attic air leaks and their sealing

Air leakage paths in our homes are driven by a very simple natural law: warm air rises... That makes the sealing of attic air leaks the best way to prevent heated air to escape from our rooms...

Do not forget: unwanted outdoor air may enter into your home through multiple openings and cracks associated with doors and windows but also with electrical outlets, floor cavities, plumbing connections, basements, rim joists, etc.

Sealing the Attic Hatch with a foam from Dow These sources of air leakage combine with openings in the attic, through air flowing... And when the heated air escapes to outside (mostly via attic air leaks), outside air is pulled into the living rooms through other air leaks located in lower parts of the house.

That's why air sealing the attic is so crucial to stop drafts and air flowing, and to increase comfort and energy savings...

Images: Dow Chemical and EERE/Energy Star/DOE

where to look for attic air leaks

When sealing the attic, take into account the many possible sources of attic air leaks:

- Holes in the attic floor associated with pipes, wires, vents and ducts. Seal them using a proper caulk or foam. Larger holes may demand a filler material (drywall, plywood...). See: Caulking Electric...

- Fireplace and chimney openings connecting with the attic. See: Chimney and Fireplace Caulking

- Knee walls, hatches and doors associated to the attic; attic exterior and interior walls and joints: caulk along the tops of these walls, where the top plates meet drywall or plaster. See: Sealing Exterior Walls

- Chase: see if there is a chase for pipes and plumbing running inside your walls up to the attic (the chase often runs from the basement to the attic, with a opening at each floor). The chase should be properly sealed with expanding foam - often the best material and the easiest to use - but in case of very large chases you may have to use rigid foam or drywall to fill the openings, and caulk or air sealing foams on the edges.

- Dropped ceilings; see: Dropped Ceilings Sealing

Attic Air sealing materials

Caulks and Foams

General purpose air sealing foams and caulks may solve most attic air leakage problems, but in some cases you will need special materials: non-flammable caulks (for air leaks associated with chimneys or electrical fixtures...), very elastic caulks (to respond to wide variations in temperatures), or expanding foams (large openings...).

Penetrations and holes associated with recessed lighting fixtures, plumbing connections or chimneys also demand specific sealing materials, namely temperature and fire-resistant products.

See: Caulking materials and Applying Caulks

Air barriers

To protect the attic walls, or the attic floor and ceiling from air leakage, you should use another type of air sealing, often a housewrap or a sheet good...

In some cases (if the type of construction do not need extra structural strength) rigid foam insulation materials - often polyurethane or polystyrene boards - may replace the sheet goods with advantage, since they provide both thermal insulation and air sealing materials...

See: Air and Vapor Barriers

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.

Most insulation 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.

See: Insulation vs. Air sealing materials

Plywood, drywall and other air barriers

Drywall, plywood and other sheathing materials can be effective air barriers. You may use them to seal large attic surfaces with air leakage problems. But, as said before, they may solve air leaking problems but will not provide attic thermal insulation... You will also need to insulate the attic.