Section 01
The protocol, stated plainly
Health Canada advises testing a home with a long-term measurement of three to twelve months, and states a minimum measurement period of ninety-one days. The detector is placed on the lowest level of the home that is lived in and normally occupied — the level where people spend time, not an unused crawl space or a sealed mechanical room. The department's measurement guide for residential dwellings sets out the detail of placement and reporting.
Follow the current published instructions rather than a remembered version of them, and record the start date, end date, device type, laboratory and placement with the result. A result without its method is not evidence; it is a number.
Health Canada's current long-term protocol is 3–12 months with a minimum of 91 days, on the lowest lived-in, normally occupied level.
Section 02
The Canadian guideline and how to state it
Health Canada states a Canadian guideline of 200 becquerels per cubic metre (200 Bq/m³) for radon in indoor air in dwellings. Cite it with the units, with the source, and with the measurement context, because the guideline is meaningful only against a measurement taken to the protocol.
This page does not interpret any result. What a measured concentration means for a particular household, and what should be done about it, is a matter for the current Health Canada guidance and for qualified radon professionals, not for editorial material.
Section 03
Why a closing-period test is not an authoritative answer
Short-duration devices exist and are sometimes used for screening, but a result taken over days sits inside the natural variation that the long-term protocol is designed to average out. Turning such a reading into a pass or a fail misrepresents what it can support, in either direction.
The practical consequence for a transaction is to treat radon as an ownership-period item. Buy the house on the evidence available, begin a long-term measurement after possession, and keep the result in the property file. If a seller already holds a long-term result, request it with its full method and dates rather than the headline figure.
Section 04
Documented: what a radon record actually contains
A defensible record contains the device type and serial identification, the exact placement including level and room, the start and end dates, the laboratory or analysis provider, the reported concentration with units, and any note about conditions during the measurement period such as an unoccupied stretch or major renovation work.
Where mitigation has been carried out, the record should also contain the contractor, the system description, the installation date, any related permits for associated mechanical or electrical work, and a post-mitigation measurement taken to the protocol. A mitigation invoice without a subsequent measurement leaves the important question unanswered.
Section 05
Not documented: what radon evidence cannot support
A measurement belongs to the dwelling measured, over the period measured. It does not establish a concentration in a neighbouring property, a street, a community or a segment of the market, and this atlas publishes no local prevalence rate, risk rate or area comparison because no such claim can be supported here.
A result also does not diagnose health, and nothing on this page interprets a medical question. Health effects and personal risk are matters for Health Canada's own material and for a physician, never for a property publication.
No neighbourhood, community or market-segment radon claim is made anywhere on this site.
Section 06
The evidence request list and the ownership plan
Request from the seller: any long-term radon measurement report with device, placement, dates, laboratory and result; any mitigation system documentation with installation date and contractor; any permits associated with mitigation work; and post-mitigation measurement reports.
Plan for yourself: begin a long-term measurement early in ownership, follow the current Health Canada instructions for placement and duration, and retain the report in the handover file. Repeat measurement after significant renovation, after changes to ventilation or the foundation, and after any mitigation work, because each of those can change conditions inside the dwelling.
Section 07
Escalation: who answers what
Health Canada answers what the protocol is and what the Canadian guideline is. A certified radon measurement professional answers how to measure a complex dwelling correctly, and a certified radon mitigation professional answers what a system for that building would involve. A qualified mechanical contractor answers questions about ventilation equipment, and a physician answers health questions.
This guide answers only one thing: what documentary evidence should exist, how it should be described, and where it belongs in the file. It draws no conclusion about any dwelling.