Damp patches on bathroom wall and outside the bathroom. Butterfly roof & coping stones

Good afternoon As a contract manager for many years water ingress was one of the issues I had to deal with on a regular basis. I would suggest the coppings were removed and a lead capping installed beneath them be sure that if there is a cavity (gap between the walls) that this is bridged with a non degradable material such like a slate as the lead will eventually sag under its own weight. Then replace the copings. The chances are that the copping them self's have become poras in there old age and this i s allowing the water to pass straight through them in to the walls below. It wouldn't hurt to coat the exposed walls and coping with a silicone based water sealer while you are having work done this will help reduce water penetration. Best regards Richard

Hi You could cap the coping with lead or elastomeric felt (evolution). Copings can crack at the joints and leak. You could rebed the copings on a new DPC. If you can provide photos of the roof I could diagnose the problem for you.. Regards Simon.