Discovering water on your windowsill after heavy rain is concerning. But before assuming the worst, it's worth understanding where the water is coming from — the fix varies significantly depending on the source. Here's a systematic guide to diagnosing a leaking double glazed window.
Water on the Inner Windowsill
If water is appearing on the inside windowsill after rain, it's coming through the window, not from condensation. The most common entry points are: the glazing bead (the plastic strip that holds the glass in the frame), perished rubber gaskets between the glass and frame, a failed seal between the frame and the wall (the outer silicone bead), or a gap where the frame sections join at the corners.
Gasket and Glazing Bead Leaks
The rubber gaskets that seal between the glass unit and the UPVC frame can harden and crack over time, especially on south-facing windows exposed to UV light. If the gasket is the source of the leak, it can be replaced independently of the glass or frame. This is a relatively straightforward repair for a professional and immediately stops the ingress.
Frame-to-Wall Seal Failure
The silicone seal between the UPVC frame and the surrounding brickwork or render is a common leak point on older installations. When this seal cracks or separates, rainwater can track behind the frame and appear on the inner sill. Re-sealing the outer frame joint resolves this. It's a quick repair but requires working from outside, usually from a ladder.
Failed Drainage Holes
UPVC window frames have small drainage holes at the bottom to allow condensation and any water that enters the system to escape. If these become blocked with debris, water builds up inside the frame and eventually overflows onto the inner sill. Clearing the drainage holes with a small brush or probe is a simple maintenance task that can prevent significant water damage.
Need a UPVC Repair in Birmingham or the Black Country?
The Glass Guardian provides fast, affordable UPVC window and door repairs across Birmingham, Dudley, Walsall, Wolverhampton, and the surrounding area. Call for a free quote.