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Roof leak between extension and garage

Discussion in 'Roofing and Guttering' started by roof, 21 Oct 2019.

  1. roof

    roof

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    I'll ask simpler questions here as the length of the post may have been a deterrent.

    Is it possible to waterproof a roof with elevated wooden fences in the way? With liquid waterproofing for example, by painting it/applying it around the base/poles?

    For more context, I moved the lengthy description to the second post

    Edit: here are some more questions:

    - am I right in that it was a mistake to have material bridging the two structures, and so this has to go?

    - the flat roof has square paving stones on top. Is it a fair assumption that that's not waterproof, and any waterproofing is done by the layer underneath (presumably bitumen)?

    - if we put new flashings starting under the waterproof bitumen layer, wide enough to end over the sedum roof, do we need copings underneath as well, or having the membrane hanging over the edge into the gap under these new flashings is enough?

    - it is better to put guttering instead around the flat roof edges instead of flashings, with a single pipe at the corner discharging the water onto the sedum roof?

    - if we use code 5 lead flashing, 600mm wide, what's max length for each section and how much overlapping?
     
    Last edited: 25 Oct 2019
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  3. roof

    roof

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    Moving the original full description here:

    We have been struggling for a month with water leaking into our extension from somewhere at the roof where it meets the roof of the neighbouring garage. The whole structure is complicated and we still don't know exactly where the water gets in or how to solve it (and we've had several roofers round to look at it already), although we know the problem is at the connection with the garage. I will try to explain it.

    The property is a converted detached Victorian house with a large garage on the side. We own the ground floor flat and three years ago we made a large extension that almost touches the back of the garage on two sides. On top of the garage there is a roof terrace that belongs to the flat above us. This roof terrace was re-done (wooden parts restored/replaced) last year. To complicate things, the garage is owned by a third person.

    The water from the roof terrace is supposed to flow on to the extension roof. However, some (actually a lot of) water manages to enter in the narrow space between the two buildings and make its way into the walls of both structures. The problem only appeared about a month ago, but investigation was tough because the damp was all around the bottom of the extension (water entered the cavity and traveled all around). After ruling out fenestration and rising damp issues we eventually isolated the issue at the connection with the garage.

    The two structures have a gap that is about 10cm on average. The extension roof has an EPDM membrane that goes all the way to the edge, then there are concrete coping stones above, and lead flashings above them to bridge with the garage roof. The garage roof sits slightly higher and has some concrete paving stones on top. The roof terrace above is made of wooden slats with gaps allowing rainwater to fall on the paving stones. I don't know whether the paving stones are supposed to be waterproof or if there's a waterproof asphalt layer under them. We think the latter, but it's very hard to see.

    Water somehow makes its way under the lead flashing and spreads on both sides to the bricks of both the garage and the extension. The amount of water that enters when it rains is a lot. Last Saturday night I went to bed after I had dried out all the surfaces under the kitchen cupboards with a wet vac and left two giant commercial dehumidifiers running overnight (they fill a bucket each overnight), and woke up the next day to a puddle of water under the kitchen cupboards (an area about 6sqm) of more than 1cm high.

    We are thinking of a few possible solutions:

    1) eliminate the mortar that acts as bridge between the two buildings, and insert a flashing at a level just below whatever the waterproof threshold is, a flashing long enough to bring the water over where we currently have coping stones (so these will go, leaving only the flashing there). The problem with this is that we don't know for sure that the garage has indeed a fully waterproof layer (but then if this fails, at least we'd know for sure that the supposed waterproof layer is not good and so the garage roof will need to be redone).

    2) make the top layer (paving stones) waterproof, and ensure that all rain water flows to the extension roof above the flashings. The problem with that is the roof terrace. Removing it and reinstating/rebuilding it would be very expensive, and also you would retain the stone bridge between the buildings which spreads water around if there is a failure on either side.

    3) Waterproofing the top of the roof without removing the terrace would be better, but can it be done? The wooden decking can easily be moved, but that would still leave the walls on the sides and some feet that the timber frame of the terrace rest on. Would pouring some liquid solution work in that case? I have searched and found some products (for example Arcaroof) that can be applied with brushes, which means we could apply it everywhere on top and over the entire side, then put back the wooden slates. Are these reliable?

    Any thoughts/ideas or other options to consider? Also, if you are a professional and want to take a look (I'm based in NW London), by all means send me a PM.
     
    Last edited: 28 Oct 2019
  4. Notch7

    Notch7

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    Did your architect provide the detailing and drawings to show how the damp arrangements should be dealt with?
    Or was that decision left to the builder.

    A new extension should always be constructed so it is isolated from damp and rain water discharge from existing structures.

    Unfortunately the pictures dont explain the construction detail.
     
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  5. Nige F

    Nige F

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  6. What were the simpler questions :?::D
     
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  7. ^woody^

    ^woody^

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    Hangers sticking up above the joists. WTF?

    I dont understand none of the other stuff, or what's going on.
     
  8. JohnD

    JohnD

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    Very interesting variety of building techniques.
     
  9. foxhole

    foxhole

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    Mucking fuddle.
     
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  11. noseall

    noseall

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    Me neither. Looks like someone chucked a hand grenade into a Travis Perkins and that's where all the stuff landed.

    Trés confusing.:confused:
     
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  12. HERTS P&D

    HERTS P&D

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    You would of being better off moving!

    Andy
     
  13. Nige F

    Nige F

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    Is that a sedum roof - or just a load of weeds ?
     
  14. ^woody^

    ^woody^

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    foto_no_exif (2).jpg
     
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  15. roof

    roof

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    The architect design has a gap between the structures with only flashing over it. Builder closed the gap with the coping stones and even some mortar underneath them (showing in one photo under the membrane).
    Hence the first solution (suggested by a roofer) is to get rid of the stones to maintain the gap as per the original design, with bigger flashings to have the water flow straight on the sedum roof
     
  16. roof

    roof

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    Cheers. So you would keep the copings and put some additional waterproof material between them and the lead flashing?
    Our concern is that water if water comes from under the flashings (on the left side as we are looking at it, as the flashings are above what is the flat roof's waterproof layer), then it enters through the mortar+coping stones bridge, and so any work on the flashings won't help.
     
    Last edited: 25 Oct 2019
  17. roof

    roof

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    I think that was temporary, there's more timber above those and in later photos I don't see hangers sticking up.

    Sorry, I added them now, at first post and also here. Perhaps not simpler, apologies for that.

    - am I right in that it was a mistake to have material bridging the two structures, and so this has to go?

    - the flat roof has square paving stones on top. Is it a fair assumption that that's not waterproof, and any waterproofing is done by the layer underneath (presumably bitumen)?

    - if we put new flashings starting under the waterproof bitumen layer, wide enough to end over the sedum roof, do we need copings underneath as well, or having the membrane hanging over the edge into the gap under these new flashings is enough?

    - it is better to put guttering instead around the flat roof edges instead of flashings, with a single pipe at the corner discharging the water onto the sedum roof?

    - if we use code 5 lead flashing, 600mm wide, what's max length for each section and how much overlapping?
     
    Last edited: 25 Oct 2019
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