Radon in a Quebec Condominium (Copropriété): Who Is Responsible, the Syndicate or the Co-owner?

Read this first. This is general information for co-owners, syndicate of co-owners directors, and condo buyers in Quebec, drawn from public sources (Civil Code of Québec, Éducaloi, Régie du bâtiment du Québec, and Health Canada). It is not legal advice. Liability for radon in a co-ownership is a question the courts have not yet settled: the answer depends on your declaration of co-ownership and on the circumstances. For a decision that binds you, consult your declaration and a notary or a lawyer. Radon results are presented against Health Canada's guideline of 200 Bq/m³; RadonTest.ca coordinates the logistics of testing and does not interpret individual results.

The short answer: in most cases, radon is first a matter for the syndicate of co-owners, not the individual co-owner. Why? Because radon enters through the ground and the foundation — that is, in the language of the Civil Code of Québec, through common portions (the ground, the building's main structural works, the pipes that run through the building). And the syndicate's very purpose is to preserve the building and to maintain the common portions (art. 1039 C.C.Q.). That said, this is not an automatic rule: everything depends on the source of the problem, on what your declaration of co-ownership provides, and on whether a high level affects the entire building or a single unit. Here is how to reason through the question, carefully and on solid ground.

Is radon a common portion or a private portion?

This is the real starting question, because in divided co-ownership everything turns on this distinction. The Civil Code of Québec divides the building into two:

• The private portions are "the portions of the buildings and land that are the property of a determinate co-owner and that are for his exclusive use" (art. 1042 C.C.Q.). In plain terms: the interior of your unit.
• The common portions are "the portions of the buildings and land that are owned by all the co-owners and serve for their common use" (art. 1043 C.C.Q.).

And here is the decisive article for radon. Article 1044 C.C.Q. lists what is presumed to be a common portion:

"The following are presumed to be common portions: the ground, yards, verandahs or balconies, parks and gardens, access ways, stairways and elevators, passageways and halls, common service areas, parking and storage areas, the cellars, the main structural works of the buildings and common equipment and apparatus, such as the central heating and air-conditioning systems and the piping and wiring, including that which crosses private portions."

Now connect this to the physics of radon. Radon is a naturally occurring radioactive gas produced by the decay of uranium in the soil and rock. It seeps into a building through the ground, through cracks in the foundation and the slab, through construction joints, and around the pipes that pass through the floor. In other words, radon travels precisely along the elements that article 1044 presumes to be common: the ground, the main structural works (the foundation, the slab, the load-bearing structure), the cellars, and the pipes that cross the units.

The logical consequence is strong: even though radon accumulates inside a unit (a private portion), the entry pathway — ground, slab, foundation — is generally a common portion. A building-wide soil-gas problem is therefore not, in principle, the problem of a single co-owner: it is a common-portion issue.

Bottom line: radon accumulates in the private portion, but it enters through the common portion. It is this distinction that shifts responsibility toward the syndicate in most situations. It is not absolute, however — the nuances are explained below.

What is the role of the syndicate of co-owners under the Civil Code?

As soon as the declaration of co-ownership is published, the collective of co-owners becomes a legal person: the syndicate. Article 1039 C.C.Q. defines its purpose, and every word counts here:

"Upon the publication of the declaration of co-ownership, the co-owners as a body constitute a legal person, the objects of which are to preserve the immovable, to maintain and manage the common portions, to protect the rights appurtenant to the immovable or the co-ownership, and to take all measures of common interest. It shall, in particular, see that the work necessary to preserve and maintain the immovable is carried out."

Three elements of this article point directly to radon:

1. "To preserve the immovable." A gas that seeps in through the foundation and poses a health risk to occupants goes to the preservation and the wholesomeness of the building.
2. "To maintain... the common portions." If radon enters through cracks in the slab or the foundation — which are common portions — their maintenance and sealing are the syndicate's responsibility.
3. "All measures of common interest." Having a building tested for radon is, by its nature, a measure of common interest: a single soil gas potentially concerns every unit in contact with the ground.

Another article reinforces this reasoning. Article 1077 C.C.Q. provides that:

"The syndicate is liable for damage caused to the co-owners or third persons by the faulty design or construction of the immovable or any lack of maintenance of the common portions, without prejudice to any counterclaim."

This is a heavy responsibility: if a high radon level stems from a faulty design or construction (for example, a foundation built without radon protection) or from a lack of maintenance of the common portions (cracks in the slab that were never sealed), the syndicate can be held liable for the damage — subject to then turning against the builder or developer (that is the meaning of "counterclaim").

Finally, article 1066 C.C.Q. specifies that "no co-owner may interfere with the carrying out, even inside his private portion, of work decided on by the syndicate that is necessary for the preservation of the immovable, or of urgent work." This matters in practice: a radon correction (sealing the slab, installing a depressurization pipe under the floor) often requires working inside a ground-floor or basement unit. The Code allows the syndicate to carry out this work, and the co-owner concerned cannot oppose it.

