What the problem is
New homes are not inherently low-radon. Tighter building envelopes actually reduce natural air exchange, so soil gas that enters has less opportunity to dilute. The difference with new construction is opportunity: while the ground is open and the slab is unpoured, the entire soil-gas pathway can be controlled for a small fraction of what a retrofit costs.
How to know if you need it
- You are building anywhere in New Mexico, where geology commonly produces elevated results.
- Neighboring homes or the subdivision have tested high.
- You are building a home with a basement or a walk-out lower level.
- You want the option to activate a system later without cutting a finished slab.
The five features of a radon-resistant build
- 1Gas-permeable layer: 4 inches of clean, coarse aggregate beneath the slab so soil gas can move to a single collection point.
- 2Vapor retarder: heavy polyethylene sheeting over the aggregate, seams lapped and sealed.
- 3Sealing and caulking: all slab penetrations, control joints, and the floor-wall joint sealed.
- 4Vent pipe: a 3- or 4-inch PVC riser from a T-fitting in the aggregate, run through the building and out above the roofline.
- 5Junction box: an electrical box in the attic beside the vent pipe so a fan can be added later without new wiring.
Process and construction sequencing
| Construction stage | Radon work |
|---|---|
| Sub-grade prep | Verify clean aggregate depth and grading |
| Before slab pour | Set the T-fitting, membrane, and riser stub |
| Framing | Route the vent pipe through chases to the attic |
| Rough electrical | Install the junction box adjacent to the pipe |
| Drywall / finish | Seal penetrations, label the pipe |
| After occupancy | Test; activate with a fan only if the result warrants it |
Expected timeline
The rough-in adds hours, not days, and happens inside stages the builder is already performing. Activation later — adding a fan to an existing riser and junction box — is typically a 1–2 hour visit followed by a verification test.
What affects the cost
- Slab area and number of risers.
- Distance from the collection point to the roof termination.
- Whether the aggregate layer already meets specification.
- Coordination with the framing and electrical schedule.
- Activation later adds the fan, electrical connection, and verification test.
What happens after occupancy
Test the finished home. A passive system alone reduces radon in many houses but not all — the stack effect that drives it is weak in mild weather. If the test comes back at or above 4.0 pCi/L, adding a fan converts the passive stack into an active system and almost always resolves it. Retest after activation, then every two years.
Related services
Keep learning
- How Radon Mitigation Actually WorksA mitigation system does not filter radon. It reverses the pressure difference that pulls soil gas into your home in the first place.
- EPA Radon Action Levels ExplainedTwo numbers drive nearly every radon decision: 4.0 pCi/L, where the EPA recommends action, and 2.0 pCi/L, where it suggests considering it. Here is what sits behind them.