At one time or another, almost all windows leak, which is becoming a huge problem because of all the consumer concerns about molds in the home. Molds and decay organisms need water to grow, and the growth can be inside the walls, out of view.
Check the exterior window and door openings twice a year for peeled or damaged caulk. Remove the damaged caulking and clean the frame of the window or door before recaulking.
Also, check the sealant or gasket between the window or door frame and the glass. Double-paned glass will have a band of metal on all four sides that seals the glass itself. If this seal fails, moisture may form between the two panes of glass, but this is not the seal you need to be checking for leaks. You may discover that the gasket has failed or is loose and is no longer watertight.
Seal the glass to the gasket using a clear silicone caulk. Check the sill, the bottom flat part of the window frame, to make sure it is pitched to drain water to the exterior. Probe the wood frame and trim with a screwdriver to check for soft or decayed wood.
With the window open, check the inside of the frame and sash, especially the underside of the operable window. If you find damp or decayed wood call a reputable contractor to investigate further. If the leaky window has been ongoing, the inside wall covering near the window may have to be removed to investigate the structure.
By Dwight Barnett – Certified master inspector with the American Society of Home Inspectors.