Here in California, most new homes have vinyl windows. Since these units are only a few inches deep, the drywaller or finish carpenter must bridge the gap between the window and the inside face of the wall. On moderately priced homes, this is done by returning drywall into the rough opening and butting it to the window. But on the high-end homes I trim, it means installing wood jamb extensions and then casings.
Early in my career as a finish carpenter, I used wood shims to align jamb extensions with the window. But I stopped using them after learning a trick from an older finish carpenter. At the time, we were installing rabbeted stools across the bottom of window openings that were to be finished top and sides with drywall returns.
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