I recently purchased and moved into a 1893 Victorian two up two down miners terrace. It's kept the old floor plan with separate front and back rooms and a kitchen extension at the back so rooms are quite small.
So far, there's water ingress in one bedroom that we can't find the source of, more water ingress in the front room that might be the same water from the bedroom above but we don't know for sure but it's put a huge spanner in the works because we can't find tradesmen to come and look so we're kind of stuck in limbo. There's yet more water ingress in the 1970's extension but we're 80% sure it's from a loose external light on the other side of the wall that I'm praying an electrician will be around today to safely disconnect so we can seal the wall.
Honestly there would be mold / damp as I can see signs where the previous owner has struggled with it but I ventilate the house religiously and so far I've not seen anything new. Humidity hovers around 60%, spikes as high as 75% in the bedroom of a morning when we wake up and same in the bathroom after a shower. We open the bedroom window every morning no matter the weather or temperature and it drops back down before we leave for work. When we shower, we squeegee down shower cubicle and open the window until all signs of condensation are gone. I also have a dehumidifier that I sometimes use, a heat pump condensing tumble dryer so no clothes drying on radiators etc.
Right now it's 6 degrees outside and 14 degrees in the back room where I'm sitting with no heating on. It's cold but not freezing, the best thing we've purchased is an electric blanket for each of us and it's more than enough to stay cozy. Obviously every house is different but we did a basic test before we moved in and set the thermostat to 16 degrees and left the heating on constantly for a week (Late December). Heating only was coming in at £4 a day in gas but we increased the temperature to 18 degrees for one day and it cost £6!
At the moment we have a love, hate relationship with the house, it's SOLID, the walls are thick, the roof is fine, the original stairs are still in place and the carpenter we had in to give us a quote of replacing them was shocked that something so sturdy should be ripped out and was gleefully pointing out the handy work done all those years ago. I have no doubt that the house will still be here in another 100 years. However, a house this old is hiding decades of botched DIY projects and patch repairs. Something can look fine on the surface but be hiding Lord knows what underneath. My house was built as a functional place to live, it doesn't have fancy period features so work to be done doesn't have to be anything grand. Also, as things like central heating and even electricity have been added, wires and pipes run along walls and can pop out in strange places which doesn't look very good but I have no intention of digging up floors and such to hide them.
At the moment our main concern is the water ingress. I've spoken to several neighbors and every single one has issues with water in one form or another.
I'd still buy this house again but I'd have probably paid a few thousand less had I known the extent of the issues. As it was our level three survey didn't find any issues and to be honest, unless you were pulling up carpet and floor boards you wouldn't have known.