In Canada, radon in a rental or multi-unit residential building sits in an awkward gap: there is no radon-specific law naming the landlord, but several duties reach the building anyway — through residential tenancy law, public health powers, occupational health and safety where staff work on site, and, from January 30, 2027, through federally regulated tenants who now carry their own binding exposure limit.
This guide sets out who owes what, what Health Canada's protocol actually requires for multi-unit buildings, and where the practical exposure lies.
TL;DR: No Canadian jurisdiction requires landlords to test for radon. But Health Canada's guideline of 200 Bq/m³ applies to all indoor spaces; tenancy legislation requires rental premises to be fit for habitation; building staff are workers owed a duty; and a federally regulated commercial tenant now has a legal limit it cannot meet without testing the space you own. Health Canada's protocol for multi-unit buildings requires testing every ground-contact unit, not a sample.
The four duties that reach a rental building
1. Habitability. Provincial and territorial residential tenancy legislation requires landlords to maintain rental premises in a state fit for habitation and compliant with health and safety standards. None of these statutes mention radon, but they are written broadly and radon is a recognized carcinogen with a national guideline.
2. Public health powers. Medical health officers hold broad powers to address health hazards in premises. British Columbia's Interior Health used exactly this kind of authority in 2017 to order radon testing in childcare facilities in its region. The same category of power exists across the country.
3. Occupational health and safety. Building superintendents, maintenance staff, cleaners and office personnel are workers. Where they spend more than four hours a day in ground-contact areas — basement offices, maintenance shops, laundry and mechanical rooms — the applicable OHS regime's general duty applies to that space.
4. Your commercial tenants' obligations. This is the new one. From January 30, 2027, a federally regulated employer — a bank branch, a telecom office, a courier depot, a Crown corporation — must ensure its employees are not exposed above 200 Bq/m³ as an annual average. That employer is the duty holder, not you. But the employer cannot discharge that duty without testing a building you own and control, which makes it your conversation whether you initiated it or not.
The tenant-versus-landlord question, settled
The amended federal wording resolves an argument that used to run both ways. The previous text said no employee "shall be exposed"; the current text says "the employer must ensure." The federally regulated employer is now the named duty holder, whether it owns the building or leases space in it.
That does not make the landlord irrelevant. It makes coordination necessary, because radon does not respect lease boundaries. It enters through the foundation and distributes through the structure. A tenant testing only its own third-floor suite may get a reassuring number that says nothing about occupants below — which is why Health Canada's guidance is to test a building in its entirety.
Practically: where a federal tenant occupies a whole building, the whole building is in scope. Where it occupies part, that part is in scope, but a partial picture is a weak basis for "ensuring" anything. Whether duties also fall on the landlord depends on the lease — access, alterations, maintenance obligations, and compliance clauses — and that is a question for your own legal advisor.
What Health Canada's protocol requires for multi-unit buildings
Health Canada's Guide for Radon Measurements in Public Buildings covers multi-unit residential dwellings explicitly — apartments, condominiums, co-ops, townhouses, dormitories, boarding houses, hotels and motels, and live/work units. The guidance is that these protocols should be applied to the whole building where practicable, regardless of whether different portions are owned by different parties.
The requirements that surprise people:
- Every ground-contact unit is measured — not a sample. Conduct a measurement in each dwelling unit that is a ground-contact apartment or dwelling, and other occupied units such as office space. This includes any unit with floors or walls in contact with the ground, or sitting over a crawl space, utility tunnel or parking garage.
- Upper floors get a sample. Consideration should be given to testing a sampling of units on upper floors to check for unusual airflows — elevator shafts, service shafts and stack effect can carry radon upward.
- Within each unit, test a room on the lowest livable level in ground contact (or above a crawlspace, tunnel or garage) that is used four hours a day or more.
- Long-term measurement — minimum three months, during the heating season.
- Quality control — duplicate detectors at 10% of locations, plus blanks.
A building with 30 ground-contact units therefore needs roughly 33 detectors once quality control is included, not one or two. Detector-count logic by building type is in our guide to commercial radon testing.
"One of my tenants is asking about radon" — what to do
This is how it usually starts. A single tenant reads something, or tests their own unit, and asks the property manager a question. The instinct is to put a detector in that unit and answer them.
That instinct produces the worst of both worlds: it costs money, it takes three months, and whatever number comes back tells you about one unit and commits you to nothing you can rely on. If the result is high you now have a disclosed problem and no context. If it is low you have told one tenant they are fine and learned nothing about the other thirty-nine.
The better answer is to test the building. Health Canada's protocol for multi-unit residential dwellings works from the bottom up: measure every dwelling unit in ground contact — including units over crawl spaces, utility tunnels or parking garages — and then sample units on upper floors to check for unusual airflows through elevator and service shafts or stack effect. Within each unit, the detector goes in a room on the lowest livable level in ground contact that is used four hours a day or more.
