Windows and Doors
Windows and doors can account for at least 30 percent of the total heat loss (or gain) in a structure. Much of this results from air infiltration through cracks around the windows and doors. This problem can be corrected by installing weather stripping, applying caulking, or installing double-glazed windows, solid wood doors, or doors with built-in insulation.
An exterior door constructed with a core of rigid insulation and faced with metal or acrylic film will have a very low U-value (as low as 0.074). Infiltration heat loss around the edges of the door can be effectively reduced with suitable weather stripping.
A typical 1-in solid wood door will have a U-value of approximately 0.64 (compare this to the U-value for the door described in the preceding paragraph). Doubling the thickness of the door will reduce the U-value to about 0.43. The addition of metal of glass storm doors will further reduce the U-value (0.39 and 0.29, respectively).
Windows with double glazing will have a U-value of 0.58, as compared to 1.13 for single glazing. Double glazing will also reduce noise transmission.