I have a few questions in regard to Rachel Wagner’s “Windows and doors in double-stud walls” article published here on GBA.  I saw this question was raised back in 2019, but other than a suggestion to look at the article there was no further comment in that Q&A.  I’m hoping to get a few more details from those who have used this approach.

Specifically, in what order is the “frame within a frame” constructed?  Are the 2×4 jambs and heads making up the frame assembled to sections of 3/4″ plywood, and the plywood is then nailed to the 2×4 trimmers in the double stud wall?  Is the polyiso insulation between the 2×4 frame members left out until the 3/4″ plywood has been nailed to the 2×4 trimmer of the exterior wall section?  What prevents the 2×4 frame members from racking or twisting, especially where they meet at the top of the opening?  (It seems that adding another section of 3/4″ plywood spanning those frame members would be good to add some rigidity there.)

Since I’ll be dealing with a framing crew that has possibly not done any double-stud wall construction I’d like to get all these details ironed out before construction starts.  Any clarification would be greatly appreciated.  Thanks!