Bay window replacement costs £1,200–£3,000 for uPVC in 2026, rising to £2,500–£5,500+ for aluminium or timber frames. Material is the biggest cost driver – uPVC costs roughly half the price of timber – followed by the number of sections (3, 4, or 5 panels) and whether you are replacing an existing bay or installing a new one where none existed before.
We compared pricing from UK bay window installers and cross-referenced quotes with trade cost databases. This guide covers bay window costs by material, style, and size, the structural costs of new installations, planning permission rules, energy efficiency, and what to budget for bay window blinds and shutters.
A bay window replacement is a bigger project than standard window replacement because of the angled framework and structural support involved. Labour alone runs £250–£300 per day with a two-person team, and most bay replacements take 1–3 days depending on complexity.
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- uPVC bay window replacement costs £1,200–£3,000 - aluminium £1,550–£4,000, timber £1,785–£5,500+ depending on size and style
- Material is the biggest cost factor - uPVC costs roughly half the price of timber for the same window configuration
- A 3-section canted bay is the most common - and the cheapest configuration at £1,200–£1,800 in uPVC
- New bay installation adds £500–£1,500 for structural work - lintels, temporary support, and making good are required for new openings
- Bay window blinds and shutters cost £200–£1,500 extra - shutters are the premium option at £600–£1,500 per bay
Bay Window Costs by Material
Bay window prices vary substantially by frame material. The table below shows typical installed costs for a standard 3-section canted bay window (the most common configuration), including supply, fitting, and disposal of old windows.
| Material | 3-Section Bay | 4-Section Bay | 5-Section Bay | Lifespan |
|---|---|---|---|---|
| uPVC | £1,200–£1,800 | £1,500–£2,200 | £1,900–£3,000 | 20–25 years |
| Aluminium | £1,550–£2,340 | £2,000–£3,000 | £2,500–£4,000 | 35+ years |
| Timber | £1,785–£2,700 | £2,400–£3,500 | £3,000–£5,500 | 50+ years (maintained) |
uPVC is the default choice for most UK homeowners – it is affordable, low-maintenance, and available in woodgrain finishes that replicate timber. Aluminium offers slimmer frame profiles (maximising light and views) and exceptional durability, making it the preferred choice for modern and contemporary properties. Timber is the premium option and often the only acceptable material in conservation areas and listed buildings – it requires repainting every 3–5 years at £100–£200 per year but can last 50+ years with proper care.
Bay Window Costs by Style
Bay windows come in four main styles, each with different cost implications. The style is usually determined by the existing architecture, but if you are installing a new bay window you have a choice.
| Style | uPVC Cost (Installed) | Description | Best For |
|---|---|---|---|
| Canted (angled) | £1,200–£2,400 | Flat front with angled side panels (typically 30° or 45°) | Victorian/Edwardian terraces |
| Box (square) | £1,300–£2,600 | Three flat panels at 90° angles | Modern properties, window seats |
| Bow (curved) | £1,800–£3,500 | 4–6 panels forming a gentle curve | Georgian/Regency properties |
| Circle | £2,200–£4,700 | Semi-circular with multiple curved panels | Statement feature, new builds |
Canted bays are the most common and affordable – they are the standard bay window found on millions of UK Victorian and Edwardian terraced houses. Box bays project straight out from the wall and are slightly more expensive due to the 90° corner joints. Bow windows use 4–6 panels to create a gentle curve and cost 40–60% more than canted bays because each panel requires a slightly different angle. Circle bays are the most expensive custom option, typically reserved for statement features on new builds or high-end renovations.
Bay Window vs Bow Window Cost
Bay and bow windows are often confused, but they differ in shape, cost, and suitability. A bay window uses flat panels joined at angles, while a bow window uses curved panels to create a smooth arc. Bow windows typically cost 40–60% more than equivalent bay windows due to the additional panels and more complex manufacturing.
In practical terms, a 3-section canted bay in uPVC costs £1,200–£1,800, while a 5-section bow window in the same material costs £2,500–£3,500. The bow window provides more interior floor space (the curve projects further) and more even natural light distribution, but the bay window is more cost-effective for the space gained. For most UK properties – particularly Victorian and Edwardian homes – the existing architecture dictates the style.
