The short answer
- Choose a bi-fold if opening the whole wall in summer matters more than the view with the doors closed, the opening is under about 6–7 m, and there is room for the folded stack.
- Choose a slider if the closed view matters most, the panels are tall, the opening is very wide, or there’s no room for a stack.
- Choose lift & slide among sliders when panels get heavy (big or triple-glazed), the site is exposed, or you want a flush threshold that seals properly.
Side by side
| Bi-fold | Slim sliding | Lift & slide | |
|---|---|---|---|
| Width that opens | Up to c. 90% | 50–67% | 50–67%, near 100% with a pocket |
| Frame when closed | One every metre or so | Very slim interlocks | One slim interlock per meeting |
| Largest panel | Small, c. 1.2 m wide | Large | Very large, up to c. 400 kg |
| Sealing | Good, many joints | Good, mostly brushes | Excellent, compressed gaskets |
| Everyday use | Traffic door, or unfold the set | Push to slide | Turn the handle, then glide |
1. The closed view
For most of a London year the doors are shut. A bi-fold then reads as a row of narrow panes with a frame every metre or so. A slider reads as two to four big panes with slim interlocks. Before choosing, ask for both elevations drawn closed, at the real size. Many clients change their mind at this point, and some confirm the bi-fold with open eyes.
2. How much opens
This is where bi-folds win. Folded to one side, they clear up to about 90% of the opening. A two- or four-panel slider opens half the width; a three-track layout opens two-thirds. Only a slider that parks in a wall pocket matches a bi-fold, and the pocket has to be designed into the structure early.
3. Weather and sealing
Every leaf of a bi-fold adds a vertical joint to seal. Good systems manage this well, but on exposed sites, high floors and noisy roads, lift & slide is the safer choice: the panel drops onto compressed gaskets when closed. Slim inline sliders sit in between, sealed mostly with brushes.
4. Everyday use and space
- Traffic door. With an odd number of leaves on one side, the end leaf works as a normal door. Without one, you fold the set every time you step out.
- The stack. Folded leaves project about one leaf width, often 700–1,000 mm, into the room or the garden. Steps, a narrow terrace or a kitchen island near the door can rule a bi-fold out.
- Children and pets. Folding leaves have pinch points at the hinges; sliders don’t, and lift & slide panels stay put at any position.
5. Cost
For the same opening, a bi-fold usually has more leaves, more hinges and more locking points, while a slider has fewer but bigger panes and heavier hardware. Which comes out cheaper depends on the opening and the system. Lift & slide usually costs more, because of the hardware. Send us the opening size for a budget figure.
Try both on your opening
The bi-fold planner and the slider sizing tool show leaf sizes, weights, the clear opening and the stack for your own dimensions.
Questions
Are bi-fold doors or sliding doors better for a London extension?
It depends on how you use the opening. Bi-folds open up to about 90% of the width, which is best for summer. Sliders keep big panes and slim frames, which is how you see the doors for most of the year, and they seal better on exposed sites.
Do bi-fold doors let in draughts?
Good bi-folds seal well, but every leaf adds joints to seal. Lift & slide doors drop onto compressed gaskets when closed and usually perform best on exposed or noisy sites.
How much space does a folded bi-fold stack need?
The folded stack projects about one leaf width, often 700 to 1,000 mm, into the room or the garden, depending on which way the doors open. Keep that area clear of steps, furniture and planting.
Which is easier to use every day?
A slider: you open one panel and walk through. Bi-folds need a traffic door, an odd number of leaves on one side, so you don’t have to fold the whole set every time you go out.