Windows
Bay and bow windows
Bay and bow windows typically cost £1,500 to £3,000 fitted because they are structural as well as decorative. A bay projects in angled sections, a bow curves in equal segments. Many carry load from the wall above, so the replacement has to be designed to support it.
A bay is the one window replacement where getting it wrong has consequences beyond appearance. In a lot of Victorian and inter-war houses the bay carries the wall above it, and the window frame is part of how that load reaches the ground.
Indicative guide, not a quote
per window, supplied and fitted
£1,500 – £3,000
These figures come from published industry price guides, not official statistics, and several of those sources are installers or comparison sites with a commercial interest. They are a starting point for a conversation, not a quote. Your installer sets the actual price after measuring.
Costwise UK new windows cost guide · checked 2026-10-09
The structural point, which is not optional
Where a bay supports masonry above, removing the old frame removes part of the support. The replacement needs either a structural frame designed for the load or separate support such as jacking posts built into the corners.
A competent installer will identify this at survey and price for it. An unusually cheap bay quote is a reason to ask specifically how the load above will be carried.
Bay, bow, and which you have
A bay is made of flat sections meeting at angles, usually three or five, and projects in a squared or splayed shape. A bow is made of more, narrower sections that form a gentle curve. Bays are more common on UK housing; bows read softer and need more width to work.
Roofs, sills and the parts people forget
Many bays have their own small roof, and that roof is frequently in worse condition than the window. Replacing the window is the sensible moment to deal with it.
The same goes for the sill board and the structure beneath a bay on a suspended floor. Ask for these to be inspected at survey, because access afterwards is much harder.
Bay and bow windows: common questions
- Why are bay windows so much more expensive?
- More frame, more glass, more corners, and usually a structural requirement. The fitting is also considerably more involved than a straight opening, often needing temporary support while the old frame comes out.
- Can a bay window be replaced with a flat window?
- Technically yes, but it changes the elevation significantly and may need planning permission. On a street of bay-fronted houses it also tends to hurt the value of the property.
- Does replacing a bay window need building regulations approval?
- Replacement windows are covered either by a competent person scheme registration such as FENSA or CERTASS, or by a building control application. Where structural support is altered, the structural work is a separate consideration.
Other windows
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uPVC windows
£400 – £850 fitted
uPVC windows cost £400 to £850 fitted. What separates a good one from a cheap one, what the regulations require, and when uPVC is the wrong choice.
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Aluminium windows
£600 – £1,250 fitted
Aluminium windows cost £600 to £1,250 fitted. Why the slim sightlines matter, what a thermal break does, and whether the extra over uPVC is worth it.
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Timber windows
£800 – £1,600 fitted
Timber windows cost £800 to £1,600 fitted. Why modern engineered timber is not the wood you remember, the real maintenance, and when it is compulsory.
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Casement windows
£400 – £850 fitted
Casement windows are the most common UK style and the cheapest to replace. Side-hung or top-hung, fire escape rules, and flush versus stormproof.
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Sash windows
£800 – £1,800 fitted
Sash windows cost £800 to £1,800 fitted. Cords and weights versus spiral balances, when repair beats replacement, and fitting double glazing.
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Tilt and turn windows
£400 – £850 fitted
Tilt and turn windows open two ways: a secure vent, or fully inwards for cleaning and escape. Why flats and upper floors usually choose them.
TrustedGlazing does not make, supply or fit windows and doors, and the prices above are published industry guides rather than our own. We match your enquiry to one vetted local installer, who quotes and contracts with you directly.