The 1996 edition of the PTI book Design and Construction of Post- Tensioned Slabs-On-Ground includes the following:

Application of these recommendations results in slab designs similar to those that [...]]]> For engineered slab-on-ground foundations on expansive soils, there are two code approved design protocols that may be used, one published by the Post-Tensioning Institute (PTI) and the other published by the Wire Reinforcement Institute (WRI).

The 1996 edition of the PTI book Design and Construction of Post- Tensioned Slabs-On-Ground includes the following:

Application of these recommendations results in slab designs similar to those that have exhibited satisfactory performance.”

The WRI publication, Design of Slab-on-Ground Foundations – An Update, includes similar wording.

Neither code approved design protocol promises that the actual deflection of engineered slab-on-ground foundations will be less than some stated amount. They do promise that actual foundation performance in terms of superstructure distress will be “satisfactory” and the distress “minimal.”

I think it is fair to say that slab-on-ground foundations designed and constructed in accordance with either design protocol will not deflect enough to cause structural (load-bearing) damage to the superstructure.  There is likely to be some degree of cosmetic distress and some minor door problems.  The levelness of the slab surface is not addressed by either design protocol.

Much of [...]]]> This is easily the most important section of this site

If you are like most Houstonians, virtually everything you “know” about foundation repair comes from radio and television ads. Unfortunately, advertisements are rarely a reliable source of any kind of technical information; that certainly holds true of foundation repair.

Much of the information in this section is well known, widely accepted and absolutely non-controversial among the slab-on-ground structural engineering community. Yet, you could listen to hundreds of hours of radio and televison ads and you would hear nothing about the subjects I address in this section:

When you talk [...]]]> Retaining a Professional Houston Engineering Inspector

€When you retain a Professional Engineer to inspect your foundation, what you are paying for is his or her judgment. This is true of any professional you retain whether it is an engineer, a doctor or an accountant.€

Questions You Should Ask Yourself When Selecting an Engineer

When you talk to the engineer on the phone ask yourself the following questions:

• Does the engineer sound as if he or she know what they are talking about?
• Does the engineer sound as if he or she know what they are talking about?
• Does the engineer answer your questions in a manner that you can understand?
• Does the engineer sound as if they are a reasonable person?

What to Listen For When You Contact an Engineer

• Assessing the performance of a slab-on-ground foundation can be done competently only by a Professional Engineer. It is technical work requiring technical knowledge and, like every technical field, it has its own jargon. When you are on the phone, note if the engineer talks excessively in jargon.
• Does he or she talk down to you or do they explain things in a more down to earth manner? You want an engineer who talks in plain language so far as the subject permits and who does not talk down to you.

Asking About Measurements

I find many potential clients ask if I make measurements; also do I use a special instrument. (The answer to both is yes.) Many people assume that if someone uses a special tool to make measurements, that they must know what they are doing.

Actually making measurements is not part of the practice of engineering. Professional Engineers should know what to measure and how to interpret the measurements. So ask him what he does with the measurements.

What you want to hear are words like bending and tilt. If all you hear is levelness, then, in my opinion, you should continue your search for a competent engineer.

Under the rules licensed real estate inspectors are required to follow, if they judge the performance of the foundation [...]]]> From a practical perspective, the difference between what a real estate inspection report and an engineering evaluation comes down to what they report if the foundation performance is judged to be deficient or inadequate.

The Real Estate Inspector Approach:

Under the rules licensed real estate inspectors are required to follow, if they judge the performance of the foundation to be inadequate, the inspector is required to report the foundation as in need of repair.

The Professional Engineer Approach:

An example of an engineering approach can be found in a publication of Texas Section of the American Society of Civil Engineers. The guidelines state that if the foundation performance is judged to be inadequate, the engineer should report to his client the options that are available to improve the performance. Those options do include structural foundation repair but also can include non-structural options such as landscaping changes, more or less aggressive watering of the foundation making cosmetic repairs and/or changes to the house and, if appropriate, doing nothing.

Why the Engineering Approach is a More Comprehensive Approach:

According to the US Army Corps of Engineers publication €Foundations in Expansive Soils, the fact that a foundation is not performing “adequately” does not mean that foundation repair is either necessary or desirable.€ Nor does it mean that foundation repair will actually improve the performance of the foundation.€

An engineer has both the training and duty to exercise his engineering and analytical training to judge adequacy of the performance of the foundation. Engineers are  also qualified to report what options are applicable to a specific house for improving poor foundation performance.€

Real estate inspectors are required only to provide an opinion as to whether the foundation performance is deficient. They are not required to provide an opinion as to the whether the foundation should be repaired or not.€

Real estate inspectors frequently recommend that you retain a Professional Engineer to determine if the foundation needs or should be repaired.

