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A-1 ENGINEERING, LLC

  A-1 ENGINEERING, LLC                      

Structural + Civil Engineering Consultants                             Serving San Antonio and Austin

Watering your foundation may be more psychological than an engineering requirement

Some engineers blame foundation movement to homeowners because the engineer did not observe soaker hoses watering a foundation. Interestingly enough these are Engineers who are hired by the home builders. So we went through manyl of our engineering design manuals, building code, theories, and software to look for the engineering parameters that influenced the foundation design if the foundation is watered or not watered. Not to our surprise we found NOTHING in terms of accounting for a soaker hose. Anyone that blames you for not watering the foundation simply doesn’t know what he is talking about. We design foundations to react to the movement of the soils based on the soil classification, relative moisture content and climate. It is important to understand that foundations are designed to move. Especially those that rely on the near surface soils for support. Let’s discuss each parameter:

 

  • Soil Classification: Soils are broken up into two general types: cohesive and non-cohesive. For simplicity, cohesive soils are clays and non-cohesive soils are aggregates, such as sand and gravel. Cohesive soils (clays) will expand (swell) when wet and shrink when dried. Non-cohesive soils will not expand (or swell) when wet but they may settle when wet or dried. Notice we that we used the words settle and shrink. They are not the same.  An easy way to remember the difference is to think that clays shrink/swell and sands settle. Shrinking soils will swell when wet, whereas settling soils will remain settled unless disturbed. If the soils around your house get “muddy” when wet then they are probably clays that will shrink or swell, not settle. On the engineering side, designing a foundation on clays is primarily concerned with clays shrinking or swelling. The amount the clay can shrink or swell has a lot to do with the classification of the clay.

 

  •  Relative Moisture Content: This is the amount of water that is absorbed by the soils. Now that you know that clays shrink and swell you can understand why you see cracks in the soils around your house. The cracks in the soil occur because the soils have lost moisture (water) and have shrunk (not settled, although your foundation will settle). When designing foundations for houses, engineers typically assume the soils are dry and so we design the foundation to move when the soils get wet and swell. The equations and software that we use do not consider if you water the soils around your foundation. We only care about what happens when the moisture content changes. Watering a foundation may actually cause soils to consolidate (be pressed down, this is not settlement) as the soils feel the pressure of the foundation. For example, you can crumble dry bread in your hand but if you add the right amount of water you can actually form it into a nice firm shape. This is consolidation also known as compaction. Clays that are loose and get the right amount of moisture will consolidate under pressure. This can happen with or without a drought. It can happen with soaker hoses. It all depends on the state of your foundation on the soil; on the one hand with addition of water, clays will expand (and raising your foundation) on the other hand, too much water might consolidate the soil. Not to get you confused, almost all the time, addition of water (moisture, actually) expands the clay soil (hence, your foundation heaves) while loss of moisture shrinks the soil (hence, your foundation settles).

 

  • Climate: El Nino is to blame for watering or not watering your foundation. However, the climate around your house is a factor in the design of foundations. Structural engineers have a factor called the Thornthwaite Moisture Index which is an index that is assigned to a region. All regions have a moisture index factor. This foundation design factor takes into account the rainfall and evaporation (droughts). This foundation design factor does not account for you watering your foundation. It is up to El Nino which is considered an Act of God for warranty companies.

 

Considering the three general foundation design factors together, if we design the foundation for your house there is no way for us to take your watering effort into consideration. We simply design for a worst case scenario which is a foundation on very dry soil that gets wet and swells up based on the historical regional factors previously discussed. If the foundation soils dry out and shrinks then the foundation design effects are the same but in the opposite direction. Something else to consider is the basic observation that the soils you are watering are not the soils that support your foundation since they are next to the foundation and not below it. 

A very important factor that does influence the performance of your foundation is the depth the foundation is below the ground. The deeper that your foundation is the less susceptible it will be to the climate. The International Building Code states that all foundations should be at least 12” below the adjacent soil. This is a minimum. A depth of at least 24” into natural soil will be less susceptible to moving soils, plus the beam will be stiffer and more capable of withstanding soil movement better than a shallower beam.  If you hire your own structural engineer to design your foundation you should insist on a deeper beam – 3ft deep minimum in San Antonio and Austin is our suggestion.

There is obviously a cost increase in the construction of the foundation but this cost will be substantially less than foundation repair later. So having a blanket recommendation to water your foundation falls short of the full consideration that structural engineers take into account for foundation design. Simply put, any engineer or home builder who tells you that you didn’t water your foundation is the problem is not clear or doesn’t know anything about foundations.

 

Does an engineer inspect the work of a foundation repair company?

Foundation design, performance and leveling are complicated concepts to understand because a variety of factors influence each other. When a foundation repair company states that an engineer certifies the work of their press pile installation they are referring to an inspection that an engineer performs to tell you what the contractor did, how they did it and the engineer may report the relative elevations of the foundation after the work is completed. The key point is that the engineer is asked to inspect the work after the fact. The inspection by the engineer does not consider a structural assessment of your building or the foundation. So if your foundation, walls or roof framing are broken then you will need to hire another engineer to assess the building, however you indirectly paid for the first engineers inspection. Many of the engineers that inspect foundation “repair” work are not structural engineers. Why does it make a difference? Because once a foundation beam is lifted off of the ground it is no longer a soil supported beam, it becomes a true  structural beam. Beware of Engineers claiming they are Structural Engineers when in fact they are not. For more info on engineers pretending to be Structural Engineers, please read Structural Engineering License in Texas.

This may sound confusing so lets discuss the difference. Basically a structural beam is a beam that spans between two points; similar to the beam that is over your window. The beam over the window spans from one side of the window to the other. A typical foundation beam is not a structural suspended beam because the beam is continuously supported by the soils, it’s considered a structural foundation, usually called a strip footing. It does not span between two definite points so structural engineers do not design foundation beams in a similar manner as a structural beam. So if the engineer that inspects the foundation “repair” is not a structural engineer they may not understand this difference and NOW a full structural beam (which is supported from pile to pile) may exceed the allowable span which is not permitted by the International Building Code (the actual code). Foundation repair companies will not ask the engineer if he/she is qualified to inspect the foundation (because they don’t care… see foundation repair page) so its imperative that you seek the engineers qualifications. 

If this was a little too technical of an explanation, we have “translated” this article under our page entitled Water Soaker Hoses for your Foundation.

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