Radon in Ontario Bungalows: Testing and the 200 Bq/m³ Guideline

A bungalow sale in Ontario can close with a thorough home inspection, a clean status on title, and still leave one major indoor-air question unanswered. Radon is a radioactive gas that comes from the breakdown of uranium in soil and rock. Health Canada describes it as invisible, odourless and tasteless, and as the leading cause of lung cancer in non-smokers in Canada. The risk depends on the concentration in indoor air and on how long people are exposed to it.

That matters for bungalow buyers because so much of the living space sits close to the ground. A finished recreation room, a primary bedroom on a slab, a walk-out lower level, or a secondary suite in a raised bungalow can all be lived-in space at or near grade. Neighbouring houses of the same vintage can have very different readings. There is no reliable way to guess the level from the listing photos, the age of the house, or the neighbourhood average. The only way to know is to test.

This is a practical walk-through of the federal guidance that applies in Ontario, how radon tends to show up in one-storey and raised bungalows, and what belongs in a purchase file before anyone treats the issue as settled.

The buyer’s starting point

Most bungalow listings in the Greater Toronto Area, Hamilton, Niagara, Waterloo Region and Barrie do not include a current long-term radon result. Sellers are not required to test as a condition of putting a house on the market. Some owners have already tested, especially after a renovation or after moving into a finished lower level, and a previous result can be a useful starting document. It is not a substitute for a test that reflects how the house is used now.

The question to settle early is not “does this neighbourhood have radon?” Health Canada is clear that uranium is common in the earth’s crust, that radon can be found in almost all Canadian homes, and that concentrations vary from one house to the next, even when the designs look similar and the houses sit next door to each other. The useful questions are: has this house been tested in the lived-in areas, was the test long enough to compare against the federal guideline, and what happens if the result is above that guideline.

Buyers who are downsizing to a bungalow often plan to spend more hours at home, including in a main-floor primary bedroom or a finished lower-level guest room. Families who want one-floor living may also finish or occupy a basement suite. Those patterns increase the amount of time spent in rooms that can accumulate radon, which is why the testing location and the occupancy of each room matter as much as the number on the report.

A short offer window does not change the science. Health Canada’s measurement advice is built around a long-term test, not a 48-hour reading taken during a busy offer period. That tension is one of the practical issues to plan for with a lawyer and, if needed, a certified radon professional, rather than assuming a hurried detector will settle the file.

The rules that apply in Canada

There is no separate Ontario radon statute that sets a different indoor-air limit for houses. The reference buyers and owners work from is the Government of Canada radon guideline. Health Canada recommends that remedial measures be taken if the average annual radon concentration in the normal occupancy area exceeds 200 becquerels per cubic metre (200 Bq/m³).

The same guideline defines the normal occupancy area as any part of the house where a person spends more than four hours per day. A finished basement or a basement apartment counts. An unfinished basement, a crawl space, a furnace room and a storage or laundry area do not, unless someone actually lives or works there for that amount of time. The test should be done in the lowest lived-in level of the home.

When a result is above the guideline, Health Canada recommends taking corrective action to lower the level within one year, and sooner when the concentration is higher. The aim is to reduce the concentration as much as is practicable. The guideline also notes that new buildings should use construction techniques that minimize radon entry and that can help remove radon after the work is finished, if needed. Those construction points are a conversation with the builder or a municipal building official; they do not replace a test in an existing bungalow.

The guide for radon measurements in homes is the document that explains how a result should be produced if it is going to be compared with 200 Bq/m³. Health Canada recommends a long-term test of three to twelve months. A long-term test, in the guide’s definition, lasts at least 91 days, and short-term measurements (less than 91 days) are not appropriate for deciding on mitigation. At least 91 days of the test should fall in the heating season — the colder months when the home’s heating appliances are in use — because indoor levels are typically higher then, and a shorter winter share can underestimate the annual average.

