French Doors UK: Composite vs Aluminium and What You Will Pay
A pair of French doors is the single most requested back-glazing feature in UK home extensions, and the price range between a basic composite set and a top-spec aluminium pair runs to £2,500. Understanding where that money goes — and what you lose by choosing the cheaper option — is the difference between doors you enjoy for twenty years and doors you regret within five.
What counts as a French door in the UK
A French door is a pair of hinged doors, both glazed, opening outward or inward, typically installed between a living space and a garden or patio. The technical distinction from a single-leaf door matters for Building Regulations: a French door pair must both close and lock, and the “inactive” leaf (the one you do not open daily) must have a top and bottom flush bolt to secure it.
French doors are also sometimes called French windows. The terminology does not change the product — but it does change the Building Regulations route. A door pair that replaces an existing window opening may need a Building Control application for the structural alteration, even if the installer is FENSA-registered. Check with your local authority before ordering.
Composite French doors: £1,500-£2,500 fitted
Composite French doors use the same slab construction as composite front doors: a solid timber core (typically 44-48mm thick) wrapped in a uPVC or GRP skin. The frame is usually reinforced uPVC.
Advantages
- Cost: The cheapest route to a French door pair. A standard white composite pair with no decorative glass will be £1,500-£1,800 fitted
- Security: Multi-point locking on both leaves, with PAS 24 achievable on most ranges
- Thermal performance: A-rated WER is standard on mid-range composites; solid-core doors lose less heat than hollow-frame alternatives
- Low maintenance: The uPVC or GRP skin needs only occasional cleaning
Disadvantages
- Sightlines: Composite frames are wider than aluminium — typically 70-80mm on each side, reducing the visible glass area by 10-15%
- Colour range: Most composites offer 10-15 foil colours; bespoke RAL matching is not usually available
- Weight: A 48mm solid-timber French door pair is heavy. Inward-opening pairs can bind on carpets or flooring; outward-opening pairs place more stress on the hinges
- Maximum width: Composite French doors are practical up to approximately 1.5m per leaf. Beyond that, the weight and hinge stress become difficult to manage
Key brands
- Solidor: The widest range of composite French door styles in the UK market; Ultion lock as standard
- Endurance: CoolSkin technology on the exterior skin reduces fading on south-facing doors; 48mm core
- Residence Collection: Flush-sash aesthetic that mimics timber at a lower price point
Composite French door pricing
| Specification | Approx. price (fitted) |
|---|---|
| Standard white, no decorative glass | £1,500-£1,800 |
| Foil colour (grey, black, woodgrain) | £1,700-£2,200 |
| Decorative glass (leaded, bevelled) | £1,900-£2,500 |
| PAS 24 upgraded specification | Add £100-£200 |
Aluminium French doors: £2,000-£4,000 fitted
Aluminium French doors use a thermally broken aluminium frame with double or triple glazing. The defining characteristic is the slim sightline — aluminium sections are typically 50-60mm on each side, providing 20-30% more visible glass than a composite equivalent.
Advantages
- Sightlines: Slimmer profiles mean more glass and less frame — the primary reason homeowners choose aluminium
- Durability: Powder-coated aluminium lasts 25-45 years with no repainting. The finish does not blister, fade, or peel
- Colour: Virtually any RAL colour is available, including dual-colour (different inside and outside)
- Width: Aluminium can span wider openings per leaf — up to 1.8m in some systems — because the metal is stronger per kilogram than composite
- Lifespan: 45+ years, compared to 20-30 years for uPVC-frame composites
Disadvantages
- Cost: £500-£1,500 more than an equivalent composite pair
- Thermal performance: Older or budget aluminium systems have wider thermal breaks, which can lead to cold bridging. Premium systems (Smart Systems Alitherm, Reynaers) achieve U-values of 1.0-1.2 W/m²K, matching or exceeding composites
- Condensation risk: Aluminium frames conduct heat more readily than composite. On very cold days, interior condensation can form on the frame itself — particularly on non-thermally-broken systems
- Manufacturing lead time: Aluminium doors are made to order, with typical lead times of 6-10 weeks
Key brands and systems
- Smart Systems (Alitherm): The UK market leader in aluminium residential glazing. The Alitherm 600 and Visofold 1000 systems are the most commonly specified residential French door choices
- Reynaers: Belgian manufacturer with a strong UK presence. Premium aesthetic, higher price
- Origin: UK-owned, focused on the residential market. Known for fast lead times and a lifetime guarantee on the frame
Aluminium French door pricing
| Specification | Approx. price (fitted) |
|---|---|
| Standard silver/dark grey, double glazed | £2,000-£2,600 |
| Powder-coated RAL colour, double glazed | £2,300-£3,000 |
| Dual colour (in/out), double glazed | £2,600-£3,400 |
| Triple glazed, any colour | £3,000-£4,000 |
uPVC French doors: the budget option
uPVC French doors use hollow-frame uPVC profiles with steel reinforcement. They are cheaper than both composite and aluminium but sit at the bottom of the market in terms of durability and aesthetic.
