Engineering the supertall: the boring fixes are the ones that shipped

TL;DR

• The rope-free lift has not arrived. TK Elevator inaugurated MULTI on 22 June 2017 and promised up to 25% more usable area. In September 2026 its own product page names no commercial installation and no launch date.
• The core still eats the building. A study published in Buildings on 22 October 2024 puts the core at 24% of gross floor area in prismatic towers and 26% in tapered and free-form ones, and finds space efficiency declines as height rises.
• What worked was incremental. Shanghai Tower cut wind loads by 24% through reshaping in a wind tunnel, Burj Khalifa's builders pumped concrete to 606 metres, and Berlin's EDGE East Side moved up to 52 people per car with double-deck lifts.

Height is sold as a materials story. It is really a logistics story with a materials footnote. Four constraints set the ceiling on every tower in the Skyscraper Day Dive:

• How you move people up.
• How much floor the shafts and risers consume.
• What the wind does to the top.
• What the frame is made of.

Between 2017 and 2026 the industry promised a revolution in the first constraint and delivered incremental engineering in the other three. The incremental engineering is what got built.

The rope-free lift is a test tower, not a product

The physics problem is real. A steel hoisting rope carries its own weight, so in a very tall shaft the rope becomes its own dominant load. KONE's answer keeps the rope and changes the material. UltraRope replaces the steel core with carbon fibre, and KONE states it "can enable future elevator travel heights up to 1,000 meters", with a 660 metre rise specified at Jeddah Tower. CompositesWorld puts the carbon rope at about a fifth of the weight of an equivalent steel rope.

TK Elevator went further and deleted the rope. MULTI runs multiple cabins in one shaft on linear motors and moves them sideways as well as up. At the inauguration on 22 June 2017 at the 246 metre Rottweil test tower, the company claimed up to 50% higher transport capacity, up to 60% lower peak power demand and up to 25% more usable area, against a stated baseline in which lift and escalator footprints "can occupy up to 40% of a high rise building's floor space". OVG Real Estate was named as the first customer, for East Side Tower in Berlin.

Nine years on, the claim has thinned. TK Elevator's current MULTI product page carries no capacity percentage, no usable-area percentage, no named building and no launch date. It sells the Rottweil viewing platform instead. For a CRE reader that is the finding: a technology with a 25% floor-area prize attached has not cleared underwriting anywhere in nine years.

Berlin bought the proven tool instead

The building MULTI was announced for was completed with conventional lifts. KONE installed 14 lifts and three escalators at the 136 metre EDGE East Side Berlin, including the first eight double-deck lifts in German-speaking Europe, running at 6 m/s and reaching the 36th floor roof terrace in 20.6 seconds. Each car takes up to 52 people on a 134 kW MX100 motor. The main tenant is Amazon.

Warsaw made the same choice at scale. Schindler put 57 lifts into Varso Place, 16 of them Schindler 7000 units and 12 of those double-deck, under a 310 metre tower of 53 floors. Two cars in one shaft, dispatched by destination control, is the European answer to vertical transport in 2026. It is unglamorous and it is bankable. Read it alongside the economics of height: every shaft you avoid is lettable floor.

The core takes a quarter of the building, and it gets worse

Every shaft, stair, riser and lobby sits in the core, and the core is dead rent. Hüseyin Emre Ilgın and Özlem Nur Aslantamer, publishing in Buildings on 22 October 2024, compared space efficiency across prismatic, tapered and free-form skyscrapers. Prismatic towers averaged around 72% efficiency with the core at 24% of gross floor area. Tapered towers averaged over 70% at a 26% core ratio, free-form towers 71% at 26%. Their headline finding is the one that governs a pro forma: "as the height of a building increases, there is a general decline in space efficiency".

That is the mechanical reason the tall-building case rests on floorplate scarcity rather than on stacking more storeys. Each extra floor drags a larger core through every floor beneath it.

At the same time, less valuable building area is needed for the lift shafts.

Erik Kahlert, Managing Director, KONE DACH

Wind is engineered out in the tunnel, not in the frame

Above roughly 300 metres the governing load is lateral, and the cheapest tonne of steel is the one the shape makes unnecessary. Peter Irwin of RWDI, writing for the CTBUH 2005 World Congress on the tower then called Burj Dubai, described repeated rounds of force-balance wind tunnel tests, after each of which "the building was reshaped to minimize wind effects". The result, in his words, was a substantial reduction in wind forces "by 'confusing' the wind". The measured prize was occupant comfort: predicted peak accelerations at a five-year return period fell from over 37 milli-g in May 2003 to about 19 milli-g, roughly half of that from better wind statistics and the rest from re-orientation, structural changes and shape.

