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I insulated external walls (internally) in my last couple of houses and it made a massive difference. The bathroom in my current house was awful but I now have a warm wall that never condensates. I lost about 100mm of floorplan but it was well worth it. Someone has done something similar in a bay window on the last couple of pages. It is something that can be done easily with basic DIY skills (plenty of guides on how to do it correctly online).
I’d love to know what the things are increasing the airborne water vapour as I haven’t cooked today and I showered at the gym.
Said it a few pages back but maybe insulation could be part of the solution. External wall is always cold to touch (single brick) so under 12 degrees is going to be pretty common for that wall.
House being at 70%RH isn’t ever going to be ideal even with warmer walls.