Raise the Roof?

January/February 2005
A version of this article appears in the January/February 2005 issue of Home Energy Magazine.
Click here to read more articles about Retrofit
January 01, 2005
The King County Housing Authority adds insulation and slope while removing ventilation to make a more energy-efficient and durable roof.
        Across the Northwest, flat roofs top apartment buildings, office complexes, and supermarkets. Cheap and easy to build, flat roofs are the obvious option for boxlike commercial and multifamily buildings. Unfortunately, they can be a bad choice in a cool,wet climate.The problem can be acute in the Northwest, particularly west of the Cascade Mountains, where it usually rains and stays cool from October to July. All that water has a tendency to pool on flat roofs and finds ways to penetrate any roof surface, whether it’s tar, bitumen, rubber, asphalt, or metal.         In addition to the risks from rainwater leaking in, flat roofs in the Northwest are susceptible to risks from other sources of moisture as well. Mandated by most city building codes, attic ventilation can be effective in some climates. Breather vents designed to draw condensation from the attic space to the exterior can do just the opposite in the Northwest, due to high outdoor relative humidity (RH).Humid air and moisture can accumulate in the attic cavity. Condensation occurs when the warm air from a building’s interior meets the relatively cold ...

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