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Draughty Windows
You can feel cold air moving at the window even with everything shut and locked.
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What's happening?
A closed window should seal in two places: the sash against the frame, on a compressible gasket, and the frame against the building, on a sealed joint at the reveal. A draught means one of those two lines has opened. On a uPVC or aluminium window the usual culprit is the perimeter gasket — a rubber strip in a channel that shrinks, hardens and pulls back from the corners over the years, leaving a gap the sash can no longer close onto. On a timber window it is more often the fit itself, as the sash and frame move with the seasons. And a draught that appears to come from the window sometimes comes from behind the plaster around it, where the original mortar or foam packing to the reveal has never been properly sealed.
What usually causes it?
- Perimeter gasket shrunk, hardened or missing from the corners, so the sash closes onto nothing
- Hinges and keeps out of adjustment, so the sash pulls tight at the handle side and stands off at the hinge side
- A dropped or bowed sash that no longer meets the frame along its full length
- Timber sash and frame shrunk apart, or old draught excluder worn out of its groove
- Unsealed joint between the outer frame and the reveal, hidden behind mastic that has cracked or behind internal trim
- Missing or ineffective cavity closer at the reveal, so the draught is coming out of the wall cavity beside the window rather than through the window
- Trickle vents mistaken for a fault — an open background ventilator is meant to pass air and is not a draught to seal up
Is it dangerous?
No, though it is worth knowing which draughts are doing a job. Where a room contains an open-flued appliance, permanently open air vents supply the air for combustion and are there to meet the gas and combustion requirements — those must never be blocked, and the ventilation guidance is clear that they are separate from background ventilation and cannot be counted as it. Everything else about a draughty window is comfort and heating cost.
Can I fix it myself?
A competent DIYer can renew a self-adhesive draught strip on a timber window and re-point cracked external mastic at the frame-to-reveal joint. Two things not to do: never seal a trickle vent or a combustion air vent, and do not pack expanding foam into the gap around a frame from the inside, which pushes frames out of square and traps water in the reveal. Where the sash has dropped or the gasket has failed, the fix is adjustment and new gasket, which needs the right profile.
When should you call a window fitter?
Call a window fitter when the draught persists with a new draught strip on, when the sash is visibly not meeting the frame evenly, or when you can feel air arriving from behind the plaster or trim rather than from the opening joint. Also call where a whole elevation of windows draughts the same way, which points at how they were installed rather than at the individual sashes.
What will the window fitter actually do?
- Work along the closed sash with the handle thrown to find where the seal line is open
- Replace the perimeter gasket with the correct profile for the frame system, running it unbroken into the corners
- Adjust or repack hinges and reposition keeps so the sash compresses evenly on all four sides
- Ease and re-hang a dropped sash, or renew the friction stays holding it out of line
- Rake out and reseal the external frame-to-reveal joint, and check that the internal side is sealed and the cavity closed
- Confirm the background ventilators still work as intended once the window seals properly again
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