Draughty sash windows: what helps tonight, and what fixes them
By Glazing London,
The heating is on, the curtains are drawn, and there is still a cold stream of air across the room from the bay. If you live in one of North London's Victorian or Edwardian terraces, the chances are it is coming from the sash windows. The good news is that a draughty sash is rarely a reason to throw the window away.
In short: close the window fully and engage the catch, find where the air is getting in, and use curtains, shutters or a draught snake for tonight. Avoid stick-on foam in the runs. The lasting fixes are a routed draught-proofing system, a repair of the worn parts, secondary glazing for period and listed homes, or replacement sashes where the timber has gone.
First, check the window is actually shut
It sounds too simple, but a lot of draughts come from sashes that are not closing properly. The top sash may have slipped down an inch because a cord has stretched or snapped. The bottom sash may not be sitting on the sill because layers of paint are holding it up. The fitch catch on the meeting rail pulls the two sashes together; if it will not turn, the rails are not lining up.
Push the top sash fully up and the bottom one fully down, then close the catch. If you cannot get them to meet, that tells you a repair is needed, not just sealing.
Find where the cold is coming in
On a windy evening, hold a strip of tissue or a feather near the window and move it slowly around the edges. Do not use a candle or lighter near curtains or old paintwork. Draughts in a sash usually show up in four places:
- The meeting rails, where the two sashes overlap in the middle. This is usually the worst point and the source of most rattling.
- The sides, where the sashes slide between the beads.
- The top and bottom, under the bottom sash on the sill and across the head of the top sash.
- Around the box frame, where it meets the brickwork and the inside plaster, especially if the pointing has cracked.
Knowing which it is helps us tell you what the fix is from photos.
What helps tonight
- Close internal shutters if your house still has them. Many in Islington, Highbury and Stoke Newington do, sometimes painted shut behind the curtains for years.
- Draw heavy, lined curtains right to the sill, or below it if there is a radiator under the window that you can keep clear.
- Put a draught snake along the sill.
- For a sash that rattles in the wind, a soft wedge pushed gently between the sash and the bead will quieten it overnight. Take it out before you open the window.
What we would avoid: self-adhesive foam strip in the runs, silicone squeezed into the gaps, or tape over the meeting rails. They work for a few weeks, then make the sashes stick, pull paint off, and can leave you with a window that will not open in a fire or on a hot day.
Why it gets worse every winter
Timber moves with the seasons. In the damp months it swells, then shrinks again when the heating dries the room. Over decades, beads wear thin, putty cracks, and the sashes end up loose in their channels. Condensation running down cold single glass soaks into the bottom rail and the sill, and once rot starts there, the gaps grow. If you see water pooling on the sill in the mornings, our guide to window condensation explains what causes it and what helps.
None of this means the window has reached the end of its life. In most of the period houses around Crouch End, Muswell Hill, Hornsey and Kentish Town, the box frames are sound, and it is the moving parts that need attention.
The lasting fixes
Draught-proofing as part of a repair. A proper system is routed into new staff and parting beads and into the sash rails, with brush pile that seals when the window is shut but still lets it slide. It is fitted together with any repairs the window needs: new cords, eased runs, re-set beads, and rot cut out and spliced. Our sash window repair page sets out each job in detail.
Secondary glazing. For listed buildings, mansion flats with strict leases, or anyone who wants to leave the original window untouched, a slim secondary pane fitted on the room side of the reveal adds a second barrier against cold and noise. It is the option for period and listed homes on our secondary glazing page, and it can sit alongside a draught-proofed sash.
Replacement. When rot runs right through the box frame or sill, or there is little original timber left to repair, new sashes or complete windows in the original pattern may be the honest answer. These are FENSA replacement windows; see sash windows for what that involves.
Getting it looked at
We work across Central and North London from Wood Green, N22. Every window is different, so we price them one at a time. WhatsApp photos of each window to 07915 903485, inside and out, with a note of where you feel the draught, or book a free survey. You get a fixed quote, with no obligation, before any work is booked.
Questions people ask
Why are sash windows so draughty?
A sliding sash needs small clearances to move, and over a century the timber shrinks, the beads wear and the paint builds up unevenly. Air then gets in at the meeting rails where the two sashes overlap, down the sides where they slide, and along the top and bottom. The window is usually not failing, just loose in its frame.
Will draught-proofing stop my sash windows opening?
Not when it is done properly. A routed brush-pile system sits in the beads and rails so the sashes still slide. Foam strip stuck into the runs is what makes sashes stiff and sticky, which is one reason we advise against it.
Is secondary glazing better than draught-proofing for a sash window?
They do different jobs. Draught-proofing closes the gaps in the window itself; secondary glazing adds a second, separate pane on the room side, which also helps with heat and street noise. For period and listed homes where the original window has to stay as it is, secondary glazing is often the route, and the two can be combined.
Do I need permission to draught-proof sash windows in a conservation area?
Like-for-like repair and draught-proofing generally need no permission. Changes to the glass or the look of the window can, and any work on a listed building is worth checking with the council's conservation officer first. We can advise at the survey.
How do I get a price for my sash windows?
Send photos of each window, inside and out, by WhatsApp to 07915 903485, or book a free survey. Each window is priced separately with a fixed quote and no obligation, so you can start with the worst ones.