| Specification | Approx. price (fitted) |
|---|---|
| Basic white uPVC French doors | £1,000-£1,500 |
| Foil colour, uPVC | £1,200-£1,700 |
A uPVC French door will meet Part L and Part Q at the basic level, but the frames discolour after 10-15 years, the hardware loosens, and the door sags on its hinges. If your budget is tight and you plan to sell within 10 years, uPVC will do. For a longer horizon, composite or aluminium pays back.
Timber French doors: the heritage choice
Timber French doors are specified for listed buildings, conservation areas, and high-end architectural projects. Engineered timber (accoya, red grandis, or oak) provides longevity and stability that softwood cannot match.
| Specification | Approx. price (fitted) |
|---|---|
| Softwood, factory-finished | £2,000-£3,000 |
| Engineered hardwood (accoya/oak) | £2,800-£4,500 |
Timber doors need repainting every 5-8 years, which adds £300-£600 per cycle. Over 25 years, the total cost of ownership can exceed aluminium. See our uPVC vs timber cost guide for the full TCO comparison.
Security on French door pairs
French doors are perceived as a weak point, and historically they were — the inactive leaf was often held only by flush bolts that could be forced. Modern PAS 24 French doors must have:
- Multi-point locking on both leaves: Locks with hook bolts or mushroom followers that engage in keeps set into the frame
- Anti-jemmy strips: Metal strips on the hinge side that prevent a crowbar being inserted
- Cylinder security: 3-star TS 007 cylinder or TS 008 handle set (see our back door security rating guide for the full standard breakdown)
If you are retrofitting an existing French door pair that does not meet PAS 24, the most effective upgrade is a pair of Patlock security brackets (£40-£60) that brace the inactive leaf to the frame, plus a 3-star cylinder replacement (£40-£80).
Thermal performance comparison
| Material | Typical whole-door U-value | WER rating | Part L 2022 compliant? |
|---|---|---|---|
| uPVC | 1.4-1.6 W/m²K | B-C | Borderline |
| Composite | 1.2-1.4 W/m²K | A-B | Yes |
| Aluminium (premium) | 1.0-1.2 W/m²K | A-A+ | Yes |
| Timber | 1.0-1.4 W/m²K | A-B | Yes |
For Part L replacements (existing homes), the target is 1.6 W/m²K. All four materials can achieve this, but uPVC is the tightest margin. For new builds, the target is 1.4 W/m²K, which eliminates budget uPVC French doors unless they use warm-edge spacers and high-performance glass. See our Part L 2022 window U-values guide for the full regulatory breakdown.
Which French door for which property?
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Standard 1930s semi with a rear extension: Composite French doors offer the best balance of cost, security, and thermal performance. A Solidor pair in grey foil with A-rated glass will cost approximately £2,000 fitted and will last 25 years with minimal maintenance.
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Modern new build or architect-designed extension: Aluminium is the natural choice. Slim sightlines, powder-coated finish, and 45-year lifespan suit contemporary architecture. Budget £2,500-£3,000 for a quality pair.
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Listed building or conservation area: Timber is likely required by the conservation officer. Engineered accoya French doors with slim-profile double glazing balance heritage compliance with modern thermal performance. Budget £3,000-£4,500.
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Budget rental property: uPVC at £1,200-£1,500 fitted achieves Part L compliance but expect to replace within 15 years.
Summary
- Composite French doors: £1,500-£2,500 fitted — best value for 20-25 year horizon
- Aluminium French doors: £2,000-£4,000 fitted — best sightlines and lifespan
- uPVC French doors: £1,000-£1,500 fitted — budget option, shortest lifespan
- Timber French doors: £2,000-£4,500 fitted — heritage compliance, highest maintenance
- Security on any French door pair requires multi-point locks on both leaves and a 3-star cylinder
- Part L 2022 compliance is achievable on all materials, but budget uPVC may need warm-edge spacers and premium glass
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