Crawl spaces have a bad reputation –as damp, dark, dirty places made even worse by nasty smells and (in some cases) even insect or rodent pests. It doesn’t have to be that way. Thanks to extensive research in the field of building science, and thousands of crawl space case studies, we know that there’s a better way to build and finish this under-house area.


Today the recommended treatment for crawl spaces is to separate this shallow foundation from exterior conditions through the process of crawl space encapsulation. Put another way: By encapsulating the crawl space, you’re making it part of the “building envelope,” the collection of components that creates a barrier to outside temperature and weather conditions. Also known as crawl space sealing, encapsulation involves different procedures and processes, including waterproofing, insulation, and dehumidification.  

Does my crawl space need a dehumidifier? 

A dehumidifier is an electrical appliance designed to remove water from the air through the process of condensation. A fan in the dehumidifier blows moist air across metal coils cooled by a refrigerant. When the warm, moist air is cooled by the coils, condensation takes place. The liquid condensate collects in a holding tank or is piped to a drainage outlet.


An astonishing amount of moisture can accumulate in a vented crawl space –one that hasn’t yet been encapsulated. This moisture can come from water that leaks through crawl space walls, through the crawl space floor, or through moist air that enters the crawl space through vent openings. The moisture absorbed by wood framing elements (support posts, joists, beams, and subflooring) attracts mold, which thrives in dark, moist areas where organic material is present. When a crawl space is encapsulated, the moisture sources mentioned above are eliminated, but the moisture remains in the wood and in other porous materials in the crawl space. Running a crawl space dehumidifier is the best way to remove this moisture and keep the crawl space dry enough to discourage mold growth.   

It’s not practical to run a crawl space dehumidifier if the crawl space hasn’t been properly sealed. If moisture is still leaking into the crawl space –through wall or floor surfaces— it will be difficult or impossible for a dehumidifier to keep the space dry. The same is true if crawl space vents remain open, allowing moist outside air to enter the crawl space. To effectively dry out a crawl space and keep it that way, the crawl space should be sealed (encapsulated), prior to running a crawl space dehumidifier.