Turning Empty Offices and Warehouses Into Homes: In Ontario, Building Code Part 11 Is the Real Gatekeeper
Cheap per-square-foot office space looks like a shortcut to downtown housing. Whether it actually becomes housing has almost nothing to do with the purchase price — and almost everything to do with the building’s bones, its fire code, its daylight, and its zoning.
The office building is cheap and half-empty — can I just convert it into apartments?
Not just convert it. In Ontario, turning an office tower or warehouse into homes is a renovation plus a change of major occupancy, and it has to clear Part 11 of the Building Code — Renovation of Existing Buildings. Structure, fire separations, means of egress, daylight and ventilation all get re-examined against residential standards. According to the Government of Ontario, the current Building Code (O. Reg. 163/24) took effect January 1, 2025, and Part 11 is the chapter that grants flexibility for renovating an existing building — with or without a change in its major occupancy. Whether a conversion pencils out is written into the building’s bones, not its asking price.
Source: Government of Ontario — Building Code, O. Reg. 163/24 (Part 11, in force January 1, 2025; ontario.ca, accessed July 2026)
I am Arthur Zhao. Every time the downtown office vacancy rate climbs, someone forwards me a listing priced at maybe half of what finished condo space costs per square foot, with one question attached: buy it, convert it to housing, and pocket the spread — easy money, right?
I get the pull. On paper, buying a downtown floor plate at commercial prices and selling it back as housing is a tempting arbitrage. But the most expensive line item in that math is rarely in the asking price: turning a building designed for offices into legally habitable homes that can actually receive an occupancy permit means clearing Building Code Part 11 — and what stops most deals there is not money, it is the building’s own bones.
This is not a piece about which building to buy. It is about the handful of things to see clearly before you commit: whether the structure holds, how the fire code changes, whether daylight and plumbing can be saved, and whether zoning even lets you do it. Skip those, and the spread you thought you saved comes back with interest during construction.
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Renovation and change of use are two different code questions
People treat “renovating the building” and “changing what it is used for” as one job. In Ontario’s Building Code they are two separate lines.
Renovation — touching the walls, floors and systems of an existing building — is governed by Part 11, Renovation of Existing Buildings. According to the Government of Ontario, the current Building Code (O. Reg. 163/24) took effect January 1, 2025, and Part 11 exists to give existing buildings flexibility when they are renovated, with or without a change in major occupancy.
Change of major occupancy — moving the building from “office” to “people living here” — is the second line. The Building Code classifies buildings by occupancy: offices generally fall under Group D, industrial under Group F, and residential under Group C. The moment the major occupancy changes, Part 11 asks you to measure the building against today’s code for its new life.
Why the distinction matters: changing the use brings sleeping occupants into the equation, and the life-safety bar for people asleep at night is higher than for people awake at a desk. You are not fitting out an office. You are promoting a building into a legal home.
ℹ️A change of use almost always needs a building permit, and in many cases site plan approval as well. Do not treat it as a “renovation” — on the approvals side it behaves more like a new project.
Structure is usually the good news
Offices and warehouses were engineered for office and industrial live loads, and a residential apartment generally imposes lighter loads than a floor full of workers, filing cabinets and equipment. The frame that carried the office is, more often than not, more than enough to carry the homes.
“Enough,” though, does not mean “unexamined.” Under Part 11, once you substantially remove and replace walls, floor or roof assemblies, or add new loads, the structure and its fire-resistance have to be recalculated against current code and reinforced where needed. Old warehouses carry a bonus here: tall floor-to-floor heights and wide column grids make them natural loft candidates, with far more design freedom than a cellular office tower.
Bottom line: structure is the friendlier gate — but “friendlier” is a conclusion a structural engineer hands you after running the numbers, not something you read off a listing photo.
Fire and egress: sleeping occupancy raises the bar
The logic is human: office workers are awake, alert and familiar with the exits by day; residents are asleep at night, and include the elderly and children. Life-safety code has always asked more of sleeping occupancies. So a change of use puts these back on the table under Part 11:
1. Fire separations and fire-resistance ratings — proper rated separations between units, and between units and corridors.
2. Means of egress — housing typically needs two independent exit paths; an old office core may not deliver that.
3. Sprinklers and alarms — coverage, fire alarm and detection often have to be upgraded or added to residential standard.
According to the Government of Ontario, where existing fire separations or fire-resistance ratings do not conform, Part 11 triggers an upgrade toward current code. This is not a line item you can “value-engineer” away — it is a precondition of the occupancy permit. Fail it and the building simply does not open.
Daylight, ceilings and plumbing: where deals actually die
Daylight and floor-plate depth. Bedrooms and living rooms need light and air. Many office towers are big open plates wrapped around a central core: the perimeter is fine, but the deeper you go toward the middle, the more you hit dead zones no window can reach. Deep plates leave a core that will not carve into compliant living space without light wells or waste — cost climbs fast. Narrow plates with windows on several sides are the prize targets.
Ceiling height. Housing has to thread new plumbing, sound isolation and ventilation into each floor. Drop the ceiling to hide all that and the clear height tightens — a height that was fine for an office can end up cramped, or non-compliant.
Plumbing. The most under-estimated item on the list. An office concentrates water in a few core washrooms; an apartment building needs a kitchen and bathroom in every unit, which means re-running risers and drainage across the whole floor. That is not a touch-up — it is major mechanical surgery.
None of these three — light, height, plumbing — appear anywhere on the cheap listing. All three routinely decide whether the deal lives.
⚠️The per-square-foot price on an office listing does not include daylight remediation, re-run plumbing, fire upgrades or sound isolation. The numbers that actually decide whether a conversion pencils are exactly the ones the listing never shows. Have a professional price them in before you buy.
