For a 1,800-square-foot, two-story home with a standard pipe route, our calculator produces a midpoint of about $2,000 for a basement, $2,250 for a crawl space, and $2,500 for a mixed foundation. These are planning figures from our published model, not contractor averages.
Side-by-side planning ranges
| Foundation | Planning range | Typical design question |
|---|---|---|
| Slab-on-grade | $1,450–$2,500 | How well does air move beneath the slab? |
| Basement | $1,550–$2,650 | Can one suction point communicate across the slab? |
| Crawl space | $1,750–$3,000 | How much membrane, sealing, and access work is required? |
| Mixed foundation | $1,950–$3,350 | Can all sections share one fan and vent route? |
Assumptions: 1,800 sq ft, two stories, standard pipe route, September 2026 model.
Basement and slab systems
Active sub-slab depressurization is a common approach for basement and slab-on-grade homes. A contractor creates one or more suction points through or beneath the slab and uses a fan to draw soil gas into a vent pipe before it enters the living area.
A simple open basement does not guarantee a simple system. Footings, additions, finished rooms, drain tile, sumps, and different slab pours can divide the area into separate pressure zones. Diagnostic testing helps the contractor determine whether one suction point can influence the required area.
Crawl-space systems
An earth-floor crawl space does not provide the solid collection surface that a concrete slab provides. A common approach is submembrane depressurization: a durable membrane is placed over the soil, its seams and edges are sealed, and a fan draws soil gas from beneath it.
Membrane area, piers, low clearance, stored materials, moisture, and difficult access can add labor. The membrane also needs a design that remains serviceable after installation. These requirements are why our calculator adds a larger allowance for crawl spaces than for a basic slab.
Mixed foundations need special attention
A home may combine a basement, slab-on-grade addition, and crawl space. Each section can behave as a separate collection zone. The contractor must determine whether the zones communicate well enough to share suction and whether one fan can serve the finished design.
Our model assigns the largest foundation adjustment to mixed homes because they are more likely to need extra diagnostics, pipe, sealing, or collection points. A compact mixed-foundation home can still be straightforward, so this adjustment should be treated as an uncertainty allowance rather than a rule.
What to show the contractor
- All lower-level rooms, crawl-space access points, additions, and slab transitions.
- Existing sump pits, drain tile, vapor barriers, and water-management equipment.
- Finished areas where exposed PVC would be unacceptable.
- Potential exterior, garage, closet, and attic routes.
- Radon test reports, including the test location and dates.
Sources and limits
System descriptions follow the EPA’s Consumer’s Guide to Radon Reduction. The EPA reports typical reductions of 50–99% for both sub-slab suction and crawl-space submembrane depressurization, while noting that results depend on the home and installation. Only an on-site evaluation can establish the appropriate system and price.