Metal roof directly on foam

Tony Aldridge
9/9/2017
4 / 12 pitch new construction.10 1/2 inch rafters. Cathedral ceiling pine tongue and groove. construction paper Rigid EPS layers to top of rafters. 2 X 4 purlins / battens 2' O/C. 1.5 inch rigid closed cell foam fitted between battens. An alternate may be mineral wool between battens to ensure no air gaps. 2 inch rigid closed cell foam on top of battens 29 guage metal roofing screwed through 2 inch foam to battens. No "roof deck" installed Care taken to fit foam and seal all gaps with backer rod / spray foam/ tape. joins staggered. Self spent 30 + years in the construction industry, both hands on and management. Self has driven many pounds of screws, into many kinds of substrates, so expect the "oil can problem" is manageable Since the EPS is a very good vapor barrier, I feel that the residential moisture will not migrate upward to the metal roofing. Target is R55 / 60 finished. Budget; we are building the house using our pensions and trying not to incur debt, so cost management is critical. This geezer is racing single handed, to get the insulation into place and the tin on before the snow, great fun. Welcome your opinions Thank you in advance, Tony
Todd Miller
Classic Products, Inc.
9/9/2017
I think this sounds well thought out and I do not have any suggestions other than perhaps a vapor barrier behind the tongue and groove ceiling.
Info @windowsonwashington.net
An informed customer is our best customer.
9/10/2017
Be sure to ADA (Airtight Drywall Approach) and you should be right as rain. I would also make sure you air seal the foam that is getting installed under the roof deck as well as on top.
Tony Aldridge
9/19/2017
Thanks for the help. A question, since I need 4 inch screws to fasten the metal through the foam and into the perlins, how many screws do I need for a 1200 sq ft roof? We will install 29 guage in two 15 ft tiers to cove the 28 ft . 40 ft wide we will lay 14 sheets per tier. Am getting different numbers from the vendors one says 1,000 screws another 600. We are installing purlins at this time so we can adjust easily if needed. Again thanks for the help, Tony.
Info @windowsonwashington.net
An informed customer is our best customer.
9/20/2017
Standard fastener placement per the manufacturer of the panel specifications. Be sure to not over pinch panels and kink them during install because the foam is able to be compressed. You need to be very cognizant of that when installing.
Tony Aldridge
9/28/2017
D'oh, after all my years in construction am embarrassed that you needed to tell me to get the screw spec from the manufacturer. A simple phone call took five minutes. Thanks, my face is still a little red.
Info @windowsonwashington.net
An informed customer is our best customer.
9/29/2017
Glad you got it all figured out. Manufacturers are the ultimate deciders when it comes to the specifics of panel fastening schedules and consumables so we default to them.

If you would like to reply to this thread, please log in. If you do not have an Ask the Experts forum user account, create one here.

Find a Contractor

Get Started Today

Take the first step to increasing the value of your home with a great looking, durable, fire resistant and energy efficient metal roof. Browse our list of qualified MRA Member Roofing Contractors in your area for a free consultation and estimate.