Why Are My Windows Draughty?

The short answer

Draughts around windows almost always come from one of three places: a failed or perished seal/gasket, a gap between the frame and the surrounding wall, or — in older windows — general wear in the mechanism that stops the sash or casement closing fully tight. The fix depends on which of the three it is, and most are straightforward to diagnose yourself before calling anyone out.

Check the seals first

Run a hand around the edge of the closed window on a windy day, or hold a lit candle or lighter near the frame (carefully, away from curtains) and watch for the flame flickering. Rubber gaskets around uPVC and aluminium windows harden and perish over 10–15 years, especially on south- or west-facing elevations that get the most sun and weather. A perished gasket is often a simple, inexpensive fix — many window suppliers sell replacement gasket strip, and it's a job a reasonably confident DIYer can often do themselves by easing the old gasket out of its groove and pressing new strip in.

Check whether the window is closing and locking fully

Over years of use, the locking mechanism on a casement or sash window can wear slightly, meaning the window doesn't pull in as tightly against the seal as it did when new. Try lifting the handle firmly while the window is shut — if it feels loose or doesn't engage crisply, the multi-point lock or the keeps (the strike plates the lock engages into) may need adjusting or replacing. This is a common, fixable fault rather than a sign the whole window needs replacing.

Check the gap between frame and wall

If the draught is coming from around the outside edge of the frame rather than where the opening sash meets the fixed frame, the problem is likely the seal between the window frame and the surrounding brickwork or render — the expanding foam or silicone sealant used at installation can shrink, crack or come away over time. This is worth checking both inside (around the plasterwork/architrave) and outside (where the frame meets the external wall). Re-sealing with a good exterior-grade sealant is usually a modest job; a persistent gap that keeps reopening can indicate movement in the surrounding structure, which is worth having looked at rather than repeatedly resealing.

Older or single-glazed windows

If the windows themselves are old — timber sashes from before double glazing became standard, for example — some draught is often inherent to the design rather than a fault. Draught-proofing strips (brush or compression seals fitted into the sash and frame) can meaningfully reduce this without replacing the window, and are a common, cost-effective first step for period properties where replacement isn't wanted or isn't permitted.

When it's a sign you need new windows, not a repair

If the frame itself has warped, cracked, or the double-glazed unit has failed (visible as persistent condensation between the panes, or a cloudy appearance), draught-proofing a seal won't fix the underlying issue. Widespread draughts across most windows in an older uPVC installation — rather than one or two — can also indicate the whole installation is coming to the end of its serviceable life, typically 20–25 years for uPVC. If the fix is more than a simple seal or gasket and you're weighing up full replacement, it's worth reading whether energy-efficient windows actually save money before committing, since the financial case is more nuanced than it first appears.

Common mistakes

• Sealing a window shut to stop the draught. This masks the symptom and can trap moisture, leading to condensation or mould issues — fix the actual seal or mechanism instead.
• Assuming all draughts mean the window needs replacing. Most draughts are a seal, gasket or adjustment issue, fixable without a full replacement.
• Ignoring a small draught for years. A perished gasket only gets worse, and a persistent gap around a frame can let water in as well as air, risking damp damage to the surrounding wall.

If you're not sure

A FENSA-registered installer or a competent glazier can usually diagnose the cause in a short visit — worth doing before assuming the whole window needs replacing, since a seal or mechanism repair is a fraction of the cost. If you do end up needing replacements, our guide to uPVC, timber and aluminium windows covers the options.