Four metres of glass, in the actual opening
Bifolds are sold on a feeling. Stand in the kitchen, hold up the phone, and the back wall disappears.
Choose a size
Drag to turn it round
Opens your camera. Point it at the back wall.
Once it appears: one finger drags it, two fingers turn it. It does not need a clear floor. Drop it where it fits and judge the size against what is already there.
What has to happen to the wall?
The doors are the cheap part. The lintel, the goalpost frame and the building control sign off are not.
Let them scan it and hold their own phone up
The camera view only works on a phone. Point the code at their camera, and this page opens on their handset. That is the moment the idea sells itself.
Lintel and beam sizes must be designed by a structural engineer for the actual loading; the guidance here is indicative only. Structural openings, thermal performance and threshold details are covered by the Building Regulations and require building control approval or a competent person scheme notification. Sightlines, stack depths and clear openings vary between systems.