Standing seam metal roof: length of the clip-strip fastener

I work for a metal roofing company, and this is a big area of concern for a lot of homeowners.

Here's what I can say: based on experience and facts.

8-10 years ago, the fasteners on exposed metal roofing were terrible. They failed CONSISTENTLY. There were very few competing fastener companies and rubber washers cracked and leaked like crazy. And when your next best option is a concealed fasten standing seam at twice the price, metal roofing was unpopular. At the time, metal roofing only represented about 2% of the residential market.

Fastforward to present day. There are several large fastener companies and there is a ton of competition for the best performing screw. Our company uses screws with a neoprene washer (already light years better than traditional rubber) that is independent from the screw head allowing overcorrection during install. They also have a slightly larger and slightly domed metal washer stacked on top which creates an umbrella for the neoprene that guards it against the UV rays that cause cracking. We are seeing screws that at this point can live roughly 50 years if not longer without failed washers. Some companies are now even offering screws with oversized heads and washers with military grade strength that are guaranteed for life, even against backing out! This year, in the Southeast, metal roofing saw a rise in popularity to 14% of the residential market, and the majority of it is an exposed fasten system. 2% to 14% in 8 years and we wouldn't have that kind of growth if the roof systems were failing consistenly.

Of course, DO YOUR RESEARCH. Buy from a reputable company that uses good screws and make sure that your installer is experienced with metal.

The best and easiest solution is unfortunately no longer possible without removing and reinstalling the metal roofing: you vent above the sheathing and below the metal roof. The way you would do this is by installing the metal roof on vertical eave-to-ridge battens, with a metal ridge vent piece at the ridge. This way, all the ventilation is on the outside and you don't have to worry about complicated interactions with your finished attic.