Phil Johnson
1/22/2018
Greetings! I started installing a standing seam metal roof over my asphalt shingles this weekend. I'm using the Menards Pro-Snap panels, following the instructions to lay fanfold insulation underneath. So far, so good. I signed up for this forum as I'm sure I'll have questions as I go along. I have two initial questions. This house was built in 1974. When I bought it the roof was sagging in a couple of spots from busted rafters. That was fixed and the roof was leveled and fortified with purlins in the attic. Though much improved, the roof on this old house will never be perfect. Will this and/or the use of fanfold insulation as an underlayment result in a bad look? Is any roof perfect? I've only got five panels up so far, so I'm not too far down the road and could change plans if need be. My second question is about venting. I kind of like the idea of essentially having two layers of roofing, and I'm not crazy about cutting a hole along the top to make a ridge vent. The house is a long ranch home, about 75 feet long....will gable vents on each end work? Should I add a fan? The house does have soffit vents running the length of the home. If a ridge vent is better, can you get away with cutting an opening on just one side of the ridge? Any thoughts are appreciated. Thanks!
Todd Miller
Isaiah Industries, Inc.
1/22/2018
Thanks so much. Soffit vents and gable vents create very limited airflow, with many stagnant areas remaining. I would suggest closing off the gable vents and installing a ridge vent. You want to have your attic either have a balance of net free airflow with the intake soffit vents and the exhaust ridge vent ... or be slightly pressurized with more intake vent. So, ultimately, you will need to calculate the airflow amounts. A great website for venting information is www.airvent.com Any dips or swales in the roof decking will telegraph through to the new roof. You might be able to let some fasteners be a little looser than some to "float" the roof a tiny bit but I would be careful to not overdo that ... the roof panel you're installing does need to be fastened down pretty tightly.

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