Unvented crawl spaces have been gaining popularity primarily due to the push for energy conservation. One of the significant adverse side affects to the earlier types of unvented crawl spaces was a concentration of Radon gas. Scientifically installed and monitored studies from North Carolina, Louisiana, Arizona and Washington state all registered a noted rise in Radon levels with an unvented crawl space. The model homes in Arizona had to have the crawl spaces re-vented because the Radon levels rose to such a high level.
It is important to know that 2003 was the last model code that allowed a "positive pressure sealed air crawl space", where an A/C duct was vented into the crawl space to provide conditioned air. Now all unvented crawl spaces must circulate air, either from the interior of the home through the crawl space to the outside or through the interior of the home and the crawl space in a circular motion. The crawl space is required to be neutral pressure or negative pressure compared to the inside of the home.
Lots of home owners, specially in the South are switching to unvented crawl spaces. Any home with an unvented crawl space should be checked for appropriate Radon gas levels for the safety of the occupants, even if the home has been previously monitored.
Beware! Unvented crawl spaces will raise Radon Gas Levels in the home!
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