It’s not only insulation and HVAC contractors who are inadvertently sabotaging our houses. Framers often construct large holes that extend from the basement to the attic in the form of chimney, plumbing, and duct chases. These chases are hidden behind drywall or are covered by fiberglass-batt insulation. But insulation alone won’t prevent conditioned interior air from escaping. Big holes should be sealed with plywood, rigid foam, or drywall and caulk or spray foam.
Kneewalls and rim joists are two more often-missed ex-
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amples. Think of them as long holes in a house. Kneewalls are the short walls found in finished attics and in bonus rooms above the garage. Insulation is usually put in the kneewall and under the floorboards, but this insulation doesn’t keep a room warm unless you block each
joist cavity or, better yet, insulate under the roof deck (see p. 16).
Rim joists also have multiple holes cut in them for dryer vents and outdoor water faucets. Rim joists are best sealed when the house is built. The top and bottom edges should be sealed with construction adhesive during framing and insulated with spray foam afterward.
Architectural Massing Can Often Mean Massive Leaking
Architects use features such as cantilevers and wraparound porches to break up the massing of a mundane facade. I have nothing against great-looking houses, but these architecturally interesting details can create giant energy nosebleeds.
Insulation and air-barrier details are often missed in cantilevered areas. The underside of a cantilever should be covered with solid sheathing (caulked in place) before finish materials are installed. Roof and wall sheathing is frequently left off below intersecting porch and garage roofs. The spaces below these roofs often connect to vented attics; they are just big air vents to the outdoors. Fancy details like tray ceilings and curved walls also can create big holes that open to attics.
Great-looking houses should also perform well. Architects should draw a line between inside and out on the blueprints, and make sure the house is built that way.
