I'm rehabbing a structure from the 1850's. As you can imagine, nothing is square, level or plumb. The walls were originally plaster on top of true 2×4's.
I've brought the house down to the studs, and am going back with exterior sheathing (0.5") on top of true 2×4's (4.0") plus drywall inside (0.5").
That gives me an actual wall thickness of 5.0".
That tells me I should order my new windows for a wall depth of 5.0"
Problem is, the walls are not straight or consistent. Should I order windows with a little extra? Like 5.5"? I had experience doing this to my first house, which was also from the 1850's, and it took me forever to get the interior trim around the windows right. I had to cut shims, and wedges, because the walls were wavy. It was a huge pain.
Specifically: If my wall has a nominal thickness of 5.0", what is a sane amount of expected deviation? Maybe 0.25"? Should I order windows for a wall depth of 5.25" and just shim out the interior trim?
Best Answer
The sanest thing is to order new construction flanged windows that are a bit smaller than the rough opening. Then you integrate the flange with the WRB that you're installing over the new sheathing (right?) and bob's your uncle. On the inside, you can cover up the lack of square-ness with new drywall or wood window boxes, shimmed to be square with the window, not the rough opening.
Since you're taking this house down to the studs and redoing the exterior sheathing, let me mention that you have a golden opportunity to add extra insulation outboard of the new sheathing. The marginal cost will be fairly low, especially if you're doing the work yourself and buy reclaimed foam.
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