Strong smell of musty damp when it rains

[jgary]

Hi all,

I'm trying to diagnose a curious damp problem in my flat (4th floor of 7).

When it rains, there's a strong damp / musty / earthy / wet wood smell that appears in areas of my flat. Mostly near the window in the bedroom. However there are no obvious areas of dampness - I've had a very good look and feel around the whole place. The windows are pretty old, wooden framed and due for replacement, but they're not rotten.

It seems to be highly correlated to rainfall, or the elevated humidity that come with the rain, as it's worst when the humidity in the flat rises to about 55% (I have a meter).

Internal sources of moisture - bathroom, kitchen etc are pretty well vented via external-exit extractor fans, so I don't think they're contributing to the problem.

What's more interesting however, is that there are other communal hallway areas of the building that have the same dampy smell - but only on wet days, or after several wet days at least.

So I'm wondering if the building has a problem, perhaps a leak from the roof that's finding ways through the building.

Or could it be something to do with the materials in the building that respond badly to high humidity?

Any advice or diagnosis procedures gratefully received!

 

[OwainDIYer]

Damp hallway areas might be due to water ingress alongside communal soil pipes that lead to the roof. They often run in pipe ducts off the common areas.

I wonder if rain is getting in to the wall from a leaky window in the flat above you and then tracking down.

With rain related damp, start at the top and work down. It's what the water does. A couple of hours in a cherrypicker basket can be most informative.