The US Army Corps of Engineers and Slab Foundation Performance

Chapter 9, Remedial Procedures

The key chapter in the US Corps of Engineers’ publication dealing with foundation performance is titled: Chapter 9, Remedial Procedures. It does not deal directly with foundation performance. To the extent that foundation performance is addressed, it is addressed implicitly. The focus is on what options are effective and appropriate for getting a foundation to perform better. This chapter is short, but it contains a lot of wisdom regarding slab foundation repair and, implicitly, foundation performance. 

Design and construction of slab-on-ground foundations

The first point that should be understood is this: slab foundations should be designed and constructed so that foundation distortion is limited to what the structure can tolerate. The exact phrase is: what the structure (meaning the house) can tolerate. What that phrase means is really simple: The foundation should not distort to a degree that the distortion damages the house. To the extent that foundation distortion causes drywall cracks, brick veneer cracks, perceptible floor slopes, etc., then it can be said that the distortion is not being tolerated by the house. Here is the relevant quote:

The foundation should have sufficient capacity (stiffness) to maintain all distortion within tolerable limits acceptable to the superstructure (house). (the terms in brackets are ours.)

Is the need for foundation underpinning subjective or objective?

The following quote is very insightful:

The amount of damage that requires foundation underpinning…also depends on the attitudes of the owner and occupants to tolerate distortion as well as damage that actually impairs the usefulness and safety of the structure.

Here is another surprising quote to the effect that most homes that experience distress should not have the foundation repaired:

Most slab foundations that experience some distress are not damaged sufficiently to warrant repairs.

This statement is somewhat misleading. The distress is not in the foundation; it is the house that shows the distress. I would reword the statement to say this:

Most houses on slab foundations that experience some distress are not damaged sufficiently to warrant repairs.

What is important here is that what makes foundation repair an option is the degree and severity of the damage that foundation movement has caused to the house. This assumes that the inspector, whether a TREC inspector or a PE, has the ability to distinguish distress caused by foundation movement from distress caused by other things such as age, poor workmanship and framing issues.

What about level surveys?

Level surveys can be used for limited uses. Here is a direct quote:

Level surveys can be used to determine the trend of movement when prior survey records and reliable benchmarks are available.

Here is the problem: if, as is almost always the case, there are no prior level survey records, nor any reliable benchmarks available, then a level survey can be used only to make approximate estimates of the distortion the foundation has experienced. Such level surveys are never dispositive.

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