Reduction and Mitigation Methods
Passive Soil Depressurization (PSD) is most often employed in Radon Resistant New Construction (RRNC) and will be addressed on the RRNC page.
Active Soil Depressurization (ASD) is the most common and effective method for reducing the radon gas concentration in a building. Soil gases are driven from the high pressure soil below into the low pressure building space above. The solution is to simply reverse the pressure. Hence we have Active Soil Depressurization (ASD). We replace the pressure with a vacuum. An inline radon fan in the attic can apply suction to a point or points under the building through a PVC pipe system and expels the radon laden soil gases above the roof to be dispersed in the atmosphere.
The basic concept is quite simple, but the implementation is mired in issues of static pressure vs. air flow, pressure field extention, soil permeability, fan dynamics, subslab central footers restricting lateral draw. Did I mention being a bit of a roofer, a plumber, concrete mason, and excavator. Okay, so it might not be so simple after all. The important thing is that it works! It works exceptionally well! In many cases we are able to reduce radon levels by eighty to ninety percent depending on original Radon levels, soil permeability, and construction. Other methods generally show only marginal improvements.
Sub-Slab Depressurization (SSD) is employed in basement and slab-on-grade
applications. The difficulty with SSD is what is unseen.
The wide range of substrata material affect
the lateral flow below the slab, referred to as the pressure field extention.
The footer layout beneath the slab often segments the more porous high level
substrata in order
to better support bearing walls in the center of the
house. This can cut off the pressure field
under much of the house. This dilemma is easily adjusted for in RRNC, but
may require additional excavation or multiple penetrations through the slab
with connecting piping or an additional fan system in existing housing. In order to effectively
diagnose unseen obstructions requires test holes, very sensitive pressure monitors,
and the knowledge and experience to interpret the results. Mapping the
results from strategically placed test holes helps to anticipate pressure
field obstructions.
Sub-Membrane Depressurization (SMD) is employed in most homes built over crawl spaces. A high density polyethylene membrane covers the entire soil floor and is sealed air tight at the perimeter and along all joints. SMD is very effective, but requires much more time and material to accomplish.
Sealing cracks and opening in floors, walls, membranes, and seams will improve the performance level of an Active Soil Depressurization system, but will do little good with out the ASD system. The scientific and experimental data from thirty years of trial and error have consistently shown Active Soil Depressurization to be the ultimate solution for lowering radon levels in buildings.