All they warrant is that after the foundation repair work the underpinned [...]]]> Most People Find The Answer Surprising

This is a question that is difficult to answer.  Surprisingly, no competent foundation repair contractor actually promises to make their foundation work better than it did prior to the repair work.

What Foundation Repair Contractors Actually Promise

All they warrant is that after the foundation repair work the underpinned area will not settle more than a specified amount, usually an inch of settlement for every 30-feet of underpinned span.  The repair work is almost always done without any definitive evidence that the foundation has settled more than an inch for every 30-feet of span.  Most homeowners who underpin their foundation have no way of knowing if their foundation has settled more than an inch for every 30-feet of span.  Nor do they normally have a rational basis for believing that the foundation will or will not settle more than the warranted amount in the future absent any underpinning.

What Improvement is Realistic to Expect

In our experience, foundation underpinning will usually reduce the future settlement by about half. Foundation repair has no effect on future uplift.

In terms that the lay person can relate to that generally means that the number of drywall and stucco cracks will be cut in about half.  The number of brick veneer cracks will usually not change but the average width of the brick veneer crack will usually be cut in half.  The number of sticking doors may also be cut in half.

Underpinning a slab-on-ground foundation is usually done with the intent to lift some foundation areas to attempt to bring the slab surface to a [...]]]> In most cases, foundations that are structurally repaired are underpinned.  This is an engineering term that, in this context, refers to the process of providing structural support under the existing slab-on-ground foundation.

Underpinning a slab-on-ground foundation is usually done with the intent to lift some foundation areas to attempt to bring the slab surface to a closer approximation to the as-constructed condition.  The underpinning is also intended to make the foundation perimeter less susceptible to future settlement.

The traditional way to underpin a slab-on-ground foundation is to place reinforced concrete piers under the perimeter of the foundation.  The bottoms of the piers are belled out.  This spreads the load transferred to the soil and prevents the pier from being pushed up when the soil swells.

The following video from Dawson Foundation Repair is the best video I could find that illustrates the foundation repair process from beginning to end.

Note to Dawson: This video could be greatly improved by removing the text descriptions and replacing them with an audio narrative.

It is unreasonable to not expect some degree of damage due to foundation movement in [...]]]> Engineers and real estate inspectors are in the business of informing potential buyers as to the condition of the house, not its marketability. However, there are a couple of points that bear on this question that can best be made by an engineer or inspector:

It is unreasonable to not expect some degree of damage due to foundation movement in resale houses in the Greater Houston Area. The combination of expansive soils, thin flexible slab-on-ground foundations and wooded lots virtually guarantees that many houses will experience some damage due to seasonal foundation movement. This type of movement rarely affects the structural stability of the frame structure of the house.

There is a wide range of opinions concerning how much cosmetic damage is acceptable or not acceptable. Some people find even hairline cracks unacceptable; others find almost any crack width acceptable so long as there are no structural safety or stability issues. If the degree-of-damage shown by a house you are considering buying makes you uncomfortable, you should probably not buy the house.

These are cracks that are frequently formed within 12-inches of the outside corners of the foundation.  They result when the brick veneer expands when it is heated by the sun.  As the brick veneer expands it pushes outward on the foundation.

The frictional forces [...]]]> The following are two examples of concrete repair that are sometimes required:

Wedge or Corner Cracks:

These are cracks that are frequently formed within 12-inches of the outside corners of the foundation.  They result when the brick veneer expands when it is heated by the sun.  As the brick veneer expands it pushes outward on the foundation.

The frictional forces on the concrete surface cause the foundation to crack at the corner.  Wedge cracks or corner cracks are not indicative of a structural performance issue.  They may, however, require concrete repair if the cracking is so bad that the brick veneer begins to fail.

Exposed Cable Ends:

In post-tensioned slabs-on-ground, the ends of the post-tensioning cables may become exposed.  When this happens, the anchors that hold the cables in place can become damaged due to corrosion.  To prevent damaging corrosion, a concrete repair should be executed that will protect the anchors.