radon mitigation
A mitigation system does not filter anything and it does not seal the house. It gives the soil gas an easier route than your floor. A pipe drops through the slab into a small pit in the gravel underneath, a fan on that pipe holds the space below the concrete at slightly lower pressure than the room above it, and the gas that used to come up through cracks goes up the pipe and out above the roof instead. Done properly it is quiet, it is unobtrusive, and it works for as long as the fan runs — which is why the gauge on the pipe matters as much as the pipe.
A mitigation system does not filter the air and it does not seal the house shut. It reverses a pressure difference. Under your slab there is a layer of gravel or soil holding radon at a slightly higher pressure than the room above, so the gas moves up through every crack and gap it can find. Put a pipe into that layer and a fan on the pipe, and the space under the concrete becomes the low-pressure side. The gas takes the pipe instead, travels up past the fan and discharges above the roofline. Nothing about the air inside the house is treated; the gas simply never gets in.
The single question that sets the price is how far one suction point can reach. Clean, coarse gravel under a slab lets a fan pull a pressure field across an entire basement from one hole. Sand, fine fill or native clay packed straight against the concrete — common in older Denver construction where nobody ever specified a gravel layer — can stop a fan reaching the far wall. We test that before quoting rather than after, because the alternative is a system that treats half a house and a retest that quietly fails.
Usually there are two or three viable routes and they cost different amounts. Up the outside wall is the cheapest and the most visible. Up through the garage is tidier. Through an interior closet into the attic, with the fan in the attic and the discharge through the roof, is the least visible and the most work. Codes and standards drive some of it — the fan is never inside the living space, and the discharge terminates above the roofline and clear of windows and intakes — but within those rules the choice is yours, and you should be shown it rather than told it.
A fan can only depressurize the sub-slab if the slab is reasonably airtight. Every open crack, every unsealed pipe penetration and every uncapped sump pit is a shortcut that lets the fan pull heated room air instead of soil gas — worse performance and a higher power bill at the same time. So sealing the floor is part of the install, not a line item added afterwards. On a house with a bare dirt crawlspace attached, that work becomes a membrane job instead, and it is usually the larger half of the day.
Every system gets a manometer on the pipe — a U-shaped tube of coloured fluid whose two columns sit at different heights while the fan pulls. It costs almost nothing and it is the only way you will ever notice a failed fan, because nothing else in the house changes when one stops. And then we test the house again. That second reading is included, because a system nobody verified and a system that failed look exactly alike from the driveway.
How long does it take? Most single-family systems go in inside a day. Complicated foundations — several slabs at different levels, an addition, a crawlspace tied in — can run to two.
These usually come up in the same conversation:
A continuous monitor in the lowest lived-in level for 48 hours, logging hourly — so you get a curve you can read, not one number that might have been a fluke.
Learn More →An open sump pit is a hole straight into the soil. Sealing pits, cracks and penetrations is what makes the rest of a system work — and it is where cheap installs cut corners.
Learn More →A second test after the system has been running. Included with every install, and available on its own for a system nobody has ever checked.
Learn More →Free · No Obligation
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