Frequently Asked Questions

This page attempts to answer the typical questions our office receives every day. It is not meant to provide professional engineering services, so please call your engineer to discuss your particular concern. It is not meant to provide legal services, so please call your lawyer to discuss legal matters.

Please feel free to e-mail or call us with your comments about this page. It is divided into three sections: concrete slab-on-ground foundations, pier-and-beam foundations, and other questions.

Concrete Slab-on-Ground Foundations

My slab is cracked. What's the best thing to do? Usually, nothing. Concrete cracks. Concrete cracks. Concrete cracks. That is why concrete is reinforced: to control cracking so that it is not objectionable.

What's important about a foundation is not whether it has one crack or one hundred cracks, but how the foundation performs its intended purpose. (Engineers call this serviceability.) The things that are important about a foundation are the following:

Was it built according to the Building Code?

Is it safe, so that it can support design loads?

Does it make the house unsanitary?

Does it make the house unlivable?

Does it make the house aesthetically displeasing to me?

Does it affect the value of my house?

How does expansive clay make my floor out of level? Expansive clay shrinks when it is dry, and swells when it is wet. The potential vertical rise (PVR) of the clay soil in Central Texas can be as high as several inches over a drought cycle. If the soil moisture content is kept constant, then the foundation will not move, but it is impossible to keep the soil moisture content constant, because the depth of seasonal moisture change can be as deep as 15 to 20 feet.

Why do Central Texas foundations deform concave down? Because of the change in soil moisture content caused by the presence of the foundation. Before the foundation was constructed, the soil moisture content values should have been constant across the footprint of the foundation. When the foundation covered the soil there, then the soil under the house was no longer subject to evapotranspiration. Because we are in an arid climate, over time the soil under the middle of a house will become wetter than the soil at the perimeter. Because clay swells when it is wet and shrinks when it is dry, the foundation heaves in the middle. In Central Texas, it can take up to five years for the initial moisture dome to stabilize.

The establishment of the initial moisture dome causes the worst of the damage from foundation deflection. Afterward, the foundation is subject to cyclic perimeter lifting and lowering from seasonal changes in soil moisture content. Because Austin normally gets most of its annual rainfall in May and October, since the summers can be quite dry, and since evapotranspiration is less in the winter, most homeowners with moving foundations find that cracks widen in the summer and close in the winter. Our telephone therefore rings off the wall in September and October with homeowners concerned about their foundations.

What if I support the foundation perimeter atop deep piers, to jack the perimeter level with the interior? You will have a temporary repair. This is because one day we will have a drought that will dry the soil under the middle of your house, and the soil then will shrink. When the soil shrinks, the slab will subside, but the foundation perimeter remains supported wholly by the perimeter underpinning piers. This causes a lot of damage. Door frames can widen so much that the doors will not latch, walls can pull from the ceiling, and walls can lift from the floor.

What if I support the foundation perimeter atop deep piers, jack the perimeter level with the interior, and fill the resulting sub-slab void with grout? Then the slab will remain fully in contact with the soil, so that if the soil swells, the slab will heave. Most foundation repair warranties do not cover swelling or heaving. The soil-supported interior still will subside when the soil dries.

How can I relevel my house without using piers? Use either mud-jacking, or else a combination of temporary footings and mud-jacking. Mud-jacking alone is capable of releveling a foundation by the hydraulic pressure of the pumped grout, but temporary footings can assist in setting key areas to the desired elevation until continuous support can be provided by the grout.

How can I repair the cracks in my foundation? Assuming no vertical displacement across the cracks, epoxy repair cement can be injected fully into the cracks to restore shear capacity across the cracks and to provide flexural continuity across the cracks. If the foundation is post-tensioned, the tendons can be restressed after the epoxy has cured. These steps may be sufficient to restore the foundation to its original integrity.

My house has cracks in gypsumboard and masonry, and doors stick in their frames. What do I do? In most cases, the most cost effective choice is to perform comprehensive cosmetic repairs of cracked components, and to adjust doors as needed. (See the questions below about crack repair.) This might be required every few years because of the cyclic deformation of the foundation, but you can fix a lot of cracks for the price of one underpinning pier. If cracks and sticking doors really bother you, then have an engineer look at your house, but before that you may wish to have your sanitary sewer tested for leaks.

Can sub-slab plumbing leaks cause this type of damage? Yes. This is because leakage contributes to the sources of moisture that cause foundation deflection. Insurance companies tell us that half of the houses that have symptoms of foundation deflection, also have openings in their sanitary sewer system.

