Opening up for bifold doors: the structural side explained
Bifolds are the glamour bit. The structural opening behind them is what makes them possible — here is what that actually involves.
The opening comes first
Before any doors are ordered, the structural opening has to be formed and the load above carried. For a wide rear opening that usually means a steel beam, and often a goalpost frame where the wall is removed down to the floor. The engineer designs it; building control signs it off.
Getting the sizes right
Bifold suppliers work to a precise structural opening size. Build the opening wrong and the doors will not fit, or you lose weeks waiting for a re-measure. We leave the opening sized exactly to your door supplier's dimensions, level and square, with the lintel or frame set at the right height for the head detail.
- Confirm the door supplier's structural opening size before steel is cut
- Beam or goalpost sized by the engineer for the span and load
- Cavity tray and weep vents above an external opening
- A level, square opening to the millimetre for the frame
Weather and the threshold
An external opening is not just structure — it has to keep water out. A cavity tray over the beam and weep vents stop damp tracking in, and the threshold detail needs thinking through early so the finished floor meets the door track cleanly.
Related questions
Do I need planning permission for bifold doors?
The doors themselves usually do not, but the works they are part of — such as an extension or a big change to the rear elevation — might. Building Regulations approval is needed for the structural opening regardless.
Should I order the doors before the opening is made?
Order them once the structural opening size is agreed, then we build the opening to that exact size. Working the other way round risks a mismatch and delays.
Ready to take it further? See our knock-throughs & new openings service.