Office to Residential Conversions and Why So Few Get Built

Walk through the financial district of almost any large city on a Friday and you will see whole floors with the lights off. Office vacancy in many North American downtowns has sat near or above 20 percent since the pandemic, and every few months a politician stands in front of one of those towers and promises to fill it with apartments. Then, quietly, very few of them get built.

Office to residential conversions are one of the most discussed project types in our industry and one of the least understood by the public. Having walked a number of candidate buildings with developers and engineers, I can tell you the obstacles are mostly physical, then financial, and only occasionally political. Here is what decides whether a tower becomes homes or stays empty.

Why Office to Residential Conversions Look Easier Than They Are

From the street, an office tower and an apartment block look similar: a frame, floors, windows and lifts. The difference is what each building assumes about the people inside. Offices are designed for lots of people sharing a few toilets and a big open floor. Homes need every unit to have its own kitchen, bathroom, natural light, fresh air and, in most codes, a window that opens in every bedroom.

That shift turns a single tenant floor with two toilet cores into a floor of twelve to twenty separate dwellings, each with its own plumbing, ventilation and fire separation. It is less a renovation than building a new interior inside an old skeleton.

The Floor Plate Problem

The single biggest predictor of whether a conversion works is the distance from the building core to the outside wall. Bedrooms and living rooms need daylight, and daylight runs out roughly 9 to 12 metres from a window. Many towers built from the 1970s onward have floor plates far deeper than that, designed for open plan desks lit by fluorescent tubes.

Building type	Typical core to window depth	Conversion outlook
Pre-war and early postwar slender towers	Shallow, often under 12 metres	Usually good
Mid-century slab blocks	Moderate	Often workable with layout tricks
Large late 20th century towers	Deep, sometimes over 20 metres	Difficult without major surgery

Designers have a few ways to deal with deep plates: putting storage, laundry and bathrooms in the dark middle, creating long narrow units, or cutting a light well through the centre of the building. Cutting a hole through a concrete tower is expensive and removes rentable floor area, but on some projects it is the only way the numbers work.

Plumbing, Windows and the Hidden Costs

Once a building passes the daylight test, the next surprises are usually in the services.

Plumbing stacks. Every kitchen and bathroom needs drainage running vertically through the floors. Offices often have two or four stacks; a residential floor might need a dozen.
Windows. Many towers have sealed glass curtain walls. Codes often require operable windows or dedicated ventilation, which can mean replacing the facade.
Floor to floor height. Generous office ceilings help, giving space to run new ducts and pipes, but raised floors and hung ceilings must often come out first.
Lifts and stairs. Residential fire codes may require different stair arrangements or compartmentation between units.

Each item on that list can add months. On many projects, the structure is the cheap part and the services are where the budget goes.

Projects That Show What Is Possible

Real buildings make the trade-offs clearer than any spreadsheet. In Lower Manhattan, 25 Water Street, a former office tower with a famously deep floor plate, has been converted into roughly 1,300 apartments, which made it one of the largest conversions in the United States. The developer handled the depth partly through unit layouts that run long from window to corridor and partly by putting amenities into the darkest interior spaces.

Calgary took a different route. Facing some of the highest office vacancy in North America after the oil downturn, the city began offering grants per square foot of converted space, and a string of mid-sized towers have since become rental housing. The lesson there was that public money helps most when it is predictable and paid per unit of space, rather than negotiated project by project.

Smaller cities have their own versions. Older bank buildings and department stores near main streets often have shallow plates, high ceilings and good bones, which is why many of the most successful conversions are not famous towers at all. We have seen similar thinking in air rights projects, covered in our look at two air rights projects over the Massachusetts Turnpike, where unusual sites only worked because the design started from the constraints.

Where the Usual Advice Falls Short

The common line is that conversions are a cheap and quick answer to the housing shortage because the building already exists. I think that oversells it. A difficult conversion can cost close to new construction per square metre, and it can take just as long once facade replacement and new services are included. It also produces fewer homes than a purpose built tower on the same site, because so much floor area is lost to dark interiors and new cores.

Conversions are worth doing, but for different reasons: they reuse embodied carbon in the frame, bring residents into districts that empty out at 6 pm, and support the shops and transit already there. Treating them as a cost shortcut sets up the wrong expectations and leads to stalled projects when the second engineering report arrives.

How to Judge a Candidate Building

If you sit on a planning committee, invest locally or simply want to read announcements critically, a short checklist goes a long way:

Measure the core to window distance on a typical floor.
Check whether windows open and whether the facade is near the end of its life anyway.
Count existing plumbing risers and their locations.
Look at the orientation, since light and solar gain shape unit layouts, as we discussed in why building orientation decides a home's comfort.
Ask what share of floor area becomes rentable homes. Below about 70 percent, the economics get hard.

Frequently Asked Questions

Are converted apartments smaller than new ones?

Not necessarily, but they are often shaped differently. Long, narrow units with windows at one end are common, and some have interior bedrooms that rely on borrowed light, depending on local rules.

Do conversions really save carbon?

Usually, yes. Keeping the concrete or steel frame avoids the emissions from making new structure, which is a large share of a building's lifetime carbon. Savings shrink if the facade and services are entirely replaced.

Why do so many announced conversions never start?

Most stall during detailed design, when surveys reveal deeper floor plates, asbestos or facade problems than expected, or when interest rates make the financing unworkable.

The Practical Takeaway

An empty office tower is not automatically a housing opportunity. Judge each one on depth, windows and services first, and treat a conversion as a long term reuse project rather than a quick fix. For more case studies from the field, browse our projects archive.