I have been installing, inspecting, and field-testing windows and doors for more than 20 years. After performing thousands of window tests in the field in California and across the U.S., I still am unable to solve one mystery: Why does the eastern half of the U.S. install windows using the American Architectural Manufacturers Association (AAMA) “A” methods, when the western states generally use the AAMA “B” methods?

AAMA “A” methods (A and A1) apply the side flashing on top of the side nailing flanges. The “B” methods install the side flashing on the rough opening before the window is set in place, resulting in side flashing under the nailing flanges. These may seem like very minor details, but they have important consequences. On a set of drawings, the...

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