The short answer
A sectional door is made of horizontal panels hinged together, which run on rollers in tracks up the opening and back under the ceiling. Torsion springs balance the weight so it opens easily by hand or motor. Insulated panels and seals on all four sides make it the best-insulated common industrial door.
On this page
How a sectional door is built
Look at a closed sectional door and you see four to eight horizontal panels stacked up the opening. Each panel is a sandwich: two steel skins with polyurethane foam between, typically 40 mm or 60 mm thick. Hinges join the panels so the door can bend as it travels. Rollers at each hinge run in steel tracks either side of the opening.
When the door opens, the rollers carry the panels up the vertical part of the track, round a curve, and back along a horizontal track under the roof. Fully open, the door lies flat overhead, parallel to the ceiling and clear of the opening.
The weight is balanced by torsion springs on a shaft above the opening. Cables run from drums on the shaft to the bottom of the door. As the door closes, the springs wind up; as it opens, they unwind and do most of the lifting. A well balanced door can be held halfway up by hand.
Where it beats a roller shutter
| Sectional door | Roller shutter | |
|---|---|---|
| Insulation | Thick foam panels, seals on all sides | Fair with insulated laths; many joints |
| Daylight | Vision panels or glazed sections | None |
| Space needed | Headroom plus a clear run under the roof | A box over the opening |
| Security | Good | High, with tested ratings available |
| Busy docks | Strong, with long-life springs | Motor and springs wear faster |
That is why the sectional door is the standard loading dock door on heated warehouses. On new non-domestic buildings in England, Approved Document L sets a limiting U-value of 1.3 W/m²K for vehicle access doors, and insulated sectional doors are commonly declared at or below that for typical sizes.
Track types and headroom
Headroom, the clear height between the top of the opening and the lowest obstruction above it, decides which track can be used.
Standard lift
The most common. It needs roughly 400 to 500 mm of headroom and a clear run back under the roof about as long as the door is high.
Low headroom
A modified track that works with less space above the opening, at some cost in smoothness and price.
High lift and vertical lift
The track carries the door further up the wall before it turns, or straight up with no turn at all. This keeps the open door above cranes, racking or lights, but needs a tall building.
Before choosing, the surveyor checks headroom, side room either side of the opening, and anything in the track path: lights, sprinkler pipes, heaters, crane rails.
Springs and safety
Springs are rated in cycles, commonly 25,000 for a standard spring. A dock door opening 50 times a day reaches that in under eighteen months, so busy docks should specify longer-life springs. A broken spring is the most common sectional door fault, which is why industrial doors carry spring-break and cable-break devices that stop the door falling if either fails.
Powered sectional doors also need a safety edge or light curtain, and are force-tested when commissioned under BS EN 12453. Every door should come with a declaration of performance under BS EN 13241.
What one costs
Most industrial sectional doors cost £2,000 to £8,000 fitted, before VAT. A typical insulated 3 x 3.5 m dock door is about £2,400 to £4,100; a 4 x 5 m drive-in door about £3,400 to £6,000. The sectional overhead doors page has a full price table, and the industrial door cost calculator works out your own sizes.
To get sectional doors surveyed and priced, send us the openings and we will find a specialist near you.