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I want to replace my roof. Exposed-fastener metal roofs are popular and common where I live, but nobody nearby has owned one long enough to really comment on the longevity. I worry that over time, the metal's thermal expansion and contraction with ambient temperature changes will eventually enlarge the screw holes to the point where a million tiny leaks will appear. That doesn't sound good. It seems that rubber or neoprene washers are used to alleviate this danger but that seems like putting a band-aid on it.

For this reason, I'm looking at metal shingle and standing seam roofs, but both are more expensive. Are my concerns about an exposed-fastener metal roof justified? Or are we talking about a difference in longevity of like 50 compared to 100 years?

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The better systems use EPDM rubber which has a much longer life than Neoprene or whatever generic rubber you mention. –  Fiasco Labs Apr 19 at 2:33

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It depends on the quality of installation, but on average exposed fastener metal roofs (which do, indeed, use EDPM washers if not of very low quality and life-expectancy) are a 15-25 year roof, while a quality standing seam job is a 50 year roof. The EDPM washer is not a band-aid - it's a part of this roofing system design (and most of the fasteners are located on top of ribs so they see very little water - also part of the design.)

Standing-seam should be very similar for the basic cost of material and forming, but is always quoted much higher (IME) making it economically dubious despite the potential longer life.

A bad job of either may not be leak-free for a month.

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Thanks. How about metal shingles? Can a good metal shingle roofing job last as long as standing seam? –  iLikeDirt Apr 19 at 20:43
    
I doubt it, though I lack data. There are specific aspects of how standing seam works that make for long, leak-free life when done correctly. I doubt metal shingles replicate those aspects, but there are many ways to make metal shingles (not a product I've seen much, though) and some may work in favor of a long useful life. Many more joints probably work against them, though. –  Ecnerwal Apr 20 at 1:03
    
True, though the joints are hidden and lapped like other shingles. Rally they're very much like regular shingles that just happen to be metal. So wind-driven rain could infiltrate underneath them, for example. But they could probably be expected to physically last longer than asphalt shingles. –  iLikeDirt Apr 20 at 1:28
    
It's things like the wind being able to get under them (period) that make them (in my estimation) probably inferior to standing seam, which manages a system that holds the metal firmly on the roof and yet also lets it move with temperature changes. A strong wind event could wreak the sort of havoc it does on other shingles, where standing seam would be much more resistant to that type of damage. Standing seam also keeps the exposure of the edge of the sheet to a minimum - that's the Achilles heel of otherwise corrosion resistant coated steel roofing materials. I presume they cost less than SS. –  Ecnerwal Apr 20 at 1:39

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