SAN FRANCISCO —Straight through the roof. That’s where the elevator cage seems headed as passengers race toward the top floor of a luxury high-rise tower that’s under construction near the water’s edge in San Francisco’s South of Market district.

And straight through the roof is where the price seems to be headed, too: $49 million for the 14,000-square-foot, duplex penthouse on the 41st and 42nd floors.

“San Francisco is hot,” said Lee Summers, a senior global adviser and broker at Sotheby’s International Realty in New York. “People are really buying up a storm there. If you have made a lot of money, you want a lot of luxury. And who wants to keep up a big home these days? So there’s a huge need for luxury condos in San Francisco.”

Even before they open in 2016, the twin towers of the Lumina luxury condo complex can be seen from the East Bay, Treasure Island and parts of San Francisco as they glitter on the ever-changing skyline near the approach to the Bay Bridge. The sky-high price of entry to this cloud-level living — even the cheapest units at Lumina go for $1 million — is a new realm for the city as San Francisco flirts with Manhattan-style real estate excesses.

“The market will just keep going up,” said Gregg Lynn, the listing agent from Sotheby’s who is handling the penthouse sale.

Whether San Francisco will ever catch up with the stratospheric $100 million prices of the highest-end places in New York remains to be seen, but Lynn predicts that the ceiling for prices in San Francisco will keep rising because wealth is enormous but available housing stock is scarce.

Still, Lumina — developed by Tishman Speyer with equity partner Vanke, based in Shenzhen, China — is pushing the sky in the South of Market district, two blocks from the Embarcadero, where businesses, restaurants and other attractions are booming in this hot economy.

Of course, Lumina’s bid for high-end real estate dominance comes amid a housing affordability crisis ignited by the boomtown tech economy. Bay Area real estate prices have been setting records, with San Francisco leading the way. The middle class is squeezed and renters have been evicted by landlords looking to cash in on development.

The pressure is everywhere: In the once funky Mission district, a typical two-bedroom apartment now rents for $3,800.

Aware of these pressures, Tishman Speyer points out that it is developing 190 units of affordable and middle-income housing on Mission Street, also in SoMa, starting in the low $200,000s. Worked out with city planners and nonprofit partners, it’s a tandem project. But the spotlight falls on Lumina, where the views would impress anyone, including the workers who are now installing the bones for the penthouse’s suggested two kitchens, five bedrooms, five full bathrooms, two half-baths and stretches of 18-foot ceilings, and curving glass walls onto terraces covering 1,200 square feet.

Developers expect high demand for the lower-end units, but who would be able to fork over $49 million for a penthouse?

Lynn described three categories of potential penthouse buyers: “big names in technology” are one, given that SoMa is bustling with workers from LinkedIn, Dropbox, Google, Uber and other tech firms. Then there are wealthy San Francisco locals, including millennials and empty nesters, who would like to get closer to the urban core with its bustle and city vibe.

And finally, foreign investors are looking to buy “trophy real estate” in a city that fascinates them. Asian buyers account for an estimated 30 percent of luxury buyers in San Francisco, Lynn said.