My wife and I recently bought a house built in 1916. It has plaster walls throughout. We came home recently after a day of rain to find every wall and ceiling in the house dripping wet. At first we thought the roof was leaking, but could not find any specific leak. And a plumber gave the hot water heater, radiators and boiler a clean bill of health. The attic and basement were bone dry. It was as if the inside of the house was literally sweating. It was very bizarre. Any idea what this was all about?