French Windows Installation and Replacement Cost Calculator

How this calculator works

This calculator estimates a realistic price range rather than a single figure, because real-world quotes genuinely vary that much. It starts from typical UK supplied-and-fitted price ranges drawn from published 2026 industry cost guides, then multiplies them by the number of units you enter and by adjustment factors for each choice you make below. The result is a low-to-high band that a fair quote is likely to fall within, not a promise of the exact price you will pay.

A French window set in uPVC typically costs around to supplied and fitted in 2026, sitting above a standard casement because it involves two full opening sashes, a flying mullion mechanism and additional locking hardware. Aluminium and timber versions carry the usual material premiums of roughly 1.5 to 2 times uPVC.

Number of French window sets

Enter how many French window sets you need, counting each pair of meeting casements as one set. They are popular on bedrooms with Juliet balconies, landings and garden-facing rooms.

Window size

Size is one of the biggest cost drivers for any glazed unit. A larger opening needs more frame material and a bigger, heavier sealed glass unit, and it usually takes longer to fit. The calculator uses three broad size bands based on common UK window dimensions: choosing the small band reduces the typical range by around 20 percent, while the large band increases it by around 40 percent. If your windows vary in size, run the calculator once per size band and add the results together.

Frame material

Frame material has a bigger effect on price than almost any other choice. uPVC is the baseline and accounts for around three quarters of UK installations. Aluminium typically costs 1.5 to 2 times as much as uPVC for the same opening, in exchange for slimmer sightlines and a longer lifespan. Timber usually costs around twice as much as uPVC and suits period properties, but needs repainting every five to eight years. Composite frames, with a timber core and aluminium outer skin, sit at the top of the market.

Specification level

Two windows that look similar from the street can sit at very different price points. Budget products use simpler profiles, standard hardware and basic glass. Mid-range covers the typical A-rated units most UK installers quote by default. Premium covers high-end systems with upgraded security hardware, better thermal performance, special finishes or designer profiles, and typically adds around 30 percent to the price.

Where you live

Labour rates are not uniform across the UK. Published cost guides consistently show installation prices in London and the South East running roughly 20 to 30 percent above the national average, driven by higher labour costs, travel, parking and congestion charges. The calculator applies an uplift of around 20 percent if you select London and the South East. Product prices themselves are broadly similar nationwide, so the difference mostly reflects fitting costs.

What else affects the price

French windows are priced by the pair of sashes and the hardware that lets both open fully with no central post. Where the set opens onto a Juliet balcony, the balustrade and its fixings are a separate cost, and glass in and around the opening must be toughened safety glass to comply with building regulations. Weather sealing at the central meeting stile is a quality point worth checking in quotes, since it is the most common source of draughts on cheaper systems.

Planning permission, building regulations and certification

Like-for-like window replacement on most houses does not need planning permission, but listed buildings always require consent and conservation areas often restrict materials and styles on visible elevations, so check with your local planning authority if either applies. Building regulations apply to every replacement window in a dwelling, setting minimum energy performance and safety glazing standards. Installers registered with a competent person scheme, such as FENSA or Certass, can self-certify compliance and issue a certificate after completion; otherwise you must arrange building control sign-off separately. Keep the certificate safe, as buyers’ solicitors routinely ask for it when you sell.