page_title: Crawl space
section_title: Designs
hierarchical_section_title: Crawl space / Designs
caption_attribution_description: English: Crawlspace access panel
context_page_description: A crawl space is an unoccupied, unfinished, narrow space within a building, between the ground and the first floor. The crawl space is so named because there is typically only enough room to crawl rather than stand; anything larger than about 1 to 1.5 metres would tend to be considered a basement.
context_section_description: Crawl spaces can be actively or passively vented, or closed. An advantage of a vented crawl space is that harmful gases such as radon or carbon monoxide (e.g. from gas furnaces or water heaters) can escape or be diluted before they can enter the living space. However, in regions with a humid climate, vents to the outside can also allow moist air to come in, which can then condense if temperatures (e.g. on cooler surfaces such as ductwork) drop below the dew point, creating a damp environment that is hospitable to indoor mold growth as well as infestations by rodents and insects, possibly including wood-damaging ones such as termites or carpenter ants. Even without condensation, relative humidity above 80% can support mold growth and rot wooden structural materials such as floor joists. Humidity in some sealed crawl spaces is controlled using a dehumidifier.
  Encapsulation is sometimes used to prevent the passage of air from the crawl space to the living environment, to save energy and improve indoor air quality, since air in the crawl space might otherwise tend to rise due to the stack effect. Encapsulation involves adding a vapor barrier to the floor, sealing off all openings to the outdoors, adding thermal insulation to the walls, and sealing off any remaining gaps and cracks (such as plumbing and wiring penetrations) between the crawl space and the floor of the home. A 2005 U.S. Department of Energy study of homes in the southeastern United States found that closed crawl spaces with sealed foundation wall vents, sealed polyethylene film liners and various insulation and drying strategies had significantly reduced space conditioning energy use compared to traditional wall-vented crawl spaces with perimeter wall vents and unsealed polyethylene film covering the ground surface. As a further encapsulation measure, crawl space access doors are sometimes located inside the home, or an airtight, insulated access door is built in the perimeter wall.
  A crawl space can be susceptible to flooding, a risk that is sometimes mitigated by such measures as using rain drainage such as rain gutters to conduct rainwater away from the house and sloping the earth away from the house.
  Crawl space wall materials may include, e.g., solid concrete or concrete masonry units.
caption: A wooden crawl space access panel, opening to the exterior of the house, that has begun rotting away from dampness
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