Steel bars for cement foundationA foundation is a structural base that supports the weight of the rest of the building. Structural engineers and repair specialists can make sure that a good foundation is constructed and provide repair for concrete foundations if cracks or other structural problems exist. Foundation design requires extensive study of the ground below the foundation and the materials to be used for the foundation itself.

Functions of a Foundation

Foundations provide overall lateral stability for building structures. They provide a level surface for succeeding construction structures. They also ensure that load is distributed evenly and fits within the soil’s maximum load bearing capacity. Foundations prevent instability by preventing soil from moving.

Depth of Foundation

Most building foundations are not laid at ground level but installed at a variety of depths. The minimum depth of a foundation is usually 18 inches to allow for variations in ground level and the removal of topsoil. However, required depth will depend on several other factors.

  • Soil Bearing Capacity – This capacity determines how much weight or force the existing soil can handle.
  • Soil Type – Each soil type has different properties that will affect how appropriately they can support a foundation.
  • Frost Depth or Frost Line – In cold climates, the foundation can be damaged if the water in the soil around the foundation freezes and expands. The frost line refers to the depth at which soil freezes during the winter. It determines the minimum depth level for a foundation.  If the foundation is built above this line, it needs to be protected from freezing by some form of insulation.
  • Groundwater Table – Groundwater height is included in a soil study because high groundwater levels can limit foundation depth and the type of foundation used.

Materials for a Foundation

Building foundations are usually made with masonry like concrete blocks, bricks, or poured concrete. Compared to wood and metal materials, masonry offers high compressive strength and is more resistant to damage caused by moisture and soil. Foundations built from masonry are usually internally secured with metal reinforcing bars.

Sand and Clay

Loader machine unloading soilBefore building begins, land needs to be graded at a level. A foundation elevated above grade level allows for better drainage. An elevated structure requires an initial layer of fill. It can also provide a route for rain water to be drained away from the building.

A bulldozer then lays and packs down a layer of sand and clay as the drainage medium. This mixture will harden after a few days of exposure to the sun.

Concrete

Concrete is a commonly used foundation material because it is hard, durable, and strong even with compression. It is also unaffected by moisture and can be made nearly watertight. This is an especially crucial factor as it prevents water from entering into a basement or into building walls above.

Many foundations are built with poured concrete. Concrete is poured into steel reinforced plywood forms. The concrete forms are then covered with insulated foam to allow the building to be more energy efficient.

Well designed and properly constructed foundations reduce the risk of the building experiencing stability issues in the future.