A sealed crawlspace is one whose floors and walls are lined with a vapor barrier, all of the edges are adhered to the foundation, and all of the seams are overlapped and taped or glued to completely encapsulate the space. Also, the vents, if any, have been closed and sealed. Sealed crawlspaces are either conditioned with the HVAC System or have a permanent dehumidifier located in them. This helps to reduce the amount of moisture in the crawlspace and consequently, in the home. Essentially, the crawlspace becomes a conditioned space as any other part of the home. By sealing your crawlspace, you greatly reduce the growth of mold, minimize the presence of radon, and decrease the amount of bugs present. I recommend sealed crawlspaces because they promote a healthier living environment and are more energy efficient.