Radon in Condos and Apartments: Should You Test?

You live on the 14th floor. Radon is a basement gas, so surely it can’t reach you up there.

For most high-floor units, that’s true. Radon seeps up from the soil, and the higher you go, the less of it there is. But “most” isn’t “all.” A ground-floor condo or a basement-level suite can test just as high as any bungalow. And plenty of owners never check.

So should you test your condo or apartment? It depends on one thing: how close your unit sits to the ground.

The short version:

• Radon comes up from the soil, so the units closest to the ground carry the most risk.
• Upper-floor condos are usually low risk. You can likely skip the test.
• Ground-floor, basement-level, and townhouse-style units should be tested like any house.
• Renters in Ontario have limited radon rights, but you can still test your own unit.
• A $35 kit or a $99 pro test answers the question. No need to guess.

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Does radon even get into condos?

Yes, but only into some units. Radon is a gas that rises from the ground under a building. It slips in through cracks, gaps around pipes, and any opening near the soil.

The key word is soil. Radon has to travel up from the ground to reach you. Every floor it climbs, the gas thins out and mixes with fresh air.

So a unit sitting right on a slab gets the full dose. A unit 12 floors up gets almost none. Same building, very different air.

Radon is the second leading cause of lung cancer in Canada, and the top cause for people who never smoked. That’s why the floor you live on actually matters for your health, not just your view.

Which floor are you on? That’s the real question

Here’s the simple rule. The closer your unit is to the dirt, the more you should care.

Your unit	Radon risk	Should you test?
Basement or garden-level suite	High. Same as a house basement.	Yes, test it.
Ground floor / main floor on a slab	Real. Radon enters at the soil line.	Yes, test it.
2nd or 3rd floor	Lower, but not zero in a low-rise.	Test if you’re unsure or a low-rise.
4th floor and up	Usually low.	Likely fine to skip.
Townhouse or stacked town	Treat like a house. It has ground contact.	Yes, test it.

Notice the townhouse row. A lot of “condos” in Ontario are actually townhouses or stacked towns. They sit right on the ground and have their own slab. For radon, they’re houses. Test them like one.

If your unit touches the ground, or sits one floor above it, test it. If you’re four or more floors up in a concrete tower, you can almost certainly relax.

Why high floors are usually safe

Think of radon like smoke from a campfire on the ground. Stand right over it and you breathe a lot. Climb a ladder and it thins out fast.

Radon works the same way. By the time the gas would reach a 10th-floor unit, it’s had to pass through floors, slabs, and moving air. Very little makes it that high.

There’s one catch worth knowing. Some towers pull air up through elevator shafts and stairwells. This is called the stack effect. In rare cases it can carry a little soil gas higher than you’d expect.

But that’s the exception, not the rule. If you’re well up a concrete high-rise, radon is near the bottom of your worry list.

Why ground-floor and basement units aren’t safe by default

Now flip it. A garden suite, a basement apartment, or a main-floor unit on a slab is a different story.

These units sit right where radon enters. There’s no stack of floors below to soak up the gas first. The soil is inches away, on the other side of the concrete.

About 1 in 15 Canadian homes tests above the national guideline, and low-lying units are where the high numbers hide. A basement apartment can read as high as any detached-home basement.

Health Canada’s action guideline is 200 Bq/m³. If your ground-level unit tests above that, it’s worth fixing, the same as any house.

Renting? Here’s where you stand in Ontario

This is the part that frustrates a lot of tenants. Ontario has no law that forces a landlord to test for radon or fix a high result.

So what can you actually do? A fair bit, as it turns out.

• Test your own unit. A long-term kit costs about $35 to $60. Nobody can stop you from placing one.
• Share the result in writing. If it’s high, give your landlord the number and a link to Health Canada’s guideline.
• Ask for a fix. Many landlords will act once they see a real number. Mitigation isn’t their legal duty, but it protects their building too.
• Improve airflow short-term. More fresh air helps a little. It’s not a real fix, but it’s better than nothing while you sort out next steps.

If your landlord won’t act and your number is high, you at least know the risk. That lets you decide about the space with real facts, not a guess.

Condo owner? Bring it to the board

If you own your unit, the ground under the building is shared property. That means a real fix often runs through the condo board, not just you.

For a high-floor unit, this rarely comes up. For a ground-floor or garden unit that tests high, it matters.

• The soil and foundation are usually common elements the board controls.
• A proper mitigation system may need board approval to touch shared structure.
• One high unit can mean neighbours are high too, which is a building-wide reason to test.

Start by testing your own unit. If it’s high, take the number to the board. A single documented result often gets a building to test more units and take it seriously.

DIY vs hire a pro

You can handle most of this yourself. Here’s the honest split for condos and apartments.

Task	DIY is fine	Hire a pro
Long-term test in your unit	Yes, $35 to $60 kit	Only if you want a faster answer
Short-term test for a sale or warranty	No, the result won’t be accepted	Yes, $99 to $399
Reading and understanding your number	Yes	Not needed
Fixing a high ground-floor or garden unit	No	Yes, the fix ties into shared structure

Here’s the plain read. Buying a kit and placing it is easy, and you don’t need us for that step. We’d rather you test than wait.

If the number comes back high in a ground-level unit, that’s when a pro earns their keep. Fixing radon in a condo touches shared walls and slabs, and it often needs board sign-off. That’s not a solo weekend job.

What to do next

Start with your floor. If you’re high up in a concrete tower, you can likely skip the test and breathe easy.

If you’re on the ground, in a basement suite, or in a townhouse, treat your unit like a house. Order a long-term kit and place it in the room you use most, away from drafts. Or book a $99 pro test if you want a faster answer.

Not sure what your number means once you have it? Read radon levels explained to see what each range really means. Wondering how much to worry in the first place? Our honest take on whether radon is dangerous lays out the real risk.

If you’re in a downtown Toronto condo, our guide to radon testing in Toronto covers why some lower units there test higher than people expect. Have a quick question first? The FAQ page covers the basics in plain terms.

You have time to do this right. The whole point is to test the units that need it and skip the ones that don’t.

Frequently asked questions

Can radon reach a high-floor condo?

Almost never at a level worth worrying about. Radon rises from the soil and thins out fast as it climbs. By the fourth floor and up in a concrete tower, very little remains. A rare stack effect can carry a trace higher, but high floors are near the bottom of the radon worry list. If you’re well up a high-rise, you can likely skip the test.

Should I test my basement apartment for radon?

Yes. A basement or garden-level suite sits right where radon enters a building, so it can read as high as any house basement. Place a long-term kit in the room you use most and leave it for 91 days. If the result is above 200 Bq/m³, it’s worth fixing.

Does my landlord have to fix high radon in Ontario?

No. Ontario has no law that forces a landlord to test for radon or mitigate a high result. You can still test your own unit for about $35 to $60, share the number in writing, and ask for a fix. Many landlords act once they see a real result, even though it isn’t a legal duty.

Who pays to fix radon in a condo?

It depends on where the radon enters. Because the soil and foundation are usually shared common elements, a fix often runs through the condo board, not just the owner. Start by testing your own unit. If it’s high, bring the number to the board, since a proper system may need approval to touch shared structure.

What radon level is too high in a condo?

The same as any home. Health Canada’s action guideline is 200 Bq/m³. Above that, plan to fix it. Below 100 is a good result. Between 100 and 200, retest to be sure before you decide.

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Test your unit for $99 →

Curious how condos compare to houses across the province? Read radon levels explained for the full picture.

Authored by the Breathe Radon Free Team. Every claim is backed by a primary source. Full bibliography at /sources.