A Do-It-Yourself Guide to Sealing and Insulating

Sealing and Insulating are often the most cost-effective ways to make a home more comfortable and energy efficient — and you can do it yourself with a little guidance.

You will be able to 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

Getting Started: 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.

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. 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.

  • 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

  • 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

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.

But locating leaks can be difficult because they are often hidden under your insulation. 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.

Common Household Air Leaks

  • Behind Kneewalls

  • Attic Hatch

  • Wiring Holes

  • Plumbing Vent

  • Open Soffit (the box that hides the recessed lights)

  • Recessed Light

  • Furnace Flue or Duct Chaseway (the hollow box or wall feature that hides ducts)

  • Basement Rim Joists (where the foundation meets the wood framing)

  • Windows and Doors

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.

Sealing Attic Air Leaks

Tips for Working in the Attic

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!

Materials Checklist for Sealing Attic Air Leaks

  • 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

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.

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.

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.

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.

These gaps should be sealed with lightweight aluminum flashing and special high-temperature (heat-resistant) caulk. Before you push the insulation back into place, build a metal dam to keep it away from the pipe. Use the same technique for masonry chimneys.

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

Identifying Attic Pipes


Flues/Vents/Pipes Made Out Of Seal Around With
Furnace/Water Heater Galvanized Metal Aluminum flashing and high-temperature silicon caulk
Chimney Masonry/Metal Aluminum flashing and high-temperature silicon caulk
Plumbing Cast Iron or PVC Expanding foam or caulk, depending on the size of the gap

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. 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.

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

Complete the Job by Sealing the Attic Hatch or Door

Finish up by sealing the access hatch with self-sticking weather stripping. 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.

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 and into the attic through leaks, cold outside air gets drawn in through basement leaks to replace the displaced air. 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.

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).

Materials Checklist for Basement Sealing

  • Silicone or acrylic latex caulk and caulk gun

  • Expanding spray foam
Caution: When sealing the furnace flue (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.

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

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 it 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.


More information, including many pictures, is available in this Energy Star Do-It-Yourself Insulating Guide. [PDF 2.1MB]

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