Passive Radon Control Feature Effectiveness in New House Construction in South Central Florida

The State of Florida has a draft radon standard for new construction. This study was conducted to evaluate the effectiveness of two slab types (monolithic and slab-in-stem wall) in retarding radon entry in new houses built in accordance with the proposed standard over high radon potential soils. Fourteen houses were monitored during their construction on sites whose soil gas radon concentrations ranged from 1000 to 12,000 pCi/L. The slab integrity was monitored over time, and post-construction ventilation and radon entry measurements were made in all the houses. The slabs-in-stem wall exhibited significantly more slab cracking than did the monolithic slabs. Those houses also had higher average radon entry rates, radon entry velocities, and concentration ratios than the monolithic slab houses. Both slab types proved to be effective in retarding radon entry, especially when penetrations were properly sealed.