Windows for New Home Construction
Energy efficient windows are an essential element in a well constructed house. The typical home loses over 25% of its heat through windows. Since even modern windows insulate less than a wall, in general an energy-efficient home in heating dominated climates should have few windows on the north, east, and west exposures. A rule-of-thumb is that window area should not exceed 8-9% of the floor area, unless your designer is experienced in passive solar techniques.
Window Design for Passive Solar Heat
If your designer is experienced in passive solar techniques, then increasing window area on the southern side of the house to about 12% of the floor area is recommended. This will allow you to harvest free solar heating during the extended cool periods of the year.
In heating dominated climates you can offset the solar heat gain during the warmer months by utilizing curtains and window blinds.
Planning Windows for Hot Climates
In cooling dominated climates, its important to select east, west, and south facing windows with low solar heat gain coefficients (these block solar heat gain). A properly designed roof overhang for south-facing windows is important to avoid overheating in the summer in most areas of the continental United States. At the very least, Energy Star rated windows or their equivalents, should be specified according to the Energy Star regional climatic guidelines.
Choosing the Most Energy Efficient Windows
In general, the best sealing windows are awning and casement styles since these often close tighter than sliding types. Pay close attention to the felting on sliding windows as this will be the primary defense against air infiltration.
Metal window frames should be avoided, especially in cold climates. Steel and aluminum windows conduct heat through the frames and reduce efficiency by as much as 38% over vinyl or wood framed windows.
During installation, always seal the wall air/vapor diffusion retarder tightly around the edges of the window frame to prevent air and water vapor from entering the wall cavities.
