Radon

Why it matters here

Radon comes from uranium decay in soil and rock, and it enters through the foundation — cracks, the slab-to-wall joint, sump pits, floor drains and service penetrations.

Levels vary dramatically between adjacent houses, so a neighbour result tells you nothing about yours.

A tighter house concentrates it, which means energy retrofits can raise levels in a house that was previously fine.

It is highest in the lowest occupied level, which in Toronto means basements and basement apartments.

It is highest in winter, when the house is closed and the stack effect draws from the ground.

And it is a recognized cause of lung cancer, which is why Health Canada publishes a guideline and recommends testing.

Long-term, not short-term

Radon levels fluctuate daily and seasonally, so a two-day test tells you very little. The recommendation is a test of at least three months, during the heating season, in the lowest regularly occupied level. Short-term tests are useful only for a quick screen or a real estate timeline, and a high short-term result should be followed by a long-term one.

Doing the test

A long-term alpha track detector, which is inexpensive and widely available including from lung health organizations and hardware suppliers.

Placed in the lowest regularly occupied level — a finished basement, a basement bedroom, a basement apartment.

Not in a crawlspace, a utility room, a bathroom or a kitchen.

Left in place for at least three months, during the heating season.

Returned to the laboratory, which issues a result against the Canadian guideline.

And retested after any major renovation, air sealing work or change to the heating and ventilation, because those can change the level.

If the level is high

The standard mitigation is active sub-slab depressurization: a pipe through the slab into the gravel below, with a fan drawing the gas out and venting it above the roof.

It is a known and well-proven technique and it typically reduces levels substantially.

Sealing cracks and the sump helps and is not sufficient on its own.

Use a certified radon mitigation professional, because the detail — where the suction point goes, the fan sizing, the vent termination — decides whether it works.

Retest after mitigation to confirm the result.

And the cost is comparable to other household mechanical work rather than to a renovation, which surprises people.