Two skyscrapers entered America's top 10 within the past year, but they're small fries among the world's tallest.

New York City's 30 Hudson Yards (1,268 feet) opened a few weeks ago. Late in 2018, the Comcast Technology Center (1,121 feet) opened in Philadelphia. Both have redefined their skylines, yet they wouldn't even rise halfway up the Burj Khalifa (2,717 feet) in Dubai, United Arab Emirates.

America is no longer the country with the biggest skyscrapers. And there are no mega-tall buildings (600 meters, or 1,969 feet) on the drawing board, so it's unlikely we'll regain that prestige any time soon.

New York, then Chicago, laid claim to the "world's tallest" throughout most of the 20th century. Then in 1998, the Petronas Towers in Kuala Lumpur snatched the top spot by 33 feet from Chicago's Sears Tower.

The world's tallest title hasn't returned since.

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Just one U.S. building cracks the world's top 10 – One World Trade Center. Its height of 1,776 feet, symbolic of the year the Declaration of Independence was signed, places it sixth among the world's tallest.

What's behind the change?

It doesn't appear to be a case of American decline. Many of the innovative techniques and talents raising skyscrapers to new heights come from America. It may be more a case of rising construction costs, elaborate building codes and changes in corporate priorities.

Cost and financing

New York is the most expensive place in the world to build. The average cost is $362 per square foot, according to a Turner and Townsend international construction market survey in 2018. By comparison, Hong Kong is $344 per square foot; the United Arab Emirates is $134; Kuala Lumpur is $96; and Beijing is $75.

Finding private investors to bankroll those costs in the USA can be difficult for developers of tall buildings. Market uncertainty can complicate deals, especially in multi-year construction projects.

Developers often turn to a variety of sources such as investors, investment banks and future building tenants, according to towerinfo.com. Many developers in China, by comparison, are owned by or have connections to the state, making funding less of a problem.

Sunlight vs. shadow

New York began restricting tall building construction in 1916, a year after the 538-foot Equitable Building went up at 120 Broadway. It threw a 7-acre shadow on the streets below, according to the New York Historical Society, triggering protests from residents who said it was like being at the bottom of a canyon.

In response, New York required setbacks and stepped-back walls – buildings such as the Empire State Building shaped like wedding cakes – to let sunlight reach the streets below. Zoning rules have since given way to other ratios to restrict size.

Building restrictions aren’t as tight in many foreign countries – some seeking the prestige that tall buildings confer.

FAA height restrictions

The Federal Aviation Administration sets a building height of 2,000 feet in most U.S. cities to make commercial flights safer. The height is closer to 1,000 feet near airports.

From offices to apartments

America’s tallest buildings used to be reserved for office space. That’s changing after the introduction of mixed-use buildings, which incorporate office space, luxury condominiums or apartments, restaurants and retailers. Residential towers are more valuable when they are tall, but they don’t have to be supertall.

For example, One57 in New York is 1,004 feet with 92 apartments and a hotel. Its duplex apartment sold for $100.5 million in 2014. 432 Park Avenue opened in 2016 and, at 1,394 feet, is the tallest residential building in the world and the second-tallest in New York. Its space has sold for more than $2 billion.

Some space in tall buildings is just … vanity space

Not all available space inside tall buildings is used. Some of it is “vanity height,” a term coined in 2013 by the Council on Tall Buildings and Urban Habitat. Vanity height is defined as the space between a building’s highest occupied floor and its architectural top, which are elements such as spires and parapets.

That space can be used to inflate building height. About 29% of Burj Khalifa is vanity height, according to the council. Nine other tall buildings in the USA, China and the UAE have 28% to 36% vanity height.

SOURCES Council on Tall Buildings and Urban Habitat; Skidmore, Owings & Merrill; towerinfo.com; Turner and Townsend, International Construction Market Survey, 2018; Federal Aviation Administration; BCW Global; Skyscraper Museum; New York Historical Society; Emaar Properties; Allianz Global Corporate & Specialty; Empire State Realty Trust