Radon testing

Radon is a radioactive gas from uranium breaking down in soil and rock. It seeps into a house through floor cracks, the gap where slab meets wall, floor drains, sump pits and the holes cut for pipes, then builds up in the lowest level. You cannot see it, smell it or taste it, and your neighbour's result tells you nothing useful about yours.

The number that matters is 200 becquerels per cubic metre. That is the Canadian guideline, and Health Canada applies it to the normal occupancy area, which it defines as any part of the building where a person is likely to spend more than four hours a day (Health Canada, Government of Canada radon guideline). Above 200, the advice is to lower the level within one year, sooner the higher the reading. Health Canada also says plainly that no level is risk free, so a result of 150 is good news rather than a certificate.

Step one: choose the level and the room. The detector goes on the lowest level someone actually uses, which in most Ottawa houses is a finished basement family room or office. If the basement is unfinished storage and nobody spends four hours down there, the test belongs on the first floor. Kitchens, bathrooms and laundry rooms are ruled out because humidity and exhaust fans skew the reading.

Step two: place it properly. Health Canada's measurement guide asks for the detector at least 30 cm above the floor, at least 30 cm from an exterior wall, and at least 1 m from vents, windows and doors (Health Canada, Guide for radon measurements in residential dwellings). A shelf or a plant hanger works. A spot on the floor beside the sump does not.

Step three: leave it for at least 91 days, in the heating season. The guide calls for a minimum of 91 days, and 3 to 12 months gives a better annual average. It also asks that the measurement fall in the heating season, when windows are shut and the furnace pulls soil gas up through the slab. Starting in October or early November suits Ottawa well, because the test then covers the coldest and tightest months of the year.

Step four: log the dates and post it the day it finishes. The lab needs exact start and end dates to calculate an average, and most detectors lose accuracy once the period is over.

How long it takes. Placement is a 20 to 30 minute visit. The measurement is 91 days at the shortest, and lab turnaround adds one to three weeks. Plan on roughly four months from the day you start to a number you can act on. A short-term test of 2 to 7 days exists for real estate deadlines and works as a screening flag, but it swings with weather and gives you no annual average.

What it costs in Ottawa in 2026. These are indicative ranges rather than quotes. A do-it-yourself long-term kit including the lab fee generally runs about $40 to $80, and Ottawa Public Health lists retail kit prices from roughly $29 to $170 (Ottawa Public Health, Radon in your home). A long-term test placed and collected by a certified professional is more like $150 to $300, because you are paying for a site visit, correct placement and a written interpretation. A short-term test for a purchase is usually $100 to $400. The drivers are the number of detectors, whether anyone drives out, and how fast the lab is asked to report.

What makes an Ottawa house different. Two studies give two pictures of this city and both are worth knowing. Health Canada's Cross-Canada Survey, using three-month detectors in the winters of 2009-10 and 2010-11, found 6.2% of the 64 homes tested in the City of Ottawa health unit above 200 Bq/m3 (final report, 2012). The Evict Radon national study, a much larger volunteer sample covering the whole Ottawa-Gatineau metro area, reports about 1 in 6 properties at or above the guideline (Evict Radon). They sampled different areas in different ways, so read them as a range rather than a contradiction.

Geology varies sharply across the city. Parts of Kanata and the west end sit close to shallow bedrock, while much of Barrhaven, Riverside South and Orleans is built on deep Champlain Sea clay with a granular pad under the slab. That pad helps a later repair, because it lets a fan draw across the whole footprint, but it also moves soil gas efficiently toward the one crack in your floor. Newer subdivisions are tighter and better sealed, which can raise indoor concentrations rather than lower them. House age predicts nothing in either direction.

Who should do the work. Nobody needs a licence to open a mail-in kit, and for a straightforward house that is a sound choice. Health Canada recommends a professional certified under the Canadian National Radon Proficiency Program when you want a measurement you can hand to a buyer, a lender or an insurer, or when the house is large, split-level or has several slab areas. C-NRPP certification comes in separate measurement and mitigation streams, and you can check a person's status on the C-NRPP certification check page.

What to ask before you hire. Are you C-NRPP certified for measurement, and what is your certificate number. Which lab processes the detector. How many detectors are you placing and where. Will the report state the start date, the end date, the placement height and the level of the house. If the result comes back high, do you also sell mitigation, and who arranges the independent follow-up test. Get the answers on the quote rather than over the phone.

A test measures one spot over one window of time, so a retest after major work is worth the small cost.