Effectiveness of Radon Control Features in New House Construction, South Central Florida

The State of Florida has a 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 were screened to be over 1,000 pCi/L. Some of the house sites had concentrations over 12,000 pCi/L. Slab integrity was monitored over time, and post-construction ventilation and radon entry were measured in all the houses. The houses with slab-instem wall foundations exhibited more slab cracking than did those with 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. Six of the houses had postconstruction average indoor radon concentrations of less than 2 pCi/L; six had average concentrations of 2 4 pCi/L; and two had average concentrations exceeding 4 pCi/L. One of the two houses with elevated indoor radon concentrations was on the site with the highest soil radium content (averaging 13.9 pCi/g), radon flux measurements through the compacted fill soil (6.1 pCi/ m2s), and sub-slab radon concentrations (12,000 pCi/L). The other house was suspected of having an inadequately sealed tub trap. Effectiveness of Radon Control Features in New House Construction, South Central Florida