Gasket compression
A uPVC window seals against draughts using a rubber gasket that runs around the sash, compressed tight against the frame when the window is locked shut. Locking cams pull the sash in to squeeze that gasket. Over years of opening, closing and general wear, the cams can lose a little of their pull, or the gasket itself compresses permanently and stops springing back, both of which leave a thin gap for air to move through even when the window looks closed.
Hinge and keep adjustment
Most modern uPVC windows have adjustable hinges and keeps specifically so a sash that has drifted slightly can be pulled back into tighter contact without replacing anything. This is usually a small hex key adjustment at the hinge, and a similar adjustment at the keeps the locking cams pull into. It sounds minor but a couple of millimetres of extra compression around the whole perimeter of a sash makes a very noticeable difference to draughts.
The paper test
A simple way to check where a draught is actually coming from is to close a strip of paper in the window at various points around the frame, then try to pull it out. If it slides out easily at one point but grips firmly a few inches along, that tells you exactly where the seal is not compressing properly, which is far more useful than just feeling around for cold air with a hand.
- Run the paper test at the top, bottom and both sides of each opening sash
- Note any point where the paper pulls free with little resistance
- Compare against a point that grips well, to confirm the gasket itself is not worn everywhere
- Repeat after any adjustment to check it has actually improved
Get your windows adjusted before you replace them
If a paper test has shown up draughts, get in touch and we will check whether adjustment or a gasket will sort it before talking about replacement.
Worn seals
If the paper test shows the paper slides out easily all the way around every sash, not just in one spot, that points to the gasket itself rather than alignment. Rubber gaskets do eventually perish, going hard, flat or cracked after enough years of UV and temperature cycling, and once that has happened no amount of hinge adjustment restores the seal.
When replacement beats adjusting
Adjustment and gasket replacement solve the great majority of draughty window complaints we see. Full window replacement becomes the better option when the frame itself has warped or bowed, when the gasket channel is damaged rather than just the rubber, or when the glass units inside are old enough that draughts are only one of several ageing issues alongside condensation between the panes or general wear. In that situation, patching the seal is a short-term fix on a window that is due for replacement anyway.