Is radon an issue in Ottawa?

Yes. The 2024 Cross-Canada Survey of Radon Exposure found 17.0 per cent of Ottawa-Gatineau houses at or above Health Canada's guideline of 200 Bq/m3, with an average of 85.9 Bq/m3. In Take Action on Radon's winter 2021 challenge, 18 per cent of 335 Ottawa homes tested over 200. Ottawa Public Health says levels vary a great deal within the city, so only a test tells you about your house.

Is it worth getting a radon test?

Health Canada recommends that every home be tested, whatever its age, type or location, and even if it already has a mitigation system. It calls radon the number one cause of lung cancer in non-smokers in Canada. Ottawa Public Health puts the cost of testing at $29 to $170, and a long-term test is the only way to know your level.

What is the safe radon level in Canada?

Canada's guideline is 200 becquerels per cubic metre (Bq/m3), averaged over a long-term test in a room someone uses more than 4 hours a day. Health Canada says the risk below the guideline is small but that no level is considered risk free, and that how much exposure to accept is each homeowner's choice.

What month is radon the highest, and is it worse in winter?

Health Canada says indoor radon is typically higher in the colder months, because windows and doors stay closed and the stack effect draws more soil gas into a heated house. That is why it wants at least 91 days of a test to fall in the heating season. In Ottawa, a detector placed in late October or November covers that easily.

What time of day is radon highest? Does it go up at night?

Radon rises and falls through the day, and Health Canada lists daily and seasonal swings among the reasons a short reading misleads. That is also why an hourly or overnight spike on a digital monitor does not count against the guideline. Health Canada says decisions rest on the long-term average of at least 91 days, not on any one hour.

Does opening windows reduce radon?

It dilutes radon while they are open, which is why a short test is run with them shut, but it is no fix for an Ottawa winter. Health Canada says a balanced HRV or ERV run continuously lowers radon by only 20 to 50 per cent, and active soil depressurization by more than 90 per cent.

Do air purifiers or HEPA filters clear out radon?

Health Canada does not list air purifiers or filters among its ways to reduce radon. Its methods are active soil depressurization, which pulls soil gas from under the slab and vents it outside, balanced ventilation with an HRV or ERV, and sealing cracks and gaps. If a test is high, the fix it recommends is a system designed by a C-NRPP certified mitigation professional.

What are the signs of radon in a house?

There are none you can see or smell. Health Canada describes radon as invisible, odourless and tasteless, and the health risk it names is lung cancer after long exposure, not short-term symptoms. A long-term test is the only way to find it.

How long before radon makes you sick?

Health Canada does not give a time. It says the risk of lung cancer depends on the radon level and how long a person is exposed, and that smoking and radon together raise the risk significantly. Ottawa Public Health adds second-hand smoke to that list. Questions about your own health belong with your doctor; the test tells you the level in your home.

Can you be in the house during a radon test?

Yes. For a long-term test Health Canada says residents should not change how they live, because the goal is your normal exposure. The rules about keeping windows shut and limiting the dryer, range hood and bathroom fans apply to short professional tests: C-NRPP sets closed-house conditions for 12 hours before a test of under 4 days, and a test run with them broken is void.

What ruins a radon test?

Health Canada lists these: placing the detector on the floor, against an outside wall, in a closet or drawer, near a vent, door, window, sump pit or foundation crack, beside a router or television, in sun or near heat, or in a humid room. A dropped or damaged detector, a passive kit used past its expiry date, and a test shorter than 91 days all need a new test.

Does radon in the basement go upstairs?

It can. Health Canada says levels are typically highest in basements and crawl spaces but elevated levels can be found throughout a home, and even apartments above the ground floor should be tested. Test on the lowest level someone uses for 4 hours a day: a basement bedroom, office or playroom if there is one, otherwise the main floor.

Is it okay to sleep in a basement with radon?

Test that bedroom first. Health Canada tells you to prioritize bedrooms on the main floor or in the basement, because people spend more time there than in any other room. If the long-term result is above 200 Bq/m3, it recommends fixing it within a year; below that, the risk is small but not zero.

Is a radon level of 2.9, 4.8 or 1.7 high?

Those readings are in picocuries per litre, the US unit. Health Canada gives the conversion: 1 pCi/L equals 37 Bq/m3. So 1.7 pCi/L is about 63 Bq/m3, 2.9 is about 107, 3.5 is about 130, 4.8 is about 178 and 5.2 is about 192. All are under Canada's 200 guideline, which is about 5.4 pCi/L. The table on this page covers more readings and what C-NRPP suggests for each band.

