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I'm building an 8'x20' storage shed for the backyard. I've done some woodworking, but I'm more comfortable with metalwork. Instead of triangular roof trusses out of wood, I'm thinking about making smoothly curved arches with a tube roller. The idea would be to lay corrugated metal roof panels lengthwise so that the "wavy" orientation bends around the curve and the stiff/"straight" orientation spans the length of the building. Like a half cylinder, or a quonset hut.

Edit: But it would not be entirely a quonset hut. The shed will have traditional straight framed walls; my question/idea only concerns the roof i.e. top portion of the structure.

My question is whether it will be a problem that the corrugations on the apex of the arch will effectively form 20' long horizontal "channels" with no slope for rainwater?

(By the way, we rarely get snow where I live, and not much accumulation. We do get ice storms every other year. We have high winds, gusts 50+ mph, throughout every season, enough to scour anything laying on the roof off of it.)

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    "My question is whether it will be a problem that the corrugations on the apex of the arch will effectively form 20' long horizontal "channels" with no slope for rainwater?" Yes it will form channels for water to sit in. Problem? maybe. Could freeze, could rust prematurely.
    – Alaska Man
    Commented Jul 28, 2020 at 21:09
  • I agree with @AlaskaMan. To combat the standing water issue, you could slope the roof from one end to the other with the standard drain slope of 1/4" per foot of run. That should provide enough slope to prevent standing water and would be an additional talking point in how unusual your shed is among all the neighborhood sheds.
    – FreeMan
    Commented Jul 28, 2020 at 22:40

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Yes it will be a problem. Not sure where you are but in my home country and minimum of 8 degree pitch (approx 1:7) is required for long run sheets, and 10 degree for end lapped sheets by the building code.

If you don't you may have the following problems:

  • Pooled water that will shorten the life and void warranty on the corrugated iron
  • Potential leakage though fixings due to the above
  • If end lapped sheets are used, blow back up under the overlappped sheet causing leakage (you mention you live in a high wind area? If so this is even more relevant).

You should also pay attention to any potential interaction between the corrugated metal and whatever material you make the curved arches out of. You may be surprised to find what will void the warranty of the corrugated metal. Some kind of underlay may be required to isolate one from the other and prevent electro-chemical interactions.

Again in my home country high wind areas also dictate a requirement for high load fixings/framing as per building code as well. As soon as you put a pitch on it, it becomes a giant airplane wing in the wind. Something to consider

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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know the details of contributing here.
    – Daniel Griscom
    Commented Jul 29, 2020 at 2:20
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Make one side wall slightly lower than the other. Water will flow off the low side.

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I agree; you have exposed a very serious flaw.

Go look at Google images of quonset huts. All of them either have

a) vertical ribs on the sides, or

b) horizontal ribs, but a vertical-rib "cap" about 10 feet wide at the apex of the structure. This is bent in the "tough to bend" direction.

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