Hey Guys-
I’ve been working on my own house for a while now (it was abandoned for 11 years when I bought it). Time to bite the bullet on the roof covering. As I mentioned in the subject heading, the roof is a low pitch (actually 2.25:12), unvented shed roof (25′ eave to ridge, 36′ wide). It was originally a hot mop and gravel roof that was about 20 years too old. After replacing a number of rafters and all of the roof sheathing, I added 3″ of rigid foam (polyiso) topped with another layer of plywood. I then applied GAF film-surfaced StormGuard (similar to Ice and Water Shield) over the entire roof, hand rolling all the seams. I had originally planned to shingle it, but now I’m having second thoughts. I’m debating shingles or standing seam metal. I’m doing all the work myself, with permits, and I’m really on the fence as far as what I should do. The roof is a cathedral ceiling underneath, with 2×8 rafters and dense-pack cellulose in the bays. I have never done a metal roof before, but I’m not afraid to do one if that would be the best option. I do not want to use any kind of rubber roof, as that would be aesthetically unacceptable for this house. There are three penetrations in the roof – a wood stove chimney and two plumbing vents. If I did shingle it, should I use three-tabs or dimensionals? Decrease the exposure? Tar the nail heads? If I should do metal, any specific recommendations? I’ve looked at products like Union Corrugating’s ML200 (good down to .5/12). Money is a concern here – the product has to be reasonably priced and I am not going to hire out the installation. I’m located in northern NJ. Any thoughts or opinions would be appreciated.
Edited 8/20/2009 12:16 pm ET by bk24
Edited 8/20/2009 12:19 pm ET by bk24
Replies
Most metal roof manufacturers that I'm familiar with limit the slope to 3:12 and steeper, but you may find one that goes down to 2.
Scott.
bump
Most architectural/dimensional/laminate shingles are good down to 2/12 with I&WS underlayment per manufacturer's instructions.
Metal roof spec's vary wildly from brand to brand and brands vary wildly from region to region. My only recommendation with metal is that you read and understand the installation instructions before buying any material. Also, I would not purchase any polyester finish materials. Stick with kynar/hylar finishes. I've replaced a fair number of miss-installed roofs as well as finish failures.
The penetrations in your roof will be troublesome with metal. Without a pretty thorough metal working skill set, you're going to be relying on caulk to keep those penetrations from leaking.
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I know GAF specs a double layer of underlayment on low slopes down to 2/12. Check their website. It has the info you need.
You might not have a shingle *guarantee* at that pitch but with the underlayment you describe you should have a good roof. Under 2:12 I wouldn't.
Jeff