Radon Mitigation in West St. Paul

West St. Paul sits on the west bank of the Red River north of Winnipeg, and flood exposure is the first thing we assess on any property here. Homes close to the river have a documented history of spring water, and many sit behind individual earthen protection or on raised pads. For crawlspaces, that proximity translates into a seasonally high water table and sustained hydrostatic pressure against foundation walls during melt — conditions that find every unsealed joint and every gap in a vapour barrier.

The soil profile is Red River clay with pockets of silt, and it moves noticeably through the year. We regularly document diagonal cracking in crawlspace stem walls, piers that have tipped as the clay beneath them shrank, and sill plates that no longer bear evenly on the wall. Where shallow footings were used — common in older additions, sunrooms and garage-adjacent crawlspaces — frost heave compounds the movement, lifting one part of the structure in January and settling it again in May.

Our work in West St. Paul usually combines structural correction with moisture control, in that order. Adjustable steel jack posts on properly sized pads stabilize sagging beams; piers founded above frost depth get rebuilt or underpinned so they stop moving seasonally. Only then does encapsulation make sense: a reinforced barrier across the floor and up the walls, sealed at penetrations, with a sump and discharge sized for melt volume rather than nuisance seepage. We finish with humidity monitoring so you can confirm the space is holding its target through a full freeze-thaw cycle.

Calls from West St. Paul tend to arrive in two seasons and two forms. In spring it is water: a crawlspace taking melt or river-driven groundwater, sometimes for the first time in years. Through the rest of the year it is movement: cracking in a crawlspace stem wall that has visibly progressed, a floor that has gone out of level, a sunroom that has separated from the main house. The two are connected, because clay that takes on water swells and clay that dries shrinks, and a shallow footing sits in the middle of that cycle.

Flood history is worth establishing property by property here, and it is usually knowable. Municipal records, neighbours and sellers can all tell you whether a particular lot has taken water, whether it sits behind individual protection, and whether the pad was raised. That history determines how we specify a system: a crawlspace on a property with two recorded events in twenty years should be built to be inspected, serviced and recovered after an event, not sealed as though water will never return.

Our first recommendation for most West St. Paul properties is to get founding depth and bearing established before anything else, because structural correction has to precede sealing. If piers under an addition are founded at 600 millimetres, they will keep cycling regardless of what barrier goes down, and the movement will eventually compromise the barrier's terminations. Correct the support, manage the water, then seal — in that order, and we will document each stage so you can see what changed.

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.