Measure the structural opening, not the door that is there
The opening a folding door lives in is the gap between the finished jambs and from the finished floor to the underside of the head. An existing door, its frame and its architraves are not the opening; they sit inside it. If a swinging door is coming out, measure the hole it will leave, not the door itself.
Measure width at the top, the middle and the bottom, and height at both sides and the centre. Write down all six. Buildings are rarely square, and the smallest of each set is the number that matters. A head that runs out by fifteen millimetres across a wide opening is normal, and it is exactly what the site measure is for.
The five numbers a quote needs
For a first quote, width and height are the two that decide most of the price. The rest tell us what kind of system the opening can take.
- Clear width between the finished jambs, smallest of three
- Clear height from finished floor to underside of head, smallest of three
- Ceiling height above the opening, if the head is not the ceiling
- Depth of wall available beside the opening for the door to stack against
- What the head is made of: timber, steel, concrete, plasterboard on a frame, or a suspended ceiling grid
The head decides more than the width
Folding doors and operable walls are top-hung, so the entire load goes into whatever is above the opening. A timber or steel head takes an accordion door without fuss. A plasterboard bulkhead with nothing behind it does not, and a suspended ceiling grid will not carry an operable wall at all without a beam. If you can see what is above the opening, say so; if you cannot, a photograph of the ceiling near the opening helps.
This is the single most common surprise on a job, and finding it at quote stage costs nothing. Finding it on install day costs a second visit.
Where the door will stack
An accordion door folds into a stack roughly ten to fifteen percent of the opening width, and an operable wall stacks deeper because its panels are wider. That stack sits against a return wall, splits to both ends, or hides in a pocket. Measure the clear wall beside the opening on the side you would like the door to stack, and note anything in the way: a light switch, a power point, a skirting heater, a doorway.
Photographs that save a visit
Photographs do not replace the measure but they answer half the questions before anyone asks them. Take them in daylight if you can, from a few metres back.
- The whole opening from each side of the room
- The head, looking up, including any bulkhead or ceiling grid
- Each jamb from top to bottom
- The floor across the opening, to show level and finish
- The wall the door will stack against
When a measure from you is enough, and when it is not
A straight replacement into a known opening, especially an accordion door going where one already was, can often be quoted from your numbers and photographs, and sometimes manufactured from them if the existing track and head are sound. Anything acoustic, anything on a suspended ceiling, anything over a few metres wide, and every operable wall gets a site measure before it is made. That is not caution for its own sake: a made-to-order partition has no tolerance for a guess.