A triple-glazed sash window costs roughly 40% more than a double-glazed casement of the same size, a price gap that can reach £800 per window before installation.
Deciding on new windows involves balancing upfront cost, energy savings, and the style of your home. The price difference between the cheapest and most expensive options is substantial. A triple-glazed timber sash window can cost around 40% more than a double-glazed uPVC casement of the same size, a gap that can reach £800 per window before installation (DESNZ cost analysis, 2026).
Your choice of frame material (uPVC, timber, or aluminium) and glazing type (double or triple) are the main factors that set the final price. This article uses published data to break down the costs and savings for each combination, so you can estimate your own budget.
How to use a window replacement cost calculator in 2026
A window replacement cost calculator is an online tool that asks for the number of windows, frame material, glazing type, and opening style (casement, sash, or tilt-and-turn). It then produces a per-unit and total estimate based on national average installation rates for labour and materials from the Glass and Glazing Federation’s (GGF) annual survey (GGF, 2026).
The calculator output is a guide only. It does not include scaffolding, structural repairs, or waste disposal, which can add 10–20% to the total cost. For example, a quote of £4,000 for 10 windows could become £4,400–£4,800 once these extras are added. Always use the calculator as a starting point and ask installers for a full written quote that itemises all costs.
uPVC, timber, or aluminium, how frame material changes the total
Frame material has the biggest impact on the per-window cost. For a standard double-glazed casement window (1200mm x 1200mm), installed costs in 2026 are as follows:
- uPVC: £300–£500 per window.
- Timber: £500–£900 per window (an extra £200–£400).
- Aluminium: £400–£800 per window (an extra £100–£300).
These figures are based on GGF 2026 trade data (GGF, 2026).
Frame material also affects thermal performance, measured by the U-value (the rate of heat transfer through the window). A lower U-value means better insulation. Timber windows typically have U-values of 1.2–1.4 W/m²K, uPVC achieves 1.4–1.6 W/m²K, and aluminium with a thermal break reaches 1.4–1.8 W/m²K (BRE, 2026). Aluminium frames are stronger and slimmer but conduct heat more, so they require a thermal break (a plastic strip inside the frame) to improve insulation. This adds cost but is essential for energy efficiency.
Double vs triple glazing, the £/U-value trade-off
Double glazing (U-value 1.2–1.6 W/m²K) costs £300–£600 per window installed. Triple glazing (U-value 0.7–1.0 W/m²K) costs £450–£1,000 per window, with the greatest savings in north-facing rooms where heat loss is highest (GGF, 2026).
The Energy Saving Trust (EST) estimates that replacing single glazing with A-rated double glazing saves a typical semi-detached home £195–£235 per year on heating bills (Energy Saving Trust, 2026). Triple glazing adds 10–15% to the installation cost but only reduces heat loss by an additional 20–30% over good double glazing. This means payback periods for triple glazing are often longer than 15 years.
Quick numbers, typical costs per window type in 2026
| Window type | Frame material | Typical cost (installed) | U-value range (W/m²K) |
|---|---|---|---|
| Double glazed casement | uPVC | £300–£500 | 1.4–1.6 |
| Double glazed casement | Timber | £500–£900 | 1.2–1.4 |
| Double glazed casement | Aluminium | £400–£800 | 1.4–1.8 |
| Double glazed sash | uPVC | £500–£800 | 1.4–1.6 |
| Double glazed sash | Timber | £700–£1,200 | 1.2–1.4 |
| Triple glazed casement | uPVC | £450–£800 | 0.8–1.0 |
| Triple glazed casement | Timber | £700–£1,200 | 0.7–0.9 |
| Triple glazed sash | Timber | £1,000–£1,600 | 0.7–0.9 |
Costs are from the GGF 2026 market survey. U-values are from DESNZ’s Standard Assessment Procedure (SAP) 2026 data (DESNZ SAP, 2026).
Which glazing and frame combination saves the most energy over 10 years?
For a typical 10-year period, a double-glazed uPVC casement window (U-value 1.4) saves £1,950–£2,350 in heating costs compared to single glazing, based on EST 2026 figures for a semi-detached home (Energy Saving Trust, 2026). A triple-glazed timber sash window (U-value 0.8) saves an additional £300–£500 over the same period, but costs £1,500–£2,000 more upfront. The net benefit is negative for most homes.
The best balance for most UK homes is a double-glazed uPVC casement window with a low-e coating and argon gas fill, achieving a U-value of 1.2–1.4 at a cost of £350–£500 per window. This combination offers the quickest payback period, typically 5–8 years depending on your existing glazing and heating system. How to choose the best window frame material for your home
How to verify your installer, MCS, FENSA, and TrustMark certification
FENSA (Fenestration Self-Assessment Scheme) certification is the primary requirement for window installers in England and Wales. It allows installers to self-certify that their work meets Building Regulations. You should only use a FENSA-registered installer (FENSA, 2026).
The Microgeneration Certification Scheme (MCS) applies only if the windows are part of a wider energy-efficiency installation, such as with solar panels or heat pumps. It is not mandatory for window-only jobs (MCS, 2026).
TrustMark registration provides consumer protection and a formal complaints process. You can check an installer’s registration on the TrustMark website before paying a deposit (TrustMark, 2026). How to check if a builder is registered with TrustMark
Frequently Asked Questions
A calculator provides a guide based on national averages from the Glass and Glazing Federation (GGF). It excludes extras like scaffolding and waste disposal, which can add 10-20% to the total cost (GGF, 2026).
The average cost per window ranges from £300-£500 for uPVC casements to £500-£900 for timber, according to GGF data (2026). A full replacement for a 10-window home typically costs £3,000-£9,000.
Triple glazing costs around 40% more than double glazing, per DESNZ cost analysis (2026). It improves energy efficiency by roughly 30% compared to double glazing, but payback depends on your heating system and usage.
uPVC windows cost £300-£500 per window installed for a standard double-glazed casement (1200mm x 1200mm), based on GGF 2026 rates. This is the most affordable frame material.
Frame material has the biggest impact, with timber costing £200-£400 more than uPVC per window. Glazing type (double vs triple) and opening style also significantly affect the final price (GGF, 2026).
