An office-to-apartment conversion works when the building's bones cooperate: floors narrow enough that every unit gets real light and windows, ceiling heights that hide new ductwork, and a structure cheap enough to gut — which is why pre-1940 office buildings convert steadily and most post-1970 towers do not. CBRE counted 169 completed U.S. office-to-residential conversions in 2024, a record year, per the brokerage's 2025 conversion report. Developers' own claims about timelines and rents are theirs, not ours.
Adaptive reuse (converting an existing building to a new purpose) is the polite term; on site it is a gut job with a facade attached. The economics and the building code do the deciding, mostly before an architect draws a unit.
Why is floor depth the whole game?
Because residential rooms need windows and apartments need through-light. A workable rule of thumb from conversion practice: livable depth runs about 25 to 30 feet from window wall to the point where daylight gives out. Office towers built after roughly 1960 push core-to-window depths of 40 feet and beyond, because desks and cubicles tolerate interior darkness that bedrooms, by code, do not. A 1930s bank or garment-district loft with 30-foot floors converts almost naturally. A 1980 plaza tower with a 45-foot floor plate leaves a doughnut of unusable dark middle — storage at best, code violation at worst.
Some designers fight the depth anyway, with light wells, interior courtyards, or units that wrap the perimeter like a racetrack. It can be done. It costs floor area, and floor area is the product.
What has to change inside?
Almost everything except the frame. Office buildings deliver air, power, and bathrooms in bulk — two restrooms per floor, off a shared corridor — while apartments need each unit to carry its own plumbing, ventilation, and kitchen. The construction sequence runs roughly:
- Strip the interior to structure and verify floor loads with an engineer.
- Rough in new plumbing risers and vents, the single costliest insertion in most conversions.
- Add compartmentalized HVAC — usually ducted or mini-split systems, since office VAV air doesn't divide legally into homes.
- Build unit layouts around the window line and the new risers, then add corridors, meters, and separate life-safety systems.
Older buildings help twice here: their ceilings run 12 feet and up, leaving room to thread ducts, and their structure is often overbuilt by modern standards.
What does it cost, and who pays?
Conversion costs land in a wide band because buildings differ so much. Industry estimates have ranged from roughly $100 to $300-plus per square foot depending on structure and extent of gutting; any specific project number is its developer's claim. On the public side, the toolkit widened in 2023-2024: HUD issued guidance opening its loan programs to conversions, and cities including New York, Chicago, and Calgary adopted tax incentives or outright rezonings for office-to-residential work — Calgary's incentive program alone committed grants to more than a dozen downtown conversions, per the city's published program totals.
Do conversions make housing people want?
The finished units skew distinctive rather than uniform: odd window rhythms, deep sills, terrazzo lobby floors nobody would spec today. What conversions rarely produce is family-sized housing at volume — the same floor plates that make small units easy make three-bedrooms rare, and unit mixes in completed projects skew heavily to studios and one-beds. The neighborhood effect runs the other way and matters more: conversions put evening and weekend life into districts that clear out at six, which is the actual argument cities are paying for.
What the record shows is a record pipeline of conversions, concentrated in older, shallower buildings, with plumbing and air as the deciding costs. What it can't show is whether any specific tower will make it — that turns on structure reports and incentives nobody can predict from the street.
For more context, read How to read a floor plan before you fall for the apartment.