How do I prepare for a radon inspection?

For a long-term test, live normally and leave the detector where it was placed. For a short professional test, C-NRPP asks for closed windows, outside doors used only to come and go, no fireplace unless it is your main heat, and as little dryer, range hood and bathroom fan use as possible, starting 12 hours before. For a mitigation quote, expect small test holes in the slab.

What is the fastest way to get rid of radon, and does it work?

Active soil depressurization. Health Canada says a system can usually be installed in less than a day and typically cuts radon by more than 90 per cent. Radon can creep back if the fan stops or the house changes, so C-NRPP calls for a short test after installation, a long-term test the next heating season, and a retest at least every five years.

Where in Canada and Ontario is radon highest?

The 2024 Cross-Canada survey names Atlantic Canada, the Prairies, the North and the BC Interior as the regions where high indoor radon is more common, and lists Thunder Bay and Kingston among Ontario cities where a quarter to half of homes are at or above 200 Bq/m3. Near Ottawa, Health Canada's 2012 survey found 19.4 per cent of tested homes over 200 in the Leeds, Grenville and Lanark health unit.

What makes a house more likely to have radon?

The 2024 survey found single-detached houses more likely to be at or above 200 Bq/m3 than semi-detached ones, and semis more likely than row houses, with rural homes above urban ones. Ottawa Public Health adds homes made more airtight without enough fresh air. Neighbours still differ: Health Canada says two similar houses side by side can test very differently.

Where does radon in a house come from?

Mostly from the soil. Health Canada says soil gas is the largest source, entering through construction joints, gaps around pipes and posts, floor drains, sumps and cracks in the slab and walls. Radon from a private well can add some, but Health Canada says to test the air and fix soil gas first.

Is the radon risk overblown?

Health Canada puts it plainly: radon is the number one cause of lung cancer for non-smokers in Canada, and no level is risk free. It also says the risk below 200 Bq/m3 is small, and that an individual's risk depends on the level and the years of exposure. A test tells you which side of the guideline your home is on.

What does a radon test kit look like?

Most are a small passive detector, an alpha track device, that sits on a shelf for three months or more and then goes back to a lab in the mail. The other kind is an electronic radon monitor that shows a running reading on a screen or phone. Health Canada recommends either, provided it is on C-NRPP's approved list.

What material stops radon?

In new Ottawa homes, the City's January 2025 advisory requires a soil gas barrier of polyethylene sheet (CAN/CGSB-51.34-M) under the slab, lapped at least 300 mm, with the slab edge and every penetration sealed with flexible sealant. In an existing house, sealing alone has limited effect, Health Canada says, and a depressurization system does the main work.

Guide

Radon Testing in Ottawa

Sources read 21 October 2026. Last reviewed October 2026.

About one Ottawa-area house in six tests at or above Health Canada's radon guideline of 200 Bq/m3. To find out about yours, run a long-term test of at least 91 days, mostly in the heating season, so a detector placed in late October or November is on time. Above 200, Health Canada says to fix it within a year.

On this page

Is radon a problem in Ottawa?
Why Health Canada says to test every home
How to test for radon in an Ottawa home
What radon testing costs in Ottawa
How to read your radon result
How radon is fixed, and what it costs
Radon rules for new homes in Ottawa
Radon when you buy or sell a home
When to test again
Ottawa companies in this directory that say they do radon work
Common questions

Is radon a problem in Ottawa?

Yes, and the share of homes over the line has been measured three times. Each survey sampled different houses with different methods, so read them side by side rather than as a trend:

2024 Cross-Canada Survey of Radon Exposure: 17.0 per cent of Ottawa-Gatineau houses at or above 200 Bq/m3, another 24.6 per cent between 100 and 199, and an average of 85.9 Bq/m3. Nationally the figure is 17.8 per cent.
Take Action on Radon, Ottawa community report (July 2022): 335 Ottawa homes tested in the winter of 2021. 51 per cent came in under 100 Bq/m3, 31 per cent between 100 and 200, and 18 per cent over 200.
Health Canada, Cross-Canada Survey (March 2012): 64 homes in the City of Ottawa health unit, 6.2 per cent above 200 and none above 600. Leeds, Grenville and Lanark, next door, came in at 19.4 per cent of 108 homes.

