Radon Tests When Buying a Home in Ontario: A Buyer's Playbook
About 1 in 12 Ontario homes read above Canada’s radon action level of 200 Bq/m³.
Radon is invisible. It has no smell. The only way to know a home’s level is to test it.
You can add that test to your offer, just like you add a home inspection. This guide shows you when to ask, how to word the clause, what a high number means, and who pays to fix it.
The short version:
- Add a radon test as a condition of your offer, the same way you add a home inspection.
- A fast test runs 48 to 72 hours, which fits most closing timelines.
- A reading at or above 200 Bq/m³ is the point where Health Canada says to act.
- A high result is a price talk, not a deal killer. Mitigation costs $2,800 to $3,800.
- For new builds bought on or after February 1, 2021, the Tarion warranty can make the builder pay.
- A real estate test with fast turnaround is $399. Sample clause wording is below.
Should you test for radon before buying?
Yes, if the home has a basement or a slab on grade. That covers almost every house in Ontario.
Radon comes up from the soil. It seeps in through cracks, sump pits, and gaps around pipes.
Two homes on the same street can read very differently. One can be fine. The one next door can be triple the limit. The only way to know is to test the actual home you’re buying.
The risk is real. Radon is the second leading cause of lung cancer in Canada.
You won’t feel it. The harm builds over years. That’s why a one time test before you buy is worth it.
When to ask for the test during the deal
The best time to ask is at the offer stage. You write the radon test into the offer as a condition.
This works just like a home inspection clause. If the test comes back high, you get options. You can ask the seller to fix it, ask for a price cut, or walk away.
Timing is the tricky part. A long radon test takes months. A home sale takes days or weeks. So buyers use a short test built for fast timelines.
A short test with a continuous radon monitor runs under closed house conditions for 48 to 72 hours. Health Canada’s measurement guide allows this faster approach for real estate deals.
Closed house conditions mean windows shut and normal heating or cooling running. No open windows. No fans pointed at the device. This keeps the reading honest.
How to word the radon clause
You don’t need fancy legal language. You need a clear condition with a deadline and a trigger number. Your real estate lawyer or agent can fit it to the standard OREA form.
Here’s plain wording you can hand to your agent as a starting point:
“This offer is conditional on a radon test of the property, at the buyer’s expense, showing a result below 200 Bq/m³. The test will be done by a qualified radon professional within [X] days of acceptance. If the result is at or above 200 Bq/m³, the buyer may, within [X] days, terminate this agreement and have the deposit returned in full, or negotiate remediation with the seller.”
Swap in the day counts that match your closing. A 72 hour test plus report writing means you want at least 5 business days in the condition window. Ask for more if you can.
Get your own lawyer to review the final wording. This sample is a starting point, not legal advice.
What to do if the radon reading is high
A high number is the start of a talk, not the end of the deal. It’s a known problem with a known fix and a known price.
A radon mitigation system removes the gas before it builds up indoors. The common type is sub slab depressurization. It pulls soil gas out from under the slab and vents it above the roof. A good system cuts indoor radon by 80 to 99 percent.
In Ontario, that install runs $2,800 to $3,800 for a standard home. So a high reading gives you three clear paths.
Your options when the test comes back high:
- Ask the seller to fix it before closing. They hire a mitigator and you close into a fixed home.
- Ask for a price cut. Take the cost off the price and fix it yourself after you move in.
- Walk away. If your clause allows it, a high reading lets you exit and get your deposit back.
Most deals land on the price cut. The seller drops the price by the cost of mitigation, and you handle the install on your own timeline.
A radon problem is cheaper to fix than almost any other home defect you’ll find. A new roof can run $12,000. A new furnace can run $6,000. A radon system runs $2,800 to $3,800 and lasts for years.
Don’t let a single high reading scare you off a home you love. Price it in and move on.
New builds: when the builder pays
If you’re buying a newer build, there’s a path where you pay nothing for the fix.
Ontario’s Tarion new home warranty covers radon for homes bought from a licensed builder on or after February 1, 2021.
