Leaking upvc window cill?

Postby scroogemonster » Sat Oct 11, 2008 12:06 pm

I have had new UPVC double glazing installed in our house (18 months ago)

The bedroom window has leaked and the plasterboard underneath the window has soaked up water and blown away from the wall during the heavy rains.

The window is a upvc bay window which sits on a timber frame hollow bay construction (weatherboarded and rendered on the outside with a cavity and plasterboard on the inside)

It would appear that water is dripping out between the base of the UPVC sill and the wooden frame on which the window sits on.

Can anyone tell me how this is happening? Any water that gets into the window is supposed to drain through the little holes and out onto the front of the window sill.

I would assume that there must be a crack in the window sill for this to happen and water is getting in during the driving rain and soaking through holes somewhere to get underneath the window sill

I have checked all the silicon sealant under the sill and around the window and its all fine including the seals on the windows themselves

Has anyone got any ideas?
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Joined: Thu Aug 16, 2007 3:41 pm


Simply Build It

Postby memento » Thu Oct 16, 2008 7:26 pm

Are you 100% certain its coming in under the cill, and not either through the glass beads or where the frame meets the cill? Also is this a load bearing bay? if so check on the corners outside where the bay pole goes through the cill as it may have been cut through to take the weight its possable the water is getting in this way well placed silicon will stop this from happening.Another common mistake is the cill has been fixed through to the timber frame before the frame was fixed in place so any wind driven rain will travel down the thread and sit on the timber.

If i was to get this call out first thing i would check is external seals as you have done then the base of the bay poles, then id remove bottom glass bead and pour pint of water in to window frame to make sure drainage is working.if drainage is working dry off frame and smear any screws in frame fixed to cill with silicone and finaly if you can see the back of plastic cill where the frame meets cill run a bead of silicone here aswell.

If none of these stop the problem then you may need to accuire about having the frame removed and refitted.
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Joined: Mon Sep 01, 2008 6:19 pm

Postby scroogemonster » Sun Oct 19, 2008 3:13 pm

Thanks for that. I got their guys who fitted it out and they removed the glass and pushed the frame forward. They had screwed through the window sill into the wooden frame but there was a drill hole without a screw. Water was getting onto the top of the cill and draining through the hole into the inside of the window sill and out through a screw thread further along. Thay have bunged it up with a big load of silicon. Seemes to be ok at the moment, I will monitor it for a while just to be sure. This isnt a load bearing bay (no bay poles) just timber frame, chicken wire and render
Posts: 23
Joined: Thu Aug 16, 2007 3:41 pm

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