We have build an ext on to an old house (50yrs), just over a yr ago. Since the building we have notice alot of condensation on windows (double glazed), and there is green mould growing on blanket box, under the bed, on lockers!!!!! Also there is black on the walls, (we had the felt replaced, still coming true). We have a old chim which is blocked up, we just put the vent in it. Also vent on the wall, and we also had the walls blown with ins. Can anybody pls, pls help with this horrible problem. Any advice would b gr8.