A bay window is a structural element, not just a window: on most Victorian, Edwardian and 1930s houses the bay carries load from above. Replacing one is a different job from replacing a flat window, and it is where installers get caught out.
In a typical bay, the window frame itself, or a steel or timber member concealed within it, is doing structural work — carrying the roof of the bay above, and sometimes the wall above that. Take the old frame out without propping and the bay above will drop.
A correct bay replacement uses a bay pole or structural jack post at the mullion positions, propped before the old frame comes out, and load transferred onto the new frame before the props come away. If a quote for a bay window does not mention structural support, ask why.
Bays are where uPVC's frame thickness hurts most. A three-section bay has two mullions, and in uPVC each of those is a fat white post interrupting the view. The aluminium equivalent is dramatically slimmer, and the corner posts can be made in a matching finish rather than as bulky add-on trims.
Aluminium also allows a true structural corner post, so on wider bays you can often avoid the extra intermediate mullion a uPVC system would need.
| Job | Typical cost |
|---|---|
| Three-section bay window supplied & fitted | £2,200 – £3,600 |
Ranges include VAT and installation. Final price depends on size, spec, access and site condition — a survey gives you a fixed number.
A three-section bay typically runs £2,200–£3,600 supplied and fitted, depending on width, glazing spec, colour and whether structural support work is needed. Five-section and two-storey bays cost more.
Replacing a bay like-for-like is covered by a FENSA or CERTASS self-certification. If the structural opening changes, or a lintel is altered, building control approval is required.
Yes, and it is one of the most common jobs we do. Old aluminium bays have no thermal break — they stream with condensation in winter. A modern thermally broken frame in the same slim proportions solves it without changing the look of the house.
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Free survey, fixed price, no pressure. Or call us and we'll give you a realistic ballpark in five minutes.
