Damp plasterboard next to stone mullion windows. Condensation or leak?

[markglos]

Dear all,

My 1700s cottage has sandstone mullion windows and the interior walls have been plastered including around the windows (plasterboard casing). Not very authentic but we didn't do it.

There is generally a lot of condensation on the window area in winter. Today there is a large damp patch along the plasterboard at the top of one of the stone windows. It has been very cold but hasn't rained for a long time now, and I can't see a reason for a pipe to exist above this area. No radiators, bathrooms etc.

It is possible that condensation has formed on the stone mullion inside the plaster casing and is now seeping through the plaster? Or is it more likely a leak from a pipe or something else?

Additional details:
- damp areas extends between 1-2 inches all the way along the top and only noticed it today
- I have prised a small screwdriver into the plaster here but no water came out. I can feel that there is a gap between the plasterboard and whatever is above it. Presumably a timber beam.
- it hasn't rained for over a week but it has been sub-zero at night for the last 5 days
- I do air the room fairly regularly but don't heat it much as it is the guest room
- the windows on the south and west experience very little condensation but the ones on the north and east can collect almost a cup of water over night. The window in question is north-facing

many thanks if anyone can help.
Certainly don't know whether to start with a roofer or builder.

 

[Toby Newell]

Pictures are worth a thousand....

 

[markglos]

here you go. Damp patch and also some condensation on window.
thanks!

 

[malcolm]

It could well be condensation. For the ceiling to get that wet the condensation might be happening higher up. Do you have access to the space above to take a look? Maybe something as daft as a bathroom extractor venting into the loft instead of outside.

Is it a loft above with good ventilation and insulation above the ceiling?

 

[Kearn]

View attachment 11944
here you go. Damp patch and also some condensation on window.
thanks!

Doesn’t look like condensation, but a saturated ceiling - presumably getting wet from above and leaking through.

 

[Toby Newell]

First of all, thank you, but a larger, upright photo would of been nice and a longer shot of the whole area, but...

Doesn't look like condensation to me. Condensation is pervasive, there would be marks or black mold around the periphery (and possibly lower down) the window would be misted / droplets / streaks with pooled water at bottom.

Looks like a leak from above, either pinhole leak from above or water ingress from outside.

 

[markglos]

thanks all for your advice and thoughts.

What is above this area is an attic bedroom. The bed is directly above the damp area and there is are no signs of damp here. No windows or drains above the area either. The humidity in a little high at about 68%. There is a bathroom adjacent to the bedroom, we only use the sink and loo.

There has been some dots of mould along the walls of the window which I cleaned up a few days ago.

Update from today:
- it rained over night and for most of the day. temp about 3degrees outside
- turned the radiator on in this room overnight
- damp patch has not grown and the condensation on the visible window stone was less
- by evening much of the damp area had disappeared but mould around the top.

Could still be a leak from somewhere. Will see what happens overnight