Installing LP Smartside over foam and 24 inch centers
We’re building a new home (SW Virginia) with 2×6 studs on 24 inch centers. We had hoped to use 1.5 to 2 inches of EPS rigid foam to the exterior of the sheathing, then 3/4 inch x 4 inch plywood furring strips, then LP Smartside lap siding. We knew we had to use the 76 series Smartside product for the 24 inch centers. Then I discovered that LP’s installation instructions specify 1.5 inch x 3.5 inch furring strips for foam greater than 1 inch in thickness, so I guess that would basically mean a 2 x 4 stud for every 2×6 stud in the wall. This is more material/expense than we had bargained for, and perhaps also more increase in wall thickness than we want for window installation, etc. Due to some ambiguity in their instructions, I called LP support just to verify this, and yes, that’s what we need to do to be warranty-compliant. (However, their instructions also seem to indicate that you need 16 inch centers if fastening to furring strips over foam. The rep told me that 24 inch centers are fine in this scenario as long as you use the 76 series.) I asked him if we could fasten the siding through the foam and furring strip with long nails or screws biting into the underlying 2×6 studs. (Wanted to keep the furring strips so we’d still have a rainscreen air gap behind the siding.) He said that sounded like a possibility but I would need to talk to some of their higher up tech people and get a warranty variance in writing to protect myself. And then you’d have the expense of all those long fasteners and not sure how that would add up vs the thicker furring strips? So I’m kind of confused about which route to take. Here’s what I see my options to be:
1) Install according to LPs specs and use a lot more lumber. Would the improved thermal performance of the wall be worth all this?
2) Install according to original plans and hope I never need to use warranty. Anybody have experience fastening Smartside lap paneling to 3/4 inch furring strips?
3) Switch to 1 inch of polyisocyanurate for a similar r value boost, and forget about the rainscreen gap. (For 1 inch of foam or less, LP says you can nail directly through the foam to the studs.)
4) Try to fasten siding through furring strips and foam with long nails or screws. Anybody tried this? Any ballpark ideas on expense of longer fasteners vs just using 2×4 furring strips?
We’re kind of stuck and don’t have a lot of experience to guide us. Any thoughts would be greatly appreciated.