Typical pier and beam foundations provide support for a raised wooden floor using an exterior concrete beam that supports the ends of the floor joists along with double 2x6 beams that rest on piers to provide additional support. The raised floor construction of pier and beam foundations gives room for installing plumbing after the floor is finished. Piers may rest on a continuous footing or use precast concrete for spot support.
The pier and beam system uses shims between the beam and floor joist. Adjusting the shims is one way of leveling the floor. Older homes using pier and beam foundation systems often use cedar blocks instead of concrete for the piers. Unfortunately, many of the blocks are undersized and compress the soil under the pier. This compression causes a loss of support for the floor joists and causes the floor to sag.
Proper design of the foundation requires placing the piers to provide support depending on the location of load bearing walls and the span capacities of the floor joists. Pier and beam foundations require ventilation to keep the support for the home dry and prevent rot. Most builders accommodate this need by installing foundation vents. There should be 1 square foot of foundation vent for every 150 square feet of crawl space.