Telescoping vertical lift

A telescoping vertical lift door is built from several rigid leaves that all travel in one vertical plane. As the door opens, each lower leaf slides up and tucks in behind the leaf above it. The finished stack is a fraction of the door's closed height, and nothing swings back into the building on flat track.

The design shows up on very tall openings in plants and warehouses, such as aircraft hangars, shipyards and mining shops. In those buildings an overhead crane often has to reach right up to the wall, so no track can hang in the way. Door Engineering builds vertical lift doors past 100 feet wide. It offers single and multi-panel versions, and lifts them with a counterweight rather than a spring.

How it differs from vertical lift and high lift

The difference is headroom math. On a standard vertical lift door, the sections keep climbing in one line, so the wall above the header has to be about as tall as the door itself. Amarr lists vertical lift headroom as the door height plus 13 inches, and points the option at buildings that have double the door height in headroom.

High lift sits in between. DASMA defines high lift track as track that makes the door rise some distance above the top of the opening before it levels out into a horizontal position. Amarr lists 12-1/2 inches of headroom for high lift on 2 inch track. Telescoping breaks the link between door height and headroom. The leaves nest, so the clear space above the header is set by the tallest leaf and its hardware. The full door height stops driving the number.

What it changes about springs and drums

It usually replaces them. A sectional vertical lift door is balanced by torsion springs on an A-frame. DASMA defines that frame as the member that fastens the spring assembly to the wall above the opening. The door also needs a vertical lift drum, a cable drum with changing radius grooves. No flat run of track takes weight off the cable near the top, so the drum has to do it.

A telescoping door does not behave that way. Its leaves separate and rejoin as they move. The load on the lifting cable steps up and down through the cycle instead of tapering off. Makers often balance these doors with counterweights, or drive them with a wire rope hoist.

One caveat matters here. DASMA's terminology sheet defines vertical lift, high lift and the hardware around both. It does not list telescoping vertical lift at all. The term belongs to the makers, so stack height and clear opening vary by builder. Ask for both in writing before the header gets framed.