Double glazing is sold as the end of draughts, so a draught from a double glazed window feels like a failure of the whole thing. It almost never is. The sealed unit is airtight by construction; the air is getting past the seals around the opening sash, or past the frame itself, and both are repairs. The first job is to find which, because the fixes range from a quarter turn of an allen key to a new window, and the trade will happily sell you the second when you needed the first.
First: is it a draught at all?
Two things feel like a draught and are not. The first is the cold that radiates off a large pane on a winter evening; glass at a few degrees pulls the warmth from your skin, and air cooled against it sinks down the glass and along the floor. No air is coming in. The second is a blown sealed unit, which runs colder than a sound one because the gas has gone, and shows condensation between the panes. That is a blown double glazing problem, fixed by a new unit, not a seal. A real draught moves: it flickers a flame, stirs a tissue and lifts a curtain with the window shut.
Find the gap: two tests and a walk round
Pick a windy day. Move a lit candle, or a strip of tissue paper, slowly around the whole frame with the window shut: along the sash edges, round the frame where it meets the wall, behind the internal trims. Where the flame leans or the tissue moves, mark it with tape. Then the paper test: shut the window on a sheet of paper and pull. Firm resistance means the gasket is being compressed there; paper that slides free means it is not. Do it at the top, middle and bottom of each side. Paper that grips at one corner and slides at the opposite one is a sash out of square, not a bad gasket. Finally, look: daylight round a frame, a gasket that has shrunk back from a corner, or a sash that sits visibly lower on the lock side than the hinge side each tell you where to go next.
The five sources, and the fix for each
| Where the draught is | What has happened | Fix | Cost |
|---|---|---|---|
| Along the sash edge, all round or one side | Cams on summer setting, or keeps out of adjustment | Turn cams to winter; move the keeps | Free |
| Along the sash edge, gasket visibly flat, hard or shrunk | Gaskets perished | Replace the gaskets | £7.50 parts; £125 to £180 for a one-window visit |
| Gap at one corner, sash rubs at the opposite one | Sash dropped on worn friction hinges | Replace the hinges | £100 to £250 fitted |
| Steady trickle from a slot at the top of the frame | Trickle vent open | Nothing; it is ventilation | Free |
| Behind the trims, or between frame and wall outside | External silicone failed, or no foam behind the frame | Reseal the perimeter | £50 per window strips or sealant; £125 to £180 full reseal |
Source: Checkatrade window seal replacement (June 2026) and draught proofing (May 2026) cost guides; DGCC 2026 repair dataset for hinges. Research in lib/research/draughty-windows-2026.md.
1. The cams: the free fix most people never find
Open the window and look along the edge of the sash for the mushroom-shaped locking cams. Each has a mark on it. With the mark facing away from the seal the cam is on its summer setting, pulling the sash lightly against the gaskets; turned so the mark faces the seal, it is on winter, pulling hard. Turn each one an eighth of a turn with a 4 mm allen key, and do every cam the same amount so the sash stays square. Then repeat the paper test. Slacken them again in spring, because a winter setting all year flattens the gaskets early, which brings you back here with a bill. Windows without cams adjust at the keeps on the frame, which sit on slotted screws; the same adjustment is described in our guide to a window that will not close or lock.
2. Gaskets: cheap part, expensive visit
The black rubber strips round the sash and the frame flatten, harden and shrink with age, and once they have, no amount of compression seals them. The parts are trivial: Checkatrade averages the materials at £7.50 a window, and bought by the metre they run from about £1 for a bubble gasket to £3.70 for a wedge gasket, around seven metres to a standard window. The visit is what costs. A professional seal replacement is £125 to £180 for a single window, of which £100 is the minimum call-out, and then £20 to £70 labour for each further window in the same visit. So one window is dear and a house is not: get every window done in one trip and the per-window figure falls to the £50 to £100 the trade quotes for a reseal. Gaskets are also a realistic DIY job on the ground floor: the old one pulls out of its groove and the new one presses in, matched to the profile.
3. Hinges: when the gap is at one corner
Open the window and watch the hinge side as you close it. A gap that opens down that side with the window shut, or a sash that catches at the bottom lock corner while gapping at the top, is a sash that has dropped on worn friction stays. Adjusting the cams will not close a gap the hinges have opened. Replacement is £100 to £250 fitted, and the same guide covers the lubrication that fixes a stay that has merely bound rather than worn.
4. The trickle vent is not a fault
A steady, slight flow of cold air from the slot at the top of the frame is the trickle vent doing what it is for. The Energy Saving Trust's advice is to leave them open all the time. Closing one in winter feels warmer and is the first step toward the condensation on the glass in the morning; the vent moves out the moisture that a sealed house otherwise puts on its coldest surface. If the flow from a vent is more than slight with its flap closed, the vent itself has failed, and the vent is replaced rather than the window.
5. Behind the frame: the draught that is not the window
If the candle leans at the trims rather than the sash, or outside where the frame meets the render, the air is coming past the frame, not through the window. The external silicone has failed, or the gap behind the frame was never foamed, or the foam has broken down. Cut out and replace the external silicone bead with low-modulus exterior sealant; where the trims come off and show a void, fill it with low-expansion foam before re-sealing. Checkatrade prices strips or sealant on a window at £50 and a full reseal at £125 to £180. Do not seal the drainage slots along the outside bottom of the frame while you are there; they are meant to be open, and blocking them is how sealed units drown from inside.
Before anyone quotes you a window for a draught, turn the cams and try the paper again. It is a four-millimetre allen key and ten minutes, and it is the fix for more draughty windows than the whole of the rest of this page put together.
