Toronto and the GTA Radon Map: Every Home Health Canada Tested, and What It Read

416 homes across Toronto and the GTA were long-term tested for radon in the two federal surveys. Every one is a dot on this map, coloured by what it read, with the number of tested homes printed beside every district figure.

The Map

Every dot is one tested house. Zoom in for street names. Shaded districts had no home tested in either survey. This page covers postal districts M, L1, L3 to L7, excluding Barrie's L4M and L4N. The whole province is on the Ontario map.

under 100100 to 147148 to 199200 and aboveno homes tested

416 measurements shown. Dot positions inside a district are illustrative, not addresses. The survey records which district a home was in, never where it stood. Tap any dot for its reading, or any district for its count and median. Rural districts here cover thousands of square kilometres, so a dot in one says very little about any particular corner of it.

Built from Health Canada's published measurements under the Open Government Licence. We do not sell radon testing or mitigation.

What the Numbers Say

2%
of tested Toronto and the GTA homes at or above Canada's 200 Bq/m³ action level
36
median reading, Bq/m³
2,307
highest single reading, in L3K

Toronto and the GTA is the lowest of the 33 places mapped with a hundred or more tested homes, at 2.2%. The highest is Halifax at 35.2%. All on the same two surveys and the same method. The spread between places is real, and the spread between houses on one street is bigger still.

The Number Changes Depending on Whose Limit You Use

Canada acts at 200 Bq/m³. The United States EPA acts at about 148. The World Health Organization sets a reference level of 100. Applied to the same 416 homes:

2%
at or above Canada's 200
7%
at or above the US EPA's 148
14%
at or above the WHO's 100

Same houses, same measurements. Why the three numbers differ, and which one to use.

By Postal District, with the Sample Sizes Shown

Read the count column before the median column. A district resting on four houses is a hint, not a verdict, and those rows are greyed. The land area column matters too: a district covering ten thousand square kilometres is an average across a region, not a neighbourhood.
DistrictLand km²Homes testedMedianHighestAt or over 200
L1G2018581310
L1J2320571730
L1H5715503211
L6H6315481930
L1R2217431490
L1K151434990
L1N3627321840
L7G12812302802

8 districts have ten or more tested homes, which is where these figures start to mean something. The table shows those; 89 districts with thinner samples are on the map but not listed here. 99 districts have no measurement at all and are shaded on the map.

What Actually Settles It

Nothing on this page describes your house. Radon varies enormously between homes on the same street, because it depends on how each building sits on and draws air from the ground beneath it. The highest reading here is 2,307 Bq/m³ and it sits in a district whose median is far below it. A long-term test in your own home is the only measurement that tells you anything about your home.

Also: every C-NRPP certified radon company here, the other city and province maps, and what radon actually is.

Sources and method. Radon measurements: Health Canada, Radon and Thoron Data From Canadian Homes pooled with the Cross-Canada Survey of Radon Concentrations in Homes 2009-2011, both under the Open Government Licence – Canada. Boundaries: Statistics Canada 2021 cartographic forward sortation area file, same licence. Percentages are calculated from the individual measurements shown, not quoted from a summary. Land areas are from the Statistics Canada boundary file.