An honest nuance. None of these articles names radon. They establish a framework — preservation of the building, maintenance of the common portions, liability for a defect or lack of maintenance — into which a building-wide radon problem fits naturally. But this is an analysis, not a rule written in black and white that "the syndicate is responsible for radon." How these principles apply to your specific situation depends on your declaration of co-ownership and, in the event of a dispute, on a court's assessment. Confirm with a notary or a lawyer.

And the individual co-owner — where do they fit in?

The co-owner is not out of the picture. Article 1063 C.C.Q. recognizes their right to make use of and enjoy freely their private portion and the common portions, "provided they observe the by-laws of the immovable and do not impair the rights of the other co-owners or the destination of the immovable." With that right come responsibilities, and there are situations where radon shifts, in whole or in part, to the co-owner's side:

• A cause located in the private portion. If a high radon level stems from something the co-owner did inside their unit — for example, unauthorized drilling of the slab, renovations that opened an entry pathway, or the blocking of a ventilation — the argument for assigning them responsibility becomes much stronger.
• A single unit affected, with no apparent common cause. If a single unit shows a high level while the others are low, the line is blurrier. The entry pathway often remains common (the slab, the foundation), but the isolated nature of the problem can feed a debate over how to share the costs. This is exactly the kind of case where the answer is not settled in advance.
• The duty to report. A co-owner who discovers significant water infiltration or a major crack in a common portion has an interest in reporting it to the syndicate. Keeping the information to oneself could, in some cases, be held against them.

What a co-owner generally cannot do alone is correct a high level that originates in the common portions: sealing the slab or installing a depressurization system under the floor is work that affects the main structural works and the building's structure. That goes through the syndicate. On the other hand, any occupant can test the air in their own unit — no authorization is required to place a detector at home and learn their number.

If you are instead a tenant of a condominium unit, or an owner who rents out their condo, the rules of the lease are added to those of co-ownership; our separate guides for renters and for landlords cover those situations.

Table: who is responsible for what?

The following table summarizes the analysis. It is not legal advice: it is how the principles of the Civil Code most often apply, subject to what your declaration of co-ownership provides.

Who pays for radon mitigation in a co-ownership?

When the mitigation involves a common portion — which is the most frequent case for radon — it is paid for by the co-ownership, and therefore divided among all the co-owners. Article 1064 C.C.Q. states the rule:

"Each co-owner contributes to the common expenses in proportion to the relative value of his fraction."

In concrete terms, a mitigation expense aimed at the main structural works (sealing the slab, installing a depressurization system under the floor of a unit in contact with the ground) is a common expense, divided among all the co-owners according to the relative value of their fraction — not only among the occupants of the units that were tested.

Where can the money come from?

• The operating budget. Each year, the board of directors sets, after consulting the meeting of co-owners, the contribution to the common expenses (art. 1072 C.C.Q.). Minor work or a testing program can be provided for there.
• The contingency fund. The syndicate must establish a contingency fund allocated solely to major repairs and the replacement of common portions (art. 1071 C.C.Q.). A substantial correction of the foundation or the slab may draw on this fund.

There is, however, one exception to be aware of. Where common portions are for restricted use (for example, a basement or a yard reserved for the exclusive use of certain co-owners), article 1064 provides that those who have the use of them alone bear the expenses related to their maintenance and routine repairs. Depending on the configuration of your building and the text of your declaration, the sharing of the costs of a localized correction could therefore vary. It is precisely for these borderline cases that you must read the declaration of co-ownership and, if needed, consult a notary.

For an order of magnitude on mitigation costs (which vary depending on whether it is a single unit or a building-wide system), see our guide on the cost of radon mitigation in Canada.

And new condos: the Construction Code and the GCR warranty

If your condominium building is recent, two elements specific to Quebec come into play.

1. The Construction Code requires radon protection. Since June 2, 2022, the Quebec Construction Code (which adopts the modified 2015 National Building Code) imposes soil-gas (radon) protection measures across the entire territory, with no distinction by "risk zones." For residential buildings governed by Part 9 of the Code — that is, as a general rule, those of no more than 3 storeys and no more than 600 m² in building area, which includes many small condominium buildings and low-rise condos — the builder must provide:

• an air-sealing system and a membrane against soil-gas infiltration under the building;
• a layer of permeable granular material under the slab;
• and a vertical, sealed, labelled pipe, installed during construction to allow, if needed, the later connection of an active radon-extraction system.

An important point: this is a passive preparation (a "rough-in"). The Code does not guarantee a low radon result and does not require a test after construction. A new, compliant condo can still show a high level — hence the need to test anyway. (We cover this in more detail in our guide on radon in new homes.)

