Radon in Condos and New Builds: What You Need to Know

The misconception

There's a widespread assumption that radon is a problem for old houses — drafty basements, crumbling foundations, homes built before anyone knew what radon was. If your home is new, or if you live in a condo on the fourth floor, the thinking goes, you're probably fine.

This is not entirely wrong, but it's not entirely right either.

Radon levels in new and multi-unit buildings are lower on average, but they're not zero, and some are quite high. Understanding why helps you figure out whether testing makes sense for your situation.

Why new builds still have radon

Modern building codes in Canada — particularly the 2015 National Building Code — include requirements for radon-resistant features in new construction. These include provisions for sub-slab vapour barriers, rough-ins for future mitigation systems, and requirements in high-radon regions.

But code compliance doesn't guarantee low radon for a few reasons:

Geological variation. Radon comes from uranium in the soil. No building code eliminates what's underneath a house. A new home built on geology with high radon potential will have higher radon than the same home built elsewhere, regardless of construction quality.

Settling and shrinkage. New concrete cracks as it cures and settles. These cracks are normal, but they're also pathways for radon to enter. A home that passes a radon test in year one may test differently in year five.

Variable enforcement. Code requirements are only as good as the inspections that enforce them. Not every jurisdiction enforces radon-related provisions consistently.

Sealed construction. This one is counterintuitive: tighter, more energy-efficient homes can sometimes accumulate radon at higher concentrations because there's less natural air exchange. Modern homes are built to minimize drafts — which is great for energy efficiency but means radon that does get in has fewer ways out.

Health Canada recommends that all Canadians test their homes, regardless of age. The recommendation for new builds is to test 1–2 years after move-in, once the home has settled and your typical living patterns are established.

Condos: floor level matters, but it's not the whole story

Ground-floor and basement-level units are most exposed to radon — they're closest to the soil, and radon levels fall as you go higher in a building. If you're on the tenth floor, your radon risk is likely low.

But several factors complicate this:

Below-grade parking garages. In many condo buildings, radon accumulates in underground parkades. If the garage isn't well-separated from living spaces (elevator shafts, stairwells, HVAC systems), radon can migrate upward into units that wouldn't otherwise have elevated levels.

Ground-floor commercial or storage spaces. A condo unit on the third floor above an unventilated storage level may have higher radon than a unit on the same floor in a different building.

HVAC design. Centralized air handling in older multi-unit buildings can distribute radon across units if the system draws from areas of high concentration. Newer buildings with individual unit ventilation are less susceptible.

Concrete slab construction. Some condo buildings, particularly mixed-use towers, have concrete slabs that sit on grade. Radon can migrate through this slab into ground-floor units in the same way it does in a house.

In general: if you're on floors 3 and above in a mid- or high-rise, your risk is low and testing is optional. If you're on floors 1–2, or in a building with below-grade parking or commercial space below, testing is worth considering — especially if you're in a high-radon region.

High-radon regions in Canada

Radon potential varies enormously across the country. Provinces with the highest average indoor radon levels include:

Saskatchewan — consistently the highest radon concentrations in Canada
Manitoba — second highest, particularly in Winnipeg and southern Manitoba
New Brunswick — notably elevated in some areas
Alberta — elevated in many parts of the province

If you live in one of these provinces, the case for testing your new build or ground-floor condo is stronger — regardless of construction type.

What to do if you're in a condo

If you live in a unit at risk (ground floor or below-grade), the process is straightforward: buy a long-term radon test kit, place it in your unit for 90+ days during the heating season, and send it to the lab.

If your result is elevated, the response in a condo context is more complicated than in a single-family home. You may need to involve your condo corporation or building management, particularly if the source is a common element (like a parking garage or shared mechanical room). This can be a slow process.

Some options for condo owners with elevated levels:

Air purifiers with activated carbon can help, though they're not a permanent solution
Improving ventilation in your unit (HRV, ERV, or simply opening windows more often) reduces concentration
Engaging your condo corporation to investigate and address the source is the right long-term approach

What to do in a new home

Test 1–2 years after move-in. The house should be settled into its regular season patterns.

Use a long-term test kit (90+ days) placed in the lowest liveable area — your basement if you have one, or the main floor if you don't. The heating season (October through April) gives the most representative result.

If you're building a new home and have the opportunity to influence the construction, ask your builder about:

Sub-slab rough-in pipe installation (inexpensive during construction, expensive to add later)
Passive sub-slab depressurization system installation
Soil gas barrier beneath the slab

These features cost relatively little during construction and make future mitigation much easier if you ever need it.