Crawlspaces need a different radon playbook
There's no slab to pull from under a crawlspace. The foundation type decides the method, and this one has its own.
A membrane instead of a slab
Standard radon work pulls soil gas from under a concrete slab. A crawlspace has no slab, just bare dirt or gravel breathing straight up into the floor above. So the industry method builds the barrier the concrete would have provided.
A heavy membrane gets laid over the exposed soil, lapped up the foundation walls, and sealed at the seams and around the support piers. A suction point goes under that liner, tied into a vent pipe and fan like any other system. Soil gas collects beneath the plastic and leaves through the pipe instead of rising into the living space. The full mitigation walkthrough shows how this fits the bigger picture.
It’s more labor than slab work, which is worth understanding before anyone quotes anything. A slab job is a hole and a pipe. A crawlspace job is surface prep, cutting and fitting sheet around every pier and corner, and sealing edges in a space you often can’t stand up in. The crawl height, the soil, and what’s stored down there all move the scope.
Around Sioux Falls, full crawlspace homes are the minority; basements rule here. Crawls mostly show up under pre-war cottages in the older central neighborhoods, under farmhouses on the acreage edges of the metro, and beneath additions bolted onto basement homes over the years.
When this is the right tool
Two situations call for membrane work.
The first is a home fully over a crawlspace. There, the liner-and-suction design is the mitigation system, and the whole job lives in that one space.
The second is more common in this metro: the combined foundation. A 1950s basement house grew a family-room addition on a crawl in the 80s. A split-level carries a crawl under one wing. In these homes the crawlspace is often the leak in an otherwise fixable system. You can depressurize under the basement slab all day, but if the crawl next to it keeps feeding soil gas, the number won’t come down. The fix ties a sealed crawl section into the same fan and pipe run as the sub-slab side.
Which design a given house needs is the foundation’s call, not the homeowner’s or the installer’s preference. What mitigation involves covers the whole toolkit this page is one piece of.
When it isn’t — said plainly
Membrane work is not the default answer, and it shouldn’t be sold as one.
Some combined-foundation homes come in below the action level with sub-slab suction alone, no crawl work needed. The retest is what tells you. Some crawlspaces are too tight, too wet, or too full of ductwork for a liner to seal well, and a different approach earns its keep. And a crawl that’s already conditioned and sealed into the house may behave more like a short basement than open ground.
None of that can be judged from a webpage or a phone description. Somebody has to get eyes, and usually knees, into the crawlspace before a method gets named. That’s why the honest sequence is assessment first, method second, and a follow-up test after installation to prove the number came down — not a design promised sight unseen.
Crawlspace under the house? Start with the assessment
Frequently Asked Questions
Does a crawlspace home really need a different system?
Yes, at least for that part of the house. Sub-slab suction needs a slab to pull under. Over open soil, the industry method is a sealed membrane with suction beneath it, doing the job the concrete would have done.
What is the membrane, exactly?
A heavy plastic sheet — thicker than a paint tarp, built for the job — laid across the exposed soil, run up the walls, and sealed at seams and piers. The vent pipe pulls from underneath it, so soil gas leaves before reaching the house.
Doesn't encapsulation alone fix radon?
Not reliably. A sealed liner without active suction slows the gas but doesn't remove it, and homes with plain encapsulation still test high. The fan and the follow-up test are what turn a liner into a fix you can verify.
What if only part of my house sits on a crawlspace?
That's common here — a crawl under an addition or a split-level section, basement under the rest. Combined foundations often need suction points on both parts, which is exactly what the assessment works out.