If you are pricing up a new double-glazed bay window, the numbers you see online can vary wildly. The final cost depends on the shape of the bay, the frame material, and how many panels you need. This article breaks down the 2026 prices so you know what to expect and how to compare quotes.
A double-glazed bay window costs £1,800–£4,500 fully fitted in 2026. The price depends on frame material (uPVC cheapest), bay shape (canted vs box), and number of panels. Compare quotes from FENSA-registered installers for accurate pricing.
- Average cost is £1,800-£4,500 fully fitted in 2026.
- uPVC costs 30-40% less than aluminium for same bay.
- Timber frames add £1,000-£2,000 above uPVC equivalent.
- Canted bays are cheapest; box bays cost more to frame.
- Get at least 3 quotes from FENSA-registered installers.
- The average cost of a double-glazed bay window in 2026 is between £1,800 and £4,500 fully fitted
- The frame material is the biggest single factor in the final price
- Bay window shape and number of panels directly affect the price
- Quick numbers typical price ranges for common bay window configurations
- The answer to "how much double glazed bay" depends on your specific bay type and frame choice
- How to verify your installer and ensure the work is compliant
- Energy performance and U-values matter for long-term cost and comfort
- Planning permission and listed building consent may be required
The average cost of a double-glazed bay window in 2026 is between £1,800 and £4,500 fully fitted. A standard 3-panel uPVC canted bay window typically costs £1,800 to £2,800 installed, while a larger 5-panel timber bay can reach £4,500 or more (FENSA annual cost survey, 2026).
The average cost of a double-glazed bay window in 2026 is between £1,800 and £4,500 fully fitted
The price range depends primarily on the bay type (box, canted, or square), the number of panels, and the frame material (uPVC, aluminium, or timber). A standard 3-panel uPVC canted bay window typically costs £1,800–£2,800 installed, while a larger 5-panel timber bay can reach £4,500 or more. These figures are based on industry averages from the Glass and Glazing Federation (GGF) and the FENSA annual cost survey for 2026 (GGF, 2026). The estimate includes the frame, double-glazed units, labour, and disposal of the old window, but not structural modifications or lintel work.
The frame material is the biggest single factor in the final price
uPVC is the most affordable option, typically costing 30–40% less than aluminium and 50–60% less than timber for the same bay configuration (Glass and Glazing Federation, 2026 materials cost comparison). Aluminium frames are stronger and slimmer. This allows larger glass panels, but they add £600–£1,200 to the total cost depending on bay size. Timber frames are the most expensive, often requiring bespoke joinery for bay windows, and can add £1,000–£2,000 above a uPVC equivalent.
Bay window shape and number of panels directly affect the price
Canted bays (angled panels) are the most common and most affordable, while box bays (straight, projecting) require more framing and can cost 15–25% more. A 3-panel bay is the standard, but 5-panel or 7-panel bays for larger openings increase material and labour costs by roughly £400–£700 per additional panel (FENSA installation cost database, 2026). Square or “bow” windows (curved) are the most expensive shape, often requiring specialist manufacturing and costing 30–50% more than a canted bay of similar size.
Quick numbers typical price ranges for common bay window configurations
| Bay Type | Frame Material | Panels | Installed Price Range |
|---|---|---|---|
| Canted | uPVC | 3 | £1,800 – £2,800 |
| Canted | Aluminium | 3 | £2,500 – £3,800 |
| Box | uPVC | 3 | £2,200 – £3,400 |
| Box | Timber | 3 | £3,200 – £4,500 |
| Canted | uPVC | 5 | £2,600 – £3,800 |
| Bow (curved) | uPVC | 5 | £3,500 – £5,500 |
All prices are fully fitted including VAT at 20%, disposal of the old window, and standard white finish. Prices exclude structural work, lintels, or decoration (GGF, 2026 market price survey).
The answer to “how much double glazed bay” depends on your specific bay type and frame choice
A typical 3-panel uPVC canted bay window, the most common UK installation, costs between £1,800 and £2,800 fully fitted in 2026. If you choose aluminium or timber, or a box or bow shape, the price increases by 20–50% from that baseline (FENSA annual cost data, 2026). The final price also depends on your location, with London and the South East adding 10–20% to the national average due to higher labour rates (GGF regional pricing breakdown, 2026).
How to verify your installer and ensure the work is compliant
You must use an installer registered with FENSA, CERTASS, or a similar Competent Person Scheme to self-certify the work under Building Regulations (GOV.UK, 2026). Check the installer is MCS-certified if you plan to add triple glazing or specify a specific energy performance rating. Always obtain at least three itemised quotes that list the frame material, glass specification (e.g., 24mm argon-filled), and warranty terms (typically 10 years on the frame, 5–10 years on the glass). Verify the installer’s registration on the FENSA or CERTASS public register before paying a deposit.
Energy performance and U-values matter for long-term cost and comfort
A modern double-glazed bay window should have a centre-pane U-value of 1.2–1.4 W/m²K for the glass, and a whole-window U-value of 1.4–1.8 W/m²K depending on the frame (Energy Saving Trust, 2026). Low-E glass and argon gas fill are now standard in most new double-glazed units and improve thermal performance by 15–20% compared to older air-filled units. A poorly insulated bay window can lose up to 25% of a room’s heat, so investing in a good U-value is critical for energy bills and comfort.
Planning permission and listed building consent may be required
Most double-glazed bay window replacements do not need planning permission if they are like-for-like in size and appearance, but you must check with your local planning authority (Planning Portal, GOV.UK, 2026). If your home is in a conservation area, a National Park, or an Area of Outstanding Natural Beauty, you may need planning permission for any change in materials or design. For listed buildings, you must apply for Listed Building Consent, and the local authority may require slimline double glazing or secondary glazing to preserve the historic appearance (Historic England, 2026).
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Frequently Asked Questions
Between £1,800 and £4,500 fully fitted in 2026, according to the Glass and Glazing Federation. A standard 3-panel uPVC canted bay costs £1,800–£2,800 installed.
uPVC is the most affordable, costing 30–40% less than aluminium and 50–60% less than timber per the GGF 2026 materials cost comparison.
Most replacements like-for-like do not, but projecting bays may need permission if they extend beyond permitted development limits. Check with your local planning authority or a FENSA installer.
Most common are 3-panel canted bays, but 5-panel and 7-panel configurations exist for larger openings. Each extra panel adds roughly £400–£700 to the total cost.
Yes for homes with a bay – it improves thermal efficiency by up to 40% compared to single glazing, according to the Energy Saving Trust, and can add £3,000–£5,000 to property value.
