Mitigation system types, matched to foundations
There is no “best” radon system — there is a best system for your foundation. This guide maps the five designs Chicagoland contractors actually install to the houses they fit, so the quotes you collect make sense on arrival.
| Design | Best fit | How it works |
|---|---|---|
| Classic sub-slab depressurization | Poured or block basements; slab floors | Suction point cored through the slab; fan pulls soil gas from beneath and vents above the roof. The regional default. |
| Sump / drain-tile suction | Homes with sump pits connected to perimeter drain tile | Airtight sump lid; suction drawn from the pit reaches the whole tile loop — often superb coverage from one point. Pump keeps working. |
| Crawl-space sub-membrane | Dirt or gravel crawl spaces (alone or in combos) | Durable membrane sealed over exposed soil; suction under the membrane captures gas before it enters. Usually tied into a shared fan. |
| Slab-on-grade variants | Ranches, townhomes, and additions without basements | Same physics through a discreet interior, closet, or garage suction point — slab homes are fully mitigatable. |
| Passive-system activation | Newer homes with builder rough-in pipes | An in-line fan and indicator added to the existing pipe converts passive to active — typically the smallest scope on this table. |
Combination foundations: the design conversation that matters
Chicagoland’s split-levels, tri-levels, and additions routinely combine two or three foundation types under one roof. The design rule is simple to state and easy to botch: every zone that touches soil gets addressed — a basement slab point here, a membrane there, sometimes a second suction point — commonly all served by one fan. When two quotes for a combination house differ sharply, the difference is usually a zone one bidder skipped. Ask each to name the zones; the confident answer is the tell.
Passive vs. active, settled
Passive systems (pipe only, no fan) rely on natural stack effect and help modestly; many homes with passive rough-ins still test above 4 pCi/L. Activation adds the fan that makes the physics decisive. If your newer home tests elevated, check the attic before pricing a retrofit — the pipe may already be there. Related: how the full system works and what each scope costs.
Common questions
Can one fan really serve multiple suction points?
Yes, when the design supports it — manifolded runs from a basement point plus a crawl membrane into a single properly sized fan are routine. The limits are airflow and pressure: too many points on too small a fan and nothing pulls hard enough. That sizing judgment is exactly what you are paying a licensed designer for, and the verification retest is how you confirm they got it right.
Do exterior and interior (attic) routed systems perform differently?
Performance is equivalent when designed well — the choice is about aesthetics, climate, and structure. Attic routing hides the pipe and shelters the fan; exterior routing is often faster and cheaper to install. In our climate, exterior condensation management is a routine design detail contractors handle. Pick on looks and quote; insist on performance via the retest either way.
Is a bigger fan always better?
No — oversizing wastes electricity, adds noise, and can pull excess conditioned air through slab leakage without lowering radon further. The right fan matches your sub-slab resistance and system layout. Treat a quote’s fan model as a design choice to be explained, not a horsepower contest to be won.
Our house needs a membrane AND a slab point. Is that overkill?
It’s the textbook answer for your foundation, not an upsell — a crawl space left untreated keeps feeding radon no matter how well the basement slab is depressurized. The retest protects you here too: if a bidder claims one zone can be skipped, ask them to put the post-mitigation number they expect in writing.
Sources
Get designs, not guesses
Describe your foundation once — up to three licensed contractors respond with real designs and real numbers.