Bay window leak - New Build

Discussion in 'Builders' Talk' started by Stuart Mackenzie, Oct 31, 2018.

  1. Stuart Mackenzie

    Stuart Mackenzie New Member

    Hi Folks,

    First post on screwfix as I felt the need to seek some sound advice before the builders (Miller Homes) attempt to fix again with a new GRP canopy.

    We have a bay window as can be seen in the attached pictures.Problem has been for a long time that in strong wind only that water is forming above the ceiling of the bay window and eventually working its way into the living room. Now the house builders have been out to fix 5 times and each time they do pretty much the same thing which is to re-apply sealant around the lead flashing as the thought is that water is being blown up (capillary action as I was told) under the flashing where it meets the GRP canopy seal and is finding a way through - we have confirmed this happens by removing the ceiling and spraying water on the flashing so its forced up behind it.

    The design of the GRP canopy seems to be that is does not tie into between the bricks it just sits against the external brick where its sealed and then the lead flashing is draped over it where the lead flashing is then sealed on the underside to the GRP canopy and house.

    Other things that have been looked at:
    1. Seals on window above bay window - these where checked to have some gaps so this was sealed but seemed to do nothing.
    2. DPC (I think it's called) can be seen from inside the house where you can feel that the cavity, certainly from under the DPC, is dry but brick work on the outside facing wall, where it can seem from inside the house under the GRP canopy is wet when it rains/high wind so suggest the problem is with the lead flashing and GRP canopy seal
    3. Vents for cavity trays checked and confirmed seem to be fitted OK
    4. GRP canopy seems to be watertight OK

    My questions are:
    1. Is this design normal where its reliant on a bead of silicon to seal it under the lead flashing?
    2. How can they best seal the lead flashing 100%
    3. One builder mentioned that it's possible that water is running down inside of external wall in the cavity, hitting the cavity tray or DPC and then being directed through the brickwork onto the outside of the external wall where it can be seen coming into the house. Basically saying the cavity trays might not be fitted right over the brick work. No other windows have this problem though and they all have cracks in the silicon on the window above!
    4. Should I try to they them to inspect the cavity trays?

    Any advice welcome and sorry for the long post!

    Lastly one possible tell tail thing we had seen is that after it was leaking bad we could see water running out of 2 vents but guess this could be the cavity trays doing job?


    1540974366102410.jpg 1540974365883953.jpg 1540974365666851.jpg 1540974365453581.jpg 1540974365241943.jpg 1540974365103304.jpg 1540974365011366.jpg
  2. KIAB

    KIAB Well-Known Member

    Water shouldn't be pouring out of the two weep vents,could be a problem higher up.
  3. Stuart Mackenzie

    Stuart Mackenzie New Member

    Thanks. The seals around the window up above had cracked with settlement. I patched these up so think that's possibly been fixed but hard to say without a storm passing. They are apparently going to re-seal all windows for this reason on Friday. Bay window still leaks though :-(
  4. jimoz

    jimoz Active Member

    Not a bad shout about problem further up. Is the cavity tray above the level of lead flashing and/or is it stepped down to lintel height. If cavity tray not installed correctly probably best off pursuing via warranty provider / building control as would of thought they'd be bang to rights
  5. KIAB

    KIAB Well-Known Member

    Exactly, spot on.

    Need to explore a bit to see if the tray is fitted & it's fitted correctly,& tray has end stops,as it's designed to collect any water,moisture & drain it through the weep vents,& stop any water finding it's way past the flashing & into the cavity,& into the room below.
    Last edited: Oct 31, 2018
  6. Stuart Mackenzie

    Stuart Mackenzie New Member

    Thanks for the reply. Can you please educate me, should the cavity tray be above the lead flashing to be clear? I thought if its above how would it catch anything coming through from under the flashing. Im also not clear how the GRP canopy is supposed to seal aginst the side of the house. What is to stop water from going up behind the flashing, then down into the house like my example in the picture. Screenshot_20181031-113121_Chrome.jpg
  7. KIAB

    KIAB Well-Known Member

    The lead flashing should be under the cavity tray, & chased in around 25mm into wall.


    Can't find correct image, but this show same thing, cavity tray over flashing.

