Damp patch suddenly appeared

[Goatrider]

This appeared on my living room wall during this morning.

It's the external wall. Above the wall is just a sloping roof (the upstairs is set back a bit with a dormer window, if that makes sense).

I've had a crawl about in the eaves and there's no leaking pipes or any signs of water.

Outside the wall there's no sign of any problems with guttering.

Any idea what it could be? (The lines are where there's cracks in the plaster)

Leaking pipe in the wall? Penetrating damp through weathered pointing or brickwork?

Go outside and take some pics for us, above the damp patch right down to ground level, will be easier to diagnose then.

Oh and what is the room above this room?

Thanks I'll take some more photos

More pics

it appears to be at the top of the wall, so it's presumably (gravity) leaking from above. I'd suspect the gutter. Climb up your ladder and see if it's blocked with leaves, or cracked, or has a loose joint.

Black marks also occur with condensation.

Does anybody drape wet washing in the house?

Thanks pigletjohn.

I've felt in the gutter and it's clear.

I do dry washing in the living room on a big clothes dryer.

I can confirm it's just at the top part of the wall. And none on the ceiling.

There's no pipes in the walls. The pipes to radiators are in a different part of the room and are external (visible) anyhow

'mmmm.

If you've got an extractor fan in the bathroom, drape it in there and leave the extractor fan running with the door and window shut

this will take the water vapour out of the house.

Meanwhile plse do a wide angle shot of that wet wall. A leak mark from the roof will usually be narrow. Condensation likely to be wide, all along the external wall, especially near the ceiling.

Tape a piece of clear plastic tightly to the wall. If water droplets appear on the wall side of the plastic, it's coming from the wall. If on the room side, it's condensation from the air.

I've cleaned it off now. It covered an area about 40cm wide. To the left are quite large French doors. There's no marks above them. And the other side is a large window, nothing above that.

I didn't have any clothes drying in there last night but I noticed there was a lot of condensation on my bedroom window this morning. I was up and out early, so didn't see the living room windows until later but I imagine they were equally wet.

Thanks for the tip on drying in the bathroom 👍

Been away for a couple of days. Come back and the wall still feels damp. I can now clearly see a damp area on the external wall too.

I don't understand what's caused it. What sort of tradesman should I get in to investigate?

Watching with interest - we have had exactly the same appear just recently. Ours is due to guttering problem/roof tiles acting as a ski jump so water misses gutter!

Now that everything's drying up I can see a wet patch on the roof 😩 I think that's where the problem is

Could it be to do with the flashing on that dormer window? It looks quite uneven from the picture

Yes, I would say the problem is with the dormer too. Get a roofer or general builder in.