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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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General: Very low pitch (1 deg) & zinc roof

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  1.  
    • CommentAuthorluz13827
    • CommentTimeFeb 6th 2022
     
    Hello, we have a small part of flat roof, by our side return extension - about 3m x 1.5m (the main part of the extension roof is pitched). It's been built with a 1 degree slope, along the 3m run. I know zinc standing seam requires min 3 degree slope. A contractor suggested we could go with batten roll, which would help to avoid water ingress at the seams. 

    Does anyone with experience with roofs think this would be OK, or better to re-do and (somehow?) add a greater slope on top of what's built so far? The only issue is if we have to re-do, we have to have the slope going the other way (on the 1.5m side), because we can't increase the height the other way due to neighbours.
    • CommentAuthorSimonD
    • CommentTimeFeb 6th 2022
     
    In terms of recommended practise in the UK for double lock standing seam, it's typically 5 degrees minimum (even though manufacturers may allow down to 3 degrees) I built part of my roof with 3 degrees as the manufacturer said this is okay providing there are no penetrations. With my roof material (steel) it's also good practise to seal the double lock standing seam which helps at low pitches.

    Recommended practise for batten roll is still minimum of 3 degrees.

    This is detail from the Federation of Traditional Metal Roofing Contractors Guide to Good Practice 3rd edition.

    Personally, I'd err on the side of caution and steer away from a 1 degree standing seam roof.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 6th 2022
     
    At 1 degree, dishing due to temporary loads and/or inaccuacies guarantee that parts of the roof will actually slope backwards and/or create pools.
    • CommentAuthorjfb
    • CommentTimeFeb 6th 2022
     
    definitely go for a bigger gradient if you can.
    • CommentAuthortony
    • CommentTimeFeb 6th 2022
     
    1:40 min
    •  
      CommentAuthordjh
    • CommentTimeFeb 6th 2022
     
    1° is about 1:55 but even at 1:40 it's very easy to get pools either in the middle or at the edges.
  7.  
    In my experience there are always freak circumstances of wind direction, strength, sudden gusts etc that can blow water back up through any gap at any angle of roof. Most of the time we simply rely on these occurences being rare, and on the likelihood of any rain that does penetrate being very thin by the time it gets inside, and quickly evaporating. It's simply a matter of acceptable risk.
    •  
      CommentAuthordjh
    • CommentTimeFeb 8th 2022
     
    Posted By: Cliff PopeIn my experience there are always freak circumstances of wind direction, strength, sudden gusts etc that can blow water back up through any gap at any angle of roof. Most of the time we simply rely on these occurences being rare, and on the likelihood of any rain that does penetrate being very thin by the time it gets inside, and quickly evaporating. It's simply a matter of acceptable risk.
    This is true, but a nearly flat roof doesn't need any freak circumstances to get wet. It's almost guaranteed to be nearly permanently wet during winter.
    • CommentAuthorluz13827
    • CommentTimeFeb 9th 2022
     
    Thanks all, we have decided to adjust the slope now - better to be safe than sorry!

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