Placement rules in that guide are specific. The detector belongs in a normal occupancy area of the lowest lived-in level, in the typical breathing zone (at least 30 centimetres, or one foot, above the floor), at least 30 centimetres from walls or ceilings, and at least one metre from vents, windows, doors or anything that interferes with normal airflow. It should have space around it, stay out of direct sun and away from heat sources, and not sit in a kitchen, bathroom, laundry room, closet, drawer, sump, crawl space, or next to foundation cracks. Bedrooms on the main floor or in a finished basement are a priority, because people generally spend more time there than in other rooms. If a house has a finished lower level that is lived in, that is usually the level to test first.

For the measurement itself, Health Canada describes two common long-term options in its note on using an electronic radon monitor as a long-term detector: an alpha-track detector, which is sent to a laboratory at the end of the test, and an electronic continuous monitor that can stay in place for months. The department’s advice is to follow the instructions that come with the device. A certified professional listed by the Canadian National Radon Proficiency Program can place a detector, interpret a result, and design a mitigation system if one is needed.

Mitigation, when it is required, is also a professional job in Health Canada’s framing. The department directs people to C-NRPP certified providers to reduce the amount of radon in the home. Typical systems draw soil gas from under the foundation and vent it outdoors, and they can be designed around a basement, a slab-on-grade floor, or a crawl space. The right design depends on the house, which is another reason a neighbouring bungalow’s system is not a template.

How this usually shows up on a bungalow

A one-storey bungalow has a large footprint relative to its height. That means a large area of floor and foundation is in contact with the soil. Health Canada lists the usual entry routes: cracks in foundation floors and walls, construction joints, gaps around service pipes, support posts, window casements, floor drains, sumps, and cavities inside walls. Mid-century Ontario bungalows often have several of those at once — a mix of poured and block foundation, later plumbing penetrations, and a sump added after the fact.

Raised bungalows and bungalows with a finished walk-out lower level add a second lived-in storey that is still partly below or at grade. A recreation room, a bedroom, a home office, or a legal suite on that level is a normal occupancy area if someone spends more than four hours a day there. Testing only the main-floor living room, and ignoring a finished lower level that is actually used, can miss the room that matters most under the federal definition.

Slab-on-grade bungalows, which show up in some post-war and later subdivisions, have no basement at all. The main floor is the lowest lived-in level. Cracks in the slab, poorly sealed control joints, and gaps around drains can still draw soil gas into living space. A buyer should not assume that “no basement” means “no radon question.”

Renovations change the picture. Opening a floor, finishing a basement, adding a suite, or tightening the building envelope can alter how air moves through the house. Health Canada notes that indoor air pressure is usually lower than the pressure in the surrounding soil, which is what draws radon in. A tighter house can still have a high reading; in some cases a tighter envelope makes it more important to test after the work, not less. Buyers who are thinking about a suite should treat radon as part of that plan, alongside the 2026 Ontario rules on secondary suites, rather than as a separate afterthought.

The same house can also test differently after a change in use. A lower level that was storage for years and is now a guest suite has become a normal occupancy area. The old “we never used the basement” history does not answer the guideline question for the new use.

Checks that belong on the property

A home inspection is still essential, and a careful bungalow inspection checklist will pick up moisture, foundation cracks, sump condition, and ventilation problems that belong in the same conversation. It will not measure radon. Unless the inspector is also a C-NRPP measurement professional and has been hired to run a proper long-term test, the inspection report should not be read as a radon clearance.

On the viewing, look at how the lower level is actually used. A furnished recreation room, a bedroom with a closet and a window covering, or a suite with a kitchenette is evidence of occupancy. Ask where people spend their time in winter. Note sumps, floor drains, obvious foundation cracks, and later plumbing or electrical penetrations through the floor — not because those features prove a high reading, but because they are the openings Health Canada lists, and they are also the kind of detail a mitigator will want later.

If a detector is already sitting on a shelf, look at it with the measurement guide in mind. Is it in the lowest lived-in room, at breathing height, away from exterior walls, vents and windows? Or is it in a laundry room, on a windowsill, or in an unused cellar? A poorly placed device can produce a number that is hard to compare with the guideline.

