In old houses, it is common for crawlspaces to have open vented areas. It was believed that the vents would allow fresh air to circulate in the area and clean out the moisture and humididy from the room. However, the air outside was often more wet and humid than the inside. Moist air that enters a vented crawl space will condense on cooler crawl space surfaces, ruining insulation and encouraging mold, mildew and wood decay to flourish. Crawl space sealing with our CleanSpace crawl space liner is the recommended treatment for a vented crawl space. This process involves the installation of different air and moisture barriers to totally separate and shield the crawl space from outside conditions. Plastic vent covers play an important role in a sealed crawl space by closing off the air movement that would otherwise occur through vent openings.