Lead flash under window sill condensation?

B

BenHen

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Hello

Recently had my loft converted and there is a damp patch in the corner of the window. I popped one of the glass panes out and did a better job of sealing between the lead and the window sill on the outside (there were one or two small gaps).

However the damp still seemed to be occurring so I pulled the sill off to look underneath and the plaster board was all mouldy (it’s a few months old). Left it now a few weeks and it appears that the lead is getting lots of damp condensation on it.

I’ve attached some photos but would be interested to know the best way to proceed?

Is it likely to be condensation causing the damp patch?

Do I trim the lead back to the sill on the inside (overhanging currently on the inside by 50mm or so) then seal the gap flush to the sill? Do I put some sort of expanding foam insulation in the gap rather than plasterboard directly on top of the lead? Any other ideas?

Would contact the loft company but we’ve fallen out due to a plethora of shoddy work they undertook.

Thanks in advance!
BH
 

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What is the window frame sitting on, a wooden frame, an opening in brick? Can you put up some pics from outside showing the treatment of the window.

Blup
 
Hi Blup and thanks for the reply. The window is sitting on the lead and the lead is sitting on a timber frame. I’m the photo you can’t quite see this but the timber frame is 99% covered by the lead, after the lead what you can see is the top of celotex board before plasterboard has been attached through that. I’m attaching a photo of what is under the sill.

I can’t get a photo outside until I’m home in the day light which will be Friday.

Thanks
BH
 

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The lead is wrong.

the purpose of the lead is to act as a tray and it should be turned up the window frame on the inside so any water penetration can’t run inside.

being flat the lead is simply creating a flat ledge for water to come in.

up the sides there should probably be a vertical DPC protecting the plasterboard from the outside - it looks like the plasterboard touches the lead.

minor failures on damp detailing are the main cause of damp appearing on plaster.
 
Is the insulated studwork under and around the window properly ventilated? Its 50mm for a cold roof, dont see why the requirements should be that different for vertical studwork. Without that the warm air gets trapped and condenses inside the frame at the nearest cold spot. The other possibilty that comes to mind is that it got soaked in rain water before it was finished and needs to dry out.

Your suggestion might be worth trying because it would be relatively easy to remove, but I would be cautious about chopping the leadwork as it might loosen the remaining part.

Blup
 
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