DIY radon mitigation: what you can and cannot do

What can a homeowner do about radon without a contractor?

Three things, and they are worth doing well: test, seal and monitor. None of them calls for special tools or a trade.

Testing comes first because every later decision hangs on the number. Health Canada recommends a measurement of 3 to 12 months and no less than 91 dayssource, and a homeowner can run that test alone with a mail-in detector. Our guide on testing your own home for radon walks through it.

Sealing comes second, and monitoring runs alongside everything else. Both are covered below, with their limits. What an owner cannot do with a tube of caulking is the thing that lowers a high reading by a large amount, and it helps to be clear about that before a weekend is spent on the basement floor.

Which jobs belong to the owner and which to a professional?

The owner's jobs are the ones that can be checked by looking or by testing. The professional's jobs are the ones where a wrong choice stays hidden. The table sorts the common tasks.

How much can sealing do?

Something, but it should not be relied on for a home that is over the guideline. Health Canada states that sealing entry routes and increasing ventilation have limited effect on their own, and that sub-slab depressurization is the most common and effective methodsource.

The reason is in how the gas arrives. Radon comes in through cracks in foundation floors and walls, construction joints, gaps around service pipes, support posts, window casements, floor drains and sumps, drawn by indoor air pressure that is usually lower than the pressure in the soilsource. Sealing closes some of those paths. It does nothing about the pressure difference, so the house keeps pulling on whichever openings remain, including ones under finished walls, behind the furnace and beneath the bathtub that nobody can reach.

Sealing is still worth an afternoon. A flexible sealant suited to concrete goes into the visible cracks and around pipes where they pass through the slab, and an open sump pit gets a tight lid. A professional would do the same things as part of a full installation, because a tighter slab lets a fan work on the soil and not on the basement air. Our page on sealing and venting a sump pit shows what a serviceable lid looks like.

Sealing and then retesting is a path for a home whose long-term result is already under the guideline, where the owner simply wants it lower: measure before and after with the same method. Above the guideline, do not spend another season finding out. Seal if you wish, and go on to a full system in the time Health Canada recommends. Bear in mind that two winters are never identical, so a small change in either direction may be weather.

Does opening windows or running the ventilation system help?

Only modestly, and at a cost in heat. Health Canada groups extra ventilation with sealing as a measure of limited effect when used alonesource, as quoted in the previous section. An open basement window in January dilutes the air for as long as it stays open, and in a Calgary winter it will not stay open for long.

A heat recovery ventilator that is already in the house should be kept running and maintained, for general air quality. We would not suggest buying one as a radon fix on the strength of anything in our sources. If ventilation changes are part of the answer in a particular house, that is a judgement for someone who has measured it.

What does a real mitigation system involve?

A pipe, a fan and a pressure difference. The national reference for the work is CAN/CGSB-149.12-2024, Radon mitigation options for existing buildingssource.

In the usual version, a hole is cored through the basement slab and a small cavity is cleared in the fill beneath it. A sealed pipe runs from that cavity to a fan that never switches off, and from the fan to the outdoors. The fan keeps the air under the concrete at a slightly lower pressure than the air in the basement, which reverses the direction soil gas wants to travel.

Health Canada reports that such a system can usually be installed in less than a day and reduces radon by more than 80% in most homessource. Those two facts together are the strongest argument against a long do-it-yourself project. The professional version is usually quick. The amateur version is slow, and in both cases the effect is known only once it has been tested. Our page on how a professionally installed radon system works goes through the design step by step.

Why are the fan and the exhaust the hard part?

Because both are design decisions that cannot be checked by looking at the finished work. A fan that is too small for dense soil under the slab may move too little air to reach the whole floor. A fan that is too large wastes electricity, makes noise and can draw heated air out of the basement through gaps in the slab. Picking between them takes a measurement of how air moves under that particular floor.

The exhaust is the other half. The Canadian mitigation standard allows a system to discharge above the roof or through a side wall near ground level, and says side-wall discharge shall be favoured in cold weather areassource. Either way, what leaves the pipe is concentrated soil gas, and where it is released is a design decision made against the standard, not a matter of convenience.

Air in the pipe after the fan is pushed, not pulled, so a leaking joint on that side lets soil gas out instead of drawing room air in. In the layout our installer uses as standard, the fan sits on the pipe inside the basement and the discharge leaves through the rim joist, which means a short length of outlet-side pipe is indoors. How that section is kept short, joined and sealed is a matter for the certified professional, not for guesswork. This is why a certified installer treats pipe joints, fan position and the discharge point as one problem, and why Health Canada recommends hiring a professional certified by C-NRPP for mitigationsource.

What goes wrong with home-built systems?

A short list of avoidable things. We list them without numbers because we have none to cite.

• A fan chosen from an online listing with no idea of the airflow under the slab.
• An ordinary bathroom or duct fan used in place of one built for continuous radon service.
• Pipe joints pushed together dry or taped, and not properly cemented.
• An exhaust that ends in the garage, in the attic or under a deck.
• No gauge on the pipe, so a stopped fan goes unnoticed.
• No follow-up test, so nobody knows what the system achieved.

The last one matters most. A system that hums is not evidence of anything.

If you build one anyway, what must not be skipped?

The standard, the gauge and the test. We do not recommend building a fan-driven system yourself, and this page is not an installation manual. Owners do it all the same, so here is the minimum that honesty requires.

• Obtain and read CAN/CGSB-149.12 before buying parts. It is the document a professional works to.
• Fit a U-tube manometer. The gauge indicates that the system is working when the liquid sits higher on one side, which is the pressure difference created by the fansource.
• Ask the authority that issues permits in your municipality what applies to the electrical and structural parts of the job.
• Run a long-term test in the first heating season after the work, and keep the report.
• Have a certified professional look at it if anything about the reading or the gauge puzzles you.

How do you know whether what you did worked?

By testing again, in the same room, with the same kind of detector. Health Canada recommends testing after a system is installed, every 5 years while it is active, and after any renovation that affects the structure or ventilation of the homesource. That applies to a home-built system at least as much as to a professional one.

A consumer electronic radon monitor is handy here, with a caveat. C-NRPP tests these consumer-grade devices and publishes the models it approves, notes that they cannot be professionally calibrated and are not approved for use by measurement professionals, and advises leaving them in place for at least 3 monthssource. Use one to watch the trend and a laboratory detector to settle the question. The result checker for radon readings will place either number against the guideline.

The line to compare with is 200 Bq/m³ as an annual averagesource, and above it Health Canada recommends bringing the level down within one year, sooner if it is high, and as low as reasonably achievablesource.

When is hiring a professional the better choice?

When the long-term result is above the guideline, when sealing has been tried and measured, or when the house is complicated. Complicated means a crawl space, more than one foundation, in-floor heating, a finished basement with no obvious pipe route, or a builder's pipe stub that needs checking before a fan goes on it. For that last case see what activating a radon rough-in involves.

Doing it yourself saves the labour and keeps the risk. Hiring a certified person costs more and moves the design, the exhaust decision and the proof onto someone trained for them. If you go that way, our checklist for choosing a radon contractor lists the questions to ask.

Whichever route you take, the starting point is identical and it is yours to do: a proper test, a sealed floor and a record of the numbers.