Accepted Industry Practices Regarding Slab Foundation Performance

First, what is an accepted industry practice regarding slab-on-ground foundation performance?

How to apply the phrase accepted industry practices to foundation performance is not unambiguous. There are inspection items for which the application of this phrase is clear. Examples are ground fault devices and electrical breakers. Accepted industry practices certainly include the National Electrical Code and the manufacturer’s instructions.

When it comes to structural issues, there is almost nothing like what is freely available for electrical and mechanical components.

With very few exceptions, the codes specify how slab-on-ground foundations shall be designed, not how well or poorly they are expected to perform.

If you look at the code-approved design methods from an engineering perspective, it is certainly possible to infer from the design manual what a structural engineer would expect regarding the performance of a slab-on-ground foundation. Unless a home inspector had some training in engineering or was self-taught in reinforced concrete engineering design, a TREC home inspector would probably not infer anything regarding performance. The fact is, while a good understanding of foundation design for expansive soils is helpful to engineers, that is not the case for either real estate agents or home inspectors.

If not the codes or the design methods, what else might the phrase accepted industry practices refer to? Elsewhere in this site, we discuss a wide array of accepted industry practices that, in our opinion, meet that description. For purposes of this article, we want to concentrate on four pieces of published material that qualify as accepted industry practices and are, in our opinion, reliable. Those four are listed below:

Accepted practice: The TREC SOP

The TREC SOP is certainly the one authoritative source agents and TREC inspectors should be familiar with: TREC definition of Performance:

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

I like this definition.  In my opinion, it is much better than the old standard: performing the function intended. Applying this definition can be difficult because it is not clear whose intent should be used. 

The phrase: with consideration of age and normal wear and tear from ordinary use is a significant improvement. Why do I say that? 

Because there is no way to assess the performance of a foundation without answering a simple question: As compared to what? It is obvious that your performance opinion must be comparative. Specifically: as compared to other foundations of similar age and normal wear and tear from ordinary use.  

With regard to foundation performance, it is common for older slab-on-ground foundations to develop more and more severe concrete cracks as it gets older. Slab-on-ground foundations typically become less level over time. 

Slab-on-ground foundations typically deflect or bend more as the foundation gets older. You should not expect a 25-year old slab-on-ground foundation to perform as well as a 12-year old foundation. Elevation measurements will normally show that the older foundation is less level and has more apparent curvature due to foundation distortion. Older upstairs floors sag and cause door frames to distort.                     

Accepted practice: US ARMY Corps of Engineers 

This document has a very useful chapter (chapter 9) on remediation. It is short, straightforward and not overly technical. It is available online and it’s free. 

For my comments about the Army Corps of Engineer document regarding remediating slab-on-ground foundations in expansive soils, please click here.

Accepted practice: Texas Section ASCE publication: Guidelines for the Evaluation and Repair of Residential Foundations, version 2

This is another document written for engineers. It is long but includes good and valuable advice. Every TREC inspector should have a copy and read it often. I learn something new every time I reread it. It is available for free online. You can download a copy here.

To read my comments click here.

Post-Tensioning Institute Guide for the Performance Evaluation of Slab-on-Ground Foundations

This is a guide published by the same organization that publishes the manual used for designing post-tensioned slab-on-ground foundations. This guide is explicitly intended to be used for both post-tensioned and conventionally reinforced slab foundations. In many ways, it is similar to the guideline published by the Texas Section of the ASCE.

The main difference is that the document does not address foundation repair: when foundation repair should be recommended and when not.

So Your House Is Built On Expansive Soils 

Published by the American Society of Civil Engineers (ASCE). It is not really a book; it is closer to a booklet at less than 60-pages. It was produced by the Shallow Foundations Committee of the ASCE headed by Warren K Wray, Ph.D., PE.

Wray’s Ph.D. dissertation formed the basis of slab-on-ground foundation design as it is practiced today. 

This booklet is addressed to homeowners who live in areas where expansive soils is an issue. The ASCE has let the booklet go out of print. r  The booklet is very hard to find at a reasonable price. Fortunately, my son and I took the booklet and we wrote a version focused on Houston and southeast Texas. Our version is a free printable pdf file.        

Has Your House Got Cracks? 2nd edition

This is a British publication. It is excellent. It is similar to the American publication titled:  Has Your House Got Cracks?, 2nd edition. The biggest difference is that, in the United Kingdom, distress and damage due to expansive soil movement may be covered by homeowner’s insurance. Not so in the United States. 

Standard engineering textbooks

There are numerous engineering textbooks on soil mechanics and foundation design. Some include a discussion on what is meant by foundation performance. An excellent example is, in my opinion, chapter 2 in Foundation Design – Principles & Practices by Donald P. Coduto. 

 Coduto stresses the importance of how a foundation is expected to perform as compared to how it is performing. 

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