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Thanks Doug. On the installation workmanship warranty, of course, it's also critical the company still be in business. I am not entirely sure how to answer your question but I can say this -- it is usually my experience that if a roof installation makes it through years 5 - 7 without a problem, it likely was installed well. I, along with most ice and watershield manufacturers, are not real thrilled about full coverage. You're right -- seals the structure up like a terrarium and could contribute to attic or roof assembly condensation. I sure wouldn't do that unless either the attic was fully foamed (closed cell) or you had really good ventilation. I am not sure I understand your reference on aluminum. Most aluminum standing seam is .032" or thicker aluminum which is a good range. As far as panel width, I really would not suggest over 16" both for oilcanning and uplift. I assume the aluminum you're looking at has a PVDF coating. I don't know exactly what your environment is but barring anything catastrophic, I'd expect a life of 40+ years and certainly it could be repainted for even an extended life.
Galvalume is still steel and I would not recommend it for your application. I'd suggest panels no wider than 16". Aluminum standing seam should be minimum thickness of .032" and it will perform very well.
Striations will help with oilcanning. However, I think you will have better wind uplift resistance with a narrower panel. Perhaps ask them for their uplift test results on 16" vs. 20".
I am considering a metal roof and have a few questions: 1) the metal roofers in my area offer workmanship guarantees from 2 years out to lifetime with a couple at 5 years. How important is it to get a longer workmanship warranty (say 20 year or longer)? 2) What underlayment is needed? One contractor is recommending 3 feet of ice & water shield with a synthetic layer, another said Ice & water shield the entire roof. I am concerned about condensation. 3) I will need an aluminum roof due to proximity to the ocean and one contractor is recommending 20" standing seam and another 16" to avoid oil canning. I know aluminum expands more (thermal cycling) so would a thinner panel be better? 4) What is the lifespan of an aluminum roof?
Thanks for the information. As follow up, my house is about 200 feet from the ocean and so aluminum seems to be the recommended metal (although some contracts are suggesting gavaluminum). Most of the aluminum standing seam quotes are for 20". Is it important to ask for aluminum strips that are narrower, like 16" ?
Another contractor said that a downside to aluminum is it's too soft and brittle if it gets stepped on. Have you found that to be true?
Thanks - again. Final question - the contractors offering 20" standing seam are recommending adding stiffening ridges for strengthening and avoid oil canning. Do these work or should I push for 16"? Thanks
