Damp

Verb

I have a newly decorated hall in late 2019 and have just spotted what looks like damp (peeling paint etc..) towards the front door area parallel to the bottom of the stairs.

I've been inspecting around the area to locate the source of any damp and this is my findings, if anyone can offer any advice.

-  My house was built in 1928

-  Its had cavity wall insulation fitted about 10 years ago

-  The ground floor is solid, no floor boards or anything

-  Behind the damp was an outside wall but is now a garage that was built around 1978

-  The garage wall behind the damp area is bone dry and there is an air brick within 400mm of the damp but no air vent inside of the house

Questions I'm asking myself is:

Should the air brick be feeding an air vent or would this only be necessary if I had a void below my floor

Is the airbrick there to allow my cavity to breath if so do I need to install additional air bricks in that area

Is the airbrick just sucking cold air in from the garage and making that area damp, should I block the air brick up all together

RelievedSheff

Does the damp patch line up with where the garage roof joins the house?

If so it could be the flashing that is failing.

Verb

The garage roof is fine I had the replaced early last year.
I think this problem has been around for a while in this house as when we bought it. Under the stairs had a had damp problem which is the same wall that joins the garage. I though I had fixed this by getting air ventilation in there and it was fine.
When I decorated the hall the wall paper came off really easy and I could wee patch plastering repairs. But now I only have painted plaster i can see the problem

RelievedSheff

The garage roof might be fine but the join between the two structures could be letting water in or holding moisture against the wall.

Have you got some pictures both inside and out?