Crawlspaces were never intended to provide air to the living space. They were a cost effective way to provide a foundation on which to build a house at a time when construction materials and practices were very different from those available today. Today's airtight construction requires that crawlspaces be improved to correct the unintended consequences that our focus on energy efficiency has had on houses with vented crawlspaces.
Simply put, close the crawlspace and then clean and dry the air in it. By closing the crawlspace - sealing the walls and dirt floor of the crawlspace - moisture from the primary sources (outside air and the earth underneath) is reduced. Encapsulating the crawlspace also reduces the amount of unconditioned outside air introduced into the conditioned living space, reducing energy costs. By dehumidifying and filtering the air in the crawlspace clean dry air is supplied to the living space when the house draws make-up air from the crawlspace. Dry air is less expensive to heat and cool further reducing energy costs. Dry crawlspaces are less subject to rot, mold growth, and insect infestations thus protecting your investment and improving air quality in your home. Encapsulating your crawlspace turns dirt to diamonds.
Energy Efficient Houses "Breathe" DifferentlyWhile living spaces were being more tightly sealed, crawlspace construction remained the same. Air began to flow through the houses differently. By tightening up the living envelope, the house is forced to pull replacement air out of the crawlspace. Make-up air is now drawn from the crawlspace below into the living space above. In turn, air is drawn from outside the house into the crawlspace.