How to Choose Bi-Folding Doors

Every extra panel adds a hinge, a seal and a potential draught point. As a rule: keep panel widths between 900mm and 1200mm. A 4-metre opening works well as 4 × 1m or 5 × 800mm, not 6 × 660mm. Decide stacking direction based on where you'll use the space — stack away from your seating area, not into it, and away from the primary view line.

A traffic door is a single leaf that opens like a normal door without folding the whole run back. If you use the doors as a daily entry point (rather than only opening the run fully on summer weekends), specify a traffic door on one end. Without it, day-to-day use becomes annoying and the folding hardware wears faster.

Standard thresholds sit 60mm above floor and deliver the best weather rating. Low-threshold options drop this to around 25mm — a good compromise on most UK installations. Level thresholds are possible with a drainage channel and gravel strip outside but require careful detailing to avoid water ingress; they're best on sheltered rear elevations.

uPVC bi-folds exist but the material isn't rigid enough for panels above about 900mm without visible sag. Aluminium bi-folds hold their alignment for the life of the door. Look for a thermally broken profile — the polyamide break in the frame is what stops the outer aluminium chilling the inner surface.

A good bi-fold demands a level, square, correctly sized structural opening. Insist on a full technical survey and, if you're mid-build, ask your installer to sign off the opening before it's finished. The number-one cause of dropping bi-folds is an out-of-level head — the door can't be shimmed to fix it once installed.