Radon Mitigation in East St. Paul

East St. Paul occupies the low ground east of the Red River just past Winnipeg's northern edge, and the water table here is shallow enough that it governs how any below-grade space has to be built. The soil is the same heavy Red River valley clay found in north Winnipeg, with poor infiltration and strong seasonal movement. During spring melt and after heavy summer rain, water perches on top of that clay and travels along any path of least resistance — which is frequently the gravel bed and backfill around a crawlspace wall.

Much of the municipality developed as country residential acreages from the 1960s onward, with a second wave of larger homes in the 1990s and 2000s. That produces two distinct crawlspace populations. The older acreage homes tend to have shallow crawlspaces with exposed soil floors, open vents and fibreglass batts stapled between the joists — an assembly that fails predictably in this climate. The newer homes usually have conditioned crawlspaces as designed mechanical spaces, where the problems we find are more often a failed sump, an undersized dehumidifier, or air sealing that was never completed at the rim joist.

Because most properties here are on private septic and well, crawlspace work needs to account for utility penetrations that a city home does not have. We seal around septic lines, well lines and pressure tanks properly, and we check that sump discharge is routed well away from both the foundation and the septic field. We also look closely at insulation at the rim joist and perimeter wall, since an unconditioned crawlspace in East St. Paul can swing from plus 25 to minus 25 across the year and drive serious condensation on cold surfaces.

The pattern of calls from East St. Paul reflects the two waves of development. Owners of the older acreage homes contact us about damp crawlspaces with soil floors, failed batt insulation and a smell carrying into the house. Owners of the newer large homes call about performance problems in crawlspaces that were built as designed mechanical spaces — a sump that failed during melt, a dehumidifier that stopped working because it drains into a bucket, a space that runs cold because the rim joist was never sealed. The older group needs a system built; the newer group needs one finished properly.

Private services shape the work here. We seal and insulate around well lines, pressure tanks and septic penetrations as a specific scope item, because these are both envelope breaches and freeze risks. Discharge routing needs to keep water away from the septic field as well as the foundation. The RM of East St. Paul administers its own permits, and we confirm requirements with them rather than assuming City of Winnipeg rules apply.

Where we usually suggest starting in East St. Paul is with the water table, because the ground here is low and the clay holds water. Establishing whether spring water arrives as surface runoff down the backfill or as a rising table through the floor determines the entire scope — grading and downspouts for the former, interior drainage and a properly specified sump for the latter. We would rather spend an hour determining that than sell you a barrier that gets undermined in its first April.

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.