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Parapet wall, box gutter, pitched roof - is this ok?

Discussion in 'Roofing and Guttering' started by Naknah, 16 Mar 2019.

  1. Naknah

    Naknah

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    I'm having an extension built at the moment which includes a pitched roof down to a box gutter and parapet wall. I've uploaded the section from the building regs drawings which show that the design has the roof joists on hangers and then the box gutter sat on top of the inner leaf of the cavity wall.

    All the construction details I've seen online show the joists sat on top of the wall instead of against it using joist hangers like my drawings.
    The builder said he hasn't seen a roof using joist hangers like this for years but the chippie is just cracking on with it.
    I don't have much confidence in the person who did our drawings (but the chippie seems good). Is this badly designed? Would it be better if the joists sat on top of the wall or does it not really matter? It does have building regs sign off so I suppose it is fine. I'm just a bit worried that it doesn't seem like the usual way of doing this.

    Cheers for any advice (y)
     

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  2. ^woody^

    ^woody^

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    Not from where I'm sitting it don't. That drawing is complete shiite.

    But hangers are fine.
     
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  3. Notch7

    Notch7

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    Im not sure what the drawing is showing (n)
     
  4. Naknah

    Naknah

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    Yeah the drawings are rubbish. We had wanted to have a box gutter with no parapet wall but he didn't know how to draw it! This is what we ended up with, and even that doesn't seem like the usual way of doing this. The chippie has taken it to mean joist hangers. Good to hear that they're ok for this, cheers.
     
  5. Leofric

    Leofric

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    :eek: more to this than how the rafters are supported :!:
     
  6. Naknah

    Naknah

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    What do you mean Leofric? Can you see a problem? I can’t understand about the blockwork getting wider and I’ll be checking that they put boards across the joists to make the fall front to back. Cavity closer?
     
  7. ^woody^

    ^woody^

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    Why does/did it need a box gutter? Is this wall a boundary or party wall?

    There are ways to design a gutter over a cavity wall, but it should only be if there are limiting factors which require it instead of something else. Box gutters are prone to blocking and longer-term maintenance issues, plus there is the issue of how to line them and design them with the correct width and fall.
     
  8. Naknah

    Naknah

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    Hi woody

    Reason for the box gutter is the proximity of the neighbour’s wall. There isn’t enough room between the walls for us to have a gutter. You can just about see the neighbour’s wall on the drawing which were shown as flashing into (neighbour has agreed to this).
     
  9. ^woody^

    ^woody^

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    OMG. Is that what it is. These really are the worst "drawings" I've seen for a long long time. I hope you did not pay for them.

    If the builder is being forced to make up this detail as he goes, then you need to try and ensure that it is suitable and won't just last for a few months until the first snow and ice or the next heavy downpour once the scaffold is down. Your building inspector may help, but you can't rely on him as that won't be his job and he may not even inspect this item anyway as it's not part of his regime.
     
  10. Naknah

    Naknah

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    That’s my plan, hence the question about the joist hangers because all the drawings of box gutters I can find online have the joists sat on top of the wall. It sounds like that’s ok though, so I’ll just check the rest matches the construction details I can find online.

    Unfortunately I did pay for these. I think I would have done a better job myself (which was my original plan). sigh
     
  11. Leofric

    Leofric

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    Can't see any construction notes but the drawing lacks detail , could be anything , so how could anybody approve it ? One thing that looks wrong is the roof window is almost in the box gutter, IIRC leadwork should extend at last 450mm up the pitch roof from this sort of gutter. What are the gutter lining, coping, leadwork , flashing details ? What are the rooflight ,insulation , vapour barrier ,ceiling finish details :?:
     
  12. Notch7

    Notch7

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    Parapet walls need detailing correctly to avoid damp or leak issues.

    Box gutters need to be large enough to cope with a certain amount of leaf blockage and snow n ice capacity.

    Even if it causes a few days delay, I would get it detailed correctly before proceeding. Theres anything complicated or expensive about getting it right. But a pain in the arris after its all finished.
     
    Last edited: 18 Mar 2019
  13. ^woody^

    ^woody^

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    How far has the work got?
     
  14. Naknah

    Naknah

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    It is all just about to be set in stone (almost literally). The brickie is up to the height that the joist hangers go in. The chippie was supposed to come today to check we can achieve the minimum pitch on the roof, which is supposed to be slate (another issue with the drawings) and tell the brickie what to add above the joist hangers.

    450mm would be a third of the length of the roof. Surely that's not right. The text on the window just says "installed in accordance with manufacturer's instructions".

    I missed the text out of the original upload. This is the full thing, although I'm not sure it adds a huge amount. This does have full plans building regs sign off...
     

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  15. ^woody^

    ^woody^

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    How long will that box gutter be? It can't be done in lead if more than 1m long unless it's stepped.
     
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