2. The GCR warranty. New residential buildings held in divided co-ownership (from the single-family condo to the multi-family building) are generally covered by the plan of the Garantie de construction résidentielle (GCR), which provides, among other things, 5 years of protection against faulty design, construction or workmanship and soil defects. The GCR does not name radon as a covered item. The only plausible route would be that of a non-compliance with the Construction Code — for example, if the mandatory radon preparation (s. 9.13.4) had been omitted or poorly installed. A simple high level in a building that was otherwise built by the rules would be much harder to have recognized. To be verified case by case with the GCR and a legal advisor; do not take for granted that radon is "covered."

Unlike Ontario (where the Tarion warranty may, in some cases, cover radon), Quebec therefore relies on prevention at the construction stage rather than on a warranty naming radon. The full provincial context is detailed in our radon in Quebec guide.

How to test a condominium building

Testing a co-ownership is not a matter of placing a single detector in the lobby. Health Canada, in its Guide for Radon Measurements in Public Buildings (which explicitly covers condominium buildings), recommends a priority-based approach:

1. Test every unit in contact with the ground. This means any unit whose floor or wall touches the ground, or that sits above a crawl space, a utility tunnel, or a parking garage. These are the units most likely to show high levels.
2. Add a sample of units on the upper floors. Radon can rise through stairwells, elevator shafts, and utility chases; Health Canada advises also testing a few units higher up to make sure abnormal air movement has not raised the concentrations. The upper floors are generally lower-risk, but not automatically below the guideline.
3. Place the detector at the lowest lived-in level of each unit tested, in a room occupied at least four hours a day, away from windows, exterior doors, and ventilation vents.
4. Use a long-term test. Health Canada recommends a measurement of at least three months (about 91 days), ideally during the heating season (October to April), because radon concentrations vary enormously from one day and one season to the next. A short-term test cannot be used to decide on a correction.

How a syndicate should go about it, concretely:

• Put the topic on the agenda of a meeting of co-owners (or have the board of directors take it on as a measure of common interest).
• Have a testing campaign approved along with its funding (operating budget or contingency fund).
• Order enough detectors to cover all units in contact with the ground, plus a sample higher up.
• Centralize the results: the syndicate keeps the reports, which also forms a useful record in case of a question from a buyer or an insurer.

From a logistics standpoint, testing several units is well handled with a long-term alpha-track kit: each detector is set out for 91 days or more, then returned to the laboratory for analysis. RadonTest.ca can supply multiple kits for a single campaign — each kit includes prepaid return shipping and an option for analysis in Canada.

What to do if a result exceeds 200 Bq/m³

If a unit in the building shows a long-term result at or above 200 Bq/m³, here is the Health Canada framework. The Canadian guideline is 200 Bq/m³ (annual average). There is no radon level considered to be without risk; 200 Bq/m³ is the threshold above which Health Canada recommends taking action. On the timeline, Health Canada recommends taking corrective action to lower the level within one year — and the higher the concentration, the sooner you should act.

For the syndicate, "taking action" means setting the decision-making process in motion: confirming the result if needed, having the situation assessed by a mitigation professional certified C-NRPP (Canadian National Radon Proficiency Program), having the work and its funding approved, then having the system installed. Mitigating a co-ownership almost always goes through active sub-slab depressurization: the soil gas is drawn from beneath the foundation and vented outside before it can enter. After installation, you retest to confirm the system is doing its job.

Our detailed guide on what to do if your radon level is above 200 Bq/m³ explains each step, and our map of Quebec's risk regions shows where vigilance is most warranted.

Order a radon test kit → — all-in, analyzed in Canada, prepaid return shipping. Ideal for testing one unit or, in multiple kits, an entire co-ownership.

Frequently Asked Questions

Is the syndicate of co-owners responsible for radon? Most often, yes — for a building-wide problem. Radon enters through the ground, the foundation, and the slab, which are presumed to be common portions (art. 1044 C.C.Q.), and the syndicate's purpose is to preserve the building and maintain the common portions (art. 1039 C.C.Q.). The syndicate can even be held liable for damage if radon stems from a construction defect or a lack of maintenance of the common portions (art. 1077 C.C.Q.). It is not an automatic rule, however: liability depends on the cause of the problem and on your declaration of co-ownership. Consult a notary or a lawyer for your specific case.

Does the co-owner or the syndicate pay for mitigation? When the mitigation involves a common portion (the usual case for radon), it is a common expense divided among all the co-owners in proportion to the relative value of their fraction (art. 1064 C.C.Q.), funded from the budget or the contingency fund (art. 1071–1072 C.C.Q.). If the cause is in a private portion — for example, work done by a co-owner — the sharing may be different. Common portions for restricted use also follow particular rules. Check your declaration of co-ownership.

