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Orkblork
Joined: 28 Jul 2005
Posts: 64
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 Posted: Thu Aug 25, 2005 7:35 pm Post subject: Flat metal roofing? |
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I am an architect looking to specify a metal roofing system for several small canopies (each is only about 4'x8') on a residential project. I don't want to use standing seam or corrugated roofing; I just want to install a flat sheet of glavanized sheet metal across the full width of the roof, and then several more courses on top of that -- each course would have maybe 8 or 12" of exposure. The closest thing to this that I have seen is the single row of sheet metal used at the bottom of a lot of asphalt shingle roofs in Vermont and New Hampshire. BUt I have never seen it installed in multiple rows.
Has anyone ever attempted or seen what I am looking to do? |
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phansford
Joined: 18 Apr 2004
Posts: 832
Location: SW Ohio
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| Posted: Fri Aug 26, 2005 4:49 am Post subject: |
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I haven't attempted it, but its is just a detailing issue IMHO. If I understand what you are doing, it thing this will be a lot like flashing at a chimney on a sloped roof.
I would use a rubberized, self-sealing underlayment like IceBarrier. Then simply lap the metal sheets like you would a shingle roof. The canopy needs to have a steep slope to reduce ice damning and perculation of water as it flows over the shingle edges. The last (or top) shingle should act a flashing and go up the wall and behind your siding material.
Your best bet is to work the final detail out with the contractor - in particular the metal fabricator/installer who will do the work. |
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Orkblork
Joined: 28 Jul 2005
Posts: 64
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| Posted: Fri Aug 26, 2005 6:46 am Post subject: |
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Thanks, Phansford, you described pretty much what I intend to do, I just forgot to mention the ice and water shield.
An additional question concerns the fastening of the metal "shingles"... I am thinking about screwing down the leading edge of each course through the reverse side, then folding the shingle up into final position. This will give the leading edge of each shingle a thicker, more finished-looking edge while hiding the fasteners. BTW, the slope will be 5/12, which is not particularly steep but I don't expect it will cause any problems.
At the side edges of the roofs (think of them as "floating" panels, they aren't engaged at the sides) I might use a conventional roof-edge flashing, or I might extend the metal sheets and fold them over the sides. The underside of the roofs will be visible too, so I might use metal there as well. BTW, the metal would simply be galvanized sheet stock, unpainted.
I think it's curious that such a roofing system is not used more often... maybe architects fear using flat sheets because they may "oil-can," dent, or otherwise show imperfections, but with a seam every 12"+/- this shouldn't be a problem.
Again, thanks, and I appreciate any additional thoughts you may have. |
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gleearch
Joined: 07 Jul 2005
Posts: 185
Location: Oakland, CA , USA
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| Posted: Sat Sep 17, 2005 2:34 pm Post subject: |
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Flat seam metal roofing. Or a variation of it. Take a look at Smacna and make sure your details are done correctly. Theoretically it sounds ok but it's in the detailing of your rolled edge seam fasterner detail. You need to take into account expansion and contraction, you need a slip sheet between your ice and water shield and the metal roof.
Watch for oil canning. Your roofs are not very big so probably no need for expansion joints but again, check with SMACNA. Yes, I know the darn book costs over $250 but the problems it solves is well worth the cost. If you're going to detail and design with metal, you should get SMACNA.
Plus sometimes it helps to talk to your local rep for Unaclad or similar manufacturer. They fabricate all kinds of metal conditions that their experience in the field can be invaluable. Plus check the standard sizes of a coil of metal roofing. Cross check with the dimensions you are thinking of using. You may end up having to do a lot of cutting lengthwise. Then make sure your sheet metal contractor can do the work.
_________________
Gerard Lee Architects
http://www.gleearchitects.com
San Francisco bay area, Oakland, CA based sustainable architecture & planning firm specializing in residential, education, commercial, community & civic projects. |
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