"Bi-fold or sliding?" is one of the most common questions on any extension or garden-room job — and the honest answer is that they solve slightly different problems. Get the customer talking about how they'll actually use the opening and the right choice usually becomes obvious. Here's the framework we'd use.
The short answer
Choose bi-folds when the goal is to open up the whole aperture and merge inside and out. Choose a slider when the priority is the biggest possible glass and the clearest view when the doors are shut, with slim sightlines and fewer frames.
Opening area — how much actually opens
This is the headline difference. Bi-folds concertina almost completely out of the way, opening up to around 90% of the aperture — the full "wall of glass disappears" effect that makes them so popular for entertaining. A slider moves one large panel behind another, so the maximum clear opening is roughly half the aperture (a little more on multi-track configurations). If throwing the whole opening wide is the point, bi-folds win.
The view when they're closed
Here it flips. For most of the year the doors are shut — and that's where sliders shine. Because a slider is just two, three or four big panels, you get expansive glass and very slim sightlines with minimal interruption. Bi-folds need a frame down the edge of every panel, so when closed you're looking through more mullions. If the customer prizes an uninterrupted view of the garden, point them to a slider.
| Bi-fold | Sliding | |
|---|---|---|
| Max clear opening | ~90% of aperture | ~50–65% of aperture |
| View when closed | More frames / mullions | Big glass, slim sightlines |
| Panels | 2–7, folds away | 2–4, slides behind |
| Everyday access | Traffic door option | Slide one panel |
| Typical cost | Higher per m² | Competitive; slimline is premium |
Everyday use and access
For nipping in and out with a cup of tea, a slider just needs one panel moved — easy. Bi-folds can be specified with a traffic door (a single leaf that opens independently) so the customer isn't folding the whole set back every time. Worth flagging at quote stage, because it changes how the door lives day to day.
Thresholds and level access
Both can be specified with a low or flush threshold for a near-seamless transition to a patio — which also helps with level-access requirements under Approved Document M. There's always a balance between a low threshold and weather-tightness, so make sure the customer understands the trade-off and specify a weathered low threshold where exposure is a concern.
Cost
Bi-folds generally cost more per square metre because there are more panels, more hinges and more hardware in the system. Standard sliders are often the more affordable way to glaze a large opening — though premium slim-frame sliding systems, with their very narrow interlocks and large heavy panels, sit at the top of the price range too. As always, the spec drives the price more than the door type.
Glazing, spans and weather
Sliding systems come into their own on very large, heavy panels — lift-and-slide gear makes big spans of glass move smoothly. Bi-folds suit a run of moderate panels folding right back. On weather performance, a well-specified slider typically edges it for air and water-tightness, simply because there are fewer opening joints. Both achieve PAS 24 security when specified correctly.
How to steer the conversation
- "I want to open the whole thing up for parties": bi-fold.
- "I mostly want to look at the garden through big glass": slider.
- "Best value for a wide opening": standard slider.
- "Slimmest possible frames, budget flexible": premium slim-frame slider.
- "In and out all day": bi-fold with a traffic door, or a slider.
- Small opening? A French door or a two-panel slider often makes more sense than either.
Whichever suits the job, we supply both bi-fold and sliding systems across the major brands — so you can price the opening both ways from one quote and let the customer decide.
