Thin off the ground

If you had to choose the most impressive trend in modern architecture, it would probably be the pencil skyscraper – tower blocks astonishingly slender in shape

Skyscrapers in New York are often compared to fashion models these days – none of them seem to be too tall, too shapely or too rich to build, because there is no concept in excess of these categories. On the contrary, as time goes by, the projects are getting bolder and more impressive. Although such towers are also being built in China, Malaysia and Taiwan, this does seem to be a species endemic to Manhattan at the moment. A combination of legal, economic and social factors have made this small area south of Central Park mushroom with such towers of imposing heights. For this reason it has come to be known as the ‘Billionaires Belt’

The thinnest, tallest and most expensive

The 111 West 57th Street skyscraper, which is under construction two blocks away from Central Park in an investment of USD 1 bln, is probably the best example of this. The tower, which is due to be completed in 2018, will be 426m in height but only 18m wide – the slimmest skyscraper in the world. Its slenderness ratio, calculated as the height to the narrowest side wall ratio according to New York construction law, will amount to 24:1. By comparison the proportion of the World Trade Centre twin towers, which used to be admired for their slender shape, was a modest 9:1.

Within a 10-minute walk to the east, the construction of 432 Park Avenue tower is also nearing completion. It is currently the tallest residential building in the western hemisphere and the tallest skyscraper in the city, except for the spire of the One World Trade Centre office building. The impressive building, which has a slenderness ratio of 14:1, making it one of the slimmest, should be completed next summer. Its 96 storeys includes 104 extra luxury apartments at prices ranging from USD 7 mln to USD 95 mln. However, the cheaper of these, the studios, have enjoyed the most popularity, having been sold out for some time. The most expensive penthouse has an area of almost 770 sqm, occupying an entire floor of the building as well as being the highest located apartment in the city. It is not New York’s most expensive, though. This distinction goes to an apartment that has been sold in the One57 pencil skyscraper, completed a year ago. And it was the startling price agreed for the apartment that has fed developers’ imaginations. The two-storey apartment with an area of just over 1,000 sqm changed hands for USD 100.4 mln at the beginning of this year.

Like reeds inthe wind

As is the case with aircraft, these days skyscrapers also undergo tests in aerodynamic tunnels on top of computer analyses. Miniature models covered in sensors make it possible to precisely establish the strength and the direction of the forces ranged against the building, such as air turbulence, vibrations and other factors impacting its behaviour and durability. Furthermore, according to the city’s current regulations, each building with a slenderness ratio in excess of 7:1 has to be peer reviewed by an engineering company other than the one that designed the structure.

However, the construction law, even though it defines the safety requirements quite precisely, does not fix everything. Even a completely stable skyscraper can sway like a tree during a hurricane. Tea regularly spilt over the table and swinging chandeliers are, however, unacceptable from the point of view of user comfort – not to mention in terms of the marketing. “If a building is not well designed, you will feel it move. But even in a very well designed building, a small percentage of people may sense the movement when the strongest winds are blowing. The goal is to limit this movement,” explains Silvian Marcus, the head of construction at US engineering conglomerate WSP Parsons Brinckerhoff.

Technological advances offer some help here. Modern reinforced concrete is now much harder than in the past. It is excellent as a construction material for the ‘spine’ of a building or its square shaft, where the lifts are located. In the case of 432 Park Avenue there is a square-shaped shaft measuring 10m x 10m with 75 cm thick walls. It also has a sturdy frame – a façade with solid beams and columns, which are interwoven with impressive windows spanning the space between the ceiling and the floor and measuring 3m x 3m. Between the façade and the spine there is a completely open residential area 10m in length, where it is possible to show off the interior design.

However, the stiffness of the structure is not sufficient in the case of the most slender buildings. This is why 432 Park Avenue is additionally divided into five sections, twelve floors each, with some space left between the sections in order to create an outlet for the wind. If this does not do the job, it is also necessary to also use mass dampers – weights filled with liquid with a much higher inertia than the building itself to cope with side-winds. These are designed to inhibit the acceleration of the movement of the building. Because the principle is the same as in a car – the movement can only be sensed inside during acceleration, so the effect has to be muted. And of course this adds to the price of comfort.

Increased investment costs are also the case for the not-so-slim skyscrapers that do not require such sophisticated solutions. According to Silvian Marcus, the borderline for this is slenderness in excess of 5:1. A simpler rule-of-thumb for increased costs, using the height rather than the ratio, says: the higher, the more expensive. “In order to transport cement from the ground to a height of 400 or 500m, you need three or four minutes. This is a very long time. It’s a bit like using a teaspoon. So you need faster lifts and stronger water pipes,” he explains.

Such elegant structures would, however, remain the stuff of architects’ unfulfilled dreams if it were not for Manhattan being so highly fashionable. Buyers include rich New Yorkers and millionaires from all over the world. In 432 Park Ave., for example, 35 pct of buyers are foreigners from a number of countries including Turkey, Saudi Arabia China, Russia, Greece and Brazil. An unobstructed view onto Central Park and the roofs of New York is very much a status symbol. And the only way to get one is to reach for the skies. In toothpick-thin skyscrapers there is little space between the windows. The lift takes you almost to the threshold of your apartment, because there are only one or two flats on each floor. However, developers must show some sensitivity to the trends expectations too. Recently USD 80 mln apartments in 432 Park Ave. have been halved in size to make them more accessible for buyers. “It’s true that you have to pay a lot for an apartment at such a height, but I believe that the construction costs of such buildings will be lower tomorrow. This way of living will become much more accessible in various locations across the world,” believes Silvian Marcus.

CEE not ready

This is, however, a song of the future. There are still only a few potential buyers with fat enough wallets and the willingness to buy such an exclusive apartment with a view onto pl. Defilad in Warsaw – certainly there are fewer than those prepared to shell out a fortune for a view onto Central Park in New York. We can see this just by taking a look at the sales of apartments in luxury towers in Warsaw. Some of the 252 apartments in Cosmopolitan – the most slender (7:1, with a height of 160m) apartment building in the Polish capital – have still to be bought four years from the launch of the sales process. However, the competition in this class is not so strong – in fact, it is limited to the neighbouring Złota 44 skyscraper (6:1, 192m) which returned to the market this year. “The market has certainly not matured yet for such luxury projects. the situation is similar, for example, in Bratislava, where apartments like this struggle to be sold. Such sales take at least a few years,” claims Stanislav Frnka, the CEO of Slovakian-based developer HB Reavis Poland, which is planning to build the tallest tower in Warsaw.

The company owns a plot at ul. Chmielna 69 in the city centre, for which it has obtained a site development conditions decision for a 310m tower (including an 80m spire). “Initially we also carried out an analysis for the possible construction of apartments; but we opted for offices in the end,” explains Stanislav Frnka. However, he insists that it will not be a pencil skyscraper. “Tenants do not want the individual floors to have such small areas. There has to be a minimum of 1,000 sqm per floor,” he says.

There is also another reason why importing the American approach will not be easy. In spite of the fact that the Warsaw market might soon be feeling the effects of an office oversupply, there is no shortage of plots for new projects – even in the inner city centre. Including in the very centre, on pl. Defilad itself. Accroding to the current zoning plan, office buildings of between 208 and 245m in height can be built on the plots. “Some plots in the city centre are narrow. However, considering the permitted heights they are not so small to make it necessary to build pencil skyscrapers. It seems that in Warsaw there is still enough space where more regular skyscrapers could be built,” says Marek Dąbrowski, the director of the Polish branch of WSP.