Crawl spaces and radon test the room above, not the dirt floor
A crawl space of bare earth or gravel is a direct entry for soil gas. In winter, when the vents are closed and the house draws air, some of that gas rises into the rooms. A vapour barrier laid on the soil without a seal at the walls slows moisture more than it settles radon.
Health Canada compares 200 Bq/m³ with the air of a normally occupied zone. The detector goes in the lower room where someone lives, not only in the middle of the crawl space. A number taken where nobody stays does not describe the exposure.
What actually gets fixed
Mitigation pulls under the membrane or from a low point, then exhausts above the roof. It is not a bathroom fan, and not an air exchanger left to chance. The system is described in how the system works. The air exchanger is a different subject: does it lower radon.
After the work
Retest the same occupied room, over 91 days, with the heat on. After a system.
Reference points: Health Canada, what you need to know about radon and the 200 Bq/m³ guideline. The two-year timeline between 200 and 600, and one year above 600, comes from Health Canada’s guide for radon measurements in homes.
The 4-day test gives a first reading. The 91-day test covers the three-month minimum Health Canada asks for. Both are $59 before tax: shipping, return and the laboratory are included, taxes extra. The PDF report is sent within 2 business days after the laboratory receives the detector.
Above 200 Bq/m³, mitigation is confirmed with a quote. Gaz Radon is C-NRPP certified for measurement and mitigation.
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