attic air sealing

Since air leakage paths are driven by the fact that warm air rises, the attic is the best place to prevent heated air to escape.

Do not forget: unwanted outdoor air may enter into home through multiple openings and cracks related with doors and windows but also with electrical outlets, recessed lighting fixtures, attic pull-down stairs, false ceilings (bathroom and kitchen soffits), surrounds of bath tubs and shower stalls, floor cavities, plumbing connections, etc. And some of these cracks and openings are directly present in the attic, or are associated with the attic through air flowing... And when the heated air escapes to outside, that will pull outside air into the living rooms

What to air seal in the attic

Attic Air Leaks When sealing the attic, take into account…

- Holes in the attic floor: seal all holes associated with pipes, wires, vents and ducts with a proper caulk or foam. Larger holes may demand a filler material (drywall, wood...)

- Knee walls, hatches and doors to the attic: See: Knee Walls Air Sealing.

- Channel for plumbing stacks: see if there is a chase for pipes and plumbing running inside your walls (the chase often runs from the basement to the attic, with a opening at each floor). Seal it with expanding foam. That’s the best and easiest solution, though in some very large channels you may have to use rigid foam or drywall to fill them (besides foams or caulk around the edges).

- Fireplace and chimney; see: Fireplaces and Chimney Openings Sealing

- Attic exterior and interior walls and joints: caulk along the tops of these walls, where the top plates meet drywall or plaster.

- Dropping ceilings; see: Air Sealing Soffits/Dropping Ceilings

What materials to use?

Caulks and Foams

If you just want to air seal the holes, cracks and penetrations of the attic, then you just have to use proper caulks and foams.

General purpose foams and caulks may respond to most situations, but in some cases you will need non-flammable materials (chimneys, electrical devices...), very elastic ones (to respond to oscillation in temperatures), or expanding foams (large openings...).

Penetrations and holes, associated with electrical outlets, recessed lighting fixtures, plumbing connections or chimneys demand specific sealing works and materials.

See: Caulking materials and Applying Caulks

Air barriers

To protect the walls, the floor and the ceiling of the attic from air leakage, you should use an air barrier: often common sheet goods (drywall, plywood) or a housewrap. See: Air Barriers and Housewraps.

In some cases (if the type of construction do not need extra structural strength) rigid foam insulation materials - often polyurethane or polystyrene - may replace the sheet goods. In that case you may get both thermal insulation and air sealing.

Insulation & Fiberglass, cellulose, mineral wool

Common attic insulation materials (fiberglass, cellulose, mineral wool...) do not stop attic air leaking. It’s common to find attic insulation materials dirty, in a clear sign that the insulation layer isn’t stopping the air movement.

These materials will not by themselves stop air leaks, and you won’t save as much as you expect if you use them to try to stop air flowing.

Plywood, drywall and other air barriers

Drywall, plywood or other sheathing materials can be effective air barriers. You may use them to seal large attic surfaces with air leakage problems. But, obviously, you will not get thermal insulation: just air sealing...