Window Specification Guidelines

Window Specification Guidelines
There are three sources of guidance to help in the the window specification guidelines. These should be used after considering the passive solar features that will be included in the house and the impact these have on the window specification guidelines. Shading to be provided by landscaping, overhangs, shutters, etc., should also be considered, especially when focusing on the SHGC needed for the windows.

2000 International Energy Conservation 
As a minimum, windows should be selected in accordance with the 2000 International Energy Conservation Code. The International Energy Conservation Code can be obtained from the International Code Council, 703-931-4533, The U-factor required for a specific climate may be dependent on the window area being installed or the efficiency of other elements of the house depending on the compliance approach chosen. The air leakage rating must be less than 0.3, and the SHGC must be less than 0.4 if the heating-degree days are less than 3,500.

Energy Star®
Energy Star is a federal initiative that helps consumers identify energy-efficient products, including windows specification guidelines. Windows carrying the Energy Star label use less energy than standard products for three major climate regions across the country. All Energy Star windows must carry the NFRC certification label. Information on the Energy Star windows specification guidelines program can be found at The following are the Energy Star window specification guidelines by climate group.

The Efficient Windows Collaborative
The Efficient Windows Collaborative provides information on energy-efficient windows, including recommendations for product selection based on climate and state. Its website ( includes a regionally-designed window selection tutorial to guide consumers through NFRC and Energy Star window criteria. The tutorial includes comparisons of the annual energy performance of various window options for an average 2000-ft house. Additional SHGC recommendations are provided compared with Energy Star criteria, and U-factor criteria are somewhat different for homes located in California.