Bifold doors — sets of two or more panels that fold and stack to one or both sides of an opening — are one of the most requested features in rear extension and kitchen renovation projects. They create a wide, unobstructed opening between the interior and garden, and their sleek frames photograph well. But they come at a price, they have practical limitations, and they are not always the best choice for every opening.
What Do Bifold Doors Cost?
Costs split into supply-only and supply-and-fit. Most homeowners have them installed as part of a wider project, so the labour is bundled into the build cost. If you are replacing like-for-like on an existing opening, expect to pay a joiner or specialist fitter £300–£600 per day for installation, with a standard 3-panel set taking one to two days.
| Configuration | Width | Supply-Only Cost |
|---|---|---|
| 2-panel, uPVC | 1.2 – 1.8 m | £900 – £1,800 |
| 3-panel, aluminium | 2.1 – 2.7 m | £2,200 – £4,000 |
| 4-panel, aluminium | 2.7 – 3.6 m | £3,000 – £5,500 |
| 5-panel, aluminium | 3.6 – 4.8 m | £4,500 – £7,500 |
| 6-panel, timber | 3.6 – 5.4 m | £5,000 – £9,000+ |
| Full-width spanning 5 m+ | Various | £7,000 – £15,000+ |
Prices are for thermally broken frames with double glazing. Triple glazing adds roughly 15–25% to the supply cost.
Standard Bifold Door Sizes
Bifold doors are manufactured to bespoke dimensions, but the industry has converged on common leaf widths:
- Minimum panel width: around 450 mm (below this, panels become difficult to fold)
- Maximum panel width: typically 900–1,000 mm per leaf for structural reasons
- Standard heights: 2,050 mm, 2,100 mm, and 2,400 mm are most common; bespoke heights are available up to around 3,000 mm
- Maximum overall widths without intermediate support: around 6 m, though structural requirements (the lintel above) become significant beyond 4 m
For most UK rear extensions, openings of 2.4 m to 4.2 m with 3 to 5 panels are the most practical and cost-effective configurations.
Material Comparison
| Material | Pros | Cons | Typical Frame Depth |
|---|---|---|---|
| Aluminium (thermally broken) | Slim sightlines, durable, low maintenance, wide colour choice | Higher cost than uPVC | 70–100 mm |
| uPVC | Cheapest option, good thermal performance | Bulkier frames, limited colours, can warp over time | 90–120 mm |
| Timber | Warm aesthetic, FSC-certified options available, paintable | Higher maintenance, susceptible to moisture | 80–120 mm |
| Timber-aluminium (hybrid) | Timber interior, aluminium exterior — best of both | Most expensive option | 90–120 mm |
Aluminium is the dominant choice in new-build and high-end renovation in the UK because the thermally broken frames are slim, very durable, and available in any RAL colour to match the house.
Building Regulations and Glazing Standards
Any new or replacement external door (including bifolds) in England and Wales must meet the requirements of Approved Document L (Conservation of Fuel and Power). Key thermal requirements for 2026:
- Centre-pane U-value: ≤1.0 W/m²K for replacement glazing (new builds have tighter requirements)
- Whole-unit U-value (window energy rating): bifold doors should achieve at least a WER Band C, with B or A being preferable
- Safety glazing: all panes within 1,500 mm of the finished floor level and within 300 mm of the door edge must be toughened or laminated to BS EN 12600 Class 1C or 2C
- Air permeability and water tightness: better-quality systems are rated to Class 4 air permeability and Class E1200 water tightness under BS EN 12208 — ask suppliers for their test ratings
For a new opening (as opposed to a replacement), you will also need structural approval for the lintel. An engineer should specify the lintel for spans over 1.8 m in loadbearing walls.
Alternatives to Bifold Doors
Bifolds are not the only way to open up a rear elevation. The main alternatives are:
Sliding patio doors (including lift-and-slide): panels slide on tracks rather than folding. They take up less floor space when open, leave a wider clear opening proportionally, and are generally more thermally efficient at the same price point. The trade-off is that at least one panel is always behind another, so the opening is never fully clear.
French doors: a classic two-panel outward-opening configuration. Excellent thermal performance, simple mechanism, lower cost (typically £1,200–£3,500 supply-and-fit for aluminium or timber), but the maximum clear opening is limited to roughly 1.5 m.
Pivot doors: a single large panel on a central pivot, creating a dramatic full-width opening. Expensive (£5,000–£20,000+) and better suited to large openings in contemporary properties.
Frameless glass walls: structural glass systems with minimal framing, moving into architectural glazing territory. Costs start around £2,000/m² and rise steeply. Requires specialist structural design.
Which Option Is Right for You?
- Choose bifolds if you want most of the opening to disappear and have enough patio space for the folded stack (the stack occupies roughly 150–300 mm per panel).
- Choose sliding doors if thermal performance and a wider unobstructed view are the priority, or if the opening exceeds 5 m.
- Choose French doors if the opening is 1.2–1.8 m and budget is tight.
What to Ask a Supplier
- What is the whole-unit U-value (not just centre-pane)?
- What are the air and water tightness class ratings?
- Is the frame thermally broken, and what is the thermal break material?
- What is the maximum span before an intermediate post or support is needed?
- What guarantees do you offer on the hardware and seals?
A quality bifold set should come with at least a 10-year frame guarantee and a 5-year hardware guarantee.
Summary
Bifold doors are a genuinely useful product for rear openings of 2.4 m to 5 m, but the cost and the space they demand when open are real limitations. For most standard openings, aluminium thermally broken bifolds at the mid-price range — £3,000–£6,000 supply-and-fit for a 3 or 4-panel set — represent good value. Always check U-values and test ratings, not just the price per panel.