How can I see whether my sewer pipes have a sub-slab opening? Get a licensed plumber to conduct a simple hydrostatic test of your sanitary sewer. In this test, the sewer pipe is plugged outside the house, and the sewer pipes are filled with water to the top of the floor slab. If the water level holds, then the pipes must be water tight. If the water level drops, then the pipes have one or more openings in them. Not all sewer openings leak under actual use, but since damage from plumbing leakage may be a covered loss under your Texas homeowner's policy, you should consider filing a claim if the hydrostatic test is positive.

How can I tell whether a sewer opening leaks? Run hydrodynamic flow tests for the suspect fixtures and pipes, and if possible, a reference fixture. (See our Atkinson Engineering Standard for Sewer Flow Test.)

Pier-and-Beam Foundations

As above, we will assume that the area of concern is Central Texas, and that the soil is an expansive clay.

Why do the cedar posts under my house appear to have settled? Cedar is not treated lumber, and with time it will rot. The rotting progresses from the bottom up and the outside in, so that the bottom of the post looks like it was placed in a giant pencil sharpener. The sharpened post pushes into the ground. Most houses in which we have seen this were fifty or more years old.

Why do the concrete piers move under my house? Probably because they were not founded deeply enough below the maximum depth of seasonal moisture change, and perhaps because they were constructed with too little reinforcement to resist uplift. In Central Texas, the design depth for concrete piers typically ranges from fifteen to thirty feet, depending upon the geologic formation and the site slope.

How do I determine how to construct piers for replacement or new construction? You do this by first getting a comprehensive geotechnical report. This report should include pier design parameters such as founding depth, allowable end-bearing pressure, design skin friction, design uplift pressure, design settlement, and lateral load considerations. The report also may address the appropriateness of particular foundation types, and anticipated site difficulties such as ground water and caving soil.

Second, the engineer performs calculations to design the foundation components so that the structural dead and live loads have a direct path to the piers, and all can safely support the design loads with appropriate serviceability according to the requirements of the Building Code.

Does my settled pier-and-beam house need more piers? Usually not, unless the occupancy has increased the service loads. Engineering calculations can determine whether structural members are compliant with the Building Code, and whether additional foundation elements are needed.

Can my house be releveled by shimming atop the existing concrete piers? Usually, yes. Often the apparent settlement has resulted from soil moisture content changes caused by the drying effects of tree roots. The longevity of such a repair then depends upon the ability to minimize seasonal changes in soil moisture content.

Other Questions

How can I tell whether a plumbing leak has damaged my foundation? This may require a comprehensive engineering investigation. It includes examination of the house, topographic measurement of the floor, measurement of the leak loss rate, and evaluation of the soil moisture content values.

I have three bids from foundation repair contractors. Which is best? This question cannot be answered without knowledge of the geotechnical properties of the soil, and evaluation of the material and structural properties of the foundation. A better approach is first to retain an engineer to ascertain the need for foundation repair, to propose repair choices for your consideration, to design the chosen foundation repair plan (based upon a geotechnical investigation and the properties of the foundation); and then to solicit bids from repair contractors to perform the repairs according to the engineer's plans.

What is a "threshold-type crack"? Threshold type cracks are as narrow as "at the threshold of detectability" and as wide as 3 mm. They occur at joints between either similar or dissimilar materials, but do not progress diagonally across the material.

What is a "minor-type crack"? Minor type cracks have thicknesses ranging from 3 to 6 mm if they occur at joints, or from hairline to 6 mm if they occur diagonally across the material.

How do I fix threshold-type cracks in gypsumboard? Threshold-type cracks at joints can be repaired by sanding the joint down to the paper surface, securing the panels with additional wallboard screws spaced 3 inches on center, and taping, floating, texturing, priming, and painting the surface. (Unless the separated panels are refastened with additional screws, they have no resistance to recracking.)

How do I fix minor-type cracks in gypsumboard? Minor-type diagonal cracks can be repaired by replacing as large a panel as is practical with new wallboard, securing the board with screws, (after installing backup boards at nonsecured joints), and finishing the straight joints as above. (Replacing panels with minor-type cracks is necessary, because panel loads cannot be transferred across a crack. The new panel is resistant to cracking at the same area because the new panel is installed without stress.) Thorough attention to detail in the repair of wallboard cracks can reduce the likelihood of their return, but repaired areas can recrack if structural movement is sufficient.

What foundation repair choice is most often overlooked? The "null" choice: do nothing. This choice should be part of the matrix of costs and benefits in determining the appropriate foundation repair choice.

Give an example of why a cost-benefit analysis is advised. Assume that you are selling your house. In its present condition, because it "needs foundation repairs," it is worth $100,000 and you have a qualified buyer. If the foundation were repaired, however, the house would have a market value of $120,000. The low bid for foundation repairs is $20,000, and the interior restoration thereafter is projected to cost another $10,000. Instead of taking the risk and the time for foundation repair, and then losing $10,000 on the investment, do nothing and save yourself $10,000.