Exposed fastener metal roof vs. standing seam?
I’m reading Martin’s awesome roofing primer: https://www.greenbuildingadvisor.com/blogs/dept/musings/martin-s-ten-rules-roof-design
And I came across something a little confusing to me: the preference of an exposed-fastener metal roofing over standing seam. I think I understand that an exposed fastener job is easier to install and therefore cheaper. But is that it?
I keep hearing that the disadvantage is that the screws will eventually back out and the holes in the panels will enlarge and it’ll leak. Is this actually true? I also see in the comments that some people screw exposed fastener roofs into 1x strapping that goes over the roofing felt. Is this to minimize the consequences of these potential problems?
So what’s the deal? Is an exposed fastener roof installed on 1x strapping going to last? Ignoring aesthetics, is there any reason to prefer a standing seam roof?
I ask because there’s a lot of local expertise for exposed fastener roofs vs standing seam, and I’d prefer to go with the flow when I redo the roof on my house.
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Replies
Nathaniel,
Standing-seam metal roofs are great roofs. If you can afford one, by all means install one.
In most areas of the country, contractors charge more to install a standing-seam roof than a through-fastened roof. But that rule of thumb may not apply everywhere.
If you are a builder who wants to install your first metal roof, you'll probably find that it's easier and cheaper to install a through-fastened roof than a standing-seam roof.
In the old days, before cordless drill/drivers were invented, through-fastened metal roof were installed with nails. These nails did, indeed, eventually back out. Since roofers switched to roofing screws with neoprene washers, however, this problem has disappeared.
I like to install metal roofing over 1x4 or 2x4 purlins because this method is a good way to handle the occasional condensation that occurs when the outdoor air is warm and humid, but the roofing is cold (either due to nighttime radiational cooling or the existence of a layer of snow on top of the roofing). If there is an air space between the condensation and the roofing underlayment, the condensation can drip harmlessly onto the asphalt felt before evaporating.
I have no reason to believe that a well-detailed, well-installed through-fastened metal roof won't last as long as a standing-seam roof. But standing-seam roofs look great and work very well -- so by all means install one if you can afford one.
Nathaniel,
My experience with through fastened steel roofs is that there is nothing to be concerned about with regards to the fasteners leaking.
I have several outbuildings with such roofs (one of which is more than 25 years old) and have never noticed any leaks - though as Martin points out they can sometimes "sweat" from the underside (this would be true for standing seam as well).
I would say your decision comes down to whether or not you think the look of a standing seam roof warrants paying a possible premium.
Thanks guys. Can you walk on a metal roof installed on purlins without running the risk of damaging it or yourself?
Nathaniel,
Q. "Can you walk on a metal roof installed on purlins without running the risk of damaging it or yourself?"
A. My answer to the first half of the question is yes. Wear sneakers.
My answer to the second half of the question -- "Can you walk on a metal roof installed on purlins without running the risk of damaging yourself?" -- is, "Of course not." Any time that you are on a roof, you are at risk of damaging yourself -- and the day you forget that is the day to retire from roofing.
Nathaniel, I started installing my own standing seam (snap-lock) roofs when I found out how much the labour component of the jobs were. Like all metal roofs the devil is in the details. Flashing openings like chimneys and skylights takes some expertise, but installing the standing seam panels is so simple as to be idiot-proof.
Unlike Lucas and Martin's experiences, I got into installing concealed fastener roofs to replace several where the gasketted screws had failed due to wind and being over-driven when first put up.
What I like about standing seam roofs is that if they are installed correctly there is nothing to fail, no where to leak. Unlike shingles or metal roofs with exposed fasteners, there are no potential weak points. You do it once and it's done. I don't spec or install anything else now.
There is a metal roof option besides exposed fastener or standing seam. There are metal shingles with hidden fasteners such as:
https://www.classicmetalroofingsystems.com/products/
which are aluminum or:
http://www.kasselandirons.com/
which are steel.
I just had the Oxford Slate Rock (from Classic Metal Roofing Systems) installed on my house. See the attached photo. It looks great in-person.