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Space/gap between rear semi-detached extensions

Discussion in 'Building' started by masamune, 7 Sep 2021.

  1. masamune

    masamune

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    Hi,

    There are a few threads on the subject. However I am no surveyor or builder, so I want some input on what would be the best approach on extension spacing and damp mitigation, based on experience. And if anything to discuss before that wall goes up.

    The neighbours are building a 4 meter extension right next to our existing one, semi-detached houses. We have already consulted with each other and their builder intends to leave a bit more than 100mm gap between walls. Our extension is pitched with tiles, theirs will come at lower height as a flat roof (~3metres tall), potentially meeting our eaves at same height.

    While researching on issue of damp, I read from a surveyor the proposed solution for debris and damp prevention, is by way of lead flashing chasing our side wall render and bridge on their roof. So that it seals the highest point between walls to prevent things falling in.

    When I put this to the neighbours, their builder responded with alternative:
    1.) They will angle the “floor” surface in the gap between the two structures to ensure no rain water can settle, that will lead out to a drain
    2.) They will look to mitigate the water/debris from entering the gap in the first place by installing guttering over the gap so it blocks any water from falling down and just runs the water down the guttering structure.

    I am not familiar with any of this, but the angle surface in the gap I imagine that is below the DPC. But gutters do leak or fail over time, so it does not sound like an ideal long term solution in my mind.

    Just being cautious here and looking into the future. If this is not done properly from the outset, it could become both our problem or I may be overthinking. Nevertheless they are looking at ways to mitigate.
     
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  3. ^woody^

    ^woody^

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    There is no damp issue. No mass debris issue. No maintenance issue. No access for maintenance issue. No issue at all with any gap, only lots of crap talking about an issue.
     
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  4. masamune

    masamune

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  5. When did you make the site visit?
     
  6. ^woody^

    ^woody^

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    Its an external wall, so whether rain from a gutter, a gap or whatever gets down there, its no different to if there was not an extension wall there!

    Likewise for the ground, rain soaks into it like it does around any extension and does not need any special sloping or whatever
     
  7. Except that with no extension wall there would be no narrow gap to trap wind-borne leaves or other detritus.

    But then youve made a site visit and established that there will not be any of those, so thats fine.
     
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  8. masamune

    masamune

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    Well exactly, this is what I'm trying to establish. If leaves and other matter fall and accumulate or get trapped over time, could they not bridge the two outside wall leaves over DPC and retain dripping water?
     
  9. 23vc

    23vc

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    There are thousands of extensions built like this, I’d assume if it was an issue it’d be better plublicised. Happy to be proved wrong but pretty sure it ain’t an issue. You won’t get a load of cr4p falling through a narrow gap and building in height above the dpc level.
     
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  11. masamune

    masamune

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    I agree on the probabilities of this occurring, which is why I asked of people's real experiences, as I would rather not rely on assumptions :)

    The amount of shoddy work around me can give the same cowboy builders who made it in the first place, enough work for another century:D

    I too hope this will not be an issue. Just feel the builder next doors is small business without many extensions under his belt, from the way he goes around work so far. Nevertheless polite and communicating!
     
  12. 23vc

    23vc

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    I built one in 2009, neighbour built theirs in 2011 with about an inch or two gap between the adjacent roof verges, no issues.
     
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  13. conny

    conny

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    The smaller the gap the smaller the chances, however, the OP is talking about a 4" gap, (100mm), not a 1" gap so the possibilities of trapped leaves are increased.
    If you are going to have a 4" gap you can knock up a 'scraper' to remove most of any debris that may collect.
    You will need a short piece of metal or thick plastic and one of those extending brush poles 04 drain rods that will extend to 4 metres. You attach the pole/rods to the plate using one of these;
    Silverline 993059 Broom Handle Bracket Metal 26-29 mm (1-1/8 Inches) Diameter : AmazonSmile: DIY & Tools

    If any debris collects you simply extend the pole to it's full length, slide it up to the back of the gap and pull the debris out. After use just collapse the pole to it's shortest length and store it away till next time.
     
  14. ^woody^

    ^woody^

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    Yeah the chances increase from zero to zero x1, whatever that equals. :rolleyes:
     
  15. masamune

    masamune

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    Good to know. Interpreting a bit freely, an inch or two off the verges means about the same gap of ~100mm, assuming verges are about 50mm each from outter walls.
     
  16. Harry Bloomfield

    Harry Bloomfield

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    Sorry Woody, I agree with Conny - any gap will collect some wind blown debris over time and it will need cleaning out.
     
  17. ^woody^

    ^woody^

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    What, one leaf per year? I'm not sure what other debris gets blown around suburban gardens.
     
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