Extension glazing budget · 2026
Extension Windows and Doors Cost
An extension often combines several ordinary windows with one expensive glazed-door opening. The door choice can dominate the glazing budget, especially when moving from French doors to an aluminium bifold system.
Quick price answer: Three medium standard windows plus French doors model at £2,252–£4,091. Four windows plus a three-panel aluminium bifold model at £4,067–£7,389 before structural opening work.
Extension glazing examples
These isolate the window-and-door supply/fitting element and do not price the extension structure itself.
Figures are modelled UK-average fitted-market estimates from the Window Price Calculator engine, using its 24 September 2026 research refresh. They include ordinary removal, standard fitting, basic making good and VAT; scaffolding, hidden structural repairs and highly bespoke work can sit outside the range.
The structural opening is the big caveat
A new extension is not the same as swapping a door into an existing opening.
Door and window products
The ranges on this page are useful for the glazing products themselves.
Building structure
Lintels or steel, masonry, insulation, waterproofing, floor levels and finishing belong to the extension build. Those costs are not represented by a like-for-like replacement model.
Specify these early in an extension design
They affect both the glazing quote and the surrounding construction.
- Approximate structural opening widths and heights.
- Whether you want French, sliding or bifold doors.
- Window frame material and colour.
- Threshold detail and finished floor level.
- Any safety, solar-control or acoustic glass requirements.
Use your own project
Start a replacement estimate.
Use the calculator to price a complete replacement window or door. Choose the closest product and project size and we’ll carry those choices into the full calculator.
Rough sizes are fine. The full personalised result is unlocked after the £2.99 checkout.Related price guides
Use the closest related guide to compare another specification or project type.
Questions people ask
How much should I budget for extension windows and doors?
Our illustrative product-and-fitting examples run from £2,252–£4,091 for three windows plus French doors to £4,067–£7,389 for four windows plus a three-panel bifold.
Does this include the cost of building the opening?
No. These are glazing product and standard-fitting benchmarks. New extension structure, steel, masonry and related building work are separate.
Are bifolds much more expensive than French doors?
Yes in the current model: a medium three-panel bifold is £2,723–£4,841 versus £1,267–£2,157 for medium French doors.
Build the glazing package before you compare quotes.
Add the extension windows and chosen door system as separate items. Treat the surrounding building work as a separate construction budget.
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