None of these can tell you about one street. Ottawa Public Health says radon varies a great deal within the city, and Health Canada says two similar houses next door to each other can test differently. The radon itself comes from uranium breaking down in the soil and rock, and it gets in wherever the house touches the ground: slab cracks, construction joints, gaps around pipes, floor drains and sumps.

Why Health Canada says to test every home

Health Canada calls radon "the #1 cause of lung cancer in non-smokers" and says the risk depends on the level and on how long a person is exposed to it. Smoking and radon together raise the risk significantly.

Outdoors, radon is diluted and not a concern. It builds up indoors, which is why the About radon page and the guide for radon measurements in homes both say every home should be tested, whatever its age or type.

That includes homes with a mitigation system already in, and apartments above the ground floor, which usually read lower but can still be over the guideline. Radon has no smell, no colour and no taste, so a test is the only way to know.

How to test for radon in an Ottawa home

When to test, and for how long

Health Canada wants at least 91 days of the test to fall in the heating season, when indoor radon is typically higher because the house is shut and warm air rising pulls soil gas in. It recommends 3 to 12 months in total. A test with fewer than 91 heating-season days that reads under 200 may be low, and Health Canada says to repeat it the next winter.

Which detector to use

You have three routes, and Health Canada accepts any of them as long as the device is on the Canadian National Radon Proficiency Program (C-NRPP) approved list:

A one-use long-term kit, usually an alpha track detector. It sits for three months or more, then goes to a lab, which sends a report. Write down the start and end dates.
An electronic radon monitor that shows a running average. Check it against C-NRPP's consumer monitor list, put in new batteries before you start, and plan to replace it about five years after purchase unless it can be recalibrated.
A C-NRPP certified measurement professional, who places the device and writes the report for you.

Short-term tests of 2 to 90 days exist, but Health Canada says they are not appropriate for deciding whether to mitigate. Take Action on Radon keeps a list of suppliers selling approved long-term kits online and in stores.

Where to put the detector

Pick a room on the lowest level that someone uses more than 4 hours a day. A basement bedroom, office, family room or playroom comes first if there is one; otherwise use the main floor. Never the kitchen, laundry room or a bathroom. Then, from Health Canada's placement rules:

at least 30 cm above the floor and 30 cm from walls and the ceiling, on a shelf or table
at least 1 m from vents, windows, doors and anything else that moves air
away from routers, computers, televisions and speakers
out of the sun, away from the fireplace and radiators, and out of humid rooms
not beside the sump pit, a crack in the slab or inside a crawl space
out of reach of children and pets, where nobody will move it for three months

What can spoil the result

Moving or dropping the device, a passive kit used past its expiry date, and a test shorter than 91 days all call for a new test. For a long-term test, Health Canada says not to change how you live; keeping every window shut for three months is not the point. The strict closed-house rules belong to short professional tests, where C-NRPP's short-term protocol voids a test if windows were opened.

What radon testing costs in Ottawa

Ottawa Public Health's radon page puts it in one line: "The cost of testing ranges from $29 to $170." It also says it has no kits for sale itself, and points to hardware, home improvement and building supply stores and online sellers. If you hire a certified measurement professional instead, ask for a written price that names the device and the test length before you book.

How to read your radon result

Compare the long-term average with 200 Bq/m3. Health Canada's guideline page, last modified 2025-09-24, says that above 200 you should take corrective action "within 1 year", sooner the higher the level, and bring it as low as practicable. C-NRPP gives the same one-year timeline.

Older pages still show a two-step timetable: within two years for 200 to 600 Bq/m3 and within one year above 600. As read on 2026-10-21, Ottawa Public Health's radon page and the 2022 Ottawa community report both carry it. Go by the current Health Canada page.

Results near the line need care. Health Canada notes that repeat tests may vary by up to 25 per cent, so a result slightly under 200 may truly be slightly over, and the reverse. A monitor can show hourly peaks over 200 while the 91-day average sits below it, and Health Canada says to decide on the average.

