Editing Basement (section)

===Underground crawl space===
{{anchor|Crawl space}}
{{Main|crawl space}}
[[File:crawl-space-inside.jpg|thumb|A typical crawl space showing crawl space vents and concrete rat-proofing. Rat-proofing is a thin, irregular concrete covering applied over the soil to prevent rodents from burrowing under the foundation wall and entering the crawl space.]]

An underground crawl space (as the name implies) is a type of basement in which one cannot stand up—the height may be as little as one foot (30&nbsp;cm), and the surface is often soil. Crawl spaces offer a convenient access to pipes, substructures and a variety of other areas that may be difficult or expensive to access otherwise. While a crawl space cannot be used as living space, it can be used as storage, often for infrequently used items. Care must be taken in doing so, however, as water from the damp ground, water vapour (entering from crawl space vents), and moisture seeping through porous concrete can create a perfect environment for mold/mildew to form on any surface in the crawl space, especially cardboard boxes, wood floors and surfaces, drywall and some types of insulation.

Health and safety issues must be considered when installing a crawl space. As air warms in a home, it rises and leaves through the upper regions of the house, much in the same way that air moves through a chimney. This phenomenon, called the "stack effect", causes the home to suck air up from the crawl space into the main area of the home. Mould spores, decomposition odours, and material from dust mites in the crawl space can come up with the air, aggravating asthma and other breathing problems, and creating a variety of health concerns.<ref>{{cite web |url=http://healthlink.mcw.edu/article/926104064.html |title=Mold Allergies |publisher=Healthlink.mcw.edu |date=22 July 2013 |access-date=2 November 2013 |url-status=dead |archive-url=https://web.archive.org/web/20090122072350/http://healthlink.mcw.edu/article/926104064.html |archive-date=22 January 2009 }}</ref>

It is usually desirable to finish a crawl space with a plastic vapour barrier that will not support mold growth or allow humidity from the earth into the crawl space. This helps insulate the crawl space and discourages the habitation of insects and vermin by breaking the ecological chain in which insects feed off the mould and vermin feed on the insects, as well as creating a physical inorganic barrier that deters entrance into the space. Vapour barriers can end at the wall or be run up the wall and fastened to provide even more protection against moisture infiltration. Some pest control agencies recommend against covering the walls, as it complicates their job of inspection and spraying. Almost unheard of as late as the 1990s, vapour barriers are becoming increasingly popular in recent years.{{when| date= October 2016}} In fact, the more general area of conditioned vs. unconditioned crawl spaces has seen much research over the last decade.{{citation needed|date=August 2020}}

[[Dry rot]] and other conditions detrimental to buildings (particularly [[wood]] and [[timber]] structures) can develop in enclosed spaces.  Providing adequate [[Ventilation (architecture)|ventilation]] is thought to reduce the occurrence of these problems. Crawl space vents are openings in the wall which allow air movement. Such vents are usually fitted with metal [[grating]], [[mesh]], or [[louver]]s which can block the movement of [[rodents]] and [[vermin]] but generally not insects such as termites and carpenter ants. One common rule is to provide vents in cross sectional area equal to 1/150 of the floor area served.<ref>2003 International Building Code, Section 1203.3, International Code Council</ref>

Modern crawl space thinking has reconsidered the usage of crawl space vents in the home.<ref name="ToVent">{{cite web|url=http://www.advancedenergy.org/portal/crawl_spaces/pdfs/To%20Vent%20or%20Not%20To%20Vent.pdf|title=To Vent or Not to Vent|publisher=advancedenergy.org|access-date=3 July 2009|archive-date=11 July 2019|archive-url=https://web.archive.org/web/20190711153223/http://www.advancedenergy.org/portal/crawl_spaces/pdfs/To%20Vent%20or%20Not%20To%20Vent.pdf|url-status=dead}}</ref><ref>{{cite web|url=http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11480|title=Crawl Space Insulation|publisher=US Dept. of Energy|access-date=3 July 2009|archive-url=https://web.archive.org/web/20090703122958/http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11480|archive-date=3 July 2009|url-status=dead}}</ref> While crawl space vents do allow outside air to ventilate into the home, the ability of that air to dry out the crawl space is debatable.<ref>{{cite web|url=http://www.advancedenergy.org/buildings/knowledge_library/crawl_spaces/pdfs/Home%20Energy%20January%202005_low%20res2.pdf|title=Closed crawl spaces do double duty|publisher=advancedenergy.org|url-status=dead|archive-url=https://web.archive.org/web/20090124142036/http://advancedenergy.org/buildings/knowledge_library/crawl_spaces/pdfs/Home%20Energy%20January%202005_low%20res2.pdf|archive-date=24 January 2009|access-date=3 July 2009}}</ref> In areas with humid summers, during the summer months, the air vented into a crawl space will be humid, and as it enters the crawl space, which has been cooled naturally by the earth, the relative humidity of the air will rise. In those cases, crawl space vents can even increase the humidity level of a crawl space and lead to condensation on cool surfaces within, such as metal and wood.<ref>{{cite web|url=http://www.advancedenergy.org/buildings/knowledge_library/crawl_spaces/pdfs/Builder%20Online%20Article%20-%202005.pdf|title=Closing the crawl|publisher=Builder magazine Oct 2005 (reproduced by advancedenergy.org)|url-status=dead|archive-url=https://web.archive.org/web/20090210210055/http://www.advancedenergy.org/buildings/knowledge_library/crawl_spaces/pdfs/Builder%20Online%20Article%20-%202005.pdf|archive-date=10 February 2009|access-date=3 July 2009}}</ref> In the winter, crawl space vents should be shut off entirely, to keep out the cold winter air which can cool hot water pipes, furnaces, and water heaters stored within.  During rainy weather, crawl space vents bring wet air into the crawl space, which will not dry the space effectively.