In Canada, the 2025 National Building Code requires at least a passive vertical radon stack in new dwelling units and home-type care occupancies. It is the most significant change to radon prevention in Canadian construction in fifteen years — and for builders, the practical questions are narrower than the headlines: what exactly has to be installed, where does it apply today, and who is responsible when a finished home still tests high?
TL;DR: The 2025 NBC requires a passive vertical radon stack — a pipe from beneath the slab through the roof, ready to accept a fan. But BC, Alberta, Ontario and Quebec write their own codes and must adopt it first, which historically takes anywhere from a few months to five years. So in the four provinces where most Canadians live, it is not yet in force. A rough-in is not a radon solution: it is preparation. Only a long-term test after occupancy tells anyone whether the house is above 200 Bq/m³.
Rough-in, passive stack, active system — the levels
CAN/CGSB-149.11-2024 defines the levels codes refer to, and the distinction decides what you actually have to build. Level 1a: rough-in with the pipe capped and sealed inside the building. Level 1b: rough-in with the pipe extended outside through a rim joist or sidewall. Level 2: passive vertical stack through the roof. Level 3: active system with a fan (now covered by CAN/CGSB-149.12-2024). Province-by-province status: is a rough-in mandatory in my province?
What the 2025 NBC actually requires
A passive vertical radon stack: a pipe running from beneath the foundation, through the building, and out through the roof, creating a vent path for soil gas. It works by stack effect alone — no fan, no power. If a post-occupancy test comes back elevated, a certified mitigation professional adds a fan and the passive stack becomes an active soil-depressurization system, at a fraction of the cost and disruption of retrofitting from scratch.
Builders also have the option of installing an active system at build, either through the roofline or through a side wall, as is standard practice for retrofit mitigation.
The requirement applies to dwelling units and home-type care occupancies. It sits alongside provisions Canadian codes have carried for years: the National Building Code has required a soil-gas barrier and a rough-in in new homes since 2010. The 2025 change raises that baseline from a capped rough-in to a passive stack.
Where it applies today — the part the headlines skip
Short answer, and the detail is in our companion guide: is a radon rough-in mandatory in my province?
“Now mandatory” is doing a lot of work in most coverage of this change, and it misses two things.
First, radon requirements already exist in much of Canada. Ontario's 2024 Building Code (in effect 1 January 2025, mandatory for all permits from 1 April 2025) requires a rough-in for a future sub-slab depressurization system in Part 9 residential buildings. British Columbia's 2024 Code (in effect 8 March 2024) applies province-wide under Subsection 9.13.4 and requires a radon vent pipe terminating outside the building. Quebec's Construction Code goes furthest — rough-in with stub, radon test results submitted to the authority having jurisdiction, and sub-slab depressurization where results require it. Builders in those provinces have been installing to these requirements for a year or more.
Second, the National Building Code is a model code. It has direct force only where a province or territory adopts it, and British Columbia, Alberta, Ontario and Quebec each maintain their own building codes, each with its own amendments and adoption timeline. Municipalities can add a further layer of review.
So the accurate framing is that the 2025 NBC raises the national baseline from a rough-in to a passive stack — a real change — and provinces will arrive at it at different times, from different starting points.
Historically, provincial adoption of a new NBC edition has taken anywhere from a few months to five years. That means:
- In the four largest provinces, the passive stack requirement is not automatically in force on national publication — but existing rough-in requirements may already apply. Check your provincial code and your authority having jurisdiction.
- In provinces and territories that adopt the NBC directly, it takes effect on their adoption schedule.
- Even after adoption, the industry needs time to train crews to install the detail correctly.
The honest answer to “do I have to install a radon stack?” is: ask your building official, because it depends on your province and on when your permit was issued. Anyone telling you it is uniformly mandatory across Canada today is ahead of the facts.
Why builders should get ahead of it anyway
Three reasons that have nothing to do with whether your province has adopted yet.
Cost. A rough-in installed during construction is a fraction of the cost of a retrofit. Running the pipe before the slab is poured is trivial; coring a finished basement and routing a system through a completed house is not.
