The most important thing to know about window designs in the UK is that style choice directly affects energy performance and property value
Choosing a window design is not only about how your home looks from the street. The style you pick determines how much heat escapes through the glazed area, which directly affects your energy bills and your property’s EPC rating. Different designs also suit different property ages, from Georgian sash windows to modern casements, and the wrong choice can lower your home’s resale value.
Casement windows offer the best energy performance for most UK homes, achieving U-values of 1.2 to 1.6 W/m²K. Sash windows are required for period properties but lose more heat. Compare designs to comply with Building Regulations and protect property value.
- Choose casement windows for best airtightness and U-values of 1.2-1.6 W/m²K
- Sash windows suit period properties but lose more heat with U-values up to 2.0
- uPVC casements cost £250-£600 per window installed (FENSA, 2026)
- Comply with Approved Document L for replacement window U-values
- Wrong window design can lower your home's resale value and EPC rating
- The most important thing to know about window designs in the UK is that style choice directly affects energy performance and property value
- Casement windows are the most common UK design with the best energy performance
- Sash windows are the traditional choice for period and listed properties
- Tilt-and-turn windows offer dual ventilation and high security but limited UK uptake
- Quick numbers — window design comparison table
- The direct answer to what window design to choose for your UK home
- How to verify your window installer has the correct UK certification
The direct answer is that casement windows offer the best energy performance for most UK homes, while sash windows are essential for period properties but come with higher heat loss and cost. Current UK building regulations set minimum U-values for replacement windows that vary by design type, so your choice must comply with Approved Document L of the Building Regulations (GOV.UK, 2026).
Casement windows are the most common UK design with the best energy performance
Casement windows open outward on hinges and offer the best airtightness of any opening style because the sash presses tightly against the frame when closed. Typical U-values for modern double-glazed casements range from 1.2 to 1.6 W/m²K, meaning they lose less heat than most other designs (Energy Saving Trust, 2026).
You can choose casements in uPVC, aluminium, or timber. uPVC casements cost £250 to £600 per window installed, making them the most affordable high-performance option (FENSA, 2026). Casements suit most post-1930s homes and modern extensions, and they are the standard choice for new-build housing in the UK.
Sash windows are the traditional choice for period and listed properties
Vertical sliding sash windows are required for many conservation areas and Grade II listed buildings where the original appearance must be preserved. Modern slimline double glazing can achieve U-values of 1.6 to 2.0 W/m²K, which is higher than casements, meaning more heat loss through the glazing (Historic England, 2026).
Timber sliding sash windows cost £800 to £2,500 per window installed, significantly more than casements. Draught-proofing is essential for sash windows; the Energy Saving Trust estimates that proper draught sealing can reduce heat loss by up to 20% (Energy Saving Trust, 2026). If your property is listed, you will need listed building consent from your local planning authority before replacing windows (GOV.UK Planning Portal, 2026).
Tilt-and-turn windows offer dual ventilation and high security but limited UK uptake
Tilt-and-turn windows open inward at the top for secure ventilation or fully inward for cleaning, which makes them popular in new-build flats and Passivhaus designs. They are less common in traditional UK homes because the inward-opening mechanism can interfere with blinds and curtains.
Typical U-values for tilt-and-turn windows range from 0.9 to 1.4 W/m²K, among the lowest available for opening windows (Passivhaus Trust, 2026). Installed cost is £400 to £900 per window, higher than standard casements. Tilt-and-turn windows are most suitable for new-build projects aiming for high energy performance standards.
Quick numbers — window design comparison table
| Window design | Average U-value (W/m²K) | Typical installed cost per window | Best-suited property age | Average lifespan (years) |
|---|---|---|---|---|
| Casement | 1.2 – 1.6 | £250 – £600 | Post-1930s, modern extensions | 20 – 30 |
| Sash | 1.6 – 2.0 | £800 – £2,500 | Pre-1919, listed buildings | 30 – 50 |
| Tilt-and-turn | 0.9 – 1.4 | £400 – £900 | New-build, Passivhaus | 20 – 30 |
| Fixed (non-opening) | 0.8 – 1.2 | £200 – £500 | Any (stairwells, bathrooms) | 25 – 35 |
Sources: Energy Saving Trust, 2026; MCS, 2026; FENSA, 2026
The direct answer to what window design to choose for your UK home
For maximum energy efficiency and lowest cost, choose casement windows in uPVC or aluminium. They offer the best airtightness and U-values for the price, and they suit most modern homes.
For period properties or conservation areas, choose timber sash windows with slimline double glazing. You will pay more and lose more heat than with casements, but you will preserve the property’s character and comply with planning rules.
For new-build or Passivhaus standards, choose tilt-and-turn windows with triple glazing. They achieve the lowest U-values of any opening window design, though at a higher cost.
For non-opening areas such as stairwells or bathrooms, fixed windows offer the lowest U-values and the lowest cost per square metre (Energy Saving Trust, 2026; GOV.UK Planning Portal, 2026).
How to verify your window installer has the correct UK certification
All replacement window installations must comply with Building Regulations. Use FENSA or CERTASS registered installers, who can self-certify that the work meets the required standards (FENSA, 2026; CERTASS, 2026).
For timber windows, check the Wood Window Alliance membership or British Woodworking Federation accreditation to ensure the products meet durability and performance standards. If you are applying for ECO4 or Great British Insulation Scheme grants, MCS certification is required for the installation to qualify (MCS, 2026).
Gas Safe Register is not relevant for windows; it only covers heating installations. Always get at least three quotes and ask for written confirmation of the installer’s certification before signing a contract. How to choose a certified window installer in the UK
Frequently Asked Questions
Casement windows offer the best energy performance with typical U-values of 1.2 to 1.6 W/m²K, according to the Energy Saving Trust (2026). They press tightly against the frame for superior airtightness.
uPVC casement windows cost £250 to £600 per window installed, as reported by FENSA (2026). This makes them the most affordable high-performance option for most UK homes.
Sash windows are primarily designed for period and listed properties, not modern homes. They have higher heat loss than casements, with U-values of 1.6 to 2.0 W/m²K.
UK Building Regulations (Approved Document L) set minimum U-values for replacement windows that vary by design type. Check the latest 2026 guidance from GOV.UK for your specific window style.
Yes, choosing the wrong window design for your property age can lower resale value. Sash windows are essential for conservation areas and listed buildings, while casements suit post-1930s homes.
