Sub slab depressurization, explained without jargon
The standard fix is a system with an unglamorous name and a simple idea. A hole is cored through the basement floor slab, a pipe is run from that hole up and out of the house, and a fan pulls continuously on it.
That constant suction makes the space under your slab lower in pressure than the room above it. Radon takes the path of least resistance, which is now the pipe instead of the crack in your floor, and gets discharged above the roofline where it disperses.
The fan runs all the time. It uses roughly as much electricity as a light bulb.
What installation involves in a typical Spokane basement
- Diagnostics. A test hole tells the contractor how well air moves under your slab, which decides how many suction points you need and how strong a fan.
- Sealing. Visible cracks, the gap around the sump pit, and floor drains get sealed. Sealing alone is not a fix, but it makes the system work better.
- The suction point and piping. Usually one, sometimes more in a large or segmented basement. Pipe runs either up through the interior and out the roof, or out the rim joist and up the exterior wall.
- Fan and manometer. The fan mounts outside the living space, in the attic or outdoors, never in the basement. A small U shaped gauge gets installed where you can see it.
- Post mitigation test. A new test 24 hours to 30 days after startup. This is not optional and it is the only proof the system worked.
Crawl spaces are different
Plenty of older Spokane houses have a crawl space rather than a full basement. There the method is a sealed membrane over the dirt, with the suction applied underneath it. It is more labor than a slab job and usually costs more.
How to know it worked
Ask for the post mitigation test result in writing, and compare it to the original. A system that takes a house from 12 pCi/L to 6 pCi/L reduced radon by half and still leaves you above the action level. Reduction is not the goal; getting under 4.0 is, and most systems land well under 2.0.