A bi-fold door folds and stacks its panels to one or both sides, opening roughly 90% of the aperture. Typical fitted cost is £3,800–£6,000 for a 3-metre, three-pane set and £5,000–£7,500 for a 4-metre, four-pane set.
Panel count is set by width. Bi-fold panels work best between about 700mm and 1,000mm wide — narrower and they look mean, wider and they get heavy and start to sag over time. A 3m opening is therefore usually three panes; 4m is four; 5m is five or six.
Then decide the stack. All panels to one side is the norm. A split stack (2+1, or 2+2) is useful where there is a wall or a rainwater pipe on one side that the stack would foul. And unless you never want to walk through them without folding the whole set, specify a traffic door — one leaf hinged conventionally as a normal door.
Almost every bi-fold problem traces back to the installation, not the door. If the head is not dead level and rigid, the rollers bind. If the opening deflects because there is no adequate lintel, the doors stop closing. If the threshold has no drainage, water sits and eventually gets in.
This is why a bi-fold quote should include the structural check. Any set over about 4m wants a properly sized steel with a deflection limit of span/500 or better — not the span/360 that would be fine over an ordinary window.
| Job | Typical cost |
|---|---|
| Bi-fold door, 3 panes, approx. 3m supplied & fitted | £3,800 – £6,000 |
| Bi-fold door, 4 panes, approx. 4m supplied & fitted | £5,000 – £7,500 |
Ranges include VAT and installation. Final price depends on size, spec, access and site condition — a survey gives you a fixed number.
As a supplied-and-fitted guide, £3,800–£6,000 for a 3-metre three-pane set and £5,000–£7,500 for a 4-metre four-pane set. Colour, glass spec, threshold type and any structural work move the figure.
Divide the opening by roughly 900mm. Panels work best between 700mm and 1,000mm wide — narrower looks cramped, wider gets heavy and is more likely to drop over time.
Any opening over about 3m almost certainly does, and the deflection limit matters as much as the load. Bi-folds are intolerant of movement in the head — specify span/500 or better, not the span/360 typical of an ordinary window opening.
Yes. Outward-opening keeps the stack outside and saves internal floor space, but the stacked panels then live in the weather and project into the patio. Inward is more common in the UK.
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