In most climate zones (even ours here in Scottsdale), conditioned crawlspaces perform better than vented crawlspaces in terms of safety, health, comfort, durability and energy consumption. Research has demonstrated how these conditioned crawlspaces also do not cost more to construct than vented crawlspaces. Crawlspace venting is a widely accepted business practice across the country. However, in humid climates, the warm humid air entering the crawlspace is more likely to condense on crawlspace framing than to help dry out the crawlspace. This is because the outside air can often have a dew point that is higher than the interior crawlspace framing surface temperature. As evidence, existing vented crawlspaces have experienced serious moisture and mold problems costing builders and homeowners significant resources to repair.
The housing industry has been reluctant to use unvented crawlspaces despite their compelling benefits and the history of problems with existing vented crawlspaces. One of the reasons commonly cited by builders and designers is “the code does not allow me to build unvented crawlspaces.” This is both generally correct and misleading. The model codes do not allow the construction of “unvented” crawlspaces—except in very limited circumstances, but they do allow the construction of “conditioned” crawlspaces. The distinction is important and necessary.
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