Readings in pCi/L, converted

Some monitors and US sites report picocuries per litre. Health Canada's measurement guide gives the factor: 37 Bq/m3 equals 1 pCi/L. The bands are from Health Canada and C-NRPP.

pCi/L	Bq/m3 (about)	Where it sits
1.0	37	Below 100: retest within 5 years or after major work (C-NRPP)
1.7	63	Below 100
2.7	100	Start of the 100 to 200 band
2.9	107	100 to 200: consider retesting in a year or two (C-NRPP)
3.5	130	100 to 200
4.8	178	100 to 200, and close enough to 200 that the uncertainty matters
5.2	192	100 to 200, and close enough to 200 that the uncertainty matters
5.4	200	The Canadian guideline
16.2	600	Above 200: fix within 1 year, sooner the higher it is (Health Canada)

How radon is fixed, and what it costs

The standard fix is active soil depressurization, also called sub-slab depressurization. A pipe goes through the basement floor and a fan on it runs around the clock, pulling soil gas from under the slab and venting it outside. Health Canada's September 2026 factsheet says a system can usually be installed in less than a day and typically lowers radon by more than 90 per cent.

Ventilation helps less. A balanced heat or energy recovery ventilator run continuously generally cuts radon by 20 to 50 per cent, and sealing cracks and gaps makes it work better.

If your house has an HRV, an HVAC company in Ottawa can check it is balanced and running. Sealing the slab and the sump lid overlaps with what basement waterproofing contractors do, but Health Canada says sealing alone has limited effect.

Take Action on Radon, the program Health Canada funds, puts a number on it in its 2022 Ottawa report: in its Radon Reduction Sweepstakes data, mitigation systems installed from 2018 to 2021 cost $2,700 on average. Health Canada says the cost is similar to other common home improvements.

The fan runs all the time. For electricity use, C-NRPP compares a small radon fan to a coffee maker and a large one to an HRV.

Hiring a mitigation professional

Health Canada recommends a contractor certified by C-NRPP as a mitigation professional. Search for your area on C-NRPP's find a professional page, and if a company shows the logo on its website, confirm it on the certification check. C-NRPP suggests asking for:

proof of C-NRPP certification and liability insurance
references or photos of past work
a written plan and schedule, including the diagnostic testing
a post-mitigation radon test showing the level came down

Expect the installer to drill a couple of small holes in the far corners of the slab and measure the pressure change before designing the system. After it is on, C-NRPP's steps call for a short test of at least 48 hours, begun after the fan has run for 24, then your own long-term test the next heating season and at least every five years after that.

Radon rules for new homes in Ottawa

Since the 2024 Ontario Building Code took effect, the City of Ottawa's Building Code Services advisory of January 2025 says new low-rise homes and additions need three things against soil gas:

a soil gas barrier, usually polyethylene under the slab, with the slab edge and every penetration sealed
a rough-in for a future sub-slab system: perforated pipe in clean granular under the slab, tied to a vent pipe of at least 100 mm that ends above the floor with an airtight cap and labels
a whole-house ventilation system, an HRV or ERV, required in every dwelling unit since 2017

The rough-in is not a working system. The advisory says the code does not prescribe passive or active systems, so a new house still needs a test. Health Canada says to test in the first heating season after you move in and again two years after the year it was built.

If the result is over 200, Ontario's new home warranty covers it. Tarion says the builder's warranty includes up to $50,000 of radon coverage for the full seven years. The claim needs a test of at least three months with a C-NRPP approved device or certified professional. Freehold owners test their own home; in a condo, owners test their unit and the corporation tests the common areas.

Radon when you buy or sell a home

A 91-day test does not fit inside most purchase timelines. C-NRPP suggests a short-term radon screening by a professional for a first look, following the Canadian Association of Radon Scientists and Technologists guideline for screenings in real estate deals, then a long-term test in the first heating season after you move in to decide whether to mitigate.

None of the sources read for this page sets an Ontario rule that a seller must test or disclose radon. If a screening or an old result matters to your offer, ask your real estate lawyer how to write it into the agreement.

When to test again

Health Canada recommends a new test in the next heating season after any of these:

a renovation that changes the structure or ventilation, such as finishing the basement (our guide to basement permits in Ottawa covers the paperwork side)
a new furnace or a new bathroom
an energy retrofit such as new windows, insulation or air sealing, including the upgrades in Ontario's Home Renovation Savings Program
digging next to the house: exterior waterproofing, drainage or a septic tank
new cracks in the slab or basement walls
a basement that becomes the lowest room someone uses daily
installing a mitigation system, then every five years while it runs

C-NRPP adds a practical order: test before a basement renovation, so a mitigation system can go into the budget, and test again after it.

