Start with the clear opening, not the product
The number that matters is how much unobstructed space you get when the doors are open. A pair of French doors gives you the entire structural opening minus the frame — nothing sits in the way. A bifold gives you the opening minus the frame minus the stacked panels, which bunch against one or both jambs.
That means at 1,500mm, French doors are actually the more generous option, because a bifold at that width would be two narrow panels stacking into a jamb. The crossover point where bifolds start to pull ahead is wide openings, typically an extension rear wall of 2,400mm or more, where a hinged pair would either need leaves too heavy to use or side panels that permanently block part of the view.
How they behave the other 360 days a year
Nobody throws the whole opening wide every day. Most of the time you want one leaf open to get out to the bin, the washing line or the barbecue. French doors do that with one handle and one movement.
Bifolds need a traffic door — a single leaf configured to open independently — or you're folding the whole stack to step outside. If a bifold is specified without a traffic door, that is a design fault, not a preference, and it's the single most common complaint we hear about them.
| French doors | Bifold doors | |
|---|---|---|
| Best opening width | 1,200–1,800mm | 2,400mm and above |
| Everyday access | Open one leaf, one handle | Needs a dedicated traffic door |
| Clear opening when fully open | Full opening less frame | Opening less frame less stacked panels |
| Moving parts | Hinges and a lock | Hinges, rollers, a track and a lock |
| Threshold | Standard, low or flush | Runs on a bottom track |
| Starting price fitted | £1,499 | Quoted per opening |
Maintenance and the track problem
A French door has hinges and a lock. Keep the hinges lubricated, keep the keeps clean, and the failure modes are few and cheap to put right.
A bifold runs on a bottom track and that track is at ground level, outside, next to a garden. Grit, leaves, sand from a patio and pet hair all end up in it. A neglected bifold track is the most common reason a five-year-old set starts dragging and eventually drops out of alignment. It is entirely manageable — brush it out, hose it, keep the drainage slots clear — but it is a job that French doors simply don't have.
Security compared honestly
Both can be secure and both can be specified badly. On French doors the weak point is the slave leaf; on bifolds it is the number of panels, because every extra panel is another hinge line and another potential lever point.
On either product, the things to insist on are the same: PAS 24 tested hardware, a TS007 three-star cylinder where there's a cylinder, shootbolts into steel keeps rather than plastic, and hinge bolts. A four-panel bifold with good hardware beats a French door with bad hardware, and vice versa. The material of the frame is nearly irrelevant to this.
Heat loss and glass area
Bifolds have more frame per square metre than a French door pair, because every panel needs its own stiles. Frame is generally a worse insulator than a modern sealed unit, so a like-for-like bifold does not automatically outperform a French door pair on heat loss despite looking more glassy.
Where either product genuinely gains is the glass. A-rated units with a warm-edge spacer and argon fill are standard on our doors, and that is where the meaningful difference against a twenty-year-old set sits — not in the opening style.
When we'd talk you out of a bifold
If your opening is under 2,000mm and you're replacing a tired old pair, a bifold is very likely to cost you more, give you a smaller clear opening, and add a track to sweep out. We'd rather say that at survey than take the bigger order.
If your opening is a genuine wide rear wall on an extension, if you entertain outdoors and actually want the wall to disappear, and if you're happy to maintain a track, a bifold earns its keep. That is a real use case and we'll fit one.
And when a patio door beats both
There's a third option people skip. A sliding patio door has no leaf swinging into the room or the garden, no track at floor level to trip on in the same way as a bifold, and very slim sightlines. You never get more than half the opening clear, but if you have furniture tight to the doors inside, or a narrow patio outside, that constraint may not matter at all.
For a 1,800–2,400mm opening where swing space is the problem, a patio door is often the answer neither of the other two gives.
Cost over the life of the doors, not the invoice
Compare these two products over fifteen years rather than at the point of sale and the picture shifts again. A French pair has two hinge sets, one multi-point lock and a pair of shootbolts. Every one of those parts is a stock item that any competent fitter can source and swap in an hour.
A bifold has a hinge set per panel junction, a roller carriage per panel, a running track, a bottom guide and a lock. That's more parts, and system-specific parts at that. If the manufacturer changes or discontinues the system, a like-for-like roller in year twelve is a phone-around rather than a stock item. It's not a reason to avoid bifolds — it is a reason to buy one from a mainstream system rather than an unbranded import, and to ask the question before you order.
The other long-run cost is the seals. A bifold has a great deal more sealing perimeter than a hinged pair, because every panel junction is a joint that has to keep weather out. Gaskets are consumable on both products, but there is simply more of it to renew on a folding set.
Planning, building regs and structural work
Replacing like for like is controlled work under the Building Regulations but does not need planning permission in most cases. Both products are treated the same way here — the certificate comes from the installer's competent-person registration either way.
Where the two diverge is when you widen the opening, which is far more common with bifolds because the whole point is a wide aperture. Widening means a new lintel, which means structural calculations and building-control involvement beyond the glazing certificate. That is real work with real cost, and it belongs on the quote from the start rather than appearing as a variation once the wall is open.
If your existing opening already suits a French pair, staying inside it avoids all of that. It's the single biggest hidden cost difference between the two options and it rarely appears in a showroom comparison.
Not sure which suits your opening?
Tell us the width brick-to-brick and how you use the space, and we'll say which of the three makes sense — including when the answer is the cheaper one.