Guest User
5/23/2010
Hi, I am having a standing seam roof installed in a couple months. To save money, I am preparing everything and the roofer just comes and installs. The pitch is a 4:12, I have cathedral ceilings with 2x8 rafters and 3/4 plywood decking. I have acquired some 3" polyiso 4x8 sheets on the cheap and would like to incorporate them into the roof. Tell me if this is crazy but........ I want to leave the 3/4" plywood (remove existing shingles), install a drainage underlayment, then the 3" polyiso sheets (which are faced on both sides with tar paper), Then top with 1/2" plywood, a metal roof underlayment and then finally the new standing seam roof. What do you think? Thanks
Info @windowsonwashington.net
An informed customer is our best customer.
5/23/2010
Very good approach. Great way to improve the insulation and thermal break between the living space and the roof. If your area is anywhere that might suffer from ice damning issues, you could incorporate some over deck venting application. The underlayment over the first layer of plywood is probably overkill, however, you would be well served to seal the seams in the existing plywood with some sort of caulking to prevent airloss from the space. http://danperkinsroof.com/articles.htm First article on this page is perfect description.
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