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Design and Structural Considerations in Virginia

Structurally, for single-family homes, the footings and the basement walls typically form the foundation. In warmer climates, houses sometimes do not have basements because they are not necessary (although many still prefer them.) In colder climates, the foundation must be below the frostline. Unless constructed in very cold climates, the frost line is not so deep as to justify an entire level below the ground, although it is usually deep enough that a basement is the assumed standard. In places with odd stratified soil substrata or high water tables, and in warmer climates where the frost line is not an issue, such as most of Texas, Oklahoma, Arkansas, Tennessee, Mississippi, Alabama, Georgia, Louisiana, and Florida, basements are usually not financially feasible unless the building is a large apartment or commercial structure.

Some residential designs choose to simply leave a crawl space under the house, rather than a full basement. 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 7 feet 10 inches (2.39 m) in height, rather than the standard full 8 feet (2.44 m) of the main floors.

Some older homes in Northern Virginia may have even lower basement heights as the basement walls were concrete block and thus, could be custom built to any height. In the late 20th Century, and the beginning of our 21st Century, modern builders offer higher basements as an option. The cost of the additional depth of excavation for residential homes is usually quite expensive and not justified. Thus, houses almost certainly never have multi-story basements though 9' basements heights are a frequent choice among new homebuyers. For large office or apartment buildings in prime locations, the cost of land may justify multi-story basement parking garages.

The concrete floor in most Virginia basements is structurally not part of the foundation; only the footers and 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 will rest directly on the concrete floor. Under the concrete floor is typically a vapor barrier directly over top of gravel or crushed stone to facilitate draining. The floor is typically four inches (100 mm) thick and rests on top of the foundation footings. The floor itself used to be sloped towards a drain point, in case of leaks, but now residential code mandates draintile or drainpipe, whichever term you prefer, and a sump pump to discharge the water to grade.

Since warm air rises, basements are naturally cooler than the rest of the house. In summer, due to the higher relative humidity, this makes basements damp. Dehumidifiers are recommended, as long as they are energy efficient. In winter, additional heating, such as a fireplace or baseboard heaters may be required or desired. 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 though modern laminate flooring is typically placed on concrete floors with a thin foam underlay. Radiant heating systems may be embedded right 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 the cold Virginia winter.

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