Sliding or bi-folding doors?
Choose sliding if the view matters more than the opening; choose bi-folding if you want the wall genuinely gone. A slim-sliding door leaves one 20 mm interlock standing when open and gives roughly 50 per cent clear opening on two panels. A bi-fold stacks every leaf to one side and gives about 90 per cent, but you look through a 52 mm frame every day of the year.
Which applies to you
- You are glazing a rear extension you will look at daily
Sliding. The doors are shut for most of the year, so the sightline you live with is the one that counts. Slim-sliding runs a 20 mm interlock and leaves to 3000 x 3200 mm, so a two-panel set covers a 6 m opening with one vertical line in the middle.
- You entertain and want the room to open into the garden
Bi-folding. A five-leaf set on a 6 m opening stacks into roughly 600 mm and leaves the threshold clear. You accept a 52 mm sightline and a stack that occupies part of the reveal.
- The opening is over 6 m
Sliding, on three or more panels. Bi-fold leaves are capped at 1200 x 2700 mm, so a wide opening needs more leaves, more stack and more hinges to keep aligned.
- You need the doors open in winter as well as summer
Bi-folding, and check the threshold. A low threshold at 15 mm is the compromise that keeps a bi-fold usable and still drains; a fully rebated one is weathertight but you step over 60 mm.
The figures behind it
- Sightline
- Slim-sliding 20 mm interlock · Bi-folding 52 mm
- Maximum leaf
- Sliding 3000 x 3200 mm · Bi-folding 1200 x 2700 mm
- Clear opening
- Sliding about 50% on two panels · Bi-folding about 90%
- Uw
- Sliding from 1.1 · Bi-folding from 1.3 W/m2K
- Both tested to
- PAS 24 · BS 6375 · Secured by Design
Products this points at
Projects that used these products
Rear of a Victorian terrace at dusk, the three-pane slim-sliding door open to the garden, warm interior light, camera low on the paving so the 20 mm interlock reads in silhouette.
4:3
Wandsworth side return
The rear elevation at dusk from the far end of the lawn, the five-leaf bi-fold fully open and the kitchen lit, the roof lantern glowing above the flat roof, the black steel screen visible through the opening.
4:3