Window Leaking When It Rains

What's happening?

Everest explains that uPVC windows are designed so water runs off the glass into the frame and drains out through holes, and that if the holes are blocked the window appears to leak, with water on the sill from the frame. Wet on the glass and frame on cold mornings is a different thing: condensation forms when moist air meets a cold surface. A genuine leak leaves wet where rain reaches the frame, the wall around it or the sill, and keeps coming in whatever the humidity. So there are three tests: pour water into the drainage holes and see whether it comes out, look at whether the wet is on the glass or only after rain, and look at the wall and sill for staining.

What usually causes it?

• Drainage holes in the frame blocked, so water backs up and appears to leak
• Condensation on the glass and frame, mistaken for a leak
• A failed seal or a gap where the frame meets the wall, which only a fitter can confirm
• Worn seals around the sash
• Water entering from above the frame, from the wall or sill, which a fitter or surveyor has to trace
• A sash that does not close tightly against its seals

Is it dangerous?

Low as a leak, but water running into the reveal can stain and damage plaster. Mop up and keep the sill dry.

Can I fix it myself?

Open the window and find the drainage holes in the frame. Pour a little water into each and check it comes out on the outside; if it does not, clear the hole with a screwdriver. Check whether the wet appears only after rain, or on cold mornings with no rain, which points to condensation. Photograph any stain on the wall and note the weather. Do not seal the frame with silicone before the cause is known.

When should you call a window fitter?

Call a window fitter if the drainage holes run freely and water still comes in, if it follows wind-driven rain, or if the wall or sill is wet. Call a damp specialist if the wet is condensation. A fitter checks the seals, the frame and the junction with the wall.

What will the window fitter actually do?

• Test and clear the drainage holes and the drainage path
• Check the sash seals and how tightly the window closes
• Inspect the junction between frame and wall for gaps
• Reseal or replace seals where they have failed
• Check the lintel, sill and wall above for another source of water

Who fixes this

• Window repair and adjustment
• Double glazing replacement

Questions people ask

Sources & References

1. Everest: why is my uPVC door or window frame leaking?
2. Everest: condensation on windows