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

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

This is partially true and mostly wrong.

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: 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.

Geological variation. Radon comes from uranium in the soil. No building code changes what's underneath a house. A new home built on high-radon geology 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. A home that tests fine in year one may test differently in year five.

Variable enforcement. Building code requirements are only as good as the inspections enforcing them. Radon-related provisions aren't enforced consistently across every jurisdiction.

Sealed construction. This one surprises people: tighter, more energy-efficient homes can accumulate radon faster because there's less natural air exchange. Modern homes are built to minimize drafts. That's great for energy bills and bad for any gas that gets inside.

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

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

Ground-floor and basement units are most exposed. Radon levels drop as you go higher in a building. If you're on the tenth floor of a high-rise, your risk is low.

But a few things 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 through elevator shafts, stairwells, or HVAC systems, radon can migrate upward into units that otherwise wouldn't be affected.

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

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

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

General guidance: if you're on floors three 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 directly beneath, testing is worth doing, especially if you're in a high-radon region.

High-radon regions in Canada

Radon potential varies enormously across the country. The provinces with the highest average indoor levels are:

Saskatchewan, consistently the highest in Canada
Manitoba, second highest, particularly in Winnipeg and southern Manitoba
New Brunswick, notably elevated in some areas
Alberta, elevated across much of the province

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

What to do if you're in a condo

If you're in a ground-floor or basement unit, the process is simple: buy a long-term radon test kit, place it in your unit for 90+ days during heating season, and send it to the lab.

If your result is elevated, the response in a condo is more complicated than in a house. 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. That can be a slow process.

Options for condo owners with elevated levels:

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

What to do in a new home

Test 1–2 years after move-in. Use a long-term kit (90+ days) placed in the lowest livable area. Heating season (October through April) gives the most representative result.

If you're still in the process of building and have input on construction, ask your builder about:

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

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