Passive vs. Active Radon Systems
A passive system is a vent pipe and sealed sub-slab membrane installed during new construction, relying on natural airflow with no fan. An active system adds an inline fan that continuously and mechanically draws radon out. Passive systems alone often aren't enough on their own to bring an elevated home below 4 pCi/L, which is why most existing-home mitigation is active.
Passive systems
Built into new construction as a lower-cost radon-resistant feature: a gravel or matting layer under the slab, a sealed vapor barrier, and a vent pipe running from beneath the foundation up through the roof, with no fan. It relies on natural stack-effect airflow (warm air rising) to move gas out. It's cheaper to install during a new build than to retrofit later, but it's not guaranteed to keep levels below the action threshold on its own.
Active systems
The same basic pipe setup, but with an inline fan added, either during the original build or retrofitted onto an existing passive system. The fan actively depressurizes the area beneath the slab, creating continuous negative pressure that pulls radon gas out before it can enter the living space. This is the standard fix once a test comes back elevated, described step by step on our process page.
Converting passive to active
If a new-construction home already has the passive vent pipe in place and a test comes back elevated, adding a fan to the existing pipe is usually far cheaper than installing a system from scratch, since the pipe routing and roof penetration are already done. This is one of the more common, lower-cost mitigation jobs.
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