Ottawa companies in this directory that say they do radon work

This directory has no radon category. On 21 October 2026 we searched the websites of the companies listed under HVAC, basement waterproofing, general contractors, electricians, plumbers and handymen (108 of 111 listings have one), plus every listing that mentions radon. These 3 say on their own sites that they do radon work, and 2 of them offer testing as well as mitigation.

This is not a ranking, and we have not checked any of them against the C-NRPP list. Use the certification check above before you book. Listings claimed by their owner come first and the rest are in alphabetical order, as on our methodology page.

John The Plumber
A plumbing company with two radon pages. One offers long-term and short-term radon tests, and sub-slab depressurization when a result comes back high. The other covers installing, repairing and upgrading radon reduction systems, with a long-term test before the design.
See the John The Plumber listing
Out Of This World Plumbing Ottawa
A plumbing company with its own radon section covering testing, mitigation and test booking. Its booking links offer a 7-day test and a 3-month test. For a decision to fix, Health Canada counts only a test of 91 days or more.
See the Out Of This World Plumbing Ottawa listing
The Foundation Guys Inc.
A foundation and waterproofing company. Its radon pages cover designing and installing mitigation systems for homes that have already tested high, inspecting existing systems, and radon in real estate.
See the The Foundation Guys Inc. listing

For a wider choice, C-NRPP's professional search finds certified measurement and mitigation professionals in your area. Two of the three above are plumbers; the full list of plumbers in Ottawa has their ratings and service areas.

