Ottawa Radon Map

The RadonTest.ca Ottawa radon map — drawing on a 69,478-test national dataset of measured long-term results — puts Ottawa at 17% of homes at or above Health Canada’s 200 Bq/m³ action guideline (about 1 in 6 homes), with a typical (geometric mean) level of 85.9 Bq/m³. Nationally the figure is 17.8%, and Ontario as a whole reads 15.8%. The highest reading in the Ottawa census division was 1,889 Bq/m³ — over 9× the guideline. Wider in the Ottawa Valley the readings go higher still: 3,165 Bq/m³ in Leeds and Grenville. The ground beneath the area reads 0.76 ppm equivalent uranium on NRCan’s airborne survey.

See Ottawa on the interactive map

Open the Canada Radon Map zoomed to Ottawa → Search a postal code to find your immediate area.

The underlying survey data is public; the RadonTest.ca Canada Radon Map is the free tool that makes it searchable — by province, city and postal code, in English and French, no signup.

Ottawa compared with its province and Canada

Radon around Ottawa, closest areas first

The City of Ottawa census division is the first row. Everything below it is within about an hour’s drive, and the numbers climb sharply as you leave the city — which is the single most useful thing this map tells an Ottawa househunter.

Areas with few tests carry a wider margin of uncertainty — treat small-sample percentages as indicative rather than precise. A 0% reading means no home tested above 200 Bq/m³ among those measured there, not that the area is radon-free.

Ottawa neighbourhoods — Kanata, Barrhaven, Orleans, Nepean, the Glebe — are not reported separately in the 2024 survey, so no measured neighbourhood figure exists for them. Anyone publishing one is modelling, not measuring. The Ottawa census division figure above covers all of them.

The same area at three different thresholds

Canada’s action guideline is 200 Bq/m³. The World Health Organization uses a stricter 100 Bq/m³ reference level, and the US EPA acts at 148 Bq/m³ (4 pCi/L). Measured against each, RadonTest.ca’s Ottawa data reads:

No level of radon is completely risk-free — the risk rises with exposure, which is why the WHO line sits lower than Canada’s. Health Canada recommends acting within a year above 200 Bq/m³, sooner at higher levels.

Why this differs from older Health Canada figures

Health Canada’s 2009–11 national survey put Ontario at about 8.2% of homes at or above 200 Bq/m³, from 3,954 valid tests (2009–11 figures as re-tabulated by the 2024 survey team), with a typical level near 55 Bq/m³. This page uses the 2024 Cross-Canada Survey of Radon — 69,478 long-term tests, the largest residential radon dataset in Canada — which puts Ontario at 15.8% from 7,734 tests, typical level 79 Bq/m³.

Two things differ. First, the sampling: the 2009–11 survey recruited by random digit dialling across 121 health regions and deliberately over-sampled sparsely populated regions for geographic coverage, while the 2024 dataset aggregates long-term tests from homes whose occupants chose to test — which skews toward older housing, ground-contact basements and areas where radon is already a known concern. Second, the weighting: the 2009–11 figures quoted above are the raw, unweighted results. Because that survey deliberately over-sampled some regions, Health Canada also published population-weighted estimates, and its headline national result is 6.9%; the 11.3% raw figure comes from the 2024 survey team’s re-tabulation of the same dataset. None of these numbers is wrong — they answer different questions. For a population-representative estimate of Canadian housing, Health Canada’s weighted 6.9% is the right figure. For the largest body of actual measured results, use this page. Both are shown on the Canada Radon Map, and both can be switched between on the RadonTest.ca map. Full detail on methodology and sources.

Ottawa sits on the edge of some of Canada's worst radon country

The Ottawa-Gatineau metro figure of 17.0% is close to the national average, but Ottawa is unusual: it straddles two provinces and sits at the doorstep of the highest-radon counties in Ontario. Drive an hour west into Renfrew County and the figure is 29.2%. An hour southwest into Lanark, 42.1%. Leeds and Grenville, 31.4%. Lennox and Addington, out past Kingston, 44.7% — the highest census division in Ontario.

The Ottawa census division itself reads 12.0% across 1,349 tests, lower than the metro figure because the metro area includes Gatineau and the Collines-de-l'Outaouais fringe on the Québec side, which reads 44.0%. If you live north of the river, the Québec numbers are the ones that apply to you.

Ottawa Public Health has run radon awareness campaigns and subsidised kit programmes, which is part of why testing density here is among the highest in Ontario. Ontario’s province-wide radon rough-in requirement took effect with the 2024 Building Code for permits applied for on or after 1 January 2025, so a capped sub-slab pipe should be present in homes permitted from 2025 onward — but not in most Ottawa homes standing today.

