Passive radon-resistant construction: gas-permeable layer under slab, gas-tight barrier, vent pipe routed through roof
Indoor airPLUS §Radon Control — passive radon system in Zones 1 + 2Description
In EPA Radon Zone 1 (high) and Zone 2 (moderate), Indoor airPLUS requires passive radon-resistant new construction (RRNC) per ASTM E1465 / EPA guidance: a 4-in gas-permeable layer (gravel) under the slab, a 6-mil polyethylene gas barrier over it lapped 12 in at joints + sealed, a 3-in PVC vent pipe stubbed from the gravel layer through the roof (active-ready), an electrical outlet in the attic near the vent for a future radon fan, and a label identifying the system. The label requires post-construction radon test results.
Why this exists
Radon causes ~21,000 lung-cancer deaths/year in the US. Passive RRNC adds ~$300-500 to a typical home — far cheaper than retrofitting an active radon system later. Architects should include the passive radon stack on the plumbing plan; it's the foundation detail most builders skip when not designed in.
Categories
Source
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Cathedral ceilings: gable-end wall stud must extend to roofline (no hinge at top plate) · HUD RSDG §5.6.2
- In high-wind zones, soffits need solid blocking at exterior walls · HUD RSDG §5.6.5
- Sill-plate anchor bolts: 1/2" diameter @ 6 ft on-center, max 12 inches from corners/splices · HUD RSDG §7.4.3
- Exterior ramps: maximum slope 1:12, minimum 36 inch clear width · HUD FHA Design Manual Chapter Two §2.7
- Ramps over 6 inches rise must have handrails on both sides · HUD FHA Design Manual Chapter Two §2.8
Last reviewed 2026-05-15.