Most wall air leakage involves the wall’s discontinuities, joints, and irregularities.
5.1.1 Built-In Cabinets/Shelves
Built-in cabinets and shelves are a feature of older homes and present challenges for air sealing. Sealing these areas from inside the cabinet requires care and attention to appearances.
ü If possible, establish both an air barrier and insulation behind the cabinet, out of sight of the occupants.
ü Install drywall or wood wherever the cabinet is open to a wall cavity after insulating the cavity.
ü Use caulking that is compatible with the colors of the surrounding wood if you seal its interior-facing side.
5.1.2 Wall Framing Around Fireplaces and Chimneys
Leaks around fireplace chimneys are often severe air leaks. Use this procedure to seal air leaks through the chimney chase.
ü Cut sheet metal to fit the gap that borders the chimney with overlaps connecting to nearby framing lumber.
ü Bed the sheet metal air seal in sealant, and then fasten the sheet metal to the framing with staples, nails, or screws.
ü Seal the metal patch to chimney or flue with a non-combustible sealant.
ü For large chimney chases, cover the chase opening with structural material such as plywood. Maintain clearances between the structural seal and the metal or masonry chimney as listed in “Clearances to Combustibles for Common Chimneys” on page 277.
When located on the second floor, cap the top of the entire wall cavity in the attic with rigid board, caulked and mechanically fastened.
5.1.4 Cooling Appliances Installed through Walls or Windows
Room air conditioners, room heat pumps, and evaporative coolers are sometimes installed through walls or in windows. The units installed in windows are often very leaky because of the temporary nature of the air seals.
• Remove window units in the fall and re-install in the spring.
• If the client doesn’t want to remove the unit seasonally, cover the unit with a room-air-conditioner cover as shown here.
• Units installed through walls should have a sheet-metal sleeve that seals well to the surrounding framing and finish. This metal sleeve provides a smooth surface to seal to the room air conditioner or heat pump.
• Seal the unit’s perimeter with one-part foam or caulking, depending on the width of the joint.
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SWS Detail: 3.1001.3 Walls Open to Attic—Balloon Framing and Double Walls |
Balloon framed two-story walls are common in older homes. Some modern homes have balloon framed gable walls, where the studs rise above the level of the ceiling joists and are cut at an angle to frame the gable. Even when these balloon framed gable walls are full of insulation, air can convect through the insulation. On occasion, windstorms have blown the insulation out of the wall cavity into the attic.
ü Dense-pack insulation into the wall cavities to reduce air leakage and convection.
ü Dense-pack insulation into an air-permeable bag inserted with the fill tube into the balloon-wall floor cavity.
ü Seal stud cavities from the attic, basement, or crawl space with an insulation plug, covered with a 2-part foam air seal.
ü Or seal the tops and bottoms of cavities with a rigid barrier, such as drywall or plywood, sealed and bonded to surrounding materials 2-part foam.
See also "Wall Insulation" on page 156.
