Visually examine indoor walls and ceilings
Go room by room, and look carefully for problems. Mostly, watch for discolouration. Yellow spots indicate water damage. Large ones on the ceiling point to a leaky roof, or if they’re next to exterior walls, ice dams. Small water spots are probably leaking or sweating plumbing pipes. Black spots on the walls are usually mould. If you spot basement mould, also look for efflorescence (powdery white deposits) along the foundation walls and concrete slab that result from water seepage. Spalling (corrosion) on concrete blocks in the crawl space or basement is another telltale sign of moisture coming in through the walls. So are bowed walls.