Reducing radon
When to act
The Canadian guideline is the one the map already displays: above 200 Bq/m³, Health Canada recommends mitigation; between 100 and 200 Bq/m³, it is worth monitoring — re-measure or consider a long-term test, with no urgency; under 100 Bq/m³, it is acceptable. (Health Canada)
The standard approach: sub-slab depressurization
The reference technique is sub-slab depressurization: a pipe runs through the concrete slab and a fan continuously draws the gas from the soil under the house, venting it outside before it can enter the living spaces. Depending on the configuration, complementary techniques are added: crawl-space ventilation, sealing cracks and joints around entry points. Sealing is a useful complement — never a solution on its own. (WHO) (EPA)
Effectiveness
A passive system, without a fan, can reduce indoor radon levels by more than 50%; an active system, with a fan, achieves even greater reductions. Whatever the technique, the result is only established by measuring again (see below). (WHO)
Cost: an indicative range
As a rough guide, having a system installed by a professional typically costs $500 to $3,000 depending on the house’s configuration and the technique used. That is a planning range, not a quote — every house is different, and the best anticipated cost is the one a professional gives after seeing yours.
Certified professionals
In Canada, radon professionals’ proficiency is certified by the C-NRPP — the Canadian National Radon Proficiency Program. For a system installed to professional standards, use the official directories of certified professionals. (C-NRPP) (— Take Action on Radon)
Re-measuring after mitigation
A mitigation is only confirmed by a new long-term measurement — 91 days or more, the same protocol as the initial test. On the map, post-mitigation measurements appear in the “800 (45)” format: the value before the work, followed in parentheses by the value measured after — the legend’s convention, which keeps visible both the corrected problem and the proof that it can be corrected.
New construction
In a new house, a mitigation rough-in can be installed during construction: the pipe through the slab is put in place, ready to be connected to a fan if a measurement later reveals a high concentration. That is far simpler and less expensive than breaking into a finished slab. (C-NRPP)