Structural Costs – New Bay Window vs Replacement
Replacing an existing bay window is straightforward because the structural support (lintel, bay window roof, and any corbels or brackets) is already in place. Installing a new bay window where none existed requires significant structural work and is the most expensive scenario.
Replacing an existing bay: The installer removes the old windows and fits new units into the existing framework. Total cost is the window price plus labour (£250–£300/day for a 2-person team, typically 1–2 days). If the existing bay window roof is in good condition, it can usually be retained – saving £500–£1,500 versus a new roof.
Installing a new bay window: This requires a steel or concrete lintel above the opening (£200–£500 for the lintel alone), temporary structural support during construction, and a new bay window roof (flat lead or felt: £400–£800; tiled or slated: £800–£1,500). A structural engineer’s report is needed (£300–£600) to specify the correct lintel size and confirm the wall can support the bay. Building Regulations approval is mandatory. Total additional cost: £1,000–£3,000 on top of the window price.
If you are replacing an existing bay window, check the condition of the bay window roof before ordering new windows. If the roof needs replacing anyway, it is cheaper to do both jobs at once – the scaffolding and access are already in place. A leaking bay window roof is a common cause of damp in the room below and should not be ignored.
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Do You Need Planning Permission for a Bay Window?
Replacing an existing bay window like-for-like does not normally require planning permission – it falls under permitted development rights. However, planning permission is typically needed if you are installing a new bay window that projects beyond the existing building line, particularly on a front elevation.
Key rules: Listed buildings always require Listed Building Consent for any window changes. Conservation areas may restrict materials (uPVC may be refused in favour of timber). Flats have more limited permitted development rights than houses. The planning application fee is £206 in England (2026). Building Regulations (Part L energy, Part N safety glass) apply to all window replacements regardless of planning status – a FENSA or CERTASS-registered installer can self-certify compliance.
Bay Window Energy Efficiency
Bay windows lose slightly more heat than flat windows of the same glass area because the angled joins and additional frame create more edge conduction. However, modern bay windows with A-rated double glazing still meet current Building Regulations (Part L requires a whole-window U-value of 1.4 W/m²K or better).
To maximise efficiency, specify argon gas fill, Low-E coated glass, and warm-edge spacer bars – all standard on quality units. Triple glazing upgrades the U-value to 0.8–1.0 W/m²K and is particularly worthwhile for large north-facing bays where heat loss is greatest. For energy efficient window options and available grants, see our dedicated guides.
Bay Window Blinds, Curtains and Shutters
Bay windows require specialist window treatments because of their angled or curved shape. Standard off-the-shelf blinds and curtain poles do not fit – you need either angled track systems or made-to-measure treatments. Budget £200–£1,500 per bay depending on your choice.
| Treatment | Cost Per Bay | Pros | Cons |
|---|---|---|---|
| Pleated blinds | £150–£600 | Fit flush to each panel, neat look | Limited blackout options |
| Roller blinds | £120–£400 | Affordable, wide fabric choice | Gaps at angles between sections |
| Curtains (curved track) | £200–£600 | Classic look, good insulation | Track costs £80–£200 alone |
| Plantation shutters | £600–£1,500 | Premium look, light control, adds value | Most expensive option |
| Window seat (built-in) | £300–£800 | Extra seating, storage underneath | Requires carpentry, may limit radiator |
Plantation shutters are the most popular choice for bay windows because they follow the angles precisely and add a premium look that increases property appeal. Hardwood shutters last 20+ years, while MDF alternatives cost 30–40% less but are less durable in humid rooms like kitchens. If you are planning a window seat, check whether the bay has a radiator underneath – it may need relocating (£200–£400 for a plumber).
How to Get the Best Bay Window Quotes
Get at least three quotes from FENSA or CERTASS-registered installers. Prices for the same specification can vary by up to 40% between companies in the same area. When comparing quotes, check whether they include VAT, disposal of old windows, making good to internal plaster, and the bay window roof (if it needs replacing).
Avoid spring and summer if possible – glazing companies are busiest from March to September, and some offer 10–15% discounts in the autumn and winter months to fill their schedule. Ask about the lead time from order to installation – standard bays typically take 4–8 weeks, while bespoke configurations can take 8–12 weeks.
For a broader cost comparison, see our complete double glazing cost guide, or use our free cost estimator for an instant price estimate. For vetted national installers, see our best window companies guide. If your bay windows are misted or have hardware issues, repairs may be more cost-effective than full replacement.
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