UPDATE!! How's the foam doing 3 years later:    • Will rigid foam cause problems? My fo...  

Better than spray foam (thermal break and relatively consistent R30+). Here's how to use 3 layers of 2 inch polyiso foam board to meet code and keep your new upstairs cozy.
**UPDATE WATCH THIS BEFORE YOU CUT FOAM    • What is the best tool for cutting foa...  
I used a 2 inch rigid polyiso foam (GAF Energyguard) I got from a local roofing supply company (ABC Roofing). It is really the type of foam they use on commercial roofs beneath a membrane. I believe mine was made by GAF, and ran me about $18 per 4x8' sheet. I cut two layers to fit in the rafter bays (so that's 4 inches), spaced 1&1/2" away from the roofdeck with scraps of 2x4s (which maxed out my 5 1/2" inch rafters). Then I put another layer across the rafters, which made a total of 6 inches of polyiso. Each inch was R5.4, so the total R value of all 3 layers was 32.4. Wherever there were gaps, I squirted some Great Stuff in, then shaved the overflow back with a flush cut handsaw. Yes, it passed insulation inspection.

My other channel:    / @scratchingthesurface2555  

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