The floor and foundation are complex structures that can be difficult to air seal. This section describes the most problematic air leakage location in the floor and foundation, and how to seal them.
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SWS Detail: 3.1001.1 Penetrations and Chases, 3.1001.2 Chase Capping |
Seal gaps with expanding foam or caulk. If the gap is too large, stuff it with fiberglass insulation, and spray foam over the top to seal the surface of the plug.
ü Fit large openings with a rigid patch bedded in a sealant like latex caulk or foam tape, which isn’t an adhesive.
ü Screw the patch in place, so that a plumber can remove the screws if necessary for access.
ü Seal holes and gaps around pipes with expanding foam or caulk.
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SWS Detail: 3.1002.1 Interior with Sloped Ceiling, 3.1002.2 Stairwell to Attic—Door at Bottom with No Ceiling Above, 3.1002.3 Stairwell to Attic—Door at Top with Finished Ceiling Above |
A variety of stairways and hatchways provide access from the building to an unconditioned basement.
The following components of these stairways may need air sealing and insulation depending on whether they are at the thermal boundary.
• The risers and treads of the stairways
• The surrounding triangular walls
• Vertical or horizontal doors or hatches
• The framing and sheeting surrounding the doors or hatches
• Sloping ceilings above the stairways
Consider the following air-sealing measures.
ü Study the geometry of the stairway and decide where to establish the air barrier and install the insulation.
ü Weatherstrip around doors and hatches if the door or hatch is at the thermal boundary.
ü Seal the walls, stair-stringer space, and ceiling if they are at the thermal boundary.
ü Seal gaps around door frame or hatch frame perimeters with one-part foam, two-part foam, or caulking.
Discontinuous wall segments can allow heated basement air to circumvent the finished and insulated wall, carrying heat with it. Complete the finished walls or at least install air barriers between finished living area and unconditioned area between the insulated wall and the foundation wall. Here are two suggestions.
ü Bridge the gap with wood sheeting, bedded in sealant, and caulk the crack around four sides of this long narrow patch.
ü Stuff the gap with pieces of fiberglass batt and spray two-part foam over the gap, at least an inch thick.
See also "Basement Insulation" on page 199.
Floors that hang over their lower story are called cantilevered floors. The underside of the overhanging floor can leak considerably. Many balconies and bay windows have cantilevered floors that leak air into a building’s floor cavity.
ü Remove a piece of soffit under the overhanging floor to determine the condition of insulation and air barrier.
ü Stuff the overhanging floor with fiberglass batts or blown fibrous insulation.
ü Bed the sheeting underneath the overhanging floor in sealant where possible. Caulk joints and seams where the sheeting isn’t bedded in sealant.
ü Seal any ducts you find in the cantilevered floor sections.