To use it, the home has to be inside its 7 year warranty window, and a qualified test has to read at or above 200 Bq/m³. If you hit those marks, the builder hires the mitigator and pays the bill.
This matters most for pre construction and assignment buyers. If the home was bought new in the last few years, check the original purchase date before you assume you’re on the hook. Our Tarion page walks through the full eligibility check.
For a resale home from a private seller, there’s no builder warranty. The fix is yours to negotiate or pay for. That’s where the price talk above comes in.
DIY kit vs hiring a pro for a home purchase
For your own home, a $30 DIY kit from the hardware store is a fine first screen. But a home purchase is different. The result has to hold up in a negotiation, and you’re on a deadline.
Here’s how the two stack up for a real estate deal:
| Factor | DIY mail-in kit | Professional test |
|---|---|---|
| Speed | 2 to 4 weeks for lab results | Report in days |
| Fits a closing deadline | Rarely | Yes |
| Trusted in a negotiation | Weak, easy to dispute | Strong, signed report |
| Closed house proof | None | Documented |
| Cost | $25 to $50 | $399 real estate test |
| Best use | Screening your own home later | Buying or selling a home |
A DIY kit is great for peace of mind after you own the place. For the actual purchase, the slow turnaround and the lack of a signed, defensible report make it the wrong tool.
When real money and a deadline are on the line, a professional test pays for itself. A signed report is hard for a seller to wave away. See our services for the full process.
How the timing fits a real Ontario deal
Buyers worry the test will blow up their closing date. It rarely does. Here’s a typical timeline.
- Day 0: Offer accepted with a radon condition.
- Day 1: Tester places a calibrated monitor in the lowest lived in level.
- Day 4: Monitor picks up after 72 hours. Report written same day or next.
- Day 5: You have a signed result and a clear next step.
That fits inside most condition windows. If your deal is very fast, ask for a slightly longer radon condition up front. Sellers grant it more often than you’d think, because a clean test helps them too.
Test in winter if you have the choice. Closed windows and a running furnace pull more soil gas in, so winter readings run higher and safer to act on.
What to do next
If you’re house hunting in the Greater Toronto Area or surrounding Southern Ontario, talk to your agent about adding a radon condition before you write your next offer. It costs you nothing to ask.
When you’re ready, we run fast real estate tests built for closing timelines. Calibrated monitor, closed house protocol, signed report your lawyer and the seller can trust.
You can read Health Canada’s plain language radon overview for the policy side, or request a quote to line up a test for your deal.
Frequently asked questions
Can I make a radon test a condition of my offer in Ontario?
Yes. You add it the same way you add a home inspection condition. Your agent writes it into the offer with a deadline and a trigger number, usually 200 Bq/m³. If the test reads high, you can negotiate, ask for a fix, or walk away based on the clause wording.
How fast can a radon test be done for a home purchase?
A short test with a continuous monitor runs 48 to 72 hours under closed house conditions. With report writing, you get a signed result in about 5 days. Health Canada’s measurement guide allows this faster method for real estate deals.
Who pays to fix radon when buying a house?
It depends on the deal. For a resale home, you negotiate. The seller may fix it, cut the price, or you handle it after closing. For a new build bought on or after February 1, 2021, the Tarion warranty can make the builder pay, up to $50,000.
Is a high radon reading a reason to cancel the purchase?
It can be, if your clause allows it. But most buyers don’t cancel. A fix costs $2,800 to $3,800 and works for years, so the common move is a price cut. A high reading is a bargaining chip in a price talk, not always a deal breaker.
Will a home inspection catch radon?
No. A standard home inspection looks at the structure and systems, not the air. Radon needs its own test with a monitor placed for a set time. If you want to know a home’s radon level, you have to ask for the test on purpose.
Book a real estate radon test for your offer →
Authored by the Breathe Radon Free Team. Every claim is backed by a primary source. Full bibliography at /sources.
Ready to test your home?
Get a quote in 60 seconds. Published prices, no sales follow-up.