I think the normal is is to put a 2x4 on the sides and top of the window opening and foam to that so the window gets full support nailed to the top and sides.I will be redoing the whole exterior of my house and replacing all the windows. House will be taken down to sheathing, Halo Exterra GPS 1.5" foam (which will also act as WRB), and then flanged windows on top of that. I will be using furring strips over the foam to install engineering wood lap siding.
I am thinking Grace Vycor flashing for the sill, then the sides, then the top. I would then install flanged window with sealant behind against the Vycor. After securing window, I would install more Vycor up the sides, then a metal head flash, and then Vycor again over the top of that.
Once window is in, it should be fully adhered to the Exterra rigid foam, and that will makeup my drainage plane. Furring strips+ lap siding after that.
Does this sound correct? There are SO many different installation methods, it is difficult to find my exact scenario.
When doing the sill pan we quit doing the top of the opening so any leak from above will go to the window and around and out the bottom.