Draughty Windows: Common Causes and Practical Fixes

A cold draught round a window is one of the most common complaints we hear in the run-up to winter, and it's rarely down to one single cause. This guide walks through where draughts actually come from, how to track them down yourself, and what's genuinely worth fixing before you consider anything as drastic as new windows.

It's rarely the glass itself

People often assume a draughty window means the glass needs upgrading, but in most cases the glass unit is sealed and airtight — the draught is coming from somewhere else in the window's construction. Worn compression seals (the rubber gaskets around the sash), gaps where the sash has dropped, or a poorly fitted trickle vent are all far more common culprits.

That's worth knowing before spending money on a glass upgrade purely to solve a draught, when a seal replacement might do the job for a fraction of the cost.

Finding the source of a draught

A simple test on a windy day is to run a lit candle or incense stick slowly around the frame, sash edges and any trickle vents — the flame or smoke will flicker or bend where air is getting through. Alternatively, run your hand slowly around the perimeter of the closed window; draughts are often surprisingly localised to one corner or edge.

• Check the rubber compression seal all the way round the sash for gaps, splits or flattening
• Check corners of the frame for gaps in the sealant to the wall
• Check trickle vents aren't stuck open or missing their internal slider
• Check the sash closes flush and isn't rubbing or dropped on one side
• Check letterboxes and keyholes on adjacent doors, which are often mistaken for window draughts

Worn compression seals

The rubber gasket that runs around a uPVC or aluminium sash compresses against the frame when the window is locked shut, creating the airtight seal. Over ten to fifteen years this rubber can harden, shrink or split, letting air straight through even though the window still looks and closes fine.

Replacing the seal is usually a straightforward job — it's pulled out of its channel and a new length fitted all the way round — and is one of the cheapest ways to noticeably cut a draught.

Dropped sashes and worn hardware

As covered in our guide on window won't open or close, worn hinges and stays let a sash drop slightly out of alignment. Even a couple of millimetres is enough to stop the seal compressing evenly, leaving a persistent draught along one edge even though the rest of the window seals fine.

Adjusting or replacing the hinges to bring the sash back square is often all that's needed, and it's a much smaller job than people expect.

Frame-to-wall gaps

Sometimes the draught isn't coming through the window at all, but around the outside of the frame where it meets the brickwork or render. Old, cracked external sealant or missing expanding foam behind the frame can let air straight through the wall build-up, and this is often mistaken for a window fault.

This is usually fixed by re-sealing the external perimeter with a suitable weatherproof sealant rather than anything to do with the window mechanism itself.

When it's genuinely time to consider glass or a full upgrade

If seals, hardware and frame sealant are all sound and a room is still noticeably cold, that's when it's worth looking at the glazing itself — our guide to energy-efficient window glass upgrades and our guide to Low-E and argon-filled units both cover the realistic next steps, from upgrading the unit to considering secondary glazing on period frames.

A sensible order to tackle draughts in

Rather than guessing, it's worth working through the cheaper, more likely fixes first before assuming the whole window needs replacing.

Call Mark on 07535 916982 or request a callback.