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A basement is any Storey of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the furnace, water heating, breaker panel or fuse box, car park, and air-conditioning system are located; so also are amenities such as the electrical system and cable television distribution point. In cities with high property prices, such as London, basements are often fitted out to a high standard and used as living space.
In British English, the word basement is usually used for underground floors of, for example, department stores. The word is usually used with buildings when the space below the ground floor is habitable and with (usually) its own access. The word cellar applies to the whole underground level or to any large underground room. A subcellar or subbasement is a level that lies below the basement or cellar. Subcellar – definition of Subcellar by the Free Online Dictionary, Thesaurus and Encyclopedia.
Basements in small buildings such as single-family detached houses are rare in wet climates such as Great Britain and Ireland where flooding can be a problem, though they may be used in larger structures. However, basements are considered standard on all but the smallest new buildings in many places with temperate continental climates such as the American Midwest and the Canadian Prairies where a concrete foundation below the frost line is needed in any case, to prevent a building from shifting during the freeze-thaw cycle. Basements are much easier to construct in areas with relatively soft soils and may be avoided in places where the soil is too compact for easy excavation. Their use may be restricted in earthquake zones, because of the possibility of the upper floors collapsing into the basement; on the other hand, they may be required in tornado-prone areas as a shelter against violent winds. Adding a basement can also reduce heating and cooling costs as it is a form of earth sheltering, and a way to reduce a building's surface area-to-volume ratio. The housing density of an area may also influence whether or not a basement is considered necessary.
Historically, basements have become much easier to build (in developed countries) since the industrialization of home building. Large powered excavation machines such as backhoes and front-end loaders have dramatically reduced the time and manpower needed to dig a basement as compared to digging by hand with a spade, although this method may still be used in the developing world.
For most of its early history, the basement took one of two forms. It could be little more than a cellar, or it could be a section of a building containing rooms and spaces similar to those of the rest of the structure, as in the case of basement flats and basement offices.
However, beginning with the development of large, mid-priced suburban homes in the 1950s, the basement, as a space in its own right, gradually took hold. Initially, it was typically a large, concrete-floored space, accessed by indoor stairs, with exposed columns and beams along the walls and ceilings, or sometimes, walls of poured concrete or concrete cinder block.
Most daylight basements naturally result from raised bungalows and at-grade walk-out basements. However, there are instances where the terrain dips enough from one side to another to allow for 3/4 to full-size windows, with the actual floor remaining below grade.
In most parts of North America, it is legal to set up apartments and bedrooms in daylight basements, whether or not the entire basement is above grade.
Daylight basements can be used for several purposes—as a garage, as maintenance rooms, or as living space. The buried portion is often used for storage, laundry room, hot water tanks, and HVAC.
Daylight basement homes typically appraise higher than standard-basement homes, since they include more viable living spaces. In some parts of the US, however, the appraisal for daylight basement space is half that of ground and above ground level square footage. Designs accommodated include split-foyer and . Garages on both levels are sometimes possible. As with any multilevel home, there are savings on roofing and foundations.Woodson, R. Dodge. Build Your Dream Home for Less. Cincinnati: Betterway Books, 1985, pp 60–61.Zeller, Dirk. Success as a Real Estate Agent for Dummies. Wiley, 2006, p. 209
Many walk-out basements are also daylight basements. The only exceptions are when the entire basement is nearly entirely underground, and a stairwell leads up nearly a floor's worth of vertical height to lead to the outdoors.
Generally, basements with only an emergency exit well do not count as walk-out. Walk-out basements with at-grade doors on one side typically are more costly to construct since the foundation is still constructed to reach below the frost line. At-grade walk-out basements on the door-side are often used as livable space for the house, with the buried portion used for utilities and storage.
Building a subbasement is more difficult, costly, and time-consuming than building a basement as the lowest floor. Subbasements are even more susceptible to flooding and water damage than basements and are therefore rare, except in arid climate and at higher elevations.
Some famous landmarks contain subbasements. The subbasement of the US Capitol Building is used as storage and that in the White House is used to store guest items.
Except for Britain, Australia and New Zealand, cellars are popular in most western countries. In the United Kingdom, almost all new homes built since the 1960s have no cellar or basement due to the extra cost of digging down further into the sub-soil and a requirement for much deeper foundations and waterproof tanking. The reverse has recently become common, where the impact of smaller home-footprints has led to roof-space being utilised for further living space and now many new homes are built with third-floor living accommodation. For this reason, especially where lofts have been converted into living space, people tend to use garages for the storage of food freezers, tools, bicycles, garden and outdoor equipment. The majority of continental European houses have cellars, although a large proportion of people live in apartments or flats rather than houses. In North America, cellars usually are found in rural or older homes on the coasts and in the South. However, full basements are commonplace in new houses in the Canadian and American Midwest and other areas subject to tornado activity or requiring foundations below the frost line.
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.
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. In fact, the more general area of conditioned vs. unconditioned crawl spaces has seen much research over the last decade.
Dry rot and other conditions detrimental to buildings (particularly wood and timber structures) can develop in enclosed spaces. Providing adequate 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 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.2003 International Building Code, Section 1203.3, International Code Council
Modern crawl space thinking has reconsidered the usage of crawl space vents in the home. 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. 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. 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.
