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Leak coming through wall under steel on new extension

Discussion in 'Roofing and Guttering' started by Flipjango, 13 Oct 2019.

  1. Flipjango

    Flipjango

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    We have a mysterious leak in our new extension and we're struggling to work out what's going on. I'm not convinced posting photos will help with understanding what's going on as the leak doesn't appear to be coming from anywhere visible so there's nothing exactly to take photos of, but to give some back story, we bought a nearly derelict house. The whole house was refurbished and a new flat roofed extension with a parapet wall and coping stones was added to the rear as well as all new render been put on the entire house. We realise now, a year on, that the builders have proved to not be particularly good, and have now quite literally vanished, so we have no chance of getting them back to rectify anything. We have had a lot of leaks so far (mostly due to using insulated breathable lime based render and finding out we needed to coat it with breathable waterproofing sealant as we're in an exposed position), but have managed to rectify all the others except this one, which we just can't work out.

    When it rains heavily, water is literally pouring down the wall in the new extension, in the corner next to the steels that have been put in to support the new opening. Its coming in directly under and slightly to the side of the steel, though not under the ceiling itself, which is higher (the steel drops down by about 30cm from the main ceiling). On the wall outside in the same vicinity there is a point where a soil pipe exits the wall so our first job was to seal around the pipe exit hole with silicone. This didn't help. There is an airbrick that ventilates the warmdeck roof level with the point the water enters, but about 45cm further along the wall. Above there is a parapet wall with coping stones. The render seems cracked around the point where the coping stones meet the render. Sky also ran their cable along this join. We siliconed along the crack, and moved the sky cable and it seemed to stop leaking for a few days so we thought "halleluja, we've fixed it!" But yesterday it leaked again worse than ever (literally a river pouring down the wall) and now i'm wondering if its just to do with the direction of the rain. The coping stones are a lot higher than the leak (the parapet is about 30cm above the flat roof, and the steel about 30cm below) and there have been no leaks at ceiling level, only lower down near the bottom of the steel, but I am aware that water travels in mysterious ways and may not be leaking where the water is coming in. There is no flashing I can see where the coping stones meet the wall, but as its rendered, its possible is is under the render. The render of the wall has been heaving waterproofed with Surfapore C three times now. I can't see anything else it can be.
     
  2. Nige F

    Nige F

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    Joints in the copings on the parapet wall ?
     
  3. Notch7

    Notch7

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    A picture externally from further back showing the overall extension would be very helpful.

    In general:
    If the house is cavity wall construction, the steel should have a cavity tray above it. (NHBC recommend even on rendered walls).

    The house extension walls where they abut the house should have vertical DPC or a continued cavity.

    Parapet walls are very prone to leaking, they need some form of cavity tray and weep holes so any water getting in duscharfed externally.

    If it was me, I would be investigating the parapet first. Its worth taking off sone coping stones and see what happening.

    You also need to investigate how the flashing detail is dealt with where the parapet meets the house
    And how the flat roof flashing works in conjunction with any parapet cavity tray.
     
  4. Flipjango

    Flipjango

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    Thanks both. Sorry, should have said that its a Victorian solid wall house, so no cavity tray. The extension walls certainly conform as everything has been inspected throughout by building control and was built (if badly) to architects specification which was signed off by BC. I can dig out the plans to see how it was built but I imagine it is however would be normal.

    Should there be weepholes in the new walls? I don't see anything that would look like that unless it discharges somewhere I can't see. Certainly nothing near the top.

    I've taken pictures as well as I am able. The house is built on the top of a very steep hill, so pictures are hard to take from the ground - the patio drops off into a haha, so the ground a far far below the extension to the rear.

    As I say, i'm not able to see any flashing where the coping stones meet the wall as the coping stones abut rendering and the flashing could be underneath. The flat roof below the parapet is flashed with lead which has been painted over with some black stuff which makes it hard to see the detail.

    I've taken some pics. The first one shows the leak on the inside - the extension is to the left, the old house to the right and the photo is of the external wall. As you can see, the leak is coming in quite low down. The second and third pics are the wall in question - the leak is just where the black pipe exits the wall. The wall looks quite wet but that's fairly normal with the breathable render that we have, especially as its been raining very heavily. The final pic shows where the parapet wall joins the old house. The messy silicone is our botched job of fixing it done in the dark in heavy rain hence the mess!
     

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  5. datarebal

    datarebal

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    leaking joints in the black pipe, no proper flashing copings to house
     
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  7. catlad

    catlad

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    It could be dropping down the cavity from the roof above.
     
  8. tony1851

    tony1851

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    "everything has been inspected throughout by building control"


    Unfortunately, that means nothing.
     
  9. ^woody^

    ^woody^

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    Over the years, we've put several "cavity trays" in 9" walls to deal with problems similar to this one.
     
  10. John D v2.0

    John D v2.0

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    Hardly any overhang on the outside on those stones, it's surely just running round the outside of the coping stone? Does water poured on the coping stones drip off cleanly or just go underneath?
    And if there is a cavity tray under there, is it just directing all the water off the end of the tray where your beam is? It could be coming through further along and running along the cavity tray and emerging there..
     
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