New felt roof, recurring flashing leak

Discussion in 'Roofing and Guttering' started by Kaymo, 5 Apr 2020.

  1. Kaymo

    Kaymo

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    Morning all, hope you are well and staying sane in these crazy times. Sorry, below bit of a long story but wanted to include all the details.

    I have had a new felt roof on flat roof of extension, which is built on to a 200 year old sandstone/whinstone house. Keep getting a leak on one section of the flashing (not sure if that's what you call it when its felt). Roofer came back out and replaced that section. He thought that it was getting in behind the joint due to crumbling parts of the stone so also dug some of this out and cemented in that section after replacing flashing and used CT1 in the joint between felt and stone.

    However, it is still leaking. Its a small leak, and it takes a lot of water to get it to happen, and as its running down the old wall I wouldn't even know about it if I hadn't opened the ceiling inside to put insulation in (I saw a damp patch and checked with a hose to see if it was residual). Having said that, I don't want to fill a void with insulation where there is even a small amount of water coming in.

    The roofer has offered to come out again and trying cutting in a bit further up, but not sure I want to just keep doing this and hoping for the best, I'd rather something more conclusive so that I can close up with confidence.

    Once thought I had was to put a render fillet above the flashing tapering away from the stone and covering the felt. Not sure if this would work. Another was to cover where the leak is with a bitumen mastic or some other product where I could make a fillet that would push the water away towards the roof.

    Anyone have any advice?

    2020-04-05 09.52.40.jpg
     
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  3. noseall

    noseall

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    If it is the flashing joint leaking then a lead cover flashing would behave better.
     
  4. Kaymo

    Kaymo

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    Thanks. In what way would the joint behave better if the flashing was lead?
     
  5. noseall

    noseall

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    If you were to chase in a lead flashing, higher up the wall, then it won't be subject to any of the movement associated with the roof.
    I'm not entirely convinced the joint is to blame, however.
     
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  6. Kaymo

    Kaymo

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    Right, I see what you mean. What I had been thinking of doing was rendering over the top of the felt and up the stone a little, feathering it up the wall, then painting over, but I suppose if there is movement the same will apply.

    Still, I am surprised that movement would have an effect this quickly. The joint has been sealed in with CT1, which is supposed to be flexible, and its been less than a week since it was done.

    As this area will not be seen (flat roof has a slate false roof to the front), is there a cheaper alternative to lead, are these plastic flashings any good for example, even flashband or something like that?
     
  7. Kaymo

    Kaymo

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    Sorry, missed this part. What do you think is more likely?
     
  8. noseall

    noseall

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    Not sure..? Is there a window above?
     
  9. Kaymo

    Kaymo

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    No window above. I've tested it pretty methodically with a hose to narrow down the area, and its either the joint or the felt. I've just trowelled on some bitumen mastic in the area I've narrowed it down to and I am going to test it again with the hose on the same area. I think bitumen mastic is waterproof more or less instantly.
     
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  11. datarebal

    datarebal

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    I assume the felt is actually into the masonary ?
    A lead flashing would have been more fitting , what with tidy lime work and all
    However, I'd be suspicious of the pointing around the stones
     

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  12. Kaymo

    Kaymo

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    Yes, a raggle was cut and felt run into masonry. On the second attempt he raked out the stones above the raggle in case it was getting behind and cemented in above the raggle, the fillet that can be seen in photo.

    I would have insisted on lead if it was visible, but it can't be seen from the ground so I left the roofer to decide what to do and he went for felt.

    I was too initially, but I brought the hose down to a few inches above the raggle and was still getting the leak.

    I have been concentrating the water on the area in the red circle, and in this photo you can see the bitumen mastic I added. However hosing again tonight after the mastic was added it was still leaking. When I lowered the hose so the water wasn't going any higher than the mastic I got no leak, so maybe I will try some bitumen paint over the cement to seal that area and try again tomorrow.

    IMG_20200405_200859246.jpg
     
  13. Kaymo

    Kaymo

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    This morning I painted a thick coat of bitumen paint overlapping the raggle joint to about 100mm above, covering to just above the cement fillet in the pic.

    Early this afternoon I rigged up the hose pointing at the position where I was getting the leak before, and ran for about 30-40 minutes and no leak. I will probably give it another hosing over the whole area later just to be sure, but that appears to be the leak fixed now.

    My thoughts turn to what to do next. Is the lead flashing still necessary, or just covering the the raggle the full length with bitumen in the same way as a belt and braces?

    The roofer also got back to me with regards to the joint and suggested a lead flashing. Not clear yet whether he is suggesting that he covers the cost of this or whether I am expected to contribute. Having spent £3.5k on the roof I am a bit put out at the amount of time I have already spent personally tracing and repairing this leak, so am interested in views as to who should foot the cost of the lead flashing?

    Thanks.
     
  14. datarebal

    datarebal

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    Why did the roofer not investigate?
    He may well now say you've messed with it your on your own
    It's not really a proper fix. Just a sticking plaster.
     
  15. Kaymo

    Kaymo

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    That's a good question, I would like to know the answer to that myself. Maybe because he has already been paid, or maybe on another job that he doesn't want to leave, or something else, who knows.

    I think that would be a bit of a stretch, given that he hasn't offered me an alternative. All I have been doing is trying to pinpoint where the leak is, and bitumen isn't going to harm felt.

    The main reason I am getting involved is the urgency. I have a hole in my kitchen ceiling that I would like to close up. I can't do that until I know there is no more water coming in. I don't want to be waiting weeks before I close up the ceiling which is right above where my family make their meals.

    The other reason is that I wanted to be sure where the problem is, because I didn't want to be chasing the roofer for something that is not his fault. Personally I think it should have been for him to prove to me one way or another, but I can't really wait.

    As it stands there is still a small leak there. I am utterly baffled by this. There was a definite leak on the raggle before he put the cement fillet in above it, but even if that leak was still there I highly doubt that water is passing through a visibly continuous layer of bitumen. I've also pressed all weather sealant into any points in the mortar where it doesn't look completely continuous with the wall.

    I am starting to wonder now if the mortar pointing is shallow and there is a void behind there. Maybe the raggle crossed this point and was a weak point, but it might be coming in at other points too. The thing is that there are no obvious gaps, and I am now wondering whether the small leak that remains is water passing directly through the lime mortar, which will be porous, but would it be so porous that water would pass through within 30 minutes of spraying?

    This is driving me demented!
     
  16. Alastairreid

    Alastairreid

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    Where in west lothian are you?
     
  17. Kaymo

    Kaymo

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    Why do you ask Alastair?

    Sorry, not so keen on putting my exact location on the forum.
     
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