Windows in Short

I recently started doing a Green Building question and answer "advertorial" series for a local newspaper and sponsors. It's already clear with the first round of solicited consumer questions that many people want the answers to green building questions to be as black and white as the newsprint. Sorry, it just doesn't happen that way.

I thought it would be good to repost the questions and the answer here. Believe me I also realize that it saves me a tremendous amount of time and with just a little cut and paste I have posts in two places. Efficiency at its' best!


Question: I am going to do a large addition to my home. What the best window is to use? From F.N., Missoula, MT.

John: The simple answer to the question is to use the best and most efficient window that your budget will allow. All windows are rated for energy performance by the National Fenestration Rating Council (NFRC.) They are rated in five different categories, but the U-value (the amount of heat loss through the window) and Air Leakage rating numbers mean the most to me. A window with a low U-Value (The current minimum for Energy Star and also available tax credits is .35 and the lower the better here.) and also a low Air leakage rate will keep the warm air in and the cold air out in the winter, and the reverse in the summer.

Windows with low U-value and low air leakage rates are available from a number of quality manufacturers in several types; wood clad, vinyl and other composites and all can perform very well. Once you’ve identified a window type and several manufacturers within your budget, ensure that the window you select has Low-E reflective coating to keep winter heat in, durable construction and hardware, and that the manufacturer has a solid warranty backing their window.

After selecting the best window that you can within your budget, it is equally important to make sure that the window is installed properly. For greatest efficiency and moisture protection, the window needs to have proper flashing and a good air sealant on the exterior and adequate insulation around the interior of the window. Following these simple guidelines will give you the best performance and most return on your investment no matter which type or brand of high performance window you choose.