Common questions

Is radon an issue in Ottawa?: Yes. The 2024 Cross-Canada Survey of Radon Exposure found 17.0 per cent of Ottawa-Gatineau houses at or above Health Canada's guideline of 200 Bq/m3, with an average of 85.9 Bq/m3. In Take Action on Radon's winter 2021 challenge, 18 per cent of 335 Ottawa homes tested over 200. Ottawa Public Health says levels vary a great deal within the city, so only a test tells you about your house.
Is it worth getting a radon test?: Health Canada recommends that every home be tested, whatever its age, type or location, and even if it already has a mitigation system. It calls radon the number one cause of lung cancer in non-smokers in Canada. Ottawa Public Health puts the cost of testing at $29 to $170, and a long-term test is the only way to know your level.
What is the safe radon level in Canada?: Canada's guideline is 200 becquerels per cubic metre (Bq/m3), averaged over a long-term test in a room someone uses more than 4 hours a day. Health Canada says the risk below the guideline is small but that no level is considered risk free, and that how much exposure to accept is each homeowner's choice.
What month is radon the highest, and is it worse in winter?: Health Canada says indoor radon is typically higher in the colder months, because windows and doors stay closed and the stack effect draws more soil gas into a heated house. That is why it wants at least 91 days of a test to fall in the heating season. In Ottawa, a detector placed in late October or November covers that easily.
What time of day is radon highest? Does it go up at night?: Radon rises and falls through the day, and Health Canada lists daily and seasonal swings among the reasons a short reading misleads. That is also why an hourly or overnight spike on a digital monitor does not count against the guideline. Health Canada says decisions rest on the long-term average of at least 91 days, not on any one hour.
Does opening windows reduce radon?: It dilutes radon while they are open, which is why a short test is run with them shut, but it is no fix for an Ottawa winter. Health Canada says a balanced HRV or ERV run continuously lowers radon by only 20 to 50 per cent, and active soil depressurization by more than 90 per cent.
Do air purifiers or HEPA filters clear out radon?: Health Canada does not list air purifiers or filters among its ways to reduce radon. Its methods are active soil depressurization, which pulls soil gas from under the slab and vents it outside, balanced ventilation with an HRV or ERV, and sealing cracks and gaps. If a test is high, the fix it recommends is a system designed by a C-NRPP certified mitigation professional.
What are the signs of radon in a house?: There are none you can see or smell. Health Canada describes radon as invisible, odourless and tasteless, and the health risk it names is lung cancer after long exposure, not short-term symptoms. A long-term test is the only way to find it.
How long before radon makes you sick?: Health Canada does not give a time. It says the risk of lung cancer depends on the radon level and how long a person is exposed, and that smoking and radon together raise the risk significantly. Ottawa Public Health adds second-hand smoke to that list. Questions about your own health belong with your doctor; the test tells you the level in your home.
Can you be in the house during a radon test?: Yes. For a long-term test Health Canada says residents should not change how they live, because the goal is your normal exposure. The rules about keeping windows shut and limiting the dryer, range hood and bathroom fans apply to short professional tests: C-NRPP sets closed-house conditions for 12 hours before a test of under 4 days, and a test run with them broken is void.
What ruins a radon test?: Health Canada lists these: placing the detector on the floor, against an outside wall, in a closet or drawer, near a vent, door, window, sump pit or foundation crack, beside a router or television, in sun or near heat, or in a humid room. A dropped or damaged detector, a passive kit used past its expiry date, and a test shorter than 91 days all need a new test.
Does radon in the basement go upstairs?: It can. Health Canada says levels are typically highest in basements and crawl spaces but elevated levels can be found throughout a home, and even apartments above the ground floor should be tested. Test on the lowest level someone uses for 4 hours a day: a basement bedroom, office or playroom if there is one, otherwise the main floor.
Is it okay to sleep in a basement with radon?: Test that bedroom first. Health Canada tells you to prioritize bedrooms on the main floor or in the basement, because people spend more time there than in any other room. If the long-term result is above 200 Bq/m3, it recommends fixing it within a year; below that, the risk is small but not zero.
Is a radon level of 2.9, 4.8 or 1.7 high?: Those readings are in picocuries per litre, the US unit. Health Canada gives the conversion: 1 pCi/L equals 37 Bq/m3. So 1.7 pCi/L is about 63 Bq/m3, 2.9 is about 107, 3.5 is about 130, 4.8 is about 178 and 5.2 is about 192. All are under Canada's 200 guideline, which is about 5.4 pCi/L. The table on this page covers more readings and what C-NRPP suggests for each band.
How do I prepare for a radon inspection?: For a long-term test, live normally and leave the detector where it was placed. For a short professional test, C-NRPP asks for closed windows, outside doors used only to come and go, no fireplace unless it is your main heat, and as little dryer, range hood and bathroom fan use as possible, starting 12 hours before. For a mitigation quote, expect small test holes in the slab.
What is the fastest way to get rid of radon, and does it work?: Active soil depressurization. Health Canada says a system can usually be installed in less than a day and typically cuts radon by more than 90 per cent. Radon can creep back if the fan stops or the house changes, so C-NRPP calls for a short test after installation, a long-term test the next heating season, and a retest at least every five years.
Where in Canada and Ontario is radon highest?: The 2024 Cross-Canada survey names Atlantic Canada, the Prairies, the North and the BC Interior as the regions where high indoor radon is more common, and lists Thunder Bay and Kingston among Ontario cities where a quarter to half of homes are at or above 200 Bq/m3. Near Ottawa, Health Canada's 2012 survey found 19.4 per cent of tested homes over 200 in the Leeds, Grenville and Lanark health unit.
What makes a house more likely to have radon?: The 2024 survey found single-detached houses more likely to be at or above 200 Bq/m3 than semi-detached ones, and semis more likely than row houses, with rural homes above urban ones. Ottawa Public Health adds homes made more airtight without enough fresh air. Neighbours still differ: Health Canada says two similar houses side by side can test very differently.
Where does radon in a house come from?: Mostly from the soil. Health Canada says soil gas is the largest source, entering through construction joints, gaps around pipes and posts, floor drains, sumps and cracks in the slab and walls. Radon from a private well can add some, but Health Canada says to test the air and fix soil gas first.
Is the radon risk overblown?: Health Canada puts it plainly: radon is the number one cause of lung cancer for non-smokers in Canada, and no level is risk free. It also says the risk below 200 Bq/m3 is small, and that an individual's risk depends on the level and the years of exposure. A test tells you which side of the guideline your home is on.
What does a radon test kit look like?: Most are a small passive detector, an alpha track device, that sits on a shelf for three months or more and then goes back to a lab in the mail. The other kind is an electronic radon monitor that shows a running reading on a screen or phone. Health Canada recommends either, provided it is on C-NRPP's approved list.
What material stops radon?: In new Ottawa homes, the City's January 2025 advisory requires a soil gas barrier of polyethylene sheet (CAN/CGSB-51.34-M) under the slab, lapped at least 300 mm, with the slab edge and every penetration sealed with flexible sealant. In an existing house, sealing alone has limited effect, Health Canada says, and a depressurization system does the main work.

Before you hire anyone for radon work, confirm their certification with C-NRPP.

C-NRPP certification check