Which side of the river you live on changes the answer

Ottawa-Gatineau is the only Canadian census metropolitan area split across a provincial boundary, and the two sides are governed differently on radon. On the Ontario side, the 2024 Ontario Building Code carries a province-wide radon rough-in requirement for permits applied for on or after 1 January 2025, and Ontario has radon-specific workplace guidance for employers. On the Québec side the Code de construction du Québec applies — but Québec, unlike Ontario, has no radon-specific workplace exposure limit. On this one point the Ontario side of the river is the more regulated of the two.

The measured numbers differ too. The Ottawa census division reads 12.0% across 1,349 tests. Gatineau reads 16.0% across 313 tests. And Les Collines-de-l'Outaouais, the rural belt immediately north of Gatineau, reads 44.0% across 175 tests — nearly four times the Ottawa figure, twenty minutes' drive away.

The Ottawa Valley is the story

Follow the Ottawa River west and northwest and the numbers climb steeply. Renfrew County, covering Pembroke, Arnprior and Deep River, reads 29.2%. Lanark, covering Carleton Place, Perth and Smiths Falls, reads 42.1% — more than two in five homes above the guideline. These are commuter communities for Ottawa, not remote areas.

The cause is the Precambrian Shield: granites and pegmatites carrying uranium, overlain by thin or permeable soils that let radon migrate freely into basements. The same geology continues southwest through Frontenac (23.4%) toward Kingston, and into Lennox and Addington at 44.7%, the single highest census division in Ontario.

If you are house-hunting in the Ottawa commuter belt, the practical takeaway is that the further from the city core you look, the more a radon test matters — and the more likely it is that an older rural home has no rough-in to connect a fan to.

A map cannot test your home

Every figure on the RadonTest.ca Ottawa radon map is an area figure. Two identical houses on the same street in Ottawa can test very differently, because radon depends on your foundation, your soil, your ventilation and how you live in the house. The map tells you the odds. Only a long-term test tells you your number.

Health Canada recommends a long-term test of at least 91 days, and you can start it any time of year. Ideally at least 91 of those days fall in the heating season (roughly October to April), and there is a simple rule for when they don’t: if your result comes back below 200 Bq/m³ on a mostly-summer test, Health Canada suggests re-testing next heating season, because a summer test can read low. If it comes back above 200, Health Canada says no re-test is needed — act on it. Test your Ottawa home — order a 91-day radon kit →

What to do if your result is above 200 Bq/m³

Health Canada recommends taking corrective action within a year above 200 Bq/m³, and sooner the higher the reading. Most Canadian homes are fixed with sub-slab depressurisation — a pipe running from beneath the foundation slab to a fan that vents above the roofline, which, when properly installed, reduces levels by more than 80% in most homes (Health Canada); results vary by house. In Ontario homes permitted from 1 January 2025, a capped radon rough-in should already be under the slab, which usually reduces the job to connecting a fan to pipe that is already there.

Work should be done by a professional certified through the Canadian National Radon Proficiency Program (C-NRPP), and the home should be re-tested afterwards to confirm the fix worked. You can also look up radon by address or postal code anywhere in Canada on the RadonTest.ca map.

Ottawa radon map — questions

How high is radon in Ottawa?

RadonTest.ca’s Ottawa radon map puts about 17% of Ottawa homes — 1 in 6 — tested at or above Health Canada’s 200 Bq/m³ guideline in the 2024 Cross-Canada Survey of Radon, with a typical level of 85.9 Bq/m³. Against the WHO’s 100 Bq/m³ reference level, 41.6% are over.

What is the highest radon reading recorded in Ottawa?

On the RadonTest.ca map: 1,889 Bq/m³ in the Ottawa census division — over nine times Health Canada’s guideline. Wider in the Ottawa Valley the readings go higher still, reaching 3,165 Bq/m³ in Leeds and Grenville. Readings like that are rare, and no map predicts them; only testing finds them.

Is there a free radon map for Ottawa?

Yes. The RadonTest.ca Canada Radon Map is free and needs no signup, and covers Ottawa at census-division and postal-area level.

Does the map show my street or postal code?

The RadonTest.ca map shows measured results for Ottawa by census division and, for many postal areas, by postal prefix (FSA). It does not show individual addresses — no radon map anywhere does, because radon is measured house by house, not street by street.

Related

• Montreal radon map
• Radon in Ottawa: testing and mitigation
• Ontario radon map
• Canada Radon Map
• Radon in Kingston
• What radon mitigation costs in Ontario
• Radon in Gatineau
• Methodology and data sources

Recommended citation: Ottawa Radon Map, RadonTest.ca, 2026. Data: 2024 Cross-Canada Survey of Radon (v1.1 (CCSR.24.1.1), ISSN 2818-8195). https://radontest.ca/pages/ottawa-radon-map Data licensed CC BY 4.0 — attribution required: “RadonTest.ca Canada Radon Map”.