@pigletjohn may I beg your assistance! Damp

[Walesrecommendations]

Moved in 3 weeks ago- house is 120 years old. Solid wall. Had a damp report done which showed some damp from roof leaks which had been fixed, damp guy said we could leave the walls affected to dry out and/or do a DPC in the Spring. In the living room, we have 2 external walls- one we discovered has a sheet of polystyrene behind the wallpaper! Unsure why as I haven't dared remove it. When we moved in we pushed our sofa back against these two walls and blocked the air brick-one of us is also sleeping in the living room as we haven't got beds sorted yet, so lots of breathing going on in there and we havent been great at opening the windows. 3 days ago we happened to pull the sofa out and the walls behind the sofa were dripping to about 2 feet up. We moved the sofa away and did some good ventilation..but now it's back! Not as wet as it was but definitely slightly wet to touch. Really worried its something awful. The previous owners used this room as a formal dining room so we saw the walls and never noticed any tidemarks, mould or anything to suggest there was an issue. Any help greatly appreciated!

Not PigletJohn but live in a similar age house with similar issues so would be interested to see what he has to say but can also offer some advice in the meantime.

The damp is from condensation of household moisture hitting the cold external walls. Dh has put polystyrene in our DIY fitted wardrobes which are basically doors fitted across the alcoves. Lack of circulating air makes the issue worse. Dh reckons that insulating the wall will help and I think it has.

Furniture against external walls is a big issue. I have one alcove in the dining room with a cupboard in and I have to pull it out frequently and bleach wash it or it gets thick black mould.

Re run a dehumidifier 24/7. We also open windows as much as possible. I keep meaning to get a window vacuum to hoover the moisture off the windows. Dh currently towels the windows down each morning.

Can you put the sofa against a non external wall? Also if someone is sleeping in there are they shutting the lounge door at night, if they could sleep with the door open it will help.

Also interested. We live in an older Victorian terrace with no DPC but also no (known) damp. Assume, in part, due to the gales that blow in from all manner of places!

@corvidcovid its a tiny house so not many options re furniture, but forewarned is forearmed so thanks for your tips! The windows dont seem to have much condensation weirdly. I'll try @pigletjohn again, not sure tagging in thread titles works.

I am going to have a go at pre emptying some of piglet John's questions...
Are there any drains or pipes on the outside of the house near to where the damp is? Is the guttering clear of leaves? Does it overflow or leak when it is raining? Are there any sources of water inside the property near to the wet bits? Radiators, water supply pipes for bathroom etc. Is the wet bit just at the bottom of the wall? Can you post pict of the external walls affected please and the guttering above.