Modeling radon entry into Florida slab-on-grade houses

Area of Science:

• Environmental Science
• Geophysics
• Building Science

Background:

• Radon gas poses a significant indoor air quality risk.
• Understanding radon entry pathways into residential structures is crucial for mitigation.
• Florida homes with concrete slab foundations on permeable block stem walls present unique radon entry challenges.

Purpose of the Study:

• To model and quantify radon entry rates into a Florida house with a specific foundation design.
• To investigate the impact of various soil, backfill, and structural parameters on radon transport.
• To identify key factors influencing radon entry and evaluate potential mitigation strategies.

Main Methods:

• Developed a steady-state finite-difference model solving Laplace's and mass-transport equations.
• Simulated radon entry via diffusion and advection through the slab, stem wall, and foundation gaps.
• Analyzed the effects of variable soil/backfill permeability, radium content, and water table depth.

Main Results:

• Radon entry rates are typically low, increasing significantly with high soil/backfill permeability or radium content.
• Variations in most parameters, except soil permeability and radium, had minor effects on total radon entry.
• Decreasing backfill permeability and using an impermeable, gap-free stem wall showed substantial reductions in radon entry.

Conclusions:

• The foundation design, specifically stem wall permeability and backfill material, significantly impacts radon intrusion.
• Implementing an impermeable stem wall combined with low-permeability backfill is predicted to reduce radon entry by 71%.
• Optimizing foundation construction can be an effective strategy for mitigating indoor radon levels.