Hello group, I am renovating a terraced house to rent out, my son has been living in it whilst it's being renovated. Initially we had a problem with what looks like moisture on the walls, it only affects certain areas. Got the house re-rendered last year after taking advice from a local builder, however the problem still persists, its a small terraced house built around 1910, with sandstone and brick solid walls, there is not much ventilation, only a few trickle vents on a few of the windows, the patches appear on both the exterior, interior & party walls in the living room, any advice would be appreciated, I have included a few photo's below, thank you.