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Can't find source of leak coming through roof of bay window

Hi, I have a tall two storey Victorian house that has been converted into two flats, my flat is the ground floor one and has a bay window with what I think is a concrete roof (this has been changed from a tile roof prior to us buying the property). The bay window room has always been a bit damp and we could never sort out the problem so thought it was just old window/building, however, with all the bad weather there has been a leak coming in through the roof of the bay. We have filled in all the render issues around the bay, and had the bay re roofer with a product that has been guaranteed for 25 years....there is still a leak!

We have water tested the bay roof with a hose pipe and no water has got in through this roof but we have had conflicting advice from two roofers and a builder that we have had to look at the property. The first roofer (who was recommended by a friend and fixed the bay) suggested the leak was actually coming from the main roof and running down the wall through the window and sill above (which had a huge amount of water on the sill inside when we looked at it) exiting in the interior of the bay window, there is a water line on the render coming from the roof down to the widow above the bay (the sill of this window sits on top of the bay). However, the upstairs owner was not happy with this diagnosis so got another roofer in who said the problem only lay with the window sill above which needed re rendering.

Another builder has now looked into the bay window roof (which has now fallen in, it is plasterboard) and says that the timber that is structural and holding up the bay (and flat above) has bowed causing the bricks above to move causing the leak. This is now clearly a major issue. This builder is going to replace to timber, fix the window sill above and says this will solve the problem.

I am fairly confident that this builder has a point as I feel the leak has gone unnoticed for a fair few years however am worried that the leak is not coming from the window but the actual roof as the first roofer suggested and causing problems with the integrity of the building. Any advice on how to locate this leak would be much appreciated.

2 Answers from MyBuilder Roofers

Best Answer

I have seen this problem on numerous occasions where buildings are rendered. The main problem is that the render tends to be at times 15mm thick and most people cut into the wall 25mm to put the lead flashing in. Into bare brickwork this is adequate but on rendered buildings I always go into the wall 50mm to be safe. This ensures that any water that may have got behind the render from driving rain cannot get behind the flashing. Hope this helps, if the problem continues probably worth getting a tradesman that deals with flat roofs on a regular basis.


Answered 29th Mar 2014

Your first builder may have a valid point. If the gutter is blocked, water may be blown back under the fascia or if the membrane is compromised, felt or other type, the water may enter just below the last slate and track down the wall


Answered 19th Dec 2018

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