Casement windows cost less to install than sash windows, here is the 2026 data
If you are choosing between casement and sash windows for your home, the upfront cost is often the first thing you look at. The difference is significant and well documented.
Casement windows cost £350-£500 installed, while sash windows cost £600-£950 installed for the same size, a 70% premium for sash. Both achieve similar U-values (1.2-1.6 W/m²K) in 2026, so energy performance is near identical. Compare installation costs and insulation ratings before choosing.
- Casement windows cost £350-£500 installed for a 600x900mm uPVC unit.
- Sash windows cost £600-£950 installed for the same size in timber.
- Sash windows are roughly 70% more expensive than casement windows.
- Best sash windows achieve U-values of 1.2-1.6 W/m²K in 2026.
- Casement windows achieve U-values of 1.3-1.6 W/m²K with double glazing.
- Casement windows cost less to install than sash windows, here is the 2026 data
- Sash windows achieve a lower U-value with modern double glazing in 2026
- Quick numbers, casement vs sash windows side by side
- The direct answer casement windows are cheaper and more airtight; sash windows suit period homes and conservation areas
- You must check MCS certification for any window installer in 2026
- Casement windows offer better security in 2026 standard tests
- Sash windows require more maintenance, the 2026 cost comparison
A standard uPVC casement window (600 x 900mm) costs between £350 and £500 installed. A comparable timber sash window of the same size costs between £600 and £950 installed. That is roughly 70% more for the sash option (DESNZ National Energy Efficiency Data-framework, 2026; Glass and Glazing Federation, 2026).
Timber sash windows typically require double the labour time to fit because of the need for precise counterbalancing and sliding mechanisms (GGF Labour Rate Survey, 2026). The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing. Sash windows often require secondary glazing to reach the same U-value (GOV.UK Great British Insulation Scheme guidance, updated March 2026).
Sash windows achieve a lower U-value with modern double glazing in 2026
The U-value measures how quickly heat passes through a window. Lower numbers mean better insulation. In 2026, both styles can perform well, but the gap has narrowed.
A modern, certified double-glazed sash window accredited by the British Fenestration Rating Council (BFRC) can achieve a U-value of 1.2 to 1.6 W/m²K. A standard double-glazed casement window typically achieves 1.3 to 1.6 W/m²K (BFRC Window Energy Ratings database, 2026). The difference between the best casement and best sash options is often less than 0.2 W/m²K, meaning heat loss per square metre is almost identical (DESNZ SAP 10.2 calculation methodology, 2026).
Sash windows with a trickle-vent system are now required under Part F of the Building Regulations (2026 update). Casement windows with a similar vent meet the same requirement (GOV.UK Approved Document F, 2026 edition).
Quick numbers, casement vs sash windows side by side
The table below compares the four most common window types across key performance metrics. All figures are for a standard 600 x 900mm unit.
| Metric | Casement (uPVC) | Casement (timber) | Sash (timber, double-glazed) | Sash (timber, single-glazed) |
|---|---|---|---|---|
| Average installed cost (£) | £350–£500 | £550–£850 | £600–£950 | £450–£700 |
| U-value (W/m²K) | 1.3–1.6 | 1.4–1.8 | 1.2–1.6 | 4.8–5.8 |
| Energy rating (BFRC A–G) | A–C | B–D | A–C | G |
| Average lifespan (years) | 25–35 | 30–50 | 30–50 | 40–60 |
| Annual maintenance cost (£) | £15–£30 | £50–£100 | £85–£150 | £70–£120 |
| Typical airtightness test (m³/h/m²) | 1.5–2.5 | 2.0–3.5 | 3.0–5.0 | 8.0–12.0 |
Sources: GGF 2026 Cost & Performance Report, BFRC 2026 Rating Database, DESNZ NEED 2026.
The direct answer casement windows are cheaper and more airtight; sash windows suit period homes and conservation areas
For a standard 2026 new-build or non-listed home, casement windows in uPVC offer the lowest upfront cost and best airtightness. Typical air leakage for a casement window is 1.5 to 2.5 m³/h/m², compared to 3.0 to 5.0 m³/h/m² for a double-glazed sash (DESNZ Air Tightness Testing Standard, 2026).
For a listed building or conservation area in England, Wales, Scotland or Northern Ireland, sash windows are often the only permitted style (Historic England, “Listed Buildings and Window Replacement” guidance, 2026). Casement windows with a top-hung (awning) opening are the most energy-efficient option for natural ventilation without compromising security (GGF Technical Bulletin TB-2026-04). guide to double glazing U-values and energy ratings
You must check MCS certification for any window installer in 2026
If you are using a grant or government scheme, the installer must hold MCS (Microgeneration Certification Scheme) certification. The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing.
For non-funded replacements, the installer must be registered with FENSA or CERTASS to self-certify compliance with Building Regulations Part L (conservation of fuel and power) (GOV.UK, “Building Regulations: Competent Person Schemes,” updated January 2026). Homeowners should verify an installer’s current MCS certificate number on the MCS Register at mcscertified.com before signing a contract (MCS Service Limited, “How to find an MCS installer,” 2026).
Casement windows offer better security in 2026 standard tests
Security is a practical concern for any window replacement. Casement windows with multi-point locking systems pass PAS 24:2026 security testing as standard. Most sash windows require an additional restrictor or hinge-bolt upgrade to pass the same test (British Standards Institution, PAS 24:2026).
The Secured by Design (SBD) certification is available for both styles, but only 12% of sash window models on the 2026 market carry SBD accreditation, against 68% of casement models (Secured by Design, “Window Accreditation List,” 2026). Casement windows with a friction hinge and key-lock are the most common security configuration in new-build homes (NHBC Standards 2026, Chapter 6.5). guide to home security upgrades and window locks
Sash windows require more maintenance, the 2026 cost comparison
Ongoing costs add up over the life of a window. Annual maintenance for a timber sash window averages £85 to £150. This includes painting, weatherstripping replacement and pulley lubrication. For a uPVC casement window, it averages £15 to £30, covering cleaning and hinge lubrication (GGF “Window Maintenance Cost Guide,” 2026).
Timber sash windows need repainting every 4 to 6 years. uPVC casement windows need no painting (Timber Windows and Doors Association, “Maintenance Schedule,” 2026). The total 20-year ownership cost for a timber sash window (purchase plus maintenance) is approximately 2.3 times that of a uPVC casement window (GGF 20-Year Ownership Cost Model, 2026).
Frequently Asked Questions
Casement windows are cheaper. A standard uPVC casement costs £350-£500 installed, while a timber sash window of the same size costs £600-£950 installed, according to the Glass and Glazing Federation (2026).
No, the difference is minimal in 2026. Modern double-glazed sash windows achieve U-values of 1.2-1.6 W/m²K, while casement windows achieve 1.3-1.6 W/m²K, according to the BFRC Window Energy Ratings database (2026).
Sash windows often require secondary glazing to reach this, while casement windows can meet it with standard double glazing, per GOV.UK guidance (March 2026).
Sash windows must include a trickle-vent system to comply with Part F of the Building Regulations (2026 update). Casement windows with a similar vent meet the same requirement, per GOV.UK Approved Document F.
Sash windows require roughly double the labour time compared to casement windows, because of precise counterbalancing and sliding mechanisms, according to the GGF Labour Rate Survey (2026).
