The short answer
A bay window typically costs £900–£2,500 fitted in uPVC, depending on size, the number of panes and whether structural support is needed. Bays cost more than a flat window of the same width because they have multiple angled sections, corner posts and often a structural head that has to carry the wall above. Aluminium and timber bays cost more again. These are typical illustrations, not quotes — see the main cost guide for context.
Bay and bow windows are a defining feature of many UK homes, especially Victorian, Edwardian and 1930s properties. They cost noticeably more than a flat window, and it helps to understand why before you read a quote. This guide sets out realistic 2026 fitted ranges, explains what drives the price, and covers the structural points that make a bay different from an ordinary replacement.
Bay window cost at a glance
- uPVC bay window (fitted) £900–£2,500
- Aluminium bay £1,500–£3,500
- Timber bay £2,000–£4,500+
- Bow window (4–5 panes) £1,200–£3,000
- Structural support work Extra, if load-bearing
- Difference vs flat window Roughly 2–3× the price
Why bay windows cost more than flat windows
A bay window projects outward from the wall in several angled sections, so it is really several windows joined by corner posts rather than a single flat pane. That means more frame, more glass, more sealed units and more labour to fit and seal each joint. Many bays also sit beneath the wall above, so the window head can be load-bearing and the installer must support the structure while the old window is removed and the new one fitted. All of this is why a bay typically costs two to three times what a flat window of similar width would. A bow window — a gentler curve of four or five equal panes — is priced similarly.
| Window type | Material | Fitted price |
|---|---|---|
| Bay window (3–5 panes) | uPVC | £900–£2,500 |
| Bay window | Aluminium | £1,500–£3,500 |
| Bay window | Timber | £2,000–£4,500+ |
| Bow window (4–5 panes) | uPVC | £1,200–£3,000 |
What affects the price of a bay
Within those ranges, several things move the figure:
- Number and size of panes — a wide five-section bay costs more than a compact three-section one.
- Frame material — aluminium and timber carry the usual premium over uPVC. See material cost comparison.
- Structural support — if the bay is load-bearing, the installer may need a steel or timber support and additional time, which adds cost.
- Glass specification — triple glazing or acoustic glass adds across each pane.
- Decorative details — leaded or astragal-bar glass, colour finishes and a roof or canopy over the bay add to the price.
Bay windows and regulations
Replacing a bay like-for-like is usually permitted development and notifiable under Building Regulations, so a FENSA or CERTASS registered installer can self-certify it — see FENSA, CERTASS and Building Regulations. If the bay is on a listed building or in a conservation area, or you are changing its style or material, you may need consent — see planning permission for new windows. This is general information; the actual cost and any consent requirements depend on your property and chosen installer.
Compare double glazing quotes
Bay window prices vary widely with size, material and structural work. Use our service to compare quotes from FENSA or CERTASS registered installers in your area.
Frequently asked questions
How much does a uPVC bay window cost fitted?
A uPVC bay window typically costs £900–£2,500 fitted in 2026, depending on its size, the number of panes, the glass specification and whether structural support is needed. Aluminium and timber bays cost more.
Why is a bay window more expensive than a normal window?
A bay is several angled windows joined by corner posts, so it uses more frame, glass and labour. Many bays also carry the wall above, so the installer must support the structure during the swap — all of which makes a bay roughly two to three times the price of a flat window.
What is the difference between a bay and a bow window?
A bay window has distinct angled sections projecting from the wall; a bow window is a gentler, continuous curve of four or five equal panes. They are priced similarly, with the exact figure depending on size and material.
Do I need planning permission to replace a bay window?
A like-for-like bay replacement is usually permitted development and notifiable under Building Regulations only. Consent may be needed in a conservation area, on a listed building, or if you change the style or material. See our planning permission guide.
Sources & further reading
- FENSA — guidance on replacement windows and Building Regulations compliance
- Glass and Glazing Federation (GGF) — consumer guidance on window types and costs
- Energy Saving Trust — double glazing and typical installation costs
- GOV.UK / Planning Portal — replacement windows and permitted development
This is general information, not advice for your specific property or installation. Costs vary with your home, the windows you choose and your chosen installer. Replacement windows should be fitted by a FENSA or CERTASS registered window installer. We are an independent information and introduction service, not an installer.