Draught-proofing sash windows
Draught-proofing is a system of brush and fin seals set into grooves routed in the sashes and beads of an existing timber window.
It stops draughts and rattles, cuts street noise, and does it without changing how the window looks or works. We fit it from inside, and we guarantee it for five years, provided the seals have not been damaged by a third party, adjusted or tampered with.
London · Draught-proofingFive-year guarantee (conditions apply)Written quotationsA studio of The Barnsbury Group, established 1980
Why sash windows draught
A sash window is designed with a gap. The sashes have to slide, so they sit a few millimetres clear of the frame and of each other at the meeting rail. Over a century, timber shrinks, paint builds up unevenly and beads are replaced badly. The result is cold air at the sill, a rattle in the wind and street noise in the room.
What we fit
- 01Remove the sashes and the staff and parting beads.
- 02Rout a groove into the sash stiles, meeting rails and the new beads.
- 03Fit a pile brush seal into each groove: the sashes slide against it, so they still run freely but air can't pass.
- 04Fit a compression seal at the meeting rail and the bottom rail, where the gap is largest.
- 05Replace cords, check weights, rebalance.
- 06Refit, adjust, test every window with you.
Nothing is visible when the window is closed, nothing is screwed or painted onto the face of the window, and the sashes still open fully.
What it does and doesn't do
It stops draughts and rattles completely on a sound window. It cuts airborne street noise noticeably, because in an old window most noise comes in through the gaps around the sashes. It reduces heat loss, though exactly how much depends on the house; we do not quote a percentage because we can't measure yours. It does not insulate the glass itself. For that, slimline double glazing is the next step and is fitted at the same time if you want it.
Cost and time
We quote per window after a survey. Because the sashes are out, any repairs found on the day are quoted before we do them.
Conservation areas and listed buildings
Draught-proofing is a repair. It does not need planning permission in a conservation area and in practice is not treated as an alteration to a listed building, because nothing is removed and nothing is visible.
The guarantee
Our draught-proofing carries a five-year guarantee on the seals and the fitting. If a seal fails, we come back and replace it. The guarantee applies as long as the seals have not been damaged by a third party, adjusted or tampered with.
Common questions
How much does draught-proofing a sash window cost in London?01
It is quoted per window after a survey, because the amount of work varies with condition. It is the least expensive of the upgrades we offer and the one with the most immediate effect.
Will I still be able to open the windows?02
Yes, fully. The seals are designed to slide.
Does draught-proofing stop noise?03
It cuts airborne noise substantially, because most of it comes through the gaps. It won't match double glazing on very loud roads.
Can you draught-proof casement windows?04
Yes, with compression seals rather than brush seals.
Do I need permission?05
No. It is a repair and nothing changes externally.
Book a survey
Send us photographs of your windows and we'll tell you what needs doing and what doesn't, with a written quotation. The digital survey is free.