Single, double and two singles
A double opening can take one wide door or two single doors, and the choice is not purely aesthetic. One double door is a single mechanism to maintain and a cleaner opening to drive through. Two singles mean one door can stay working while the other is repaired, and each door is lighter, which is gentler on springs and motors.
Where there is a central pillar you have no choice. Where there is not, the width of the opening and the weight of the finished door usually decide it — beyond about 5 metres, a single door starts asking a lot of its springs and its top section.
Sectional, roller or tip-up
Sectional doors are the default for a reason: they lift straight up and run back along the ceiling, so nothing swings out into the driveway and you can park right up against the door. They need headroom above the opening — typically around 300mm for a standard track system, less with a low-headroom kit.
Roller doors coil into a barrel above the opening and need almost no backroom, which makes them the answer for garages with beams, storage racks or a low ceiling running back. Tip-up doors are the single-panel type that swings out and up; they are cheap and simple, but they claim the space in front of the door and they are the type most often replaced during a renovation.
Where headroom is genuinely tight, the honest answer is sometimes a roller door rather than a low-headroom sectional kit, and we will say so at the measuring stage rather than after the door arrives.
Measuring: headroom, side room and backroom
Three clearances decide whether a door can be fitted at all. Headroom is the distance from the top of the opening to the ceiling or the nearest obstruction. Side room is the space either side of the opening for the vertical tracks — usually around 90mm each side. Backroom is how far the horizontal tracks can run into the garage, which must exceed the door height plus the motor rail.
Obstructions are the usual surprise: a lintel, a lighting rail, a roller-shutter box from a previous door, a geyser, or a beam that crosses exactly where the tracks want to go. All of them have solutions; none of them has a solution that can be chosen from a photograph.