Sub-Slab Depressurization: How It Works

Most sub-slab depressurization installs are completed in about a day, though homes with multiple foundation types or crawl spaces can take longer.

Sub-slab depressurization (SSD) is the standard, most effective method for reducing indoor radon, and it's what a PA DEP-certified contractor installs in the large majority of York County homes.

The mechanism

A suction pipe is inserted through the foundation slab (or, for crawl spaces, beneath a sealed vapor barrier) into the soil or gravel layer underneath. A continuously running radon fan draws soil gas — including radon — out from beneath the house and vents it above the roofline, away from windows and living space, before it can enter the home. The slab and any other openings (sump pits, cracks, utility penetrations) get sealed as part of the same job, since an unsealed opening gives radon another way in and reduces how well the vacuum can pull.

Why it works so well

Because SSD intercepts radon before it enters the house rather than trying to filter or dilute it once it's already indoors, properly installed systems reduce indoor radon levels by 50–99%. It's the same underlying approach EPA and PA DEP both point to as the standard fix, whether the home sits on a slab, over a basement, or above a crawl space.

Sub-slab depressurization systems run continuously and need only occasional attention — mainly checking the manometer gauge to confirm the fan is still under vacuum, and eventual fan replacement over the system's lifespan.

A small manometer (u-tube gauge) mounted on the vent pipe gives a visual, at-a-glance way to confirm the system's still working — no monitoring service or subscription required.

Is SSD right for every home?

The core method is consistent, but placement and pipe routing vary by foundation type — which is exactly why this is a licensed-contractor job, not a DIY project. See radon mitigation cost for what installation typically runs, or have a mitigation system installed for the local picture.

Get a Free Radon Estimate to find out what an SSD system looks like for your home.