Many homes built in the middle of the 20th century were single-story with a large “expansion attic” above. These areas frequently became finished living space—and were often uninsulated or insulated improperly. Because of the complexity of the framing and the difficulty gaining access to some of the areas that need to be insulated, the story and-a-half can present an insulation and air-sealing challenge. But, considering that so much heat can escape through the top of a building, proper air-sealing and insulating of these structures is essential.
If the attic space has never been framed or finished, insulating and air-sealing can follow the standard practices as if it were new construction. If, however, knee walls and ceilings are in place, special care must be taken to ensure a good result. (Note that the same approaches to sealing and insulating also apply to homes that have an attic above a second floor—a “two-story-and-a-half.”)
What about open ceilings or flat roofs?
Insulating a cathedral ceiling, A-frame house or flat roof is an especially difficult job, because there is little or no space between the ceiling and roof. One option is professional installation of spray-in insulation materials; alternatively, building out of roof rafters to allow additional insulation is also possible. A third option is to have foam insulation applied beneath the roof deck during a re-roofing project. All options must also provide appropriate ventilation to current code.
Knee wall insulation - Attention to detail is critical when insulating and sealing the knee wall area in an expansion attic. Because heat rises, any insulation voids or unsealed cracks will allow large amount of air to escape, reducing thermal performance and increasing energy costs.
Four surfaces must be sealed and insulated
There are four parts to a typical story-and-a-half framing system (along with the vertical gable ends). Each part requires a slightly different approach to provide proper air-sealing and insulation.