Can a co-owner test their condo without the syndicate's authorization? Yes. No authorization is required to place a long-term detector in your own unit and learn your radon concentration. What requires the syndicate's involvement is correcting a high level that originates in the common portions, since the work affects the slab or the foundation.

Do all units in a building have to be tested? Health Canada recommends testing every unit in contact with the ground (ground floor, basement, units above a crawl space or a parking area), plus a sample of units on the upper floors. The upper floors are generally lower-risk, but radon can rise through stairwells and utility chases — no unit is presumed clear without a test.

My condo is new: am I protected against radon? Not necessarily. Since June 2, 2022, the Quebec Construction Code requires a soil-gas preparation in the new homes it covers (generally up to 3 storeys and 600 m²). But it is a passive preparation: the Code does not guarantee a low result and does not require testing after construction. Test anyway.

Does the GCR warranty cover radon? The GCR does not name radon as a covered item. A claim would only be plausible by the route of a non-compliance with the Construction Code (for example, if the mandatory radon preparation had been omitted or poorly installed). A high level in a building that is otherwise compliant would be hard to have recognized. To be verified case by case with the GCR and a legal advisor.

Can the syndicate enter my unit to correct radon? Yes, to the extent the work is necessary for the preservation of the building or is urgent. Article 1066 C.C.Q. provides that no co-owner may interfere with such work, even inside their private portion. The syndicate must, however, give the occupant the required notices.

What radon concentration is acceptable in a co-ownership? There is no level considered to be without risk. Health Canada's guideline is 200 Bq/m³ (annual average): above it, you are advised to act within one year, and sooner if the level is high. The only way to know a unit's concentration is a long-term test of at least 91 days.

In summary

In the vast majority of cases, radon in a co-ownership is a common-portion issue, and therefore a matter for the syndicate: the gas enters through the ground, the foundation, and the slab (presumed common, art. 1044 C.C.Q.), and the syndicate has the duty to preserve the building and maintain the common portions (art. 1039 C.C.Q.). But it is not an absolute certainty: a localized problem, a cause created inside a unit, or the particular text of your declaration of co-ownership can change the analysis. The first step depends on no one but you: test. A co-owner can test their unit without authorization, and a syndicate can organize a building-wide test as a measure of common interest. For a decision that binds you on liability or cost-sharing, read your declaration of co-ownership and consult a notary or a lawyer.

Order your RadonTest.ca kit → — analysis by a C-NRPP–certified laboratory (with an option for analysis entirely in Canada), tracked round-trip shipping, and your result delivered with clear Health Canada context. Available as a single kit or in multiple kits for a co-ownership campaign.

Sources

1. Civil Code of Québec, CQLR c. CCQ-1991 — divided co-ownership: arts. 1038–1039 (establishment; objects of the syndicate), 1042–1045 (private and common portions; presumptions), 1063 (rights of the co-owner), 1064 (common expenses), 1066 (preservation work), 1071–1072 (contingency fund; annual budget), 1077 (liability of the syndicate). LégisQuébec: https://www.legisquebec.gouv.qc.ca/en/document/cs/ccq-1991
2. Éducaloi — Divided Co-ownership (Condominiums): common and private portions, role of the syndicate, declaration of co-ownership. https://educaloi.qc.ca/en/capsules-categories/divided-co-ownership-condominiums/
3. Régie du bâtiment du Québec (RBQ) — Soil-gas (radon) protection measures, in force June 2, 2022, throughout Quebec (Construction Code, Building chapter, based on the modified 2015 NBC). https://www.rbq.gouv.qc.ca/en/areas-of-intervention/building/the-regulations/building-chapter-of-the-construction-code/
4. Garantie de construction résidentielle (GCR) — Applicable protections (1 year poor workmanship / 3 years latent defects / 5 years faulty design, construction or workmanship and soil defects) and technical sheet FT-9.13.4 on radon preparation. https://www.garantiegcr.com/en/buyer/the-protections-that-apply/
5. Health Canada — Radon guideline (200 Bq/m³ guideline; act within 1 year; no level without risk). https://www.canada.ca/en/health-canada/services/health-risks-safety/radiation/radon/government-canada-guidelines-radon.html
6. Health Canada — Guide for Radon Measurements in Public Buildings (covers condominium buildings; test every unit in contact with the ground plus a sample of upper floors; measurement of at least three months). https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/radiation/guide-radon-measurements-public-buildings-schools-hospitals-care-facilities-detention-centres.html

General information and not legal advice. Liability for radon in a co-ownership depends on the facts and on the declaration of co-ownership; confirm with a notary or a lawyer. Radon concentrations are presented against Health Canada's guideline of 200 Bq/m³. Laboratory analysis is performed by a C-NRPP–certified laboratory; RadonTest.ca coordinates the logistics of the kits and does not provide medical, legal, or warranty advice. Details that may change should be confirmed with the responsible body.