Radon Mitigation in Lorette

Lorette, southeast of Winnipeg in the RM of Taché, sits on heavy Red River valley clay with poor drainage characteristics. The clay here is strongly expansive: it takes on water through spring and early summer and swells, then dries and shrinks through late summer, pulling away from foundation walls and leaving gaps that funnel the next rain straight down. Over a decade of that cycling, crawlspace walls accumulate cracking and piers lose their even bearing. It is slow, unspectacular damage that shows up as sloping floors and sticking doors long before anyone looks underneath.

The community has grown steadily as a commuter town, so housing spans roughly five decades. Mid-century homes often have small crawlspaces under part of the structure, with soil floors and open vents. Newer homes have better envelopes overall but frequently include an unheated crawlspace under an addition, sunroom or mechanical area. In both cases the recurring findings are the same: condensation on cold surfaces in summer, frost on the underside of the subfloor near vents in winter, elevated wood moisture content, and mould wherever humidity and organic material meet.

Because Lorette is largely on private water and septic, our sealing details account for well lines, pressure tanks and septic penetrations, and we insulate those lines where they pass through unheated space. The system we usually recommend is interior drainage where groundwater warrants it, a reinforced vapour barrier sealed to the walls and penetrations, perimeter insulation to keep the space conditioned, and humidity control with a drain that will not freeze. Structural work — properly founded jack posts, rebuilt piers — goes in first where the floor system has been moving with the clay.

The Lorette calls we take are mostly about slow, cumulative symptoms rather than dramatic events: a sunroom floor that has gone noticeably out of level, doors that bind seasonally, a smell that appears in spring, insulation hanging out of the joists in a crawlspace nobody has entered in fifteen years. These are the signatures of expansive clay working a shallow foundation over decades, combined with a space left outside the heated envelope.

Private water and septic mean the envelope has more penetrations to detail, and in a space that runs near outdoor temperature those penetrations are freeze risks as well as air leaks. We seal and insulate well lines, pressure tanks and septic penetrations as specific scope items. Structural work falls under the RM of Taché's permitting, which we confirm with them directly.

Our usual first step in Lorette is to determine founding depth under any addition, because that single fact decides whether you have a maintenance problem or a structural one. Piers founded above the frost line will keep moving, and no amount of sealing or insulating changes that. Once support is on stable bearing, the rest of the work — drainage where needed, barrier, perimeter insulation, humidity control — has something stable to attach to.

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.