Foundation Facts of Piers & Beams

Basics

• The basic, simple structure of the pier and beam starts with the lowest part, a large, concrete square called a footer buried at least 12 inches into the ground. The depth is based on the frost depth, which is the deepest part of the soil affected by frost. The deeper the frost depth, the deeper the footer. Atop the footer is placed a concrete or brick beam. Pressure treated wood beams are placed horizontally over these piers, creating a strong structure that is not too firmly embedded in the ground. Floor joists are placed across the beams, then the wood floor itself. This means that in the average pier and beam foundation, there are at least three levels between the soil and the wood floor. This creates a crawlspace averaging between 18 and 21 inches that permits the air to flow freely.

Purpose

• Since the pier and beam structure is meant to protect the wood from contact with wet soil, these foundations are used in fairly stable weather environments that can be soggy. The deep South, for example, uses them often, but they should not be used in places where hurricanes or tornadoes are common, since the home is not heavily anchored. There should be a minimum of 18-20 inches of space under the beams to the soil.

Dimensions

• The minimum wood size for a beam is a 4x6. Smaller might be used if there is going to be less space between them. Sagging and buckling of the wood floor is a problem in poorly designed foundations. The main problem here is too few beams, too-small beams, or joists spread too far out. It is better to err on the side of more joists than fewer. The concrete footer should cover as much area as is practical. The greater the footer surface area, the more weight it can take without sinking into the ground. Crawl spaces should be a minimum of 18 inches, which also permit air to flow, keeping the area dry. Termite and moisture shields should be placed between the pier and the beam. On average, block or poured concrete piers should be placed every 6 feet.

Problems

• Any soil that expands and contracts with weather changes, such as clay, are never suitable for pier and beam construction. The wood must be well-treated with a copper compound for the maximum lifespan of the home. The weather should basically be temperate to minimize any shifting of piers in the soil. Dallas-based Bedrock Foundation Repair LLC states that the main causes of pier and beam problems are poor planning, poor construction and the use of materials that are substandard for this complex approach to foundation building. Sagging of floors and the shifting of piers are the two most common and serious problems with this design.