Does the New Brunswick building code require radon testing before finishing a basement and what level requires mitigation?

The New Brunswick Building Code does not explicitly mandate radon testing before finishing a basement, but Health Canada strongly recommends it, and any responsible contractor in NB will advise you to test before enclosing walls and floors. Installing a radon mitigation system before finishing is dramatically easier and cheaper than retrofitting one after your basement is complete — the difference can be thousands of dollars.

Radon is a naturally occurring radioactive gas that seeps up from the ground through cracks in foundation walls and floors, gaps around pipes, and sump pits. New Brunswick has elevated radon levels in many areas across the province, making this a genuine health concern rather than a theoretical one. Radon is the second leading cause of lung cancer after smoking, and because it is colourless and odourless, the only way to know your exposure level is to test. Health Canada's guideline is clear: if radon levels in your home exceed 200 Bq/m³ (becquerels per cubic metre), mitigation is required.

Testing is simple and affordable. A long-term passive test kit costs $30 to $50 and sits in your basement for 3 months during the heating season (October through March) when windows and doors are typically closed and radon concentrations are highest. This gives the most accurate reading. A professional short-term test costs $150 to $300 and provides faster results, though a long-term test is considered more reliable. Place the test device in the lowest lived-in area of your basement, at least 50 centimetres off the floor, away from exterior walls, windows, and sump pits.

If your test results come back above 200 Bq/m³, the standard mitigation approach is a sub-slab depressurization system. This involves drilling a hole through your basement concrete slab, inserting a pipe that runs up through the house and out through the roof, and attaching a small fan that draws radon gas from beneath the slab and vents it safely outside. The cost for a complete system is typically $2,000 to $4,000 in New Brunswick. The critical point for anyone planning a basement renovation is this: if you install the sub-slab piping and seal the slab before finishing, a mitigation system can be added easily later by simply connecting a fan. If you finish the basement first, a contractor may need to cut through your new flooring, drill through your finished ceiling, and run piping through completed rooms.

For NB homeowners planning a basement renovation, the smart approach is to test for radon early in your planning process — ideally months before construction begins. If levels are elevated, have the mitigation system installed during the rough-in phase, before insulation and drywall go up. Many basement contractors in Moncton, Fredericton, and Saint John are familiar with radon mitigation coordination and can build it into your renovation timeline. Even if your initial test comes back below 200 Bq/m³, consider having a rough-in pipe installed beneath the slab during construction — it costs very little at that stage and gives you an easy path to active mitigation later if levels change.

The areas around Fredericton, parts of the Saint John River valley, and certain zones in northern NB tend to show higher radon concentrations, but levels can vary dramatically even between neighbouring houses. Do not assume your home is safe based on your neighbour's test results. Test your own basement, plan accordingly, and protect your family's health as part of your renovation investment.

---

Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• Thirty Four Renovations
• Gionetterenovations