The New York Times today has an interactive feature explaining how converting pre-war offices to apartments is a lot easier than converting modern office buildings. Simply put, before the 1940s, no one had air conditioning, so the buildings had more light and air:
These kinds of buildings, often dating to the early 20th century, make for simpler conversions because the same logic that shaped how they were designed as offices a century ago determines how apartments are planned today. Both share a rule of thumb that no interior space be more than 8 or 9 meters from a window that opens.
Iconic prewar skyscrapers like the Empire State Building were designed to this standard, and with this smallest unit in mind: a single rentable office 3 to 6 meters wide and about 8 meters from the windows to the common corridor. That was just the right amount of space for a receptionist’s anteroom and a windowed office.
Dan Kaplan, a senior partner with the architecture firm FXCollaborative in New York, identifies the private-eye suite in any film noir as a classic example: frosted glass doors, a secretary framed by interior transom windows, and then the detective in his private office flooded with natural light.
But the conversion puzzle gets more complex with offices built after World War II. That’s because the modern office has strayed far — increasingly far — from the window rule.
Two inventions liberated office space from the window: air-conditioning and the fluorescent light bulb. Just as the elevator and steel-cage construction enabled buildings to grow taller in the late 19th century, the architectural historian Carol Willis has written, fluorescent lighting and air-conditioning enabled their floor plates to become much deeper.
Then local rules add still more complexity: Maybe the building has to meet stricter seismic requirements as an apartment than as an office (much of the West Coast), or the whole facade must be replaced to meet current wind-load standards (hurricane-prone places). Or you can only convert 18 of the 32 existing office floors into residential use (in Manhattan, such use caps depend on a building’s age and location). Or units must average at least 500 square feet in size per building (downtown Chicago). Or every legal bedroom must have its own working window (New York requires this but Philadelphia and San Francisco don’t).
Still, the commercial real-estate collapse of the last three years has made conversions imperative in big-city downtowns like the Chicago Loop.
The result, probably in only a few years, will be to transform former dense commercial districts like the Loop into dense mixed-use districts that people want to live in.