Any idea? Damp?

[Ollivander84]

Any ideas on what this looks like? Ground floor, one wall only and only up to knee height if that

Piglet - I don't dry washing anywhere nearby, it's the other end of the place! Heated airer, trickle vent and window open usually. Never dry clothes on radiators

He's basically said until someone moves back into that house I'm going to have mould unless I get some of those gel moisture things or a heater. Wall is cold to the touch, radiator is on the external wall. Wouldn't say it was any colder between the two walls though as the external and party wall meet in the corner and it's only the party wall with mould....

Picture for clarity! Radiator visible on external wall. The party wall is where the TV is, that corner then just out of view

Condensation mould.

The wall is colder than the surrounding atmosphere and water will condense out of the air onto the cold surface.

Like the cold tap when you run a hot bath.

The dehumidifier is a good idea - taking moisture out of the air will prevent it condensing.

To add, I've been here since it was built. Everything is the same from the heating times to my window opening habits 😂😂
So in 11 years I've never had this issue before, it does seem to have started only when next door moved out

I have managed to quickly look at next door, no sign of leaks or damp, I caught her as she was moving the last of her stuff and she said it had been empty for around 2-3 months, checked everything and no sign of any mould/leaks on her side

Next door will be nearly as cold as outside at this time of year, but there may well be less/no insulation between you and them, which could possibly be making that wall colder than your 'proper' outside walls (which hopefully are insulated) - and this would make it more prone to condensation than the proper outside walls.

Do you know if it will be re-occupied? Can the landord/owner be persuaded put the heating on at least very low, to prevent too much damp in the empty house? Otherwise you may indeed need to put an oil-filled radiator or similar near the wall in that corner of the room. Dehumidifier would also help, but noisier!

Drying laundry indoors is such a big source of moisture - think how heavy the washing is when it comes out of the machine - all water! Make sure you keep the airer room door closed to the rest of the house at all times (sounds like you probably do).

There may well be buildng faults in the party wall, that have only become a problem since the neighbours moved out. But not straightforward to identify or repair! Hopefully since you didn't ahve the issue before, it will resolve when the nieghbours come in and you are sharing your ehat again. At the moment it's all one way

We bought the small portable aero 360 dehumidifers, they don't plug in, they have really worked well, the plug in ones only have a slight hum.

I've been in empty houses in winter. They don't get as cold as the outdoors. In terraces and semis, there will be heat passing from next door, and there will almost always be solar gain through the windows. On a cold frosty night the insulation, and the thermal mass, prevents the house getting frosty.

It will be occupied hopefully by early January which should improve things even with some body heat and heating on

And yes, airer room door is shut. Contractor said it was ridiculous I have a garden and can't use it and he's advising management company that I need to be allowed to dry washing outside as no room for tumble dryer

The radiator churns out a fair bit of heat but that side of the room just doesn't heat up really. It's a double skin(?) wall, I can hear nothing from next door (which is good!)