Hello all, Back again, this time with a basement retrofit question. I have seen several articles recently about using nailbase (half-SIP) panels either for exterior retrofits or basement retrofits. I was thinking about using Hunter/Atlas nailbase panels in the configuration below. Note that I am right on the border of ceiling height allowed by code. As such, the combination of the backer and the insulation of the panels on the floor would just get me in at the right height while maintaining suggested R-value. (going 2" XPS then plywood then finish floor will put me over). I don't have any bulk water issues. I realize that polyiso will absorb water, which is why I added the drainage mat and vapor barrier. My thought is that the wall will dry to the outside (portion above grade), rim joist inside. The xps will provide drainage plane to drainage mat/barrier keeping the floor poly dry. Any thoughts on this buildup? Thanks, Garret

You can use nailbase iso on the walls but not the floor, for the very moisture-retention reasons you cite, as well as for the rockering-issue at the seams over time. Use 1.5" XPS and half-inch t& g or ship-lap ply/OSB sheathing for a subfloor, and stagger the seams of the ply with that of the XPS. Even without the moisture issue, walking on nailbase iso will compress the iso at the panel edges over time unless you added a second layer of subfloor, or went with a more structural flooring such as hardwood, not laminates. Some laminate flooring is very low perm as well- try to fine specs.

If you have no wall-moisture issues you can use fiber-faced iso (a 5" nailbase panel) rather than XPS on the walls, which would provide better drying capacity for the wall toward the inteiror, which is protective of the foundation sill. At 2" you still have some drying capacity toward the interior with XPS, but with the facer of the nailbase added onto it you're down in ~0.2-0.3-perms territory, lower vapor permeance than a kraft facer on a batt. With a fiber-faced nailbase panel you're between 0.5-1 perms, similar to 1" XPS.

I see an arrow allegedly pointing to 1x3 furring, but can't figure out where it is in the stackup- or did you mean to say the XPS is dadoed to accomodate 1x3 furring?