Is this dampness or mould

[BuddingGardener]

Have just noticed this in our daughters bedroom and built in cupboard. We are in a 7 year old semi detached house have been here since built. It’s dry and is only on the one side of the house, north east. Nowhere else in the house has it, I haven’t checked the loft as I don’t know what to look for. Looking for help as to what it is and how to get rid of it and prevent it returning and also who would I get to repair it? I haven’t had the roof or gutters done for a year or two could that be the cause of it? Thanks for any help

It definitely looks like water has soaked in from somewhere. I'd check that bit of your loft for signs of condensation and look again the next time rain is coming from that direction. Check externally for any signs of cracked or slipped tiles or displaced ridge tiles or flashing that isn't lying flat.

the second pic certainly looks like a leak. It resembles what you see in the ceiling under a bathroom. Modern plasterboard often has a foil backing so small amounts of water penetrate where the ceiling meets the walls, and at joints between boards.

You need to go into the loft with a torch.

If the house contains too much water vapour, for example if you have steamy showers without an effective extractor, or throw buckets of water at the walls, or drape wet washing over radiators which amounts to the same thing, water vapour will rise through the house until it either escapes, or finds a cold surface to condense on. In winter that is often the roof felt under the tiles, and it will run down or drip off.

Water vapour gets into a loft more easily if the hatch is loose fitting, or there are holes in the ceiling, for example for downlighters.

Thanks for the replies. I will look in the loft and at the roof tiles. Our extractor fan comes on when the shower is on and I don't dry clothes on the radiators although I do dry them on a clothes horse not in that room though. What am I looking for in the loft? Signs of water ingress?

On a cold morning (probably tomorrow) look at the underfelt that (probably) lines the roof under the tiles. Are there droplets of water?

What is above that wet mark? A wall? Eaves? A pipe? Or a duct?

Show us a photo of the extractor fan please.

Do any of the windows go misty in the morning?

Hi yes my daughter says her window is misty in the morning, she has her radiator switched off and doesn't open her window every day above her room is the loft. Here is a picture of the extractor fan in the bathroom. I didn't realise how dirty it was, it's getting replaced next week when we get a new bathroom I haven't managed to get up in the loft yet I've got a chest infection and feeling yucky.

Misty windows suggest the room is humid, which will cause condensation. This might be due to not opening the windows, or there could be another cause, possibly related to moisture from the bathroom.

I can't make out what size the fan is, but I expect it will be 100mm diameter. It looks like it is in the ceiling and blows steam into the loft.

It is very important in that case, that the steam passes into a sealed duct and passes out through a wall or eaves to escape outside the house. If the duct leaks, steam will escape into the loft and cause excessive condensation. If the duct is not well insulated, or the flexible type, condensation is liable to collect inside it and leak out.

If you're refitting the bathroom, and the fan is the ceiling type, I strongly recommend an inline ducted fan, which can be much more powerful, and quitter, than the old one, and new rigid ducting laid with a slight fall so that any condensation drips outside the house. Wrapping the duct in mineral wool quilt will minimise condensation.

This will be more expensive than flexible duct, but a better job. A plumber can probably do it because the duct is very like plastic soil-pipe. It may mean crawling about in a dusty loft though.

This is an example of a ducted fan. The one I show is a good make, there are cheaper ones. It has two or three times the power of the sort builders usually fit in bathrooms, and should be wired to the bathroom light so it comes on with the light switch, and runs on with a timer. Cost of electricity, and noise, are trivial.