Material choice for spacing window nailing flanges around rigid foam
Figured someone else has been faced with this one, so figured I would ask:
I putting 1″ rigid foam on the outside walls of a new construction building. I was strongly encouraged to build some kind of spacing frame around the outside of each window opening so that I was not compressing the rigid foam underneath the nailing flanges for the windows.
I was first considering using 5/4″ PVC trim to build this spacer as it is impervious to water/termites/rot etc. After some investigation, I was told that using this in a “buried” application was very prone to severe warpage over time, particularly in hot months, because the material was not free to “breathe.”
It seems that fiber cement is simply too brittle?
Am I down to using pressure treated lumber and pray it doesn’t twist, warp, and split? Any other ideas?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
There's no reason it needs to be pressure treated. You could just use some regular lumber.
Also, you could double up rips of left over 1/2" plywood if you're using any onsite already.
Midwayman,
Where is your WRB? How are you detailing the window opening?
Great use case for ThermalBuck. You can get 1” thick variety to match the thickness of your foam so that everything is on plane with each other. Are you doing furring strips and rainscreen?
Thanks for the replies!
Steel building with steel girts. 1" of foam outside of the steel girts, glued/taped, then house wrap ran vertically and taped. Plan to make these "spacers" 1.5" wide so that it sticks out from behind the window nailing flange.
I would certainly like some feedback on the best way of terminating this housewrap. As far I know there are two ways:
1. Cut the housewrap back from the window 1/2" or more and use flashing tape to seal the wrap to the sheathing and to the nailing fin (and spacing material in my case) simultaneously.
2. Wrap the housewrap to the inside of the window opening and tape to the framing material.
Thoughts on which would work best for this application?
Thermalbuck is interesting. I am not sure I have access to anywhere that even sells this stuff.
I would pay attention to thermal bridging on an all steel building. I would go with the Thermalbuck product. It can be ordered online. Additionally, the Thermalbuck website has a number of successful details that you can parrot to fit your situation.