It is never possible to predict exactly what will happen but I frequently see maintenance required by these roofs after about 7 - 10 years to tighten the fasteners and the fasteners being replaced sometime in 15 - 20 years. For a coastal application, you may want to consider aluminum rather than steel.
+1
Has to be aluminum in your case. Done properly, we tend to see the exposed fastener roofs up here last about 10-15 years on the fasteners.
Fastener installation is quite sensitive though and is the most prominent source of failure on those systems.
I've gotten a bid to replace my shingle roof with metal. I thought I was going with standing seam but got sticker shock at the difference between exposed fasteners vs standing seam. My question is I thought that the time frame that problems might arise from exposed fasteners was relatively short, like 5 yrs or so. But I was told by the roofer that gave me the bid that you shouldn't have a problem for like 20 years. What does the panel think? Btw, I live on the water in Florida.
