the ceiling drywall.
10. 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.
11. ATTACH hook-and-eye fasteners to the door and stops. Position the eyes so that the weatherstrip is compressed when you latch the hooks.
7. Complete the job by sealing the hatch
When you’re done sealing your attic bypasses, push the insulation back into place with an old broom handle or stick as you back out of the attic. Then finish up by sealing the access hatch with self-sticking foam weatherstrip (image 10 and 11). If your hatch rests directly on the moldings like ours did, add 2-1/2-in.-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.
Check for backdrafting
Whenever you make energy improvements—like sealing attic bypasses—that result in a tighter house, install carbon monoxide (CO) alarms if you don’t already have them.
Allow one per floor. Also have a pro check your combustion appliances for backdrafting at the next servicing.
Recessed can lights— no easy solution
Cut a 6-in, hole in your ceiling and add a 100-watt bulb—enough heat to bake cookies—and you have a recipe for dams. That’s what a recessed light does. Here are the huge heat loss as well as a major contributor to ice solutions we recommend if you have recessed can lights protruding into your attic:
• Replace incandescent bulbs with cooler-operating compact fluorescent bulbs.
• Replace your old recessed lights with new airtight models available at some home centers and lighting stores. This is the best solution for those with electrical skills. New cans are relatively inexpensive—about $20 apiece plus decorative trim and bulb—and can usually be installed in a few hours each.
Energy-Saving Goof: Insulation surprise attack
After moving into our new/old house, I decided to add 6 in. of insulation to our attic. Our attic is accessed through a small closet (36 x 30 in.) with a 30 x 14-in. opening at the top. I figured the best way to insulate the attic and keep the mess of fiberglass insulation out of the house would be to squeeze the tightly packaged rolls through the closet opening and I open them in the attic.
Intending to pull them up after me, I climbed into the attic and proceeded to pull on the first roll of insulation. I found out very quickly that it wasn’t going to fit. So rather than getting down from the attic, I decided to reach down and cut the plastic wrapping with the roll sitting on the closet shelf and pull up the pieces individually.
The roll exploded open and engulfed the small closet with insulation, leaving me trapped in the attic. (Attics sure are quiet and HOT.) The insulation was so tightly bound in the closet that I couldn’t push it out of the closet or pull it up. I finally had to use a utility knife to cut the insulation into smaller pieces so I could make my itchy, scratchy escape!
Next: Heating Season