Double Glazing Cost Calculator Team
What draught proofing is worth
The Energy Saving Trust puts draught proofing around windows, doors and floors at a saving of around £55 a year in Great Britain and £80 in Northern Ireland, on figures updated in May 2026, against a cost of around £250 for a whole house done professionally and much less done yourself. Some cost guides still repeat an older £85; the current figure is £55. Put beside a whole-window replacement, which the same body puts at £85 a year for a semi going from single to A-rated double, it is a large share of the benefit for a small share of the cost, which is why sealing what you have comes before replacing it.
| Fix | 2026 cost | Notes |
|---|---|---|
| Turn cams to winter, adjust keeps | £0 | 4 mm allen key, an eighth of a turn each, every cam the same |
| Gaskets, DIY | £7 to £26 per window in parts | £1 to £3.70 a metre by profile; about 7 m per window |
| Gaskets or seals, professional | £125 to £180 for one window | £100 minimum call-out, then £20 to £70 per extra window |
| Reseal double glazing (per window) | £50–£100 | Specialist resealing where the gasket or seal has failed. |
| Replace window hinges | £100–£250 | Parts from around £27.50 a pair plus labour. |
| Draught strips or sealant, professional | £50 per window | Checkatrade draught proofing guide, May 2026 |
| Whole house draught proofed, professional | around £250 | Energy Saving Trust, May 2026; saves around £55 a year in GB |
Source: Checkatrade (May and June 2026); Energy Saving Trust (20 May 2026); DGCC 2026 repair dataset.
Do not seal the house shut
The Energy Saving Trust's caution is worth taking literally. A home that has no trickle vents, no wall vents and no mechanical ventilation "may already be too airtight", and further draught proofing "may not be suitable". Never block trickle vents, airbricks, wall vents or extractor fans; never draught proof a room with an open fire or a flueless gas heater, which need the air to burn safely; and do not draught proof internal doors. Old double glazing without trickle vents was ventilating the house through its imperfections, and sealing all of them at once moves the moisture from the gaps to the glass. Our condensation guide covers what happens next and how to manage it.
When a draught means the frame has gone
A draught that survives new gaskets, a winter cam setting and a reseal is not a seal problem. Four signs point at the frame. A uPVC sash that touches the frame at the top and bottom but gaps in the middle has bowed, and nothing in this guide straightens it. A frame whose diagonals differ by more than a few millimetres has moved in the opening. Timber that a screwdriver sinks into at the bottom rail, meeting rail or sill has rotted past patching; the sash specialists are blunt that draught-proofing badly worn timber gives "marginal, short-lived improvements". And gaskets that cannot be sourced for an obsolete profile leave you with nothing to fit. The commonest tell is repetition: the same window resealed more than once in a few years with the draught coming back. At that point the comparison is with a new window, which the uPVC window calculator prices, and the decision rule is in repair or replace. The window fault checker walks the symptoms if you are not sure which you have.
If the frames have had their time
A draught on a sound frame is a seal, a cam or a hinge, and the figures above are the whole cost. Where the frames have bowed, moved or rotted and the draught keeps returning, resealing is money spent on a window that is leaving. If you want the replacement priced on your own openings, tell us what you have and Leads 2 Trade will arrange quotes from installers covering your postcode.
Frequently asked questions
One of five reasons: the rubber gaskets on the sash or frame have flattened, hardened or shrunk; the sash has dropped on worn hinges so the seal no longer meets the frame all the way round; the locking cams are on their summer setting and not pulling the sash tight; the trickle vent is open, which is not a fault; or the gap between the frame and the wall behind the trims has lost its foam or external silicone. A cold sealed unit that has blown feels chilly but does not move air, which is how you tell it apart.
On a windy day, move a lit candle or a strip of tissue slowly round the frame with the window shut; a flicker marks the gap. Then shut the window on a sheet of paper at several points round the sash and pull: paper that slides free means the sash is not compressing the gasket there. Look for daylight round the frame and behind the trims, and listen for whistling. Curtains that move with the window shut are a gap, not your imagination.
Turn the locking cams to their winter setting. Open the window, find the mushroom-shaped cams along the edge of the sash, and turn each one an eighth of a turn with a 4 mm allen key so the mark on the cam faces the seal; do the same on every cam so the sash stays square. That increases the pressure on the gaskets. Slacken them back in spring, or the gaskets flatten early. Adjusting the keeps on the frame does the same on windows without cams.
The gaskets themselves are cheap: £7.50 on average per window in materials, or £1 to £3.70 a metre bought by the length. The cost is the visit. Checkatrade puts a professional seal replacement at £125 to £180 for one window including a £100 minimum call-out, then £20 to £70 labour per extra window in the same visit, which is why the per-window figure falls to £50 to £100 on a house.
The Energy Saving Trust puts draught proofing around windows, doors and floors at around £55 a year in Great Britain and £80 in Northern Ireland, on the May 2026 figures, for a cost of around £250 for a whole house done professionally or much less as DIY. Some cost guides still quote an older £85 figure; the current one is £55.
When the frame rather than the seal is the problem: a uPVC sash that has bowed so it touches the frame at the top and bottom but gaps in the middle, a frame that has moved in the opening, timber that a screwdriver sinks into at the bottom rail or sill, or gaskets you cannot source for an obsolete profile. The tell is repetition: if the same window has been resealed more than once in a few years and the draught comes back, the frame has reached its limit.
No. A home without trickle vents, wall vents or a mechanical system may already be too airtight, and the Energy Saving Trust says further draught proofing may not be suitable for it. Never block trickle vents, airbricks, wall vents or extractor fans, and never draught proof a room with an open flue or a flueless gas heater. Seal the gaps that are faults, keep the ventilation that is designed in, or you trade a draught for condensation and mould.