One advantage of pier foundations is that they are less costly to construct than continuous wall foundations, simply due to the fact they use less material. Standard pier foundations can be built from concrete, brick, hollow concrete block, and stone rubble. Having said that, a rule of thumb building designers follow is that whenever your pier height is more than ten times their width, they should be constructed of reinforced concrete.
How They Work
A pier foundation can be visualized as a common table. The structure is a system of vertical columns- which sit on concrete pads called footings- placed at specific locations around the outside perimeter of the building. These columns transfer the building load to the soil. Beams are built on top of the vertical columns that hold up the walls of the house or structure.
Many older homes and smaller vacation homes are supported completely by piers, but modern construction favors continuous perimeter foundation walls, with concrete piers being used as support for long span load-bearing beams. Concrete pier foundations are also useful for decks and storage or garden sheds.
Choosing a buildings structural design is a balancing act between costs and load requirements. This holds no less true for the specific case of pier foundations. The more piers you build, the more weight you can support and the closer together the piers are located.
However, more piers means more material and higher cost. On the other hand, when using less piers at a greater spacing in order to cut costs, you will be forced to design a floor structure with heavier spanning beams, due to the longer span, which in turn drives cost back up.
Reinforced concrete piers are constructed on-site by pouring concrete into forms. Rectangular forms for square piers are built from wood or wood and steel. For cylindrical piers, a stay-in-place prefabricated tube form is used which is made from fibreglass or concrete pipe. Reinforcement consists of vertical lengths of steel rod, or re-bar, 3/8 to ½ inch in diameter, depending on the height of the pier.
An anchor bolt is cast in as well, for attaching the foundation span beams. It is placed in the top of the pier when the concrete is has cured to be firm enough to hold the anchor but not yet completely hardened.