London Radon Map: Every Home Health Canada Tested, and What It Read

254 homes across London 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 N5 and N6. The whole province is on the Ontario map.

under 100100 to 147148 to 199200 and aboveno homes tested

254 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

6%
of tested London homes at or above Canada's 200 Bq/m³ action level
60
median reading, Bq/m³
483
highest single reading, in N5P

London sits 29th of the 33 places mapped with a hundred or more tested homes, at 6.3% at or above the action level, between Halifax at 35.2% and Toronto and the GTA at 2.2%. 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 254 homes:

6%
at or above Canada's 200
12%
at or above the US EPA's 148
21%
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
N6P1654841250
N5Y1214802621
N5C12611733032
N6G489722212
N6A66691040
N6J98682011
N5H28410641320
N6E1512621940
N6H3416602832
N5X1217593402
N6B3757720
N6K3419561800
N5R2922533633
N5L66249800
N5V385491080
N5W18848780
N5Z10946980
N5A16134412081
N5P29428394832
N6C1313381120

11 districts have ten or more tested homes, which is where these figures start to mean something. The districts with no measurement at all are N6L, N6M, N6N.

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 483 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.