Substitute for rigid foam on unconditioned attic wall?
I have a simple single story gable roof house with an unconditioned attic. I plan on adding some exterior rigid foam to the walls, but I don’t need the foam’s insulation value, or any air sealing details, on the gable walls of the attic. I figure I could put tyvek on the sheathing, lap it over the top of the rigid foam of the lower story, and then install some wood spacer blocks on the gable wall that are the same depth as the foam below, and screw the headloks through them when I attach furring strips. This would save me a couple hundred bucks on materials.
Are there any examples of this being done? I can’t find anything, but I have a hard time imagining it is a new idea. I’m a little worried that the foam will compress a little bit, but the wood blocks won’t, and there could be a visible alignment issue. But I wouldn’t think that foam would get compressed enough for that to be a problem. Also, I’m not sure how large the blocks should be to maintain the rigidity needed to support the siding — or if that is even a realistic concern. The foam would be 2-4″ thick.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part