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The structure of a home is a home’s most fundamental element, a skeleton of a house. Though building methods varied at times and from region to region, some basic elements are present in all homes. These include the foundation on which the structure stands, the walls, floors, ceilings, roof framing and support members.


Basic Foundation Types
The three common foundation types found in the United States are basements, crawlspaces and slab-on grade.

  • Basement: an area below the first floor with a minimum height of 6 foot 8 inches. Basement foundations have foundation walls placed on footings.
  • Crawlspace: a shallow and uninhabitable area, between the soil and the first floor of the home. A crawlspace usually extends below the frost line or to a stable substrate. Crawlspaces are generally constructed with foundation walls and footings, however, piers may be used when the crawlspace is above grade.
  • Slab-on-grade: a concrete floor (slab) that is poured directly at grade (ground level) and acts as the first floor sub-surface. The slab is usually supported by a continuous (spread) footing, piers or piles and grade beams.
    Foundations transfer the weight or load of the house to the footings.

Foundation Walls

Foundation Walls
Foundation walls are walls that extend below grade and rest on a footing.  The foundation wall must be able to transfer the weight (load) of the exterior walls and first floor to the footing and withstand the lateral forces applied by the exterior soil.  With modern construction, foundation walls are usually 8 to 10-inch-thick, poured reinforced concrete or 8 to 12-inch-wide concrete masonry units (CMUs or concrete blocks). The thickness of the wall is determined by the weight (vertical load), depth below grade (lateral load) and the material used.  Other materials that are used include brick, stone, cinder block, clay tiles and wood.  Each has its own advantages and disadvantages.

Concrete (3000 psi)
Thickness of Wall Maximum Height* of Backfill (Slab to Grade)
8 inches 4 feet
8-12 inches 7 feet 6 inches
*Note: Maximum height refers to the height of the soil against the wall and not the height of the wall itself.


Concrete Masonry Units or Cement Blocks
Thickness of Wall Maximum Height* of Backfill (Slab to Grade)
8 inches 4 feet
10 inches 6 feet
12 inches 7 feet



Spread Footings

Spread footings provide a stable base or platform that prevents the house from settling into the ground.

The wide base (width) helps create a large area to transfer the weight of the structure to the ground and prevent the structure from sinking. The thickness of the footer provides the footer with the strength needed to support the weight of the structure. In modern construction, a footer is usually 16 to 24 inches wide and 6 to 16 inches thick and made with poured concrete that is rated to withstand 2,000 to 5,000 pounds per square inch (psi) of compression pressure. The dimensions of the footer may vary according to the soil conditions under the structure, the weight (or load) placed on the footing and construction style of the home. Other footing materials used are wood, crushed stone, blocks (granite) and field stones.

A continuous spread (or strip) footing is usually found around the entire perimeter of the structure to support the weight (load) from the exterior or foundation walls. In areas subject to seasonal frost, a footing must be placed below the frost line to prevent frost heaving that may lift and damage the footing and structure.

Pad Footing

A pad footing is like a spread footing but it is usually used to support a single point of contact, such as under a pier or post. In modern construction, a pad footing is usually a 2-foot by 2-foot square pad, 10 to 12 inches thick and is made with poured concrete that is rated to withstand 3,000 to 5,000 pounds per square inch (psi) of compression pressure.

Alternatives to Footings

Piles are wood, concrete or sometimes metal columns that are driven into the ground, used to support the structure and prevent it from sinking into the ground. Piles are either driven down until they rest on a solid substrate, such as bedrock, or to a depth where the soil friction against the side of the pile is sufficient to prevent any further downward movement. A continuous grade beam is placed across the top of the piles, forming the platform on which the structure is constructed. Piles are used in areas where footings are not feasible or desirable, such as with poor soil quality or a high water table near a beach. In general, piles are more expensive to install than spread footings.


Piers are columns that are designed to support a specific point of contact on a support beam or girder. In modern construction, they are usually made with poured concrete or concrete blocks (CMU) and supported by a pad footing. Piers are also constructed with stone, brick and wood.

Piers (CMUs) are commonly used in crawlspaces as a supplementary support to prevent the over-spanning of beams and girders. Concrete piers are commonly used to support porches and decks. Also, concrete piers are used as an inexpensive primary support system for small additions to the home, in place of a continuous foundation wall and footing.


A basement is an area below the first floor with a minimum height of 6 feet 8 inches. Basements may be unfinished and used to store personal belongings and to house the mechanical systems such as the HVAC system, electrical panel, and main plumbing controls. Other basements may have portions that are finished and used as a living area. But finished or unfinished, it is estimated that 90 to 95 percent of all basements will experience a water penetration problem. For more information on basements, see our comprehensive guide on basements.


A crawlspace is a shallow and uninhabitable area, usually between the soil and the first floor of the home. Crawlspaces usually provide access to the electrical, plumbing and heating, ventilation and air conditioning (HVAC) systems located below the first floor. The following general guidelines are required in new homes:

  • Minimum access opening is 18 inches by 24 inches.
  • Minimum access opening if mechanical equipment (i.e. if an HVAC system is located in the crawlspace) is 30 inches by 30 inches.
  • Minimum clearance between the soil and joists is 18 inches and 12 inches between the soil and beams.
  • Minimum ventilation, every 150 square feet of floor space, requires a one square foot ventilation opening.

For more information on crawlspaces, see our comprehensive guide on crawlspaces.