Architects explain how they're turning office buildings into apartments with high ceilings and more natural light

• With offices empty and housing scarce, commercial buildings are being turned into homes more often. 
• Architects say the hardest part of these conversions is picking the right building.
• After that, they have to do everything from adding stairs to cutting out the centers of structures. 

Vacant downtown office buildings may be the next SoHo lofts. That is, after they go through the costly process of being converted into apartments and condos. 

Elected officials in cities across the US are trying to solve a housing shortage, empty offices in a remote-work world, and the climate crisis by converting underused commercial space into homes.

Steven Paynter, an expert in office-to-residential conversions at the architecture firm Gensler, thinks converted office buildings will be a trendy, new type of housing. Like the loft apartments converted from former manufacturing spaces that have become some of the most desirable homes in Manhattan, New York, former offices offer unique features and history you can't find in a new building. 

"A lot of the residential conversion is now providing a better product than ground-up residential because no one builds residential with that high ceilings, or that kind of interesting structural system, or that kind of heritage facade, or building with brick skin," Paynter said.

And even in a worst-case scenario, where units are strangely laid out or dimly lit, there can still be unique benefits to living in an old office.

"A lot of people might not care that they get a ton of daylight into their bedroom if it means their rent is cheaper or they live a five-minute walk from work," Mark Hogan, a San Francisco architect who has advised the city government on policy reforms concerning office conversions, said.

But renovating old office buildings is no simple task. Insider spoke with four architects who'd tackled these projects. They said that turning a cubicle farm or conference room into a livable space involved addressing a host of issues, including inoperable, poorly insulated windows and the dark depths of a skyscraper's center.

Here's what it takes to turn an empty office skyscraper into much-needed housing.

The first step is finding the right building

The most difficult part of the conversion process comes before any of the construction begins: selecting the buildings to convert, Paynter said. He and his team have developed an algorithm to determine which buildings are ripe for conversion. It takes into account building size, layout, location, and how updated its facade is. Of the 950 buildings he and his team have surveyed, just 30% are suitable for conversion. People in the industry call them "Goldilocks buildings."

"If you get the right building, you can make a really great project out of it," he said. "If you start with the wrong building, you've got no chance.

Older, prewar buildings are generally easier to turn into homes than newer skyscrapers. That's because buildings constructed before air conditioning generally have smaller floor plates, with building interiors no more than 25 or 30 feet from windows that can open. Newer buildings often have deeper floor plates and windows that don't open, which can make conversion tricky since residential buildings need light, air, and bathrooms all over. 

"A lot of older buildings that are U-shaped or E-shaped, or kind of smaller in floor plate are perfect candidates for conversion," Charles Bloszies, a San Francisco architect and structural engineer, told Insider. 

In some cases, particularly when it comes to postwar high-rises, it's more economical to tear old office buildings down and replace them with new housing, Hogan said. He thinks older, smaller buildings are much more eligible for conversion. 

"That is lower-hanging fruit, and I think those are the type of projects you'll be more likely to see sooner," Hogan said. 

Many buildings need more stairs to meet modern fire codes

The first step in turning a commercial building into homes is figuring out where the staircases will go to meet modern fire regulations, especially in older and smaller buildings, Hogan said. In the US, most apartment buildings more than 4 stories high must have two staircases and exits. Those staircases need to be connected by a corridor, and that shapes how apartments are laid out around them.

"There's a lot of existing buildings that have a fire escape as a second means of egress in San Francisco," Hogan said. "In a building where you're changing the use, you typically have to bring it up to code, and so adding extra stairs is a really major intervention and is just going to change the available square footage pretty dramatically." 

Cutting out the middle of skyscrapers to add more windows

Key to the interior design in converted buildings is maximizing the amount of exterior wall per unit to get each home the most light and air possible. In some newer office buildings, architects will cut out a portion of the center of the building to create a courtyard or shaft for air and light. Sometimes that lost floor space will be made up by adding several floors to the building. 

John Cetra, a Manhattan architect who has worked on office conversions since the 1980s, is leading the second-largest office-to-residential conversion project in Manhattan. The building — at 25 Water St. in the financial district — houses JPMorgan's offices and is set to have 1,300 apartments eventually. But first, sections of the center of the building, including excess elevators, are planned to be cut out, with new floors added. 

"We created the hole in the doughnut to bring the light and air into the middle of the space," Cetra said. "And we took some of the floor area that we eliminated, and we're building 10 stories on top of the building." 

In another such project completed in 2007, Bloszies and his team turned the oldest skyscraper on the West Coast — San Francisco's Chronicle Building — into 100 homes. They stripped off a metal shroud that had been added to the building, restored the original facade, and added 8 stories to the top of the building — one of the largest vertical additions to a historic building in the world at the time.

Rebuilding a skyscraper can get expensive

Not all buildings can accommodate a renovation like this. Some building foundations can't handle the extra weight of additional floors. Cetra said he and his team "draw the line" at reinforcing foundations, a process that he said was too expensive and disruptive to be worthwhile.

Changing an older building's use often triggers requirements to have it abide by modern building codes. This includes updates like seismic retrofitting, which strengthens buildings to protect them against earthquakes. It also includes abiding by modern energy-efficiency standards. New plumbing, mechanical systems, and heating, ventilation, and air-conditioning systems are also usually part of the construction process. 

Renovating the facades and windows of buildings is also a costly but often necessary endeavor. Many buildings, particularly those constructed after 1960, don't have operable windows, and even if they do, they don't meet modern energy-efficiency standards. 

When Gensler renovated Franklin Tower, a vacant 1970s office building in downtown Philadelphia, it fully reconstructed the facade and windows. It also solved some of the problems associated with a large floor plan by creating smaller amenity spaces on several floors occupying many of the windowless spaces in the center of the building, Paynter said.