Building a home on a steep hillside or in poorly drained soils calls for a different type of foundation. The monolithic or beam foundation can solve the problems of a shifting load that these types of conditions can present. Monolithic beams can be described as one, large poured piece of concrete. In other words, the entire foundation beam is poured in concrete at one time, with no separation to the heavy-duty home support.
A typical poured concrete foundation for the home is placed on a concrete footer. Both of these structures can be built in sections. The footer is generally 12 to 18 inches wide and 8 to 12 inches thick. It supports the foundation wall which can range in widths from 8 to 10 inches. The foundation beam or monolithically poured foundation is formed and poured all at on time. There is no separation to the ends of the beam wall. The foundation beam is also poured on top of concrete support posts that may extend 20 to 40 feet underground.
The deep support posts, pilings or drilled holes are filled with reinforced metal bars called rebar. These rebar cages are wired together and carefully placed in the deep holes with a crane. The pilings are then filled with high tensile strength concrete. The pilings may be laid out to be dug every 10 to 12 feet around the perimeter of a beam foundation. The top of these concrete support posts come to the same height to form a grade mark. This level grade is used to identify the bottom of the foundation beam.
The foundation beam is formed to size by the use of reusable concrete forms. Rebar is laid in the form and wired together to make a square or rectangular steel cage. This rebar cage gives concrete the strength it needs to support the structure or home. The poured concrete beam can range in size from 12 to 18 inches in width to 24 to 36 inches in height, depending on the structure to be supported.
The support pilings are mechanically connected to the foundation beam by the rebar cages. This allows the weight of the home to be transferred deep underground. This type of construction is typically used in areas of steep slopes or extremely wet soils. Regular foundations have been known to slide downhill on steep slopes during times of heavy rains. Or in freezing and thawing conditions of winter.
Layout and use of a beam foundation will be different for every building site. Architects or engineers should always be considered when building on these types of soils. Ignoring proper construction methods can be the difference between having a stable home and one that will literally move down hill or sink into the ground.