When homeowners first learn their radon level is high, the idea of "fixing" an invisible gas can feel mysterious. The reality is reassuringly simple. The most common and effective approach — sub-slab depressurization — uses basic physics to intercept radon before it ever enters your living space. Here is how it actually works.
Radon gas forms in the soil beneath your home and is under slightly higher pressure than the air inside your house, especially during Calgary winters when furnaces create a gentle vacuum indoors. That pressure difference pulls soil gas up through cracks in the concrete slab, gaps around plumbing, sump pits, and other openings. A mitigation system reverses that flow.
Sub-slab depressurization works by creating an area of lower pressure beneath your foundation slab than the pressure inside your home. Once the space under the slab is at lower pressure than your living area, radon no longer has a reason to migrate upward. Instead, it is captured below the floor and routed safely outdoors before it can enter.
The installer cores a hole through the concrete slab and excavates a small cavity in the gravel or soil beneath it. This "suction pit" becomes the collection point. In homes with permeable sub-slab material, a single well-placed suction point can influence the entire footprint of the foundation.
A sealed PVC pipe connects the suction point and runs up through the home (or along an exterior wall) to a discharge point above the roofline. This routing ensures the radon is released high enough to disperse harmlessly and not re-enter through windows or soffits.
An inline fan, mounted outside the living space (in an attic, garage, or on the exterior), continuously draws air from beneath the slab through the pipe and expels it outdoors. The fan is sized to your home's specific soil conditions — tighter Alberta soils require more powerful suction, while loose gravel needs less.
A simple U-shaped pressure gauge on the pipe shows the system is running. If the liquid levels are uneven, the fan is working. If they sit level, that is your signal the fan has stopped and needs attention.
Before or alongside installing the active system, a quality contractor seals major radon entry points — large foundation cracks, the perimeter of sump pits, and openings around utilities. Sealing alone rarely fixes a radon problem, but combined with active depressurization it makes the fan far more efficient and helps achieve the lowest possible levels.
Dirt-floor crawlspaces use a variation called sub-membrane depressurization. A sealed plastic membrane is laid over the soil, and the fan draws radon from beneath that membrane. The principle is identical — create low pressure under the barrier so gas is captured rather than entering the home.
A correctly designed sub-slab system routinely reduces radon by 80 to 99 percent, bringing homes that started well above the 200 Bq/m³ guideline down to a small fraction of it. That is why C-NRPP recognizes active soil depressurization as the primary mitigation method.
A system is only finished once it is proven. After installation, a follow-up radon test confirms the new, lower level. At Onyx Radon, every installation includes a post-mitigation test so you have documented evidence that your home is protected — not just a promise. That verification is the difference between a system that looks right and one you can truly trust.
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