Warranty exposure. In Ontario, the new-home warranty administered by Tarion may cover radon mitigation within its warranty window — which means an elevated result in a home you built can become your problem after closing. Other provinces' warranty programs vary. Our province-by-province warranty guide covers what each program says.
Buyer expectation. Radon awareness is rising fast, and a passive stack is becoming a visible marker of build quality. Builders installing them now are ahead of both the code and the market.
The thing a rough-in does not do
A passive stack does not tell you where the house stands, and it does not guarantee the house is below Health Canada's guideline of 200 Bq/m³.
Radon levels in a finished home cannot be predicted at the design stage. Two houses on the same street, built by the same crew to the same plan, can test very differently — because levels depend on the soil beneath that specific foundation, on how the building interacts with pressure differences, and on how the eventual occupants live in it.
Which is why every code in Canada that addresses radon does so by requiring preparation, not by promising a result. The passive stack makes the fix easy. Only a long-term test after occupancy establishes whether a fix is needed.
Post-occupancy verification — the piece most builders are missing
As passive stacks become standard, an obvious question follows: are they working? A passive system is a newly widespread building practice in Canada, and its performance in real houses, in real soil conditions, is not yet well characterized.
For a builder, post-occupancy testing does three useful things at once:
- It closes the warranty loop. A documented long-term test showing a home below the guideline is a record you hold if the question is raised later.
- It tells you whether your detail works. If stacks in one subdivision consistently underperform, that is a construction-practice finding worth having early rather than after fifty closings.
- It differentiates the build. “Radon-tested, with results” is a stronger claim than “radon rough-in installed.”
The method is Health Canada's: a long-term test of at least three months, during the heating season, in the lowest lived-in level of the home, using a C-NRPP-approved device analyzed by an accredited laboratory. Short-term tests are not acceptable for deciding whether remediation is needed.
Who is certified to install and inspect
C-NRPP certifies a specific credential for this work — Controlling Radon in New Canadian Homes (CRNCH) — for professionals who specify, install, inspect and maintain radon rough-in systems, including active-ready and passive systems without fans. It is a short certification: a four-to-six-hour course and a 50-question exam.
Worth knowing: CRNCH is by a wide margin the smallest certification pool in the Canadian radon industry. As provincial adoption arrives, demand for people who can specify and inspect the detail correctly is likely to run well ahead of supply.
Common questions
What is a radon rough-in?
A capped vertical pipe running from beneath the foundation through the building envelope, installed during construction so a fan can be added later if testing shows elevated radon. Passive by default; active once a fan is fitted.
Is a radon rough-in mandatory in new Canadian homes?
The 2025 National Building Code requires at least a passive vertical radon stack in new dwelling units. Whether that applies to your project today depends on whether your province has adopted the 2025 NBC — BC, Alberta, Ontario and Quebec each maintain their own codes and adopt on their own schedules. Confirm with your building official.
Does a rough-in mean the house won't have a radon problem?
No. It means the fix will be simple if one is needed. Radon levels cannot be predicted before a house is built and occupied; only a long-term test establishes the level.
Who pays if a new home tests high after closing?
It depends on the province and the warranty program. In Ontario, Tarion's coverage may apply within the warranty window. This is worth understanding before you build, not after a buyer calls.
When should a new home be tested?
After occupancy, over at least three months during the heating season — so a home closing in spring is typically tested the following winter.
For the inspection sequence, labelling and the CRNCH credential: radon rough-in inspection for builders and building officials.
Read next
Radon in new construction homes · Canadian building codes and radon · New-home warranty coverage by province
RadonTest.ca provides testing logistics and laboratory submission. We do not perform radon mitigation, we do not install rough-in systems, and we do not interpret health risk — Health Canada is the health authority on radon in Canada. This page describes publicly available code and guidance information and is not legal advice, nor engineering or code-compliance advice; confirm requirements with your authority having jurisdiction.
Sources
National Research Council Canada, National Building Code of Canada 2025; Health Canada, Canadian radon guideline; Health Canada, Guide for Radon Measurements in Residential Dwellings; C-NRPP certification types (CRNCH); CAN/CGSB-149.11 (radon control options for new construction) and CAN/CGSB-149.12 (mitigation options for existing buildings).