Unvented roof with standing seam

Guest User
I have an older 1890 Victorian house. We are renovating our 3rd floor into a bedroom and bath with a cathedral ceiling. There is currently no insulation in our 3rd floor and roof. Our roof rafters are only 6 inches deep. We do not have soffits and don't have a practical way to do a traditional vented roof. We are not willing to use spray foam inside our house. Our current plan is to remove our asphalt shingles and install a 24 gauge standing seam metal roof. Our building code (in Zone 5) states that if we protect our roof sheathing from above with a vapor barrier and at least R-20 of rigid foam (4 inches) then the sheathing is protected enough to prevent condensation. In addition, we plan to use cellulose blown in between roof rafters from inside to get up to a R-38. We will end up with an unvented "Hot" roof. My questions are: 1. Can the standing seam roof be installed right on top of the rigid 4 inch insulation our do we need an air space? 2. Where should the vapor barriers be installed and what products should we use? 3. Is a single 4 inch sheet of foam okay or should we use 2 layers of 2 inch foam and stagger the seams? Thanks for your help
Eric Novotny
An informed customer is the Best Customer!
1. Yes. I can go overtop as long as there is a good and solid substrate. (i.e. plywood decking is recommended here). 2. The foam will actually serve as all the vapor control you need here. 3. Single is fine but will be cost prohibitive. Use multiple layers. Call or email me directly and I can walk you through what is the best way to do this project. You don't have to use SPF but you will need to seal up the assembly from the bottom really well to get maximum performance. Have notes on the construction ready (i.e. existing roof deck to come off, type, etc.). Eric Novotny [email protected]

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