Experienced contractors sometimes tell me that replacement windows are a poor substitute for “real” windows, and that their installation does little more than earn the salesman a quick commission and the installer all kinds of headaches. And it’s true that my company — which specializes in solving rain-related building-envelope problems — has investigated hundreds of leaking retrofit window installations over the past decade or so. But in every case, the problem has been caused by a tradesman who did not understand how to correctly install the window, and not by the window itself.

While there are obviously lots of different types of replacement windows of varying levels of quality, I think that in general they are a terrific alternative to traditional new-construction windows. One of the tools my company uses to test leaky walls and windows is a calibrated spray rack. We’ve sprayed replacement windows from Milgard, Anlin,...

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