A pipe and a fan that take soil gas from under the floor and vent it above the roof. A day's work in most houses, and it routinely removes most of the radon.
The standard fix is called sub-slab depressurization. A hole is cut in the basement floor slab, a pipe is run from the gravel or soil beneath it up through the house or along an outside wall, and a continuously running fan draws soil gas up that pipe and discharges it above the roofline, where it disperses harmlessly.
The point is not to filter anything. It is to make the space under the slab lower pressure than the house, so soil gas goes up the pipe instead of in through the floor.
In a typical house with a basement, one working day. A core hole in the slab, some pipe, a fan usually mounted outside or in an attic, an electrical connection, and sealing around the obvious entry points. It is not structural work and it does not require anyone to move out.
Houses with crawlspaces, multiple slabs, or additions on different foundations are more involved, and that is where quotes start to differ.
Costs in Canada vary with the house rather than with the going rate: foundation type, how far the pipe has to travel, whether the fan can be mounted easily, and whether more than one suction point is needed. Get more than one quote from C-NRPP certified companies, and compare what is included rather than the headline number.
The fan runs continuously and uses a modest amount of electricity, which is a real but small ongoing cost.
Yes, and reliably. A properly installed system routinely cuts levels by most of the way, and the only way to know what yours achieved is to measure again afterwards. Insist on that.
Do not panic, and do get it fixed. Radon risk is cumulative over years, so a high reading does not mean anything is happening to you this week. Health Canada suggests acting within two years for readings between 200 and 600 Bq/m3, and within a year above 600. Get two or three quotes from certified mitigation companies.
There is no rule. It is negotiated like any other condition and it goes all three ways depending on the market and how the inspection was worded. Knowing the actual cost early helps, because a number turns an open-ended worry into an ordinary line item.
It lowers readings while they are open and the effect stops when you close them. In a Canadian winter that is not a plan. It is also why a test taken during a week of open windows understates the house.
No. Radon comes in continuously from the ground, so cleaning the air already in the room does not address the source. Neither do plants. Venting soil gas before it enters is what works.
Building codes in much of Canada now require a rough-in for a radon system in new homes, which makes installing one later far cheaper. If you are building, ask whether the rough-in is included and where it terminates. Some certified companies do this work specifically.
Sources. Health Canada radon guidance and published measurement data; the 2024 Cross-Canada Survey of Radon; World Health Organization Handbook on Indoor Radon; United States Environmental Protection Agency; Canadian National Radon Proficiency Program. Costs described are general ranges, not quotes.