The radon resistance of different residential construction features was evaluated for the Florida residential construction standard to distinguish regions requiring active radon controls from those where passive controls suffice. Radon resistance, defined as the ratio of reference indoor radon levels to levels with a particular construction feature, was estimated individually for candidate features using model simulations and indoor radon measurements. Active radon control by sub-slab ventilation (suction pit or ventilation mat systems) was most effective, followed by sub-slab vapor barriers, increased house ventilation, improved slab-foundation design, improved concrete quality, sealed slab cracks and openings, and sealed pipe penetrations. Sealing cracks related to slab reinforcement and soil compaction made little difference. For Florida residences, passive features reduce indoor radon by more than a factor of two, and active features give further reductions to exceed a factor of ten. This work was funded by the Florida Department of Community Affairs.
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