The IRC and the window replacement industry have not been friendly to each other or to building officials, contractors, and homeowners for quite a long time. Besides the codes that govern installation practices, the reason for this animosity has to do with the four major aspects of code compliance that deal with windows: energy conservation, safety glazing, fall protection, and emergency escape/rescue. 

For the first two aspects, the requirements for replacement windows in existing framing are the same as those for new windows in new framing. That is, energy codes limit the U-factor and solar-heat-gain coefficient, and if the window is located in one of seven locations deemed “hazardous” by the IRC, then it must be safety glazed, typically...

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