Where the closing timeline is short, talk with the lawyer about how a long-term test can still be built into the deal. Options that sometimes appear in practice include a holdback, a post-closing test with a remediation obligation if the result is above 200 Bq/m³, or a professional assessment that starts as soon as access is granted. None of those arrangements is automatic. They have to be written into the agreement. A two-day detector used only to “get a number for the offer” is not what Health Canada recommends for a comparison with the guideline.

If the result will be used to decide on mitigation, hire a C-NRPP professional rather than relying on a device of unknown quality or a contractor with no radon credential. The certification program exists so that measurement and mitigation follow a consistent standard.

Documents worth requesting

Ask whether any radon test has already been done, and if so, request the actual report rather than a verbal summary. The useful details are the start and end dates, whether at least 91 days fell in the heating season, the room and level where the detector sat, the type of detector, and the result in Bq/m³. A one-week reading from a midsummer open-window period does not answer the same question as a six-month heating-season test in a finished recreation room.

If a mitigation system is already in place, ask for the installer’s report, the C-NRPP credential, the date of installation, and any follow-up measurement that confirmed the system brought the level below the guideline. A pipe running from the floor to the eavestrough is not, on its own, proof that the system was designed or verified. Health Canada also recommends that homes with active mitigation systems be retested every five years to confirm the system is still doing its job.

Renovation invoices for a finished basement, a new suite, or a major air-sealing project help explain whether the house has changed since the last test. A result that predates that work may no longer describe the house you are buying.

None of this paperwork replaces a current, properly placed long-term test if the existing file is thin. It simply tells you whether you are starting from a documented baseline or from a blank page.

Points that are often misread

“The neighbour tested low.” Health Canada’s own wording is that levels vary from house to house, even next door, and that testing is the only way to know. A neighbour’s result is not a measurement of this foundation, this slab, or this finished lower level.

“A short test is good enough if the number is low.” The federal measurement guide is built around a long-term test for comparison with 200 Bq/m³, with a substantial share of the days in the heating season. A brief reading can be a conversation-starter. It is not the protocol the guideline is written around.

“Unfinished basements have to be tested because radon starts there.” The guideline ties testing to normal occupancy. An unused cellar or a furnace room is not the measurement location unless it is actually occupied for more than four hours a day. Once that space is finished and used, the analysis changes.

“A new furnace, new windows, or a ‘tight’ renovation solved it.” Those upgrades can change air movement, but they are not a radon mitigation system and they do not produce a radon result. The house should be tested as it will be lived in.

“Mitigation will ruin the look of a bungalow.” A certified installer can often run a discreet interior pipe to a vent location that is designed for the house. The design is a professional question. It should not be dismissed, or promised, from a hallway glance.

“If the listing does not mention radon, there is no issue.” Absence of a mention is not a test. Many otherwise careful notes on hidden problems in older bungalows still leave indoor radon as a separate measurement, because it cannot be seen on a walk-through.

Questions that come up on viewings

Has a long-term radon test been done in the lowest lived-in level, and can the report be provided with dates, placement and the result in Bq/m³?

How is the lower level used in winter? Is there a bedroom, a suite, or a recreation room where someone spends more than four hours a day?

If a mitigation system is visible, who installed it, when, and was a follow-up test done after installation?

Have the basement, the slab, or the air sealing changed since the last test?

Who will do a new long-term test if the existing file is incomplete, and how will the agreement treat a result above 200 Bq/m³?

Those questions belong alongside the usual ones about foundation movement, moisture, and heating, not in place of them. They also belong in writing. A confident hallway answer is not a measurement report.

A note before you go further

Radon is one of the few bungalow issues that cannot be settled by a flashlight and a good inspector’s report. The federal guideline is clear, the measurement protocol is published, and certified professionals exist to test and, if needed, to reduce the level. What a buyer cannot usefully do is infer the number from the street, the era of the house, or the city.

If you are comparing one-storey homes now, treat a documented long-term test the same way you would treat a survey or a heating-system record: as part of the file, not as an optional extra. Current bungalows listed for sale still have to be judged house by house. The scientific advice from Health Canada is the same in every city: test the lowest lived-in level, compare the result with 200 Bq/m³, and involve a C-NRPP professional when the number, or the gaps in the file, call for it.