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Flat roof edge detailing

Discussion in 'Roofing and Guttering' started by jonnypron, 22 Jun 2017.

  1. jonnypron

    jonnypron

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    Location:
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    About to wrap my timber framed garden office with the breathable membrane and battens but am unsure how the edge detail is finished with an EPDM roof. The cold roof rafters end flush with the stud wall rather than any overhang.

    If I go by the limited diagrams seen so far (see attached), then this would be membrane right up to the top of the roof edge, with EDPM sitting on/up to the flashing kit, sitting just over the cladding. Any diagrams to help me understand would be great.

    I'm unsure of the breathable space too: Does the walls air gap under the cladding join up with the roof air gap (at least front and back) and all work as one free flowing air space? Does the fascia/flashing kit not prevent some of this air flow?

    Also, not sure if anyone has any experience with Klober Permo Frame Breathable Membrane but have just ordered some from https://www.aboutroofing.com/permo-frame-breathable-membrane-50mtr-x-1-5mtr.html and it's unbranded? Not sure which side is the external i.e. cladding side and which is the insulation / stud wall side. I want to be sure it's the correct membrane as all the photos show it being branded.

    Thanks in advance.
     

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  2. ^woody^

    ^woody^

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    Cladding should have a continuos 25mm air gap around the top and along the the bottom to form a drained cavity. Typically you would make the roof over-hang the cladding (the more the better in terms of weather protection), and then have a vent in a soffit. But there are other detail options. You need to have a mesh insect screen over the ventilation opening.

    There is no requirement for wall and roof ventilation to meet up, but in practical terms it might on at least two opposite sides.

    You will need to build the roof out with noggins or timber joists to form any required overhang/soffit.

    Membrane writing goes outwards. The outer surface tends to be slightly fibrous, and then inner more plastic looking
     
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  4. jonnypron

    jonnypron

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    Great, thanks for that. The Klober Permo membrane I have doesn't actually contain the writing anymore apparently so glad you mentioned the shiny side inwards, fibrous outwards as this is the natural way it's rolled, and sales at Klober didn't know but said either way which I really wasn't sure was correct.

    re the roof - i was going for the box shape without overhang (like the attached pics) so think you just have rear batten to support the flashing edging kit for the EDPM, but was unsure how to keep the top ventilated if it's effectively covered by the roof edging? I've also attached a pic of shed part built plans to show the structure.
     

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  5. ^woody^

    ^woody^

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    Those images show very poor design detailing. No overhang leads to increased weathering and water shading at the top edge, especially with timber such as cedar. They look great new, not so great in a few years time.

    They also do not have any cavity vent. In those cases, the vent strip would need to go in the vertical face, but would need a way of preventing water ingress to behind the cladding.
     
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