A worked example: four storeys, ten units per floor
| Level | What gets measured | Detectors |
|---|---|---|
| Ground floor (10 units, in ground contact) | Every unit | 10 |
| Floors 2–4 (30 units) | A strategic sample to check for upward movement — typically units above shafts, near elevators, and a spread across the footprint | Sample, sized to the building |
| Common and staffed areas in ground contact | Laundry, storage-adjacent offices, mechanical rooms, superintendent's office — anywhere staff spend four hours a day or more | As applicable |
| Quality control | Duplicates at 10% of locations, plus blanks | Additional |
For a building of that size the total is comfortably into the twenties, not one. That is the honest cost of being able to answer the question properly — and it is still a fraction of what a single mitigation job costs.
The point a property manager should hold onto: what you need to be able to demonstrate is that you captured the entire building, not one unit. A building-wide measurement answers every tenant who asks, this year and for the next several. A single-unit test answers one tenant, once, and leaves the question open for everyone else.
Why partial testing creates a false sense of security
Radon levels vary substantially between units in the same building. Measured results routinely differ from unit to unit and from one side of a building to the other — driven by soil conditions beneath that part of the foundation, foundation penetrations, and how air moves through the structure.
The practical consequence for a property manager is that a good result in one unit is evidence about that unit and nothing else. A documented building-wide measurement is a defensible position; a spot check is not.
What the record has to contain
Whoever performs the testing, the record is what you will be asked for later — by a tenant, a purchaser, an insurer or a regulator. Where the building houses a federally regulated employer, the regulations specify the content of a test record: the date, time and location of the test; the substance tested for; the sampling and testing method; the result; and the name and occupation of the person who made the test. A one-page laboratory certificate supplies only the result.
For a multi-unit building that means a per-unit placement log, not a single summary sheet. Reconstructing which detector was in which unit two years after the fact is the situation the record exists to prevent.
Disclosure, and the question tenants are starting to ask
Radon awareness is rising, and prospective tenants and buyers increasingly ask whether a building has been tested. Where a landlord or property manager holds a known elevated result, disclosure obligations may arise under provincial rules on latent defects and material facts — the specifics vary by province and by whether the transaction is a tenancy or a sale, and it is worth getting advice on your jurisdiction rather than assuming.
The awkward position is not having tested. It is having tested, found an elevated result, and done nothing documented about it.
If a result exceeds 200 Bq/m³
Health Canada recommends remedial action within two years for results between 200 and 600 Bq/m³, and within one year above 600 Bq/m³, carried out by certified mitigation professionals, with retesting to confirm the reduction. Responsibility for remediation and its cost rests with the building owner. In multi-unit buildings, mitigation design is more involved than in a single home — sub-slab depressurization has to account for the whole footprint and the building's ventilation — which is a reason to involve a certified professional early.
When does a building need retesting?
There is no fixed interval for a building that tested below the guideline. The trigger is change: renovation, modified or rebalanced HVAC, altered airflow, a change in occupancy or in how ground-contact rooms are used, or anything affecting how the building meets the soil. In multi-unit buildings that list is hit more often than owners expect — a laundry converted to storage, a superintendent's office relocated to a basement, a ventilation retrofit, or a unit turned into an office all raise the question. Mitigated buildings are retested after the work and rechecked every five years. That interval comes from Health Canada's residential guidance; the public-buildings guide sets no post-mitigation retest interval, so it is applied to workplaces by extension rather than by rule.
Building services and ventilation: radon, HVAC and ventilation.
Common questions
Are landlords required to test for radon in Canada?
No jurisdiction imposes a radon-specific testing requirement on landlords. Habitability duties under tenancy legislation, public health powers, and OHS duties to building staff all reach the building, and Health Canada recommends testing all indoor spaces.
Who is responsible if a federally regulated tenant needs a radon test?
The employer is the named duty holder under the amended federal regulations. But the test happens in your building, so access, timing and often cost become a landlord conversation. Check what your lease says about compliance and access.
Can we test one unit and apply the result to the building?
No. Health Canada's protocol calls for measuring every ground-contact unit, with a sample of upper-floor units. Levels vary between units in the same building.
Does a condominium corporation have duties?
Common elements and any staffed areas fall to the corporation; individual units are more complex and depend on the declaration and provincial condominium legislation. Worth specific advice.
When should a multi-unit building be tested?
Detectors placed in the fall, measured over at least three months of the heating season. Coordinating access across many units is the main scheduling constraint, so plan earlier than you think you need to.
Read next
How commercial radon testing works · Which rules apply to your workplace · The workplace radon legal brief · Canada radon map
RadonTest.ca provides testing logistics and laboratory submission. We do not perform radon mitigation and we do not interpret health risk — Health Canada is the health authority on radon in Canada. This page describes publicly available regulatory information and is not legal advice; tenancy, condominium and disclosure obligations vary by province and warrant advice on your specific circumstances.
Sources
Health Canada, Guide for Radon Measurements in Public Buildings, §5.3 (multi-unit residential dwellings); Health Canada, Canadian radon guideline; Canada Gazette, Part II, Vol. 160, No. 3 (SOR/2026-10); Community Care and Assisted Living Act, S.B.C. 2002, c. 75; CCOHS, Radon in Buildings.