Roofing Question

What could be causing leak in upstairs bay window?

There is a thin long wet patch in the front of the bay window (along the crease of where the roof meets the wall), also we have now noticed wet patches under the window sill (on the inside) in the joins of the bay window which are now spreading along the wall (into the middle of the bay). We do get quite a lot of condensation inside the window which I have to regularly wipe off the window frames. Also we have had a lot of severe weather recently (driving rain, lots of wind and large hail stones). I first thought it was a problem with the roof but now the damp patches have appeared under the window sill I'm not so sure, any help would be greatly appreciated!

Many Thanks!

3 Answers

Best Answer

You dont say what the roof covering is above the bay window, but sounds like a flat roof.
The crease if its felt or lead is probably split, the water will get in there and could also travel to the head of the window, if the roofs falling in that direction.
The material has probably come to the end of its life and you need a new roof covering.

Answered 3rd Jan 2012


Member since 29 Oct 2008

You seem to have two problems. The bay window has a flat or pitched roof. The usual problem is that the flashing between roof and wall is poor quality, so water gets in and causes damp where you describle. It is much more common with a flat roofed bay window, and it might be a leaking flat roof is causing all of your problems.

Condensation of the windows is usually due to having no trickle vents, these are small vents above each window, but can also be caused by no shower and kitchen extraction, for example.

Damp patches under the windows is most likely caused by poor sealing of the window frames to the bay. All of these problems are all easy to identify by a skilled person with a damp meter and easy to cure, you just need a competant survey of the problem. That will then lead to a complete cure. Hope this all helps.

Kind regards,

Paul Albright

Answered 3rd Jan 2012

Aspire Housing

Member since 23 Nov 2011

From a window fitting point of view it is also possible that internal drainage holes within the frame (usualy unseen on a bay) are either blocked or missing entirely. I've seen some very poorly fitted/ fabricated bays over the years.
More likely though it origin is in the roof area. only way to find out for sure is for a thorough investigation. Good luck.
Dale Jones

Answered 12th Jan 2012

Pennine Glazing & Windows Installations Limited

Member since 26 May 2010

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