What is the correct way to fasten furring strips over 2" foam? I believe I had read that screws like HeadLok spaced 24" was the correct way? The structure underneath the foam is plywood with 2x6's every 24". The plan is to use cement board siding.

5" GRK or Fastenal torque head also work well. You'll want to go 1-1/4" into the stud, so 5" would be good, 12" OC.

I predict that glued and screwed will allow fewer and smaller screws with less chance of them bending.

You said fiber cement siding 24oc 2x6 . Has anyone seen results with the siding applied over furr strips at that spacing? Are the results just a bit wavy in appearance? Or does it appear to need more support for the siding between studs? I'm wrangling with this same set up myself only 2 inches may be 3 inches of iso foam and 1x4 furr strips. I'd like to use LP smartside but haven't seen any install literature that didn't require 1 1/2 inch penetration into studs. Has anyone out there used LP smartside 24 oc with 2x6 walls, foam, and furr strips? I have to use either Hardie plank or LP smartside for this development.

Thanks

I've used Hardi Board over strapping & 2" of foam with studs 16" OC; no issues. We use GRK tourque head screws, about 2 every 16" vertically. I do not use the pan head as they can bottom out & strip the wood, lessening the holding power. 5" length will work well for your application & give you 2-1/4"into the stud. Fastenall carries similar screws and Truss Lock makes a similar product. The weight if cement board is much greater than LP, so that would work just fine. I'd suggest using 1x3 or 1x4 pine for the strapping - rough if available in your area - as it'll hold the siding nails better than spruce without cracking.

Thanks Bob ! Anyone else out there tried it with 2x6 and 24 oc? I wouldn't dismiss it but if I had to I'd do 2x6 on 16 oc. The additional bridging would kill me. Yes the Hardie product has about 30%more weight than the LP product.

Would anyone consider doing say OSB, 1.5 inch iso foam, Strap with a 2x4, then place 1 inch iso foam between strappings creating a 1/2 inch rain screen gap? Or would this be asking for trouble by semi surrounding the straps and asking for rot? LP needs 1 1/2 inch to secure siding to .