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Air Leakage In Homes - Part 3

Attic Air Remediation

Figure 1 indicates the most common areas of air leakage in an attic:

  • Plumbing stacks
  • Ductwork cutouts
  • Balloon framing
  • Top wall plates
  • Recessed light fixtures
  • Drop ceilings
  • Attic access
  • Chimney chase

Follow the numbers, in the circles, for proper air remediation sealing of the designated problem area in the attic of your home.

Areas of attic air leakage in a home
Figure 1 - Areas of attic air leakage in a home

When sealing around plumbing stacks the sealing material used must be able to expand and contract, because the plumbing stack does exactly that as the hot water is run in your home. When the plumbing stack was installed a rubber or vinyl boot should have been slipped over the pipe to seal the transmission of air between floors, as shown in Figure 4. If a rubber boot is not present you can create the same sealing by clamping or taping polyethylene to the stack and stapling or taping it to the floor in the attic.

sealing around attic plumbing stacks
Figure 4 - Sealing around plumbing stacks in the attic
Sealing around ductwork cutouts in attic
Figure 5 - Sealing around ductwork cutouts in attic

Wherever ductwork moves from one floor to another there will be spaces between the ductwork and the floor in the attic, as shown in Figure 5.

The space between the ductwork will determine the product required to seal the gap. A gap of less than 3/8 inch can be sealed using caulk.

A gap larger than 3/8 inch can be sealed using expanding foam This applies to all ducts including those from vent fans in bathrooms, vent hoods in kitchens and your primary forced air HVAC system.

Balloon framing is not allowed, in most jurisdictions, under most building codes. However it was very common a number of years ago and homeowners doing air remediation on older homes may experience this type of construction, as shown in Figure 6.

Sealing air leakage around balloon framing
Figure 6 - Sealing air leakage around balloon framing
Sealing air leakage through top wall plate
Figure 7 - Sealing air leakage through top wall plate

To seal the gap in balloon framed construction use heavy duty cardboard stapled against the floor joists or as an alternative you can use fiberglass insulation placed in plastic bags and pushed in between the floor joists.

Any mechanical, electrical or plumbing materials that rise from the lower floor and into the attic will do so through a hole in the top plate of a wall, as shown in Figure 7.

These holes, depending on size, are easiest filled with expanding foam or an appropriate caulk. In some cases there may also be an air gap between the drywall installed on the ceilings where it butts up against the wall drywall. These gaps, if they exist should also be sealed with caulk.

Note: Recessed light fixtures that are not identified as IC (insulated ceiling) cannot and should not be sealed. Sealing, building a box around or placing insulating in contact with a non IC light fixture can create a fire hazard!

Additional information on: Insulating recessed ceiling light fixtures

You can now purchase recessed light fixtures that are airtight and replacing current non airtight fixtures with new units is the best solution to the problem. If that is not within the homeowners budget, an alternative is to replace the current trim with an airtight trim. As a final alternative seal the gap between the fixture and the attic flooring using an appropriate caulk or expanding foam as shown in Figure 8.

Sealing air leakage around recessed light fixtures
Figure 8 - Sealing air leakage around recessed light fixtures
insulating and sealing drop ceilings
Figure 9 - Insulating and sealing drop ceilings

If you have drop ceilings, in bathrooms and/or soffits in other rooms of the home the best method to seal them is to seal the attic floor above them, as shown in Figure 9.

Use materials such as plywood, drywall or polyethylene sheets to create a floor and then insulate the floor using batts, blankets, or loose fill insulation.

Sealing all the smaller holes to prevent attic to living quarter air leakage has little value if you do not seal the biggest entry point of all. That being, the attic access door, Figure 10. There are 4 things to be done:

  1. Where the frame around the hatch meets with the ceiling plaster or drywall should be caulked.
  2. You should install a foam weather strip around the edge of the hinged access door.
  3. Install a latch that draws the access door tight to its frame, as shown in Figure 11. A good choice is the same style of latching devices used on double hung windows.
  4. Apply a layer of foam or fiberglass insulation to the attic access door.
  5. Additional information on: Insulating the attic access.

Sealing air leakage from attic access
Figure 10 - Sealing air leakage from attic access
Attic access door latching mechanism
Figure 11 - Attic access door latching mechanism
attic sealing around chimney chases
Figure 12 - Sealing attic air leakage around chimney chases

The chimney chase general runs the full height of the home, from the basement through the roof. Seldom is it sealed properly by contractors. The best method to seal the chimney chase is to install a metal flashing (do not use wood as the chimney can transmit a lot of heat) around the chimney, as shown in Figure 12.

Nail the metal flashing to the attic floor joists and use an appropriate high temperature caulking compound to seal all the joints.