cut n cobble

[BOOT]

I'm insulation two walls with foam board and using the cut n cobble method. The wall studs are kinda jigsaw puzzle from some large windows that use to be there, so fiberglass insulation would have been almost just as pita. Plus the foam board should be cheaper and have a higher R value.

My questions is I am stacking two layers to fill the void, 2" & 1.5". Some use spray foam and others use caulk, I am leaning towards caulk. Should I seal the outer edge between sheets or after the last sheet has been inserted? For example place the 2" section in snug, caulk all around the outer edge and then insert the 1.5" sheet before it cures.

 

[Jon_E]

Same plan I have. I'm using 2 layers of 2" polyiso recycled from a roofing project. I put the first layer in, a little construction adhesive to hold it in place. Then the second layer, same deal. Then foam around the perimeter. I wouldn't use caulk, it really doesn't provide any insulating value.

 

[Cyberbear]

Unless there is some indication of cold air infusion into the building interior, I'd think sealing the rigid foam pieces around their perimeter isn't necessary. Older style wood or aluminum siding covered frame buildings were often plagued with air drafts and needed a plastic sheeting to prevent air entering a building on a windy day. The sheeting and interior drywall usually cured air draft problems. No sense wasting the foam or labor unless necessary.

 

[BOOT]

New T1-11 wood siding over this section and alum on the rest, no plastic sheeting.

 

[BOOT]

When I was reading about the cut n cobble method, it was thought that caulk provided a better seal than spray foam. Also when caulking to make the fit tight and looser (1/4" min) when spray foaming the perimeter.

I'm still cutting the pieces so I'm not set on caul or foam yet.

 

[DC73]

It doesn't really matter where you caulk as long as you prevent air movement through the wall. Spray foam should work as well as caulk and might be preferable if the gaps are fairly large. With tight gaps, caulk might be easier and less messy. If you want to go to the overkill route, caulk each cavity before you insert any insulation and then caulk around the edges of the final piece of insulation.

DC