do i need to use wood strapping for metal panels over asphalt?

Guest User
10/22/2010
I have a detached garage with a single layer of asphalt shingles. I want to put metal on top of existing. Do I need to use wood strapping? I've had some say absolutely and others say not needed since existing asphalt is vapor barrier
Eric Novotny
An informed customer is the Best Customer!
10/22/2010
If the garage is unconditioned space, a properly slip layer will be all that you should need. If it was conditioned space, I would recommend purlins and over deck venting.
Guest User
10/25/2010
Thanks for your response. So the existing shingles would be a "properly slip layer" ?
Todd Miller
Isaiah Industries, Inc.
11/1/2010
Always adhere ot manufacturer instructions. If you have a vented attic then I would say strapping is not essential. I would suggest a layer of underlayment such as a synthetic underlayment down over the old shingles regardless.
Eric Novotny
An informed customer is the Best Customer!
11/2/2010
Asphalt is not the slip layer as Todd indicated. Synthetic underlayment would likely serve this purpose perfectly but check with the manufacturer on their recommendations. If it is above an un-heated garage, you really don't have any ventilation requirements.
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