Radon Mitigation in Oakbank

Oakbank sits east of Winnipeg in the RM of Springfield, on the same heavy clay that covers most of the Red River valley. The clay is slow draining and strongly expansive, so water from snowmelt and summer storms tends to sit on and move along the surface rather than soak in. Where a house has a crawlspace, that surface water finds the backfill trench around the foundation — the loosest, most permeable path available — and travels down it. This is the single most common reason we are called out here in April.

The community grew quickly as a commuter area from the 1970s onward, with substantial additional development through the 2000s. Many homes are large, well built and on private services, but crawlspaces frequently appear as secondary structures: under additions, sunrooms, mechanical rooms and attached garages. These secondary crawlspaces are the problem children. They are often built on shallower footings than the main house, insulated as an afterthought, left unheated, and never given a vapour barrier or a drainage path. Frost-heaved piers, frozen supply lines and heavy condensation on cold rim joists are the predictable outcomes.

Our scope in Oakbank usually begins with exterior water management, because fixing grading and downspouts often removes most of the load before any interior work starts. From there we install interior drainage and a sump where groundwater warrants it, encapsulate with a reinforced barrier sealed to the walls and around every well, septic and plumbing penetration, and insulate the perimeter so the space can be kept conditioned through a Manitoba winter. Where piers have been cycling with frost, we rebuild or underpin them so the structure stops moving.

The Oakbank calls we take are heavily seasonal. In the first warm week of spring, homeowners find water in crawlspaces under additions and sunrooms, having arrived down the foundation backfill while the clay below was still frozen. In deep winter, the calls are about frozen lines and cold floors in those same spaces. The common factor is a secondary crawlspace built to a lower standard than the house it attaches to — shallow footings, no barrier, insulation in the joists, and no heat.

Because most Oakbank properties are on private services, the envelope has more penetrations than a city house: well line, pressure tank, septic, sometimes a cistern. Each needs sealing and insulating as a deliberate scope item. Sump discharge needs routing clear of both the foundation and the septic field. Structural work falls under the RM of Springfield's permitting process, which we confirm directly rather than assuming city rules.

Our standard first recommendation in Oakbank is exterior water management, because on flat, dense clay it does a remarkable amount of work for very little money. Extending downspouts well clear of the wall, re-establishing positive grade where clay backfill has settled, and keeping winter snow off the foundation frequently removes most of the load before any interior system is specified. We will tell you after an inspection whether that is likely to be sufficient on its own or merely the first stage.

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.