Tall Buildings and Modern Elevator Innovations

Past a certain height, a building cannot be served by one set of elevators. The cars would stop too often, the shafts would swallow too much floor area, and the ropes would get too heavy to carry their own weight. This page walks through the design choices, drawing on public academic and standards-body sources: zoning and sky lobbies, double-deck cars, destination dispatch, speed and rope engineering, energy recovery, ropeless concepts, and the space elevator as a curiosity. The basics of how an ordinary elevator works are in How elevators and lifts work.

What counts as tall

The Council on Vertical Urbanism (the organization formerly named the Council on Tall Buildings and Urban Habitat) says there is no absolute definition. A building of 14 or more stories, or more than 50 meters (165 feet), could typically be used as a threshold. Its tall building criteria define a "supertall" as 300 meters (984 feet) or taller and a "megatall" as 600 meters (1,968 feet) or taller, and they even list "specific vertical transport technologies" among the characteristics that can make a building count as tall. When that page was captured it counted 173 supertalls and only 3 megatalls completed globally.

Zoning and sky lobbies

The first trick is to stop making every elevator serve every floor. A review of tall-building elevator technology published in the journal Buildings, describes the arrangement used in the Burj Khalifa: elevators are arranged in zones, with a sky lobby, an intermediate floor where passengers change from an express elevator to a local elevator that stops at every floor within a segment of the building. That tower's sky lobbies are on levels 43, 76 and 123. The review also describes One World Trade Center in New York, where tenants above the 64th story take an express shuttle to a sky lobby on that floor and transfer to local lifts, and Shanghai Tower, whose express and local elevators serve nine zones.

Fewer floors per car means fewer stops per trip, and the review notes that in high-rises elevators occupy more space than any other service. Transfers cost passengers a little convenience and save a great deal of core space.

Double-deck cars

A double-deck elevator stacks two cabs one above the other in a single car frame, so one hoistway (the vertical shaft) moves twice the passengers. In the usual arrangement, as the review describes it, one cab serves even-numbered floors and the other odd-numbered floors. The review quotes an industry technology head who gives an example: a 52-story office building that once needed 24 single-deck cars in three zones could be designed with two zones and 13 double-deck elevators, cutting 11 hoistways from the core. That is an industry-side figure, an illustration rather than a rule.

There are costs. Double-deck cars must load and unload two decks at once for local service, and passengers need stairs or escalators in the main lobby to reach the second level. The review says the type became less popular for those reasons, and that pairing it with destination dispatch softens the problems. It also says double-deck elevators and sky lobbies tend to be useful above roughly 60 floors. In the Burj Khalifa, two of the 57 elevators are double-deck cars used for the observation deck.

Destination dispatch

In a conventional system a passenger presses up or down, and whichever car arrives takes everyone. Destination dispatch asks for the floor first. The review explains that it was introduced in the 1990s, after microprocessors became more capable, and that it groups passengers headed to the same destinations into the same elevators, reducing the stops each trip makes. The review adds a reason this matters at speed: in a fast elevator, a single stop can take 10 to 13 seconds.

Accessibility rules had to adapt. The US Access Board describes destination-oriented elevators as systems in which passengers indicate the floor destination when calling an elevator, usually through a keypad, and lobby indicators then designate which car to use. It notes that the requirements for elevators in the ADA Standards apply to these systems, with some provisions and exceptions unique to them, such as audible and visible signals that identify the assigned car.

Speed, ropes and shafts

Height creates a mechanical problem. Steel rope gets heavier as it gets longer. The Buildings review reports an estimate that in very tall buildings almost 70 percent of the elevator's weight is attributable to the rope itself, and an industry source it quotes puts the rope for a 2,000 kilogram elevator with a 500 meter travel at about 27,000 kilograms. Long ropes also sway in strong winds, and the review mentions that in the former World Trade Center towers cable movement wore holes in shaft walls over the decades.

The industry's answer is lighter rope. The review describes one carbon-fiber-cored rope as extremely light, claimed to allow travel up to 1,000 meters, double the then-current 500 meter limit, and quotes a technologist calling it "the biggest change in elevators since 1853." Those are industry claims in a 2015 paper, and projects it describes as under construction have since changed. Speed is also a design lever: the review lists 10.16 meters per second for One World Trade Center's observation express cars (about 40 seconds for the 394 meter trip) and notes that people become restless after waits of around 28 seconds. A tall hoistway is still a hoistway, and the safety principles in Elevator, lift and escalator safety apply to it in the same way as to any other.

Regenerative drives

A traction elevator uses a counterweight sized for a car loaded to about 40 to 50 percent of capacity, so a light car going up or a heavy car going down is partly driven by gravity and must be braked. A conventional drive turns that braking energy into heat. A regenerative drive lets the motor act as a generator and sends the electricity back for use. The review says such a drive can generally reduce energy consumption between 20 and 40 percent, with the result depending on trip length, usage pattern and equipment age.

Ropeless and multi-car concepts

If rope is the limit, remove the rope. The review describes concepts that use magnetic propulsion instead: a system meant to move multiple cabins vertically and horizontally in a loop, with a stated aim of raising capacity by up to 50 percent; a circulating multi-car design verified only on a one-tenth-scale model that, in the review's words, needs further development to meet international safety standards; and a "vertical subway" idea that raises unresolved safety concerns about braking at high speeds. These are the paper's account of proposals as of 2015, not proof of installed systems.

How codes and inspection work is covered in Inspection, maintenance and regulation explained.

The space elevator, as a curiosity

The longest rope idea of all has no building at its base. NASA's technical reports server hosts a paper describing a space elevator as a tether structure extending through geosynchronous earth orbit to the surface of the earth, with its center of mass in that orbit so that it stays in step with the planet's rotation. The paper reports that in 2004 and 2005 the NASA Marshall Space Flight Center worked with a research institute under a cooperative agreement to study feasibility. It concludes that the most critical technology is ultra-high-strength carbon nanotube-reinforced composites for the ribbon, in the 100 GPa range. The Buildings review mentions a proposal for a station about 36,000 kilometers up. Nothing of the kind exists. The older history of the elevator, which began with far more modest hoists, is in A short history of the elevator.

The short version

Tall buildings stay usable through zoning, sky lobbies, double-deck cars and destination dispatch, while lighter ropes and regenerative drives push against the limits of height and energy use. Ropeless and multi-car designs and the space elevator remain ideas to read about, not products to expect. Rules differ by jurisdiction, and local authorities and qualified professionals have the final word.