An office to residential conversion is hard because the building was engineered for the opposite of what housing needs. Offices want deep, open floor plates, sealed curtain walls, two toilet rooms per floor, and one big air handler. Apartments want every room near a window, glass that opens, a wet wall every 25 feet or so, and a separate system in each unit. Gensler’s office-to-residential scorecard finds that only about 25% to 30% of the buildings it studies are good candidates, and that is before anyone prices the plumbing.
Here is why.
Why do so few office buildings qualify?
Three things sort the candidates from the rest, and you can read all of them off a floor plan.
- Floor plate depth. A pre-war tower with a 12,000-square-foot plate and windows on four sides converts almost naturally. A 1980s plate of 30,000 square feet with the elevators in the middle leaves a ring of dark space that no bedroom can occupy. You end up with interior “flex rooms,” oversized units nobody wants, or a light well cut through the slabs, which is the expensive way to admit the plate was wrong.
- The window wall. Fixed curtain wall glazing was fine for a sealed office. Housing codes in many cities require operable windows or natural ventilation in habitable rooms; New York’s Multiple Dwelling Law, for one, requires a window in every habitable room. Replacing a curtain wall is a facade project on top of a conversion.
- The core and the columns. Elevator banks sized for a 9-to-5 rush sit exactly where the corridor wants to be. A 20- to 30-foot column grid is workable; a transfer girder at the second floor is not your problem until the structural engineer says the new wet walls cannot go where the plan needs them.
The point of running Gensler’s scorecard early is to say no cheaply. A scorecard afternoon costs the client a few hours; a failed schematic design costs a phase.
What does the code make you do when B becomes R-2?
The IEBC (International Existing Building Code, 2024 edition current) governs the work, and a change of occupancy from Group B (business) to Group R-2 (apartments) is the most consequential thing you can do to an existing building short of adding floors. Chapter 10 of the IEBC covers change of occupancy, and the short version is that the new occupancy meets new-construction rules for life safety, with some relief elsewhere.
Expect the following:
- Sprinklers throughout. The IBC (International Building Code) requires an automatic sprinkler system in every building with a Group R fire area, so an unsprinklered office gets a full system, often a fire pump, and a bigger water service.
- Egress re-examined. Two stairs are usually there, but corridor ratings, travel distance, and dead ends get measured against residential rules, and stair pressurization becomes a question in a high-rise.
- Accessibility. Group R-2 pulls in the IBC Chapter 11 requirements for Type A and Type B dwelling units (the accessible and adaptable unit categories), plus a Fair Housing Act review if counsel decides the conversion counts as new covered multifamily. The unit bathrooms are where the plan gets redrawn.
- Energy and ventilation. New dwelling units mean new mechanical under the current energy code, and kitchen and bath exhaust for every unit means a riser problem on every floor.
- Structure. Going from B to R-2 usually does not raise the risk category, but local seismic ordinances in California cities can pull a retrofit in on their own, and every new slab opening gets engineered either way.
None of this is exotic. It is the same list as any ground-up multifamily building, applied to a structure that was not built for any of it.
Where does the money actually go?
Plumbing, first and always. An office floor has two toilet rooms stacked on a core. A residential floor has a kitchen and one or two baths in every unit, which means new risers in new locations, sleeved through every slab. If the slabs are post-tensioned (cast with steel tendons stressed after the concrete cures), every core hole gets scanned first, and the tendon map dictates where the risers go, which dictates where the kitchens go, which dictates the plan. We have watched a unit layout get redrawn three times around a tendon map.
Then the facade, if the windows have to become operable. Then mechanical: the central system comes out and per-unit equipment goes in, with refrigerant lines run through a building that never had chases for them. Then the efficiency loss. An open office floor rents nearly all of its area; an apartment floor gives up corridors, demising walls, and shafts, so the same gross area yields less rentable area than the pro forma (the developer’s spreadsheet of costs and returns) assumed on the napkin.
Add the soft costs. Government regulation accounts for roughly 41% of multifamily development costs in the 2022 study by NAHB (the National Association of Home Builders) and NMHC (the National Multifamily Housing Council), and a conversion carries the full permitting load of a new residential building plus a change-of-occupancy review on top.
When does an office to residential conversion pencil?
The math works in a narrow band: the building has to trade at a steep discount to replacement cost, and residential rents have to be high enough to carry the conversion cost plus that basis. That describes a handful of downtowns, not the country.
Hybrid work keeps the pipeline alive. Gensler’s Global Workplace Survey 2025 finds hybrid remains the majority pattern for office workers, so the older, deeper buildings keep losing tenants and getting cheaper. ULI’s (Urban Land Institute) Emerging Trends in Real Estate 2026, published in fall 2025, still lists conversions among the strategies developers weigh for that stock, alongside the less glamorous option of demolition. NAIOP, the commercial developers’ association, frames the same choice from the owner’s side.
Cities have noticed and are paying. New York State’s 2024 budget created a tax exemption for conversions that include affordable units, and Chicago (LaSalle Street Reimagined) and Washington, D.C. (Housing in Downtown) have run their own subsidy or abatement programs for downtown conversions. When a program like that closes the gap, the pro forma can work on a building the scorecard rated marginal. Without it, the scorecard is usually right.
How should your firm scope a conversion?
Sell the feasibility study as its own job, hourly with a not-to-exceed cap, and make it clear that “no” is a legitimate answer. The deliverable is a test fit (a quick unit layout on two typical floors), a code path memo, a plumbing riser diagram, a structural and facade read from your consultants, and a rough cost from a contractor who has done one. Three to six weeks. If the project dies there, the client paid for a real answer and you did not eat a schematic phase.
Get existing conditions right before the test fit; our post on existing-conditions documentation covers the scanning side. Bring structural, MEP (mechanical, electrical, and plumbing), and a facade consultant into the feasibility fee rather than waiting for SD (schematic design), and carry a contingency in your own hours, because the building will contradict the drawings at least once.
Conversions are the hardest case of the broader adaptive reuse trend, which is why they show up in our rundown of architecture trends heading into 2027. The firms that make money on them treat feasibility as the product and the conversion itself as the occasional bonus.
AECPulse Project Manager carries the feasibility study as its own phase with an hourly cap and a live burn against it, so the hours spent proving a building will not convert get billed rather than absorbed.