Damp patches appeared overnight

[Bollard]

In a first floor bedroom, on the chimney breast on an external wall. Literally overnight, about 6 damp patches appeared. No extreme weather, the gutters look ok. We have open fireplaces and had the chimney swept a few months ago. The external isn't particularly exposed and the brickwork looks ok, but we'll get someone in to check it out.

We're a bit baffled. Any ideas? First step get the brickwork checked, second step get the chimney checked??

[msfreud]

Your roof might be leaking - possibly the lead flashings have failed or the rendering on the chimney is cracked. I just had something similar in my house.

[ouryve]

Is it your first winter?

It could be condensation, if you've not been using the fire.

[Bollard]

There's another room above this one and no damp there. But yes, I'm wondering if it's something structural.

We've been in the house 10 years but haven't used the fireplaces in that chimney much so maybe it's condensation. Although I'd have imagined that would appear more gradually?

Thanks for the replies.