A bay is the most expensive window most people will ever replace, and the price is hard to guess from the outside. For uPVC bay windows the typical range is about £1,800 for a small bay to £6,000 for a large bow or full-height one. The frame is only part of it. What holds up the roof above the bay often decides the final figure.
Typical bay window prices
Typical uPVC bay window replacement costs in Hampshire, supplied and fitted
| Job size | What it usually covers | Typical cost |
|---|---|---|
| Small | Square or shallow three-facet bay, standard glazing | £1,800–£3,000 |
| Typical | Front bay on a Victorian or 1930s house, with a canopy or roof above | £3,000–£4,500 |
| Large | Bow bay, full-height bay, or one with extra structural work | £4,500–£6,000 |
The shape matters
A square bay has flat sides at right angles and is simple to build. A three-facet bay has angled sides, usually 135 degrees, and costs more because every joint has to match your existing opening. A bow is a gentle curve built from several narrow facets, which pushes the price towards the top of the range. Measurement is the critical step. Bay frames are made to the angle of your existing bay, and a small error at survey shows up as a gap at fitting.
What holds the bay up
Many older bays have a timber or steel head that carries the roof or wall above, and the old window is sometimes doing part of that job. A replacement bay is usually built with load-bearing bay poles or structural couplers where the structure needs support, so that the frame is not taking weight it was never designed for. This is why one installer can quote noticeably more than another. Ask each of them how the roof above the bay will be supported while the old frame is out and what stays in place afterwards.
- Canopy or roof over the bay. Lead, felt or tile work may need disturbing, and replacing it is an extra cost.
- Cill and sub-cill. Rotten timber cills and cracked stone cills add to the price.
- Internal finishing. Plaster around the reveals often needs patching.
- Opening sashes. Each opening vent adds hardware and cost over a fixed pane.
- Colour and woodgrain. As on any uPVC window, these cost more than white.
Bays in Hampshire homes
Bay fronts are common on Portsmouth and Southsea's Victorian and Edwardian terraces, and on the 1930s semis of places such as Cosham and Fareham. Terraces in a conservation area may have rules about materials and proportions, so check with the council before you order, particularly if the bay is on the front elevation. The slim glazing bars of original sashes are hard to match in uPVC, and a good installer will say so rather than promise an exact copy.
Bay frames are normally made to order. Ask whether the installer manufactures them or buys them in, how long the lead time is, and what happens if the delivered frame does not fit the measured opening.
Checks before you commit
- A written statement of how the structure above will be supported
- Whether the roof or canopy work is included or priced separately
- FENSA or building control sign-off, such as through FENSA
- The guarantee on the frame, glass and any support poles
For a single flat window, see our casement window cost guide. If you are buying a house with a tired bay, the guide to buying with old windows lists what to check, and the cost calculator puts a bay alongside the rest of the house.
Frequently asked questions
How much does a replacement bay window cost in Hampshire?
As a guide, a small bay costs about £1,800–£3,000, a typical front bay £3,000–£4,500, and a large bow or full-height bay up to roughly £6,000.
Why is a bay so much dearer than normal windows?
It is made up of several joined frames cut to your angle, it often needs structural support for the roof above, and it takes longer to fit.
Can a bay window be replaced in a day?
Many are fitted in one to two days. Extra roof or cill work can stretch that, so ask for a programme in writing.
Do I need building control approval for a new bay?
Replacing an existing bay with the same structure is normally covered by a competent person scheme. Enlarging a bay or changing its structure is different, so check with the council first.
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