How to Fix Draughty Sash Windows

Quick Answer

Draught-proof with brush seals (£250–£400/window) for a quick fix. Full overhaul with new cords, beads, and seals (£400–£700/window) if the frames are sound. Replace entirely (£1,500–£2,500/window) if there’s significant rot or the windows are beyond economical repair.

Why Sash Windows Get Draughty

Victorian and Edwardian sash windows were never designed to be airtight. They predate modern sealing technology by a century. But the draughts you feel today are worse than when the windows were new, because:

Timber shrinks and expands over decades, opening gaps between sashes and frame
Original putty has crumbled away, leaving gaps around the glass
Parting beads and staff beads have worn thin, no longer holding the sashes snugly
Sash cords stretch, so windows don’t close fully
Pulleys seize, so people leave windows slightly open

A typical 150-year-old sash window can have 5–10mm gaps around both sashes. That’s the equivalent of having a hole the size of a brick in your wall.

📷 ADD REAL PHOTO: Gap between sash and frame showing draught path — close-up

Your Options — Cheapest to Most Expensive

Solution	Cost per Window	Draught Reduction	Thermal Improvement	Lifespan
Self-adhesive foam strips	£5–£15	30–40%	Minimal	1–2 years
Professional brush seals	£250–£400	80–90%	Moderate	15–20 years
Secondary glazing	£200–£500	60–70%	50–65% heat loss reduction	15+ years
Full overhaul + draught-proof	£400–£700	90%+	Moderate	20–30 years
New timber sash windows	£1,500–£2,500	99%	70–80% (double glazed)	60–100 years

Option 1: DIY Draught Strips (£5–£15)

Foam or rubber strips from a hardware shop. You stick them around the sash meeting rail and sides. They compress when the window closes, blocking the gap. Cheap, quick, and better than nothing — but they deteriorate fast, can prevent windows from closing properly, and look messy. A temporary fix, not a solution.

Option 2: Professional Brush Seals (£250–£400)

A joiner removes both sashes, routs channels into the frame, and inserts nylon brush pile seals. The sashes slide against the brushes, creating an almost airtight seal while still allowing smooth operation. This is the sweet spot for most homeowners — significant improvement, reasonable cost, invisible when done properly.

Option 3: Secondary Glazing (£200–£500)

A second pane of glass mounted on the interior side of the window. Excellent for noise reduction and thermal improvement. The downside: it’s visible, can trap condensation between the panes, and doesn’t fix the actual sash draughts — air still gets past the sashes into the cavity between primary and secondary glazing.

Option 4: Full Overhaul (£400–£700)

The complete service: strip out both sashes, replace cords, replace parting and staff beads, re-putty all glass, fit brush pile draught seals, ease and adjust for smooth operation. If the timber is sound, this can give you another 20–30 years from your original windows. We do this regularly on Victorian properties where the frames are still in good condition.

📷 ADD REAL PHOTO: Before/after sash window overhaul — draught strips fitted

Option 5: Full Replacement (£1,500–£2,500)

When the frame has significant rot, the sill is crumbling, or the sashes are warped beyond adjustment — it’s time for new windows. Modern timber sash windows with double glazing, factory-finished paint, brush seals, and spiral balances eliminate draughts completely and cut heat loss by 70–80%.

Check the Price of New Sash Windows

Use our 3D configurator to design your replacement sash windows and get an instant price.

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When Repair Stops Making Sense

We always recommend repair over replacement where possible — it’s cheaper and preserves the character of your home. But replacement makes more sense when:

The sill has rotted through and is soft to touch
The frame has structural rot (not just surface decay)
The sashes are warped and no longer sit square
You’re already spending £500+ per window on overhaul — at that point new windows with 60-year lifespan are better value
You want double glazing — retrofitting sealed units into original sashes is possible but not always practical

Peter — Skylon Joinery

We manufacture and install timber windows and doors across London and the Home Counties. Over 15 years in the trade. Every window made in our own workshop. This page is written from hands-on experience, not a template.

Frequently Asked Questions

Why are my sash windows so draughty?

Sash windows become draughty because timber shrinks and swells over decades, creating gaps between the sashes and the frame. The original putty crumbles, parting beads wear down, and sash cords stretch — all creating air paths. A typical Victorian sash window can have 5-10mm gaps around the sashes.

How much does it cost to draught-proof sash windows?

Professional draught-proofing with brush seals costs £250–£400 per window. A full overhaul including new cords, beads, and draught strips costs £400–£700 per window. Replacement with new timber sash windows costs £1,500–£2,500 per window installed.

Is secondary glazing worth it?

Secondary glazing reduces heat loss by 50-65% and significantly cuts noise. At £200–£500 per window it is the cheapest thermal upgrade. However, it adds a visible internal panel, can trap condensation, and does not fix the draughts from the sash gaps themselves.

Can old sash windows be repaired?

Yes, if the frame is structurally sound. A skilled joiner can replace rotten sections, re-cord, re-putty, fit draught strips, and overhaul the whole window. It only becomes uneconomical when the frame or sill has extensive rot.

How much heat do draughty windows lose?

Single-glazed sash windows without draught-proofing can account for 20-30% of a home's total heat loss. Draughts alone can add £200–£400 per year to heating bills in a typical Victorian terrace.