💡 Here is Part 11 in one sentence: it grants conditional flexibility, not a blanket break for old buildings. Keep the existing performance level and create no new unsafe condition, and you need not chase every current clause. Change the use, or gut and rebuild, and you trigger the obligation to bring things up to today’s code. The flexibility is a reward for light-touch work — a change of occupancy hands it back.
Zoning is the first phone call, not the last
A building can be perfectly convertible on structure and fire and still be a dead end if its parcel is designated for employment or commercial use with no residential permission. Clear every Building Code hurdle you like — without the right zoning, the residential use permit never comes.
How open each city is to as-of-right conversion — converting under existing zoning without a case-by-case application — varies and is shifting fast. Take Toronto: according to the City of Toronto, Council adopted Official Plan Amendment 804 on May 22, 2025 by By-law 477-2025, updating employment-area policy to align with the province’s Bill 97 — and that amendment was then appealed to the Ontario Land Tribunal by a number of landowners. In other words, the conversion rulebook itself is still being contested and rewritten.
So the order of operations is: confirm zoning first (and whether you need a rezoning, official plan amendment or site plan approval), then spend money on a Building Code feasibility study. Reverse it and you risk pouring money into a building the zoning will never let you convert.
🚨If zoning does not permit residential, the best building in the world is still a dead end. Never firm up an offer before you have written confirmation of zoning — or a clear rezoning path. It is the easiest and most expensive order-of-operations mistake to make.
The market picture: real growth, still a sliver
Is conversion a real business yet? The data says: growing, but still a sliver.
According to Statistics Canada, across the six years from 2018 to 2023, conversions of non-residential buildings authorized 12,302 dwelling units Canada-wide, averaging roughly 2,050 a year. The pace then picked up: in January to July 2024, conversions authorized 2,086 units (worth about $278.9 million), versus 1,131 in the same period of 2023 — an increase of about 84% year over year. But in context, new residential construction was authorized for 163,162 units over that same window, so conversions were only about 1.3% of new housing — and more than 81% of conversion permits sat in census metropolitan areas.
A big driver of the momentum is financing. According to a 2024 report by the Canadian Urban Institute, funded by CMHC, Canada leads on residential conversions in large part because of CMHC’s favourable lending terms for multi-unit projects tied to affordability and sustainability.
How to read it: the policy and financing tailwinds are real, but this is not yet a mature, playbook-driven business. You would be entering an early, highly case-by-case field — do not expect an off-the-shelf formula to copy.
A pre-commitment reality check
If a cheap-looking office or warehouse is in front of you right now, here is the order I would work the risks before anyone signs:
1. Check zoning first. Does this parcel allow residential? Will it need a rezoning or official plan amendment? First call, not last.
2. Commission a Part 11 feasibility study from a code consultant. Structure, fire, egress, daylight, ceiling height, plumbing — walked through one by one, before you buy, not after.
3. See the floor plate and the windows yourself. Deep plate plus central core equals dead daylight zones — you can screen out a lot of buildings with your own eyes.
4. Price the mechanical work in. Plumbing, fire, ventilation, sound isolation — this is what eats the spread.
5. If it is industrial, test the soil. Moving from industrial to a more sensitive residential use generally requires a Record of Site Condition under Ontario’s environmental rules; do the contamination due diligence early.
6. Talk to CMHC financing early. For multi-unit, affordable projects, the lending terms can be the piece that makes the whole math work.
The honest summary: the office really is cheap, and the conversion really is hard. Those two facts do not cancel out. The real question is whether this particular building is “hard but doable” or “cheap but impossible.” See that clearly — then commit.
Frequently Asked Questions
Can I just buy a vacant office and turn it into apartments?
Not directly. In Ontario that is a renovation plus a change of major occupancy, so it has to clear Building Code Part 11 — structure, fire separations, egress, daylight and plumbing all re-checked against residential standards — and the parcel has to be zoned to allow housing in the first place. Structure is usually fine; zoning, daylight and plumbing are where most of these deals stall.
Are old warehouses easier to convert than office towers?
Often yes on the building side — warehouses tend to have tall ceilings and wide column grids that suit loft-style units. But they carry a hurdle offices usually don’t: soil and environmental condition. Moving from an industrial use to a more sensitive residential use generally requires a Record of Site Condition under Ontario’s rules, meaning contamination has to be investigated and, if needed, remediated. Do that due diligence early — discovered late, it can undo the whole pro-forma.
What is Ontario Building Code Part 11, and which version is current?
According to the Government of Ontario, the current Building Code is O. Reg. 163/24, in force since January 1, 2025. Part 11 governs the renovation of existing buildings — it grants conditional flexibility for renovating, altering or changing the use of an existing building, while spelling out when you must upgrade to current code (for example, when fire separations or fire-resistance ratings do not conform).
Is converting an office cheaper than building new?
Not necessarily. Conversion saves the main structure and part of the envelope, and can be faster and lower-carbon — but daylight remediation, re-run plumbing, fire upgrades and sound isolation can eat much of that saving. It is highly building-specific: the deciding factors are the frame and the zoning of that particular building, not the broad category of conversion. Price it case by case; averages will mislead you.
Does CMHC finance office-to-residential conversions?
Yes. According to a 2024 report by the Canadian Urban Institute funded by CMHC, favourable CMHC lending terms for multi-unit housing — tied to affordability and sustainability — are a major reason Canada leads on residential conversions. Whether a given project qualifies, and for how much, depends on its unit mix and affordability, so it is worth engaging early.
Arthur Zhao
Real Estate Broker · FRI · ABR · SRS · PSA · MCNE · E-PRO · CLHMS & GUILD Elite · REAIS
VP & Branch Manager, Bay Street Group Inc.
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