    Last edited: Oct 31, 2018
  8. Stuart Mackenzie

    Stuart Mackenzie New Member

    Thanks. I did a quick paint drawing of what i think my setup then looks like which from looking it would suggest im on right tracks. It would suggest that there is a point where water could get through if the sealant (in red) was not done correctly. Does this then meet building regulations?
  9. KIAB

    KIAB Well-Known Member

    You need to know whether a cavity was fitted,& if so,the water could be draining of the ends of the tray & then finding it's way down & eventually below the sealant.(Water can take some very strange routes going from A to B.)

    Need a flexible inspection camera to have a nosey in cavity & see what is going on.
  10. Stuart Mackenzie

    Stuart Mackenzie New Member

    OK thanks for the replies. I ask the builders on Friday if they can do an inspection of the cavity. Cheers!
  11. Stuart Mackenzie

    Stuart Mackenzie New Member

    Update: Miller homes came out and replaced the canopy in a rush job so they could finish at 3pm and what do you know it leaked in the following stormy weather. Nothing was checked cavity wise but its definitely coming in from under the flashing. It's only leaking in one area now. They also never resealed the silicon on the windows so we are furious and have raised a complaint with NHBC. I have asked them if they will let us get it fixed independently now and have them reimburse us as this will be the 5th or 6th time now they have failed to fix it. I believe its a design flaw as many other homes have the same thing.

    Can anyone recommend someone the the Glasgow area who could fix this for us?


    Attached Files:

  12. jonathanc

    jonathanc Active Member


    Get 3 quotes from three builders to fix the issue. Send them to Miller homes and say that if the issue is not resolved within 14 days the matter will go to small claims court
  13. KIAB

    KIAB Well-Known Member

    Would easily win.

    I would rip the lot off & have a warm roof with OSB3 & GRP covering,& forgret using the preformed grp canopy.
  14. jimoz

    jimoz Active Member

    Was that lead flashing like that when you bought the house? Just looks wrong to me. Why does it go so far past the canopy on the right? Also looks like you have weep holes in two different courses?! Clear ones above lead and red ones one course higher.
    Have a look at the silicone around that first floor window. At the bottom near the cill brickwork junction. Maybe water entering cavity there and no or inadequate tray below this above bay window
  15. jimoz

    jimoz Active Member

    Sorry have re read posts and seen you're already onto this. My guess is lack of stop ends or fold on cavity trays. Water flowing over ends and tracking back into cavity above bay. Reckon there's nothing wrong with canopy or flashing (as messy as it looks!)
  16. KIAB

    KIAB Well-Known Member

    Well spotted.:)

    You have a four weep vents 2 courses above flashing, then I just noticed grey clips/vents fixed to top edge of flashing.:confused:
  17. KIAB

    KIAB Well-Known Member

    I also thought that earlier,which is why I said have a nosey in cavity & see what's going on.
  18. jimoz

    jimoz Active Member

    One thought though. The water is showing on the external side of the wall not in the cavity. Am I off my head or could it be the case that the cavity tray has been put in and the flashing is inserted above this in the same course. Therefore any water is running out and coming down the inside of the flashing into the house. If you ripped that flashing off and inserted it one course lower it could solve the problem. 150mm would still be correct upstanding here. Not sure if has to be higher in Scotland. Is easier to drop flashing than lift cavity tray though
  19. Stuart Mackenzie

    Stuart Mackenzie New Member

    If you look at the diagram I sent Im pretty sure the water is coming in through the flashing as all there is to stop it is sealant as far as I can tell from the design. Before they replaced the canopy it was leaking in 4 different places and now just seems to be one. They mention that when they lifted the flashing they could see that the canopy was not sealed right to the brick work. I was thinking I could maybe try sealing the bottom, sides and overlaps of the flashing with lead mate so it's 100% sealed off. Would that cause any problems? At least I could then tell if it's coming through the flashing or down from the cavity. I worry if I **** about with it Miller homes might use that as an excuse though. I'm just sick of it. It's been like this for months now. Cheers
  20. Stuart Mackenzie

    Stuart Mackenzie New Member

    Update: they have been out and replaced all of the cavity trays so had a bunch of bricks out. Anyway long story short it now leaks in 3 places instead of one. They have not used any sealant this time so it's just the flashing tied in with the brick work with morter. Now they want to take the window out up above but I don't know how it could be the window above if the cavity trays are doing what they are supposed to do. I think im going to have a bash at sealing it myself with lead mate behind the flashing and then all round the edge of the flashing top and bottom. I don't want them do rip anymore of the house apart and I'm sure it's coming in behind the flashing.

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