Rigid foam overcoat method on my own house
Been reading this website on and off for the last 7 years or so. I really appreciate the knowledge base here.
It is time to re-roof my own house, Denver, climate zone 5b. I plan on incorporating something similar to the JLC August 2014 article, “Project Overcoat” with a couple of caveats.
Starting at the bottom: Existing 2×4 rafters 24″ OC with R13 paper faced FG stuffed (from an attic conversion in 90’s), 1×6/1×8 skip sheathing, 4″ tall 2x sleepers on edge screwed through 1x and into 2×4 rafters, (2) 2″ Fiberglass faced poly iso insulation in 4″ cavity, 1″ XPS (for thermal break), 2x sleepers laid flat screwed through XPS into 4″ sleepers, 15/32″ OSB, synthetic roof paper, and asphalt shingles.
My SE likes the 4″ sleepers for strength (granted its a thermal break) and I will run them long and build new fascia/soffit from them, similar to cutting rafter tails in the air after the roof is stacked. I will cut away the existing sloped soffit/tails.
Will adding 1″ of XPS add enough of a thermal break?
Do I need a bituminous membrane (Grace) over the existing 1×6/1×8 (or over a layer of OSB applied directly on top of the 1×6/1×8) for air control? The attic space is finished with drywall on the ceiling/knee wall, no can lights, just fixtures mounted to the peak.
What else am I missing?
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