Crawlspace Radon Mitigation in Peoria, IL

Why Crawlspaces Need a Different Approach Than a Slab

In a basement or slab-on-grade home, the concrete itself does some of the work, since it is a relatively continuous barrier with only cracks, joints, and pipe penetrations as entry points. A crawlspace has none of that. Exposed dirt is porous across its entire surface, so soil gas has essentially unlimited entry points into the crawlspace air, and from there it moves up through the subfloor into the house above through the same stack effect that pulls air through a slab, just working across a much larger, more open surface.

This is why simply venting a crawlspace, which used to be common advice for moisture control, does not solve a radon problem and can sometimes make one worse by pulling in more soil gas as ventilation air moves through the space. The membrane approach addresses the actual entry surface directly rather than trying to dilute the air after the gas has already entered the crawlspace.

How Submembrane Depressurization Is Installed

Installation starts with prepping the crawlspace floor: removing debris, grading out any major low spots, and clearing the space so the membrane can lie flat and make full contact with the soil surface. A heavy-duty, puncture-resistant vapor barrier is then rolled out to cover the entire dirt floor, sealed at every seam with specialized tape, and sealed up the foundation walls and around every support pier, plumbing penetration, and other obstruction in the space. Any gap in that seal is a place radon can bypass the system, so seam and edge sealing is where the quality of a crawlspace install really shows.

A suction point is set beneath the membrane, typically a small pit dug into the soil connected to a perforated pipe or fitting that draws air from underneath the sealed barrier across a wide area. That connects to PVC pipe routed up and out of the crawlspace, through the house or along the exterior, and up to discharge above the roofline, driven by the same style of continuously running inline fan used in a sub-slab system, with the same U-tube manometer for visual confirmation that suction is active.

• •Heavy-duty vapor barrier sealed across the entire dirt floor
• •Every seam, wall edge, and pier taped and sealed airtight
• •Suction point beneath the membrane tied into a continuous fan
• •Vent pipe routed to discharge above the roofline

Combination Foundations: Basement and Crawlspace Together

A lot of homes in this area were built or added onto in stages, and it is common to find a basement under the original structure with a crawlspace under a later addition, or the reverse. Radon does not respect that boundary, and treating only one section usually leaves the problem partly unsolved, since gas can still travel from the untreated section into the living space above it, or in some cases migrate along shared foundation walls into the treated section's low-pressure zone in ways that reduce overall system efficiency.

For combination foundations, we design a system that addresses both sections, sometimes with a shared fan pulling from suction points in each area, sometimes with separate systems depending on how the two sections connect structurally. This is one of the more common judgment calls in mitigation design in older Peoria area neighborhoods, and it is exactly why a site assessment matters more than a generic quote.

Timeline, Cost, and What a Good Install Looks Like When Finished

Crawlspace jobs generally take a bit longer than a straightforward single-point sub-slab install, often one to two days depending on the size of the crawlspace, how much prep work the floor needs before the membrane goes down, and whether multiple suction points are required. Access matters too. A tight, low crawlspace with limited entry takes longer to work in than one with generous headroom.

Because crawlspace jobs involve more material, the membrane itself plus more sealing labor, they tend to land toward the higher end of the typical $900 to $2,500 range that a straightforward single-point sub-slab system might cost, and larger or multi-point crawlspace systems can run above that range depending on square footage. As with any mitigation work, a firm number comes after we have actually been in the crawlspace and seen what the floor, piers, and access look like, not from a phone estimate. When the job is done right, the membrane lies flat, every seam is sealed, the fan runs quietly, and the manometer gives you a simple way to confirm the system is doing its job for years afterward.

Frequently Asked Questions