A bi-fold door folds its leaves back in a concertina to open most of the width. The hardware is a folding carriage system plus the hinges between leaves.
Top-hung or bottom-rolling
- Top-hung: leaves hang from carriages on the head track; the bottom has a light guide. Best for weather sealing and a clean threshold, but the head lintel carries everything.
- Bottom-rolling: leaves run on a floor track. Easier to support, but the track is a trip and dirt line at the threshold.
Top-hung is the usual choice for external bi-folds today.
Leaf configuration
Describe a bi-fold as, e.g., “5 leaves, 4+1” — four leaves fold one way, one leaf is a traffic door hinged like a normal door for everyday use. Even leaf counts fold cleanly to one or both sides; odd counts usually need a traffic leaf. The stack (folded thickness) is leaf thickness × number of leaves plus clearances — check it clears the reveal.
The parts
- Folding carriages (top) or rollers (bottom), sized to leaf weight.
- Leaf-to-leaf hinges rated for the weight, usually three per joint.
- A multi-point lock on the traffic leaf and shootbolts on the folding leaves.
- Bottom guides, a weather cill, and brush/fin seals between leaves.
Weights
Each leaf is typically 25–45 kg with double glazing. Size the carriages above that and keep individual leaves within the system’s maximum width, or they sag and the door stops folding square.
Send the opening size, the leaf count and fold direction, and the glass, and we will spec the system.
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