I am having a disagreement on a roofing technique that a friend of mine has been told is okay about Ice and Water Shield with Asphalt Shingle roofing.
He has decided to apply it to the entire roof. The underside of the plywood will be closed cell spray foam because he has no attic and the slope on half the building is only 3/12pitch if that).
I first suggested rolled roof cold process because of his budget and time schedule but he had advise to shingle it. Therefore I had told him to put 2 layers of tar paper over the ice shield which he has advise to just shingle over it without paper??
Any comments??
If those shingles ever need to be removed then I would think it will be torture. But I have seen guys do it in the rural areas on dumpy houses with old wood plank roofs.
This is brand new plywood.
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Down here in windy Florida code requires a secondary membrane which is basically Ice and Water under the shingles. If the shingles need to be removed they will install another layer or possibly just go over it again.
Sorry to tell you that your friend is having some issues thinking long term. The second thought I had was, "Cheap construction causes expensive long term repairs." I am wondering if he is planning on selling this house and getting rid of a problem.
Just my thoughts.
He has been told that tar paper is not necessary. I think it should be applied. I will have to find time to look at manufactures directions. Just thought I would get other opinions.
Fine homebuilding podcast yesterday discussed this issue. It would be worth a listen. The consensus seemed to be that it is not a good idea.
Then the people agreeing with the consensus have never been under a roof where the shingles get stripped off by the wind and the rain water comes pouring in through all the nail holes and seams between the plywood sheets. That thicker material will seal all the seams and many nail holes are partly sealed even when the nails get pulled out. Tests have been done that bear this out.Besides a water tight assembly you end up with an air tight assembly.
The more informed seems to be leaning more and more to a peel and stick synthetic roof membrane instead of felt paper. Many of the synthetic roof membranes are akin to an ice and water shield with 2 inch or 50 mm overlaps where seams might normally be. Instead of being applied along the edges and in valleys it is supplied in roils designed so that it covers the entire roof.
Why the stick on stuff? Because in a high wind if the shingles aren't stuck together, the shingles may come off but the peel and stick is adhered to the plywood. Once stuck and properly rolled, it isn't coming off unless the plywood gets pulled off too. In addition, it seals all the joints in the plywood. Anything else is very dependent on careful construction and most of us know what that means. In high wind areas the nailing is different too. The edges should have nails spaced on 3 inch centers and the interior nails should be on 6 inch centers. Basically one half the spacing of a standard nailing pattern.
In addition, some builders are also using an adhesive to stick down the sheathing. The plywood is nailed and glued. I would do it even if I wasn't in a high wind area.