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Have a overhang / leantoo built off the garage that was never completed and covered with a tarp. I've stripped the rotten plywood off and have new OSB to install. The slope is 5" in a 12' run. A fraction more than 1/4" per 1'. My thought is to install a layer of felt paper then rolled asphalt nailed at the top edge and adhesive along the bottom??

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    There are roof underlayments that are tapered fiberboard that will change the pitch of the roof without adding a lot of weight and no need for framing. FWIW, the roof slope you have is at the minimum slope acccepted by the UBC, so I just seen on this website epsindustry.org/roofing-systems/tapered-roofing-systems I need to mention, your proposed idea for the roofing will not hold up. Neoprene, hot mop or torch apply at the least. PVC as mentioned below sounds intriguing, although I have never known of it... – Jack Jun 27 '17 at 6:54
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I don't think what you are proposing will work. Asphalt rolled roofing is NOT waterproof. Sealing at the joints and eave will stop wind blown rain, but standing water will saturate the paper and it will leak. (The paper is not UV resistant either.)

I wouldn't use a "peel and stick" membrane either, like Grace "Ice and Water Shield", because they can only be used on slopes down to 2:12. (...plus they have no UV protection.)

I'd use an PVC membrane. I would not use an EPDM membrane. The main difference is that EPDM's seams are chemically sealed and PVC seams are heat welded together. The EPDM seams can breakdown over time.

...but back to your question, No, I would not use roll roofing sealed with mastic.

  • Trying to incorporate this into my understanding of roofing, does "roll roofing" have mineral grains on the surface intended to be exposed to the sun? – Jim Stewart Jun 27 '17 at 15:28
  • Hmmm... I think of "roll roofing" as anything that is a building paper or felt, (asphalt impregnated.) Some is solid and some is perforated (to help absorb asphalt). Roofing systems have various components, like: nailable base sheet, layers of felt, cap, etc. Cap sheets can be smooth or granular. However, all the components are applied into a layer of asphalt, coal tar or mastic. In my opinion, that system is nearly impossible to install correctly...there are always voids in the asphalt or mastic...and that leads to roofing failures. @JimStewart That's a long-winded answer... – Lee Sam Jun 27 '17 at 23:56
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I'm guessing that the reason your not going to torch it down is your uncomfortable with fire? If so then I would contact a roofing supply and get a two part roll roofing system that has a nail base. It essentially has a sheet you nail down then a sheet you glue down ontop or some systems even include a peel off backing to be applied to the nailed base. And are very easy to apply if instructions are followed correctly. Oh and minimal slope for most rolled roofing products is 1/12

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