Sash Window Draught Proofing Cost

What it costs to draught proof sash windows, how brush seals and compression seals compare, and whether DIY kits deliver the same results as professional fitting.

Last reviewed: 2026-07-20 • 4 min read • Verified against 5 installer quotes

Sash Window Draught Proofing Costs

Professional draught proofing takes 2-3 hours per window. DIY kits take 1-2 hours per window and require no special tools (scissors, screwdriver).

Brush Seals vs Compression Seals

Two main seal types are used for sash window draught proofing. Each suits different window conditions and budgets.

Brush Seals (Best for Period Sash Windows)

Nylon bristles held in a plastic or aluminium carrier strip. The bristles compress against the sash or frame, blocking air gaps.

Pros: Work well with uneven gaps (period timber moves over time, creating variable gap widths). Tolerate sash movement without jamming. Long-lasting (15-25 years before bristles wear down). Invisible when window is closed.

Cons: Slightly less effective than compression seals (80-90% vs 85-95% draught reduction). Can collect dust in the bristles over time.

Cost: £140-£220 per window professionally fitted (routed into grooves), or £30-£50 for DIY surface-mounted kits.

Brush seals are the standard choice for Victorian and Georgian sash windows because the timber has moved over the decades and gaps aren't uniform. Compression seals work poorly on uneven gaps.

Compression Seals (Best for Modern Sashes)

Silicone or foam strips that compress when the sash closes, forming an airtight seal.

Pros: Better seal than brush (85-95% draught reduction). Effective against noise and dust as well as draughts. Work well on modern replacement sashes with flat, even surfaces.

Cons: Need flat, even surfaces (don't work well on warped or uneven period timber). Can cause sash to jam if gap is too narrow. Shorter lifespan (10-15 years before foam perishes).

Cost: £160-£280 per window professionally fitted.

Only use compression seals on post-1950 replacement sashes or newly fitted timber sashes. Period sashes (pre-1950) almost always need brush seals.

Where Draught Seals Are Fitted

A complete draught proofing system seals all gaps around both sashes. Professional installers fit seals at four locations:

• Staff beads (outer frame): Vertical strips either side of lower sash, and horizontal strip at top. Seals prevent draughts between lower sash and outer frame.
• Parting beads (between sashes): Vertical strips separating upper and lower sash. Seals prevent draughts between the two sashes and around upper sash sides.
• Meeting rails (where sashes meet): Horizontal seal where the top of lower sash meets bottom of upper sash when closed. Often the biggest draught source.
• Sill (bottom of lower sash): Seal along the sill where lower sash bottom rail sits when closed.

DIY kits usually include seals for staff beads and meeting rail only (the two biggest draught sources). This achieves 60-75% draught reduction. Professional systems seal all four locations for 80-95% reduction.

Energy Savings from Draught Proofing

Draughty sash windows lose heat through air leakage (cold air infiltrates, warm air escapes). Draught proofing reduces this air exchange by 80-90%, cutting heat loss.

Energy prices at 20p/kWh gas (2026 average). Savings are higher for larger windows, colder climates, or higher heating use.

For a 10-window Victorian terrace with single glazed sashes, draught proofing saves £800-£900 per year. Professional draught proofing costs £1,400-£2,200 for the whole house, paying back in 2-3 years.

DIY vs Professional Draught Proofing

DIY makes sense if you're on a tight budget, comfortable with basic DIY, and willing to accept visible seal strips and lower performance. Professional fitting is better for listed buildings (hidden seals maintain appearance), high-value properties, or if you want maximum draught reduction and longevity.

What Professional Draught Proofing Includes

A professional draught proofing service (£140-£280 per window) typically includes:

• Survey to assess sash condition and gap sizes
• Remove sashes (staff beads and parting beads)
• Rout grooves in beads for seal carriers (3-5mm grooves)
• Fit brush or compression seals into grooves
• Ease sashes if sticking (plane high spots)
• Adjust sash balance for smooth operation
• Replace worn sash fastener if needed
• Refit beads and check seal compression

The sash adjustment is critical. Adding seals increases friction, so sashes often need easing (planing down slightly) to slide smoothly. DIY kits don't include this, which is why DIY-proofed sashes sometimes stick.

Sources

Pricing verified against:

• Ventrolla draught proofing quotes (London and Southeast, Jan 2026)
• The Sash Window Workshop draught seal price list (Dec 2025)
• Reddiseals DIY brush seal kit prices (retail, 2026)
• MyBuilder draught proofing specialist quotes (regional, 2025-2026)
• Energy Saving Trust heat loss data for draughty vs proofed sash windows (2024)