SOM's finished tower is 828 metres over a hexagonal buttressed core, with spiralling setbacks so that "wind vortices can never coalesce because the wind encounters a different building shape at each tier". CVU records 163 floors above ground and a top lift speed of 10 m/s, where SOM's own project page says 160 storeys.

Shanghai Tower monetised the same method. Thornton Tomasetti reports that refining the 632 metre tower's twisting form "reduced building wind loads by 24 percent, which resulted in a lighter structure and reduced material cost". Where shape runs out, mass is added. Taipei 101 hangs a 660 tonne steel sphere between its 87th and 92nd floors, recognised by Guinness World Records on 31 December 2004 as the largest tuned mass damper, with a maximum extension of 1.5 metres. Every damper is a permanent tenant of premium floor area and a large embodied-carbon line, which is where this meets carbon and the tower.

Concrete does the quiet work

The least discussed supertall technology is the mix design and the pump. Burj Khalifa consumed 330,000 cubic metres of concrete, and its builders set a vertical pumping record of 606 metres using a Putzmeister BSA 14000 SHP-D. In summer, ice went into the mix and pours were run at night, when the air was cooler and humidity higher, to control the heat of hydration. Those are logistics decisions, not architecture, and they are what allowed a concrete core to reach that height at all.

The same logic is running now in Jeddah. Thornton Tomasetti confirmed the 100th floor complete at 400 metres on 20 April 2026, and by early August 2026 the tower stood at 430 metres over 107 floors, advancing roughly one storey and four metres a week against a target of more than 1,000 metres and completion in 2028. At that rate the kilometre is a construction-management problem, not a structural one. The Gulf context sits in the Dubai proving ground.

Timber has a ceiling, and it is around 100 metres

The material question is open again after a century, but the numbers are modest. The CVU tall-timber database records Ascent in Milwaukee at 86.6 metres over 25 floors, completed in 2022 as concrete-timber composite over a concrete base, and Mjøstårnet in Norway at 85.4 metres over 18 floors, completed in 2019 and all-timber. Moelven states Mjøstårnet was ratified by CTBUH as the world's tallest timber building at the time. Roots in Hamburg HafenCity reached 65 metres in September 2024.

The European step up is Rocket, at Lokstadt in Winterthur. Implenia reports the building permit was issued in April 2025 and the project passed to owner Cham Swiss Properties, describing it as one of the tallest timber residential buildings in planning at the time of development, not the tallest. The CVU database now lists it at 100 metres over 32 floors and under construction. That is roughly an eighth of Burj Khalifa.

Timber changes nothing about the four constraints. A timber tower still needs a lift strategy, still surrenders a quarter of its floor to the core, still has to be shaped for wind. What it changes is the embodied-carbon line and the end-of-life option, which is the real argument in what happens when a tower ages: a frame that can be disassembled is a different asset from one that can only be demolished.

Winners & losers

Who gains:

• Incumbent lift manufacturers. KONE and Schindler sold double-deck cars and destination control into Berlin and Warsaw while the disruptive system stayed in a test tower.
• Wind engineers. A 24% load reduction bought with geometry is cheaper than any structural upgrade that buys the same margin.
• Concrete supply chains and pump makers, whose logistics set the practical height limit on a core.

Who pays:

• Developers of tapered and free-form towers, who buy the silhouette and lose 26% of gross floor area to the core.
• Timber-tower promoters in wind-exposed European markets, where the built record sits around 100 metres and insurance, not engineering ambition, sets the pace.
• Anyone who underwrote a 25% usable-area gain from rope-free lifts in a 2017 feasibility model.

What to watch

Two dates. Jeddah Tower is climbing about one storey a week against a 2028 completion target, so by the end of 2027 the industry should know whether a kilometre of concrete core can be delivered on a commercial schedule. Rocket in Winterthur is under construction at 100 metres, and its topping out will be the first hard European data point on whether a timber residential tower clears the three-figure mark on cost as well as on permit. If TK Elevator has still named no MULTI building by the end of 2027, a decade after Rottweil, the rope-free lift should be treated as a research programme rather than a product line in any tall-building appraisal.