The North Shore Is a Low-Radon Area. Test Anyway.

The regional picture, and why it does not settle anything

Radon is a radioactive gas that comes from uranium breaking down in soil and rock. It seeps into buildings through whatever is in contact with the ground, accumulates indoors, and is a known cause of lung cancer. Outdoors it disperses to nothing. Indoors it can build.

Testing across BC has shown that areas west of the Coast Mountains, which takes in the Lower Mainland, Vancouver Island, the Fraser Valley and the Sunshine Coast, tend to have low residential radon levels, meaning below the Canadian guideline of 200 becquerels per cubic metre. The interior and the north of the province are a different story.

So far so reassuring. Here is the qualifier that comes attached to that finding in the source material itself: indoor radon accumulation can vary widely from building to building, even in the same neighbourhood, so individual testing is still recommended.

That sentence is doing more work than it looks like. Two houses on the same Lynn Valley street, built the same decade on the same soil, can produce different radon readings, because the number depends on the specific path the gas takes into that specific building and how that building handles air. A crack in one slab and not the other. A sump with a lid and one without. A basement that gets used and one that gets sealed up. The geology sets the supply; the building decides how much gets in and stays.

The number that matters

The Canadian guideline for radon is 200 becquerels per cubic metre. Health Canada recommends taking corrective action to lower the level within one year where the annual average in the normal occupancy area exceeds it, and states that the higher the concentration, the sooner action should be taken.

One honest caveat comes directly from Health Canada rather than from us: while the health risk below the guideline is small, there is no level considered risk free. The guideline is a decision threshold, not a line between safe and dangerous.

That framing changes how you should read a result. A house at 210 does not need panic and a house at 190 is not sealed against physics. What the guideline gives you is a point at which the cost of fixing it is clearly worth paying.

How to test so the result means something

This is where most homeowners go wrong, and it costs them either money or false comfort.

Health Canada recommends conducting radon tests over a period of 3 to 12 months, with a minimum of 91 days of the test falling during the heating season. All measurements should be made in a normal occupancy area of the lowest lived-in level of the home. And on device choice, the guidance is direct: long-term devices are recommended, and short-term measurements are not appropriate for informing mitigation decisions.

Three things follow from that. Radon levels swing with weather, season and how the house is being run, so a weekend reading captures a moment rather than an average. The heating season matters because a closed-up house in January behaves nothing like the same house with the windows open in July. And lowest lived-in level means the finished basement where the family watches television, not the crawlspace nobody enters and not the main floor.

The practical version: buy a long-term alpha track detector, put it in the lowest room you actually use, start it in the fall, and leave it alone until spring. It is the cheapest test in home ownership and the only one that produces a number worth acting on.

If you are buying a house and need an answer in weeks rather than months, a short-term test can flag an obviously high result. Just understand what you have. A short-term number is a screening signal, and Health Canada is explicit that it should not be the basis for a mitigation decision.

• Test for 3 to 12 months, with at least 91 days in the heating season
• Place the detector in the lowest lived-in level, in a normal occupancy area
• Use a long-term device; short-term results should not drive mitigation decisions
• Start in autumn so the test spans the closed-up months
• Retest after work that changes the basement, the slab, or the ventilation

What the BC Building Code already requires

The code approaches radon by geography. Table C-3 of the BC Building Code lists locations in British Columbia requiring radon rough-ins, classifying places demonstrated to have elevated risk of indoor radon above 200 Bq/m³ as Radon Area 1. Rough-ins are required in those Radon Area 1 locations.

A rough-in is not a mitigation system. It is the plumbing for one. Current provisions for a subfloor depressurization rough-in require a radon vent pipe that extends through and terminates outside the building, so the designer has to account for routing that pipe at the design stage rather than discovering later that there is no path from the slab to the roof.

The reason that detail matters to a renovating homeowner has nothing to do with whether your municipality appears on the list. It is that installing the pipe route is cheap while the slab is open and expensive afterwards. If you are pouring a new slab, underpinning a basement, or doing a full basement renovation down to the ground, running the rough-in is a small line item at that moment and a genuinely disruptive retrofit at any other.

We treat it the way we treat blocking behind a future grab bar. The cost of doing it during construction is close to nothing. The cost of wishing you had is measured in demolition.

If the number comes back high

The standard fix is active subslab depressurization. A pipe is set into the material below the slab, a fan draws soil gas out and vents it above the roofline, and the slight negative pressure under the floor means radon goes up the pipe instead of into the house. It is a well-understood system and it works.

The work that makes it effective is the sealing that goes with it. Slab cracks, the gap around the perimeter, service penetrations, and above all the sump: an open sump pit is a direct opening into the soil, and a sealed lid on it is often the single highest-value item on the list.

Retest afterwards. A mitigation system that is not verified is a hopeful piece of pipe. And keep in mind the fan runs continuously, so it draws power and eventually needs replacing, which is a small ongoing cost rather than a one-time purchase.

One North Shore specific note. Plenty of houses here sit on slopes with basements dug into the hillside, which means more below-grade wall in contact with soil than a flat-lot house has. That is a factor in how soil gas can enter, and another argument for testing rather than assuming, particularly on the steeper lots through Canyon Heights, Delbrook and the upper slopes.

When to bother

Honest guidance rather than a sales pitch: for most North Shore homeowners this is a long-term test kit and a season of waiting, and the result is very likely to be reassuring. That is worth doing precisely because it is cheap and it ends the question.

The moments that genuinely warrant attention are the ones where something changes. Finishing a basement turns a space nobody occupied into a bedroom or a suite, which changes both exposure and airflow. A new heating system or a tighter building envelope changes how the house moves air. Underpinning or a new slab changes the ground contact entirely.

If you are converting a basement into a secondary suite, the case is strongest of all. You are creating a lowest-level living space that someone will occupy full time, and it is worth knowing the number before a tenant is in there rather than after.