Excavation for the footing is the first task to be done. The footing is usually comprised of steel-reinforced concrete and is poured two to three times the width of the foundation thickness. Building codes require that the foundation is constructed below the frost line of the area.
This is to ensure that the natural freezing and thawing of the building site does not put undue stress on the foundation. The thickness or depth of the footing depends upon the weight of the structure that will be supported. A thicker footing will support more weight; therefore, this would be a good time to plan for possible future expansion.
Wood beams were added to this house's foundation, which was initially poorly constructed. (Photo courtesy of Angie's List member Dylan L.)
After the footing trench has been excavated to the proper depth, a form is built to contain the footing. After the concrete has been poured, the form may be reinforced by backfilling. The footing must be allowed to cure before additional weight is placed on it. Because this is a crucial part of construction, patience must be exercised here. Not only does the curing process solidify the concrete, it also compacts the soil underneath the footing to keep the foundation from shifting.
When the footing has to cured, it is time to remove the forms and build the foundation. The foundation may be constructed of either concrete block and mortar or a concrete stem wall. Foundations can also be constructed of other materials such as wood, steel or stone.
The best course choice will be to construct the foundation using strong, long lasting and water resistant materials. Because the foundation is such a critical part of the building, it is desirable to consult a structural engineer to assist in designing it. The engineer will know how to properly size the foundation and be able to specify the materials needed for successful construction.
When the foundation is constructed of concrete, anchor bolts, also called J-bolts, are often used to assist in securing the framework of the house to the foundation. The anchor bolt is usually ½ inch in diameter and 6 inches long in residential construction. The J shape of the bolt prevents it from being pulled out of the concrete.
Holes are drilled in the bottom plate of the wall framework for attachment. Most of the foundation is constructed underground; therefore, dirt is back filled into the trench once construction is completed, filling it back up to grade level.
You should plan for future expansion when designing your foundation. For example, a slab type foundation is used for patios and parking areas. Foundations for slabs are generally not as strongly built as foundations, crawl spaces, or full basements. If there is a possibility that the patio or parking space will be enclosed in the future, it would be expedient to use a foundation for that future expansion possibility.