Radon Mitigation in Stony Mountain

Stony Mountain takes its name from the limestone escarpment it sits on, and like neighbouring Stonewall, the shallow rock defines crawlspace conditions. Soil cover is thin in many locations, so foundations are often shallower than the frost depth we design for elsewhere in the region. The practical result is seasonal movement: crawlspace piers and stem walls lift as the ground freezes and settle as it thaws, and the floor system above them racks slightly every year until something cracks, separates or sags.

Drainage here is counterintuitive. Thin soil over fractured limestone can shed water quickly in one spot and channel it straight toward a foundation in another. We have inspected crawlspaces in this area that stayed bone dry through two wet springs and then took sustained water after a neighbouring property changed its grading. That unpredictability is why we always map where water arrives — downspout discharge, lot grading, driveway runoff, snow storage — before recommending a system.

Most Stony Mountain properties are on private services, with wells, pressure tanks and septic lines passing through or near the crawlspace. Those penetrations need deliberate sealing and insulation, both to keep the envelope intact and to prevent freezing. We commonly pair encapsulation with perimeter wall insulation rated for our winter temperatures, structural support where piers have been moving, and a conditioned-space strategy so the crawlspace stays above freezing without wasting energy. Radon testing matters here too, given the rock and the province's elevated readings.

Stony Mountain calls are dominated by movement and freezing rather than flooding. Thin soil over limestone means many foundations are shallower than our design frost depth, so we hear about doors that stick every January, cracks that open and close through the year, and floors that have gone out of level. The second category is winter: frozen well lines and supply pipes in crawlspaces that sit near outdoor temperature because they were insulated in the floor above rather than at the walls.

Private services and the escarpment geology combine to make freeze protection a design priority here. Well lines, pressure tanks and plumbing in a crawlspace that runs at outdoor temperature will eventually freeze, and pipe insulation only slows the process. Bringing the space inside the heated envelope with perimeter wall insulation and rim joist air sealing is the durable answer, with individual line insulation or heat trace reserved for specific vulnerable runs.

Where we suggest starting on a Stony Mountain property is with founding depth, because seasonal movement is the condition most likely to undo other work. If support is bearing in soil that freezes, it will keep cycling, and a sealed barrier fastened to a wall that lifts every winter will eventually tear at its terminations. Establish what is moving, correct it to stable bearing, then seal and insulate. We will tell you what can and cannot be achieved given the rock depth on your particular lot.

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It is colourless and odourless, it moves upward through soil, and it enters buildings through any opening in contact with the ground. Health Canada identifies it as the second leading cause of lung cancer after smoking, and sets a guideline of 200 becquerels per cubic metre for indoor air, recommending remedial action above that level. Manitoba consistently records some of the highest residential readings in Canada, which makes this a local issue rather than an abstract one.

A crawlspace is the most efficient radon entry point a house can have. Where there is exposed soil, or a thin unsealed membrane, soil gas moves into the space essentially unimpeded — and from there into the living area, because the stack effect pulls air upward through a house continuously during the heating season. Our long heating season means that pressure difference operates for a large part of the year. A house with a sealed basement slab but an open crawlspace under an addition can still have substantially elevated levels.

Testing has to come before mitigation, and it has to be done correctly. A long-term test of at least three months, ideally during the heating season when windows are closed and the stack effect is strongest, gives a representative result. Short-term tests are useful as a screening indicator but fluctuate too much to base a decision on. We will arrange or guide testing, and we would rather you test first than buy a mitigation system you may not need — though in a crawlspace with exposed soil, sealing the floor is worthwhile on moisture grounds regardless of the radon number.

Where mitigation is needed, the standard approach in a crawlspace is active sub-membrane depressurization. A sealed membrane is installed across the floor and up the walls — the same membrane used for encapsulation, which is why these two projects belong together — and a dedicated fan draws continuously from beneath it through a perforated collection pipe, venting above the roofline. That negative pressure under the membrane captures soil gas before it can enter the space. The system is simple and highly effective, but it depends entirely on how well the membrane is sealed, which is why installation quality matters more than equipment selection.

Post-mitigation verification is not optional in our view. After the system is running and the building has returned to normal operating conditions, the space and the living area should be retested to confirm the reduction. We also label the system, explain what the manometer reading means, and tell you what to check — because a mitigation fan is a mechanical device that will eventually fail, usually silently. A system nobody monitors is a system that may have stopped protecting you years ago.

Pressure and building dynamics explain why two apparently identical houses can test very differently, and why your neighbour's result tells you nothing about yours. Radon entry depends on the pressure difference between the soil and the building interior, and that depends on stack effect strength, exhaust appliances, mechanical ventilation balance, wind, and how tight the building is. A house with powerful kitchen and bathroom exhaust and no make-up air runs at a greater negative pressure, and draws correspondingly more soil gas. This is also why sealing work and mechanical changes can shift a reading in either direction, and why testing after any significant envelope work is sensible.

System design details separate a mitigation that works from one that merely hums. The collection point beneath the membrane needs a permeable layer — clean gravel or a drainage mat — so the fan can draw from the whole footprint rather than a single spot. The fan has to be sized to the soil's permeability and the area served: too little suction leaves parts of the footprint uncaptured, too much wastes energy and can pull conditioned air if the membrane has gaps. The exhaust must terminate above the roofline and away from windows and air intakes. And the pipe needs a manometer, so the system reports its own status.

Timing relative to encapsulation is the practical advice we give most often. If you are sealing a crawlspace for moisture reasons and you have not tested for radon, test first. The collection pipe and gravel layer belong under the membrane, installed before it goes down; retrofitting them means cutting open a barrier you just paid for and compromising its continuity. A long-term test takes three months, which is usually compatible with planning a project anyway. If the number comes back low, you have lost nothing but gained a documented baseline. If it comes back high, you have saved yourself from doing the job twice.