Damp plaster upsatirs

[drizzy]

I have a persistent damp area on the wall of an upstairs room. I have removed some of the wallpaper (see picture).
On the left hand side the plaster is crumbing, however the middle area is also feels slightly damp.

There is no obvious dampness in the room directly below, so im thinking it may be a roofing issue (the roof slopes down directly above the wall).
The house is Victorian - built around 1900.

What are the possible causes of this, and who should i contact first - a roofer to check if there is a leak?
Thanks

 

[Deleted member 265726]

Have you looked at the roof and guttering on the outside where this room is? Can you take a pic of the roof and guttering and post it? Also, a pic of the exterior of the wall directly outside the damp area would help too.