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French Door Calculator
Estimate the cost of French doors in uPVC, timber, aluminium or composite with sidelights. Check Part L U-value compliance for UK installations.
Structural opening width
Structural opening height
Base supply and install cost
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How We Calculate This
This calculator estimates French door costs based on material, configuration, glazing specification and optional extras.
The formula
Total = Base price × Material factor × Config factor × Glazing factor + Extras
- Material: uPVC (1.0x), aluminium (1.5x), timber (1.8x), composite (2.0x)
- Config: pair only (1.0x), +1 sidelight (1.35x), +2 sidelights (1.65x)
- Triple glazing adds approximately 20% to cost
U-value and compliance
The quoted U-value is an indicative modern-product figure. Under Approved Document L (2021), a replacement glazed door in an existing dwelling has a limiting whole-door U-value of 1.4 W/m²K (or DSER band C); modern double-glazed uPVC, timber and thermally-broken aluminium doors all readily meet this. Triple glazing is shown at ~1.0 W/m²K. Always use the manufacturer’s stated whole-door U-value for the actual compliance check.
Sidelights and leaf width
Sidelights sit either side of a fixed ~600mm door pair (so each leaf stays within the ~900mm practical hinged-leaf limit). The calculator only applies the sidelight premium when the opening is wide enough for a real panel, and warns if a plain pair would force leaves wider than ~900mm.
Cost multipliers are indicative UK market rates, not a published standard — obtain itemised installer quotes. Estimated assembly weight is approximate (a 4-16-4 sealed unit is ~20 kg/m² of glass; the remainder is frame and ironmongery). For sliding patio doors, use our sliding door cost calculator, which prices inline, lift & slide and pocket systems to the same Part L check.
Frequently Asked Questions
In 2026, uPVC French doors typically cost £1,000-£1,500 supply and install. Hardwood timber French doors range from £1,800-£2,800. Aluminium options cost £1,500-£2,200. Adding sidelights increases costs by 35-65%. Bay/bow configurations are significantly more.
The most common French door opening is 1800mm wide by 2100mm high, giving two 900mm-wide door leaves. Openings can range from 1200mm (narrow pair) to 2400mm with sidelights. The maximum practical leaf width is about 900mm before the door becomes too heavy for hinges.
Yes. Replacement French doors in an existing dwelling must meet Part L thermal requirements — a maximum whole-door U-value of 1.4 W/m²K (or DSER band C for doors with more than 60% glazing). Glass in critical locations (the door itself, and glazing below 1500mm at door sides) must be safety glass under Part K (Approved Document K, K4) — Part N was withdrawn in England in 2013 and its safety-glazing rules moved into Part K; use toughened or laminated glass meeting Class 3 of BS EN 12600. Part Q security (PAS 24) is mandatory only for new dwellings or a material change of use — for a like-for-like replacement it is best practice, not a legal requirement. Use a FENSA or CERTASS registered installer to self-certify the work.
Modern French doors tested to PAS 24:2022 (+A1:2024) — the current enhanced-security standard that underpins Approved Document Q — are very secure, with multi-point locking, reinforced frames and toughened or laminated glass. PAS 24:2016 was withdrawn and superseded. Look for Secured by Design accreditation for enhanced security, and make sure the slave (first-closing) leaf has robust shoot bolts top and bottom.
French doors are more affordable, provide a classic look and offer good ventilation. Bi-fold doors create a wider opening (up to 6m+) and fold neatly to one side, but cost 2-3 times more. French doors suit standard openings; bi-folds suit wider spans where you want to open up an entire wall.
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Last updated: June 2026
Verified against UK standards · estimates only, confirm with your supplier.