Excavation using a backhoe or excavator is commonly used to dig a basement. If shelf rock is discovered, the need for Rock blasting may be cost prohibitive. Basement walls may need to have the surrounding earth backfilled around them to return the soil to grade. A water stop, some gravel and a french drain may need to be used to prevent water from entering the basement at the bottom of the wall. Walls below grade may need to be sealed with an impervious coating (such as tar) to prevent water seepage. A polyethylene of about 6 mil (visqueen) serves as a water barrier underneath the basement.
Some designs elect to simply leave a crawl space under the house, rather than a full basement due to structural challenges. Most other designs justify further excavations to create a full-height basement, sufficient for another level of living space. Even so, basements in Canada and the northern United States were typically only in height, rather than the standard full of the main floors. Older homes may have even lower basement heights as the basement walls were concrete block and thus, could be customized to any height. Modern builders offer higher basements as an option. The cost of the additional depth of excavation is usually quite expensive. Thus, houses almost certainly never have multi-storey basements though basements heights are a frequent choice among new home buyers. For large office or apartment buildings in prime locations, the cost of land may justify multi-storey basement parking garages.
The concrete floor in most basements is structurally not part of the foundation; only the basement walls are. If there are posts supporting a main floor beam to form a post and beam system, these posts typically go right through the basement floor to a footing underneath the basement floor. It is the footing that supports the post and the footing is part of the house foundation. Load-bearing wood-stud walls rest directly on the concrete floor. Under the concrete floor is typically gravel or crushed stone to facilitate draining. The floor is typically four inches (100 mm) thick and it rests on top of the foundation footings. The floor is typically sloped towards a drain point, in case of .
Modern construction for basement walls typically falls into one of two categories: they will be made of poured-in-place concrete using concrete forms with a concrete pump, or they will use concrete masonry units (block walls). Rock may also be used, but is less common. In monolithic architecture, large parts of the building are made of concrete; in insulating concrete form construction, the concrete walls may be hidden with an exterior finish or siding. Inside the structure, a single Lally column, steel basement jack, wooden column or support post may hold up the floor above in a small basement. A series of these supports may be necessary for large basements; many basements have the support columns exposed.
Since warm air rises, basements are typically cooler than the rest of the house. In summer, this makes basements damp, due to the higher relative humidity. Dehumidifiers are recommended. In winter, additional heating, such as a fireplace or baseboard may be required. A well-defined central heating system may minimize this requirement. Heating ducts typically run in the ceiling of the basement (since there is not an empty floor below to run the ducts). Ducts extending from the ceiling down to the floor help heat the cold floors of the basement. Older or cheaper systems may simply have the heating vent in the ceiling of the basement.
The finished floor is typically raised off the concrete basement floor. In countries such as Canada, laminate flooring is an exception: It is typically separated from the concrete by only a thin foam underlay. Radiant heating systems may be embedded within the concrete floor. Even if unfinished and unoccupied, basements are heated in order to ensure relative warmth of the floor above, and to prevent water supply pipes, drains, etc. from freezing and bursting in winter. It is recommended that the basement walls be insulated to the frost line. In Canada, the walls of a finished basement are typically insulated to the floor with vapor barriers to prevent moisture transmission. However, a finished basement should avoid wood or wood-laminate flooring, and metal framing and other moisture resistant products should be used. Finished basements can be costly to maintain due to deterioration of waterproofing materials or lateral earth movement etc. Below-ground structures will never be as dry as one above ground, and measures must be taken to circulate air and dehumidify the area.
The main water cut-off valve is usually in the basement. Basements often have "clean outs" for the sanitary and storm sewers, where these pipes can be accessed. The storm sewer access is only needed where the drain into the storm sewers.
Other than with walk-out or look-out basements, windows in basements require a well and are below grade. A clear window well cover may be required to keep the window wells from accumulating rain water. There should be drains in the window well, connected to the foundation drains.
If the water table outside the basement is above the height of the basement floor, then the foundation drains or the weeping tiles outside the footings may be insufficient to keep the basement dry. A sump pump may be required. It can be located anywhere and is simply in a well that is deeper than the basement floor.
Even with functioning sump pumps or low water tables, basements may become wet after rainfall, due to improper drainage. The ground next to the basement must be graded such that water flows away from the basement wall. Downspouts from roof gutters should drain freely into the storm sewer or directed away from the house. Downspouts should not be connected to the foundation draintiles. If the draintiles become clogged by leaves or debris from the rain gutters, the roof water would cause basement flooding through the draintile. Damp-proofing or waterproofing materials are typically applied to outside of the basement wall. It is virtually impossible to make a concrete wall waterproof, over the long run, so drainage is the key. There are draining membranes that can be applied to the outside of the basement that create channels for water against the basement wall to flow to the foundation drains.
Where drainage is inadequate, waterproofing may be needed. There are numerous ways to waterproof a basement, but most systems fall into one of three categories:
The waterproofing system can be applied to the inside or the outside walls of a basement. When waterproofing existing basements it is much cheaper to waterproof the basement on the inside. Waterproofing on the outside requires the expense of excavation, but does offer a number of advantages for a homeowner over the long term. Among them are:
As the description suggests, this type of basement, which also might be called "half-finished", is likely used by teenagers and children. The entire family might utilize a work-out area. It is also common to have a secondary (or primary) home office in a partially finished basement, as well as a man cave, workbench and/or a space for laundry appliances.
Toilets and showers sometimes exist in this variety of basement, as many North American basements are designed to allow for their installation.
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