16. Crafting your performance opinion

The TREC SOP requires that you render an opinion as to the performance of the foundation.                    

What is a performance opinion?

I am regularly surprised, when reading the foundation section of reports by TREC inspectors, how often the report fails to state an opinion of how well or poorly the foundation is performing. Let’s start with a definition straight from the TREC SOP.

Definition of performance:

Achievement of an operation, function or configuration relative to accepted industry practices standards with consideration of age and normal wear and tear from ordinary use.

What is the function of a slab foundation on expansive soils?

The main function of any foundation is to transfer the load from the building and the foundation to the supporting soil without excessive foundation settlement. This is rarely a problem with expansive soils. The soils are too strong and the loads are too light.

Expansive soils present a design consideration that is unique to expansive soils. When a slab foundation is placed, moisture begins to accumulate in the supporting soil. This makes the soil swell, especially in the middle area of the slab. This causes the slab to tilt and to bend into a tilted mound shape. As the slab bends, it causes distress in the house structure typically in the form of diagonal drywall cracks, stair-stepped cracks in the brick veneer, sloping first story floors and door issues.

You should form an opinion concerning foundation performance by looking at the house