Draughty Sash Windows: Causes and How to Fix Them
Sash windows are one of the best features of a London Victorian or Georgian property, but they're notorious for draughts. Here's why it happens and what can realistically be done about it without ripping out original joinery.
Why sash windows are draughty by design
Traditional sliding sash windows work by moving within a wooden box, sliding past the frame rather than compressing against a rubber gasket like a modern uPVC casement. That sliding action inherently leaves small gaps around the meeting rail and sides — which is where the draught comes from.
This isn't a fault as such — it's how the mechanism has always worked — but it can be significantly reduced with the right seals.
Common contributing problems
On top of the inherent gaps, a few specific faults make draughts worse over time.
- Worn or missing parting beads and staff beads, which should sit snug against the sash
- A meeting rail that doesn't sit flush because of a dropped or misaligned sash
- Gaps around the frame itself where it meets the surrounding wall
- Old, brittle putty around single-glazed panes letting air through the glazing itself
Brush and blade draught-proofing
The most effective fix without altering the window's appearance is a proper perimeter brush-seal (or blade-seal) system, routed into the sash and frame. Fitted correctly, it closes the running gaps around the sides, top and meeting rail while still allowing the sash to slide freely.
This is usually combined with re-cording if the sash cords are worn, since both jobs involve taking the sash out of the box.
What's not worth doing
Sealing a sash shut with mastic or filling the running channels solves the draught but stops the window opening, which isn't a real fix and can trap moisture. Secondary glazing is an alternative worth considering for particularly exposed or noisy elevations, but it's a different job to draught-proofing the sash itself.
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Frequently asked questions
Will brush seals stop draughts completely?
They significantly reduce draughts — typically the biggest single improvement you can make to a sash window's comfort — though a sliding sash will never seal as tightly as a compressed rubber gasket on a modern casement.
Does draught-proofing change how the window looks?
No — the seals are routed into the timber and are barely visible once fitted, so the window keeps its original appearance from inside and out.
Can this be done on listed buildings?
Brush draught-proofing is generally one of the least invasive upgrades for period and listed properties since it doesn't alter the original glazing or joinery, though it's always worth checking any specific conservation conditions that apply to your property.
Should I re-cord the sash at the same time?
If the sash is already coming out of the box for draught-proofing, it's usually sensible to fit new cords at the same time rather than pay for two separate visits later.
Call Mark on 07535 916982 or request a callback.