I’m a contractor for over 20 uears, in San Francisco area and have a client with a perodic leak in an interior hallway, of a 30 year old building.
No staining in ceilings either above or below.
There does not appear to be any plumbing in the adjacent walls, (i.e. no baths or kitchens in this area). The building has hot water baseboard heating, but it seems unlikely that it would run close to an interior hallway with apartments on either side. Any ideas out there, short of opening walls or concrete floor. Tenants complain of leak, but when I get there the carpet is dry, – no symptoms. Puzzled!!!!! Thanks Vincent.