Sub-slab depressurization is the technical name for the pipe-and-fan system used in most radon fixes. The name sounds complicated; the underlying idea is not.
Why radon gets into a house in the first place
Radon is a gas produced by the natural decay of uranium in soil and rock — it’s present almost everywhere in Colorado soil to some degree. Homes are, air-pressure-wise, usually slightly negative relative to the soil beneath them (a mix of the stack effect, HVAC systems, and wind). That small pressure difference is enough to pull soil gas up through slab cracks, sump pits, and utility penetrations.
What the system actually does
A sub-slab depressurization system doesn’t filter or clean the air — it changes the pressure balance. A suction point beneath the slab, connected to a fan running continuously, creates negative pressure in the soil beneath the house that’s stronger than the pressure difference pulling gas upward. Radon gets pulled sideways into the piping instead of upward into your living space, and is vented above the roofline where it disperses harmlessly.
Anatomy of a system
- Suction point: a cored opening in the slab connected to a small excavated pit, giving the system access to the gravel or soil layer beneath the foundation.
- Piping: PVC pipe routes from the suction point to an exterior termination point above the roofline.
- Fan: an inline fan runs continuously, providing the negative pressure that keeps the system working.
- Exhaust: the termination point is positioned away from windows, doors, and roof eaves so vented gas disperses rather than re-entering the house.
Why sizing matters
Soil under a slab isn’t uniform — some soil is loose and permeable (easy for a system to pull air through a wide radius), some is dense clay (which needs a stronger fan or multiple suction points to cover the same footprint). A system sized for the wrong soil type either underperforms or wastes electricity running harder than it needs to.
Frequently asked questions
Does the fan use a lot of electricity?
A correctly sized fan typically costs somewhere in the range of a couple dollars a month to run continuously — oversized fans cost more without doing more good.
Can this be a DIY project?
The parts are simple, but correct suction-point placement and fan sizing depend on foundation-specific factors that are hard to judge without experience — get it wrong and you can end up with a system that doesn’t actually lower your number.
Want to know what this would look like for your specific foundation? See our mitigation services or request a quote.