Foundation Repair

When a homeowner in the DFW area suspects the foundation of his house needs repairing, he is faced with having to decide which repair methodology is best. Given the financial investment in the typical Dallas-area home, the prospect of a foundation repair project of any magnitude can sometimes be overwhelming.  With all the different technologies available and the myriad of foundation repair companies in the Dallas/Ft. Worth area, this important decision is made more difficult. There are literally hundreds of foundation repair contractors in the area, each claiming their proprietary product or solution is best.  For most homeowners, sifting through the options and choosing a solution is a confusing process; that is, unless they find someone they can trust who can guide them through the repair process. 

The following foundation repair description might help you understand more about the causes, repairs, and prevention of foundation problems.

Foundation Movement

Most slab foundations are not completely rigid. In other words, if the soils below the foundation move, the foundation will usually move also. When they move, some slab foundations will tilt and others will move differentially. Tilting occurs when the foundation moves uniformly and tilts much as a regular table would if one edge of the table was lifted up. Differential movement occurs when one portion of the foundation moves more than another portion of the foundation. This type of movement is more common than tilting and causes more distress in the sheetrock, brick, doors, etc. than tilting.

When a foundation moves, it is in the form of either upheaval or settlement (or both). Upheaval occurs when the clay soils experience expansion and this expansion pushes the foundation upward. This upheaval is usually the result of the clays in the dirt absorbing excess water.

The more common type of foundation movement is settlement. Settlement can be the result of several factors as more fully described in the following paragraph.

Foundation Settlement

Foundation settlement can be caused by numerous factors, some of which are:

• The drying out of the soils around the outer perimeter of the foundation.

• The effects of the root structure of mature trees / landscaping near the foundation.

• Inadequate watering of the foundation during dry weather.

• Loosely compacted fill materials. (Fill material is dirt brought in by the builder to help level a lot prior to constructing a foundation on it.)  

Settlement of a foundation that is caused by seasonal factors is especially noticeable during the hot dry summer months. This is the period of time in the DFW area when the clay soils can dry out.  Sometimes as deep as 10 to 15 feet below ground level, depending upon climate and environmental conditions. The drying of the soils occur because of both evaporation and transpiration (water being removed because of trees and shrubs). As the soils dry, they tend to consolidate; as they consolidate, a slab-on-grade foundation settles.  The outer perimeter is more susceptible to the settling because of the factors such as a higher evaporation rate and proximity to the landscaping.

If a foundation settles because of problems with fill materials, it is usually because the fill dirt used by the builder/developer to help level the lot prior to the construction of the foundation was not properly compacted. This loosely compacted dirt consolidates over time as a combined result of gravity, water, and the weight of the structure, causing a foundation can settle.

Foundation settlement can usually be remedied by the installation of piers, and under certain circumstances by “mudjacking”.  

Foundation Upheaval

Because the soils in the DFW area are known for their expansive, highly plastic characteristics, they tend to expand when the moisture content of the soil increases.

Usually the winter months are wet so the clay soils tend to swell, this can cause some foundation upheaval, especially around the outer perimeter of a foundation. Foundation movement caused by simple seasonal changes (wet/dry cycles) can certainly cause some cosmetic distress but, when compared to the other types of upheaval, seasonal foundation movement usually caused only relatively minor distress.

However, there are factors other than “normal” seasonal changes that can cause foundation upheaval, which,  unfortunately, can  result in significant problems.  Some of these factors are:

• A slab foundation was initially constructed over dry clay soils.
• Poor to marginal drainage conditions around a foundation.
• Plumbing leaks that cause water to soak into the soils below a foundation.
• A slab foundation built over an area where, prior to the construction of the foundation, the soil was “cut” down to help make a lot level.  

It can be somewhat complicated to correct a foundation that has experienced significant upheaval. Because of the complexities, it is highly recommended that the homeowner consult with an independent engineer to determine the best remedy for his or her specific situation.

What installing piers does

There are basically two reasons to install piers: 

• To stop any further downward movement (settlement) of the foundation – in the area of the piers. Under normal circumstances, a pier will only influence an area within a 7 or so foot radius. In other words, it is possible that the unpiered portions of the foundation may experience settlement/upheaval in the future. This includes settlement caused by seasonal factors, improperly compacted fill materials and settlement caused by trees. The entire slab will still be susceptible to upward movement (upheaval of the soils) and / or settlement in the unpiered areas. This means that the foundation may heave upward off of the newly installed piers. It is important to note that most, if not all, foundation repair contractors will warrant their work for settlement only – not upheaval.

• To help bring portions of the foundation to a more “level” position – in the area where the piers were installed.

About Piers

Generally speaking, when an engineer designs a pier, he considers several factors, including the characteristics of the region’s soil (i.e., how deep is it to “bedrock”, how expansive the clay soils are, etc.). If piers are installed under a foundation, it is important that the piers be installed deep enough so they are founded in a stable bearing strata.

If a properly designed pier is founded in a stable strata, then the foundation can not experience any further settlement, in the area of the pier. However, if the pier is based in a bearing strata that is subject to movement, then there is a potential for continued foundation movement since the pier itself may move.

If this latter condition occurs, it usually occurs because the pier is based in the zone where the moisture content of the soil still varies from changes in  climatic conditions (i.e., rain, no rain, evaporation, etc.). Therefore, unless a pier is firmly placed in a stable bearing strata, then that pier has the potential to move as the soil expands and/or contracts.

The types of piers

Although there are differences of opinion between professional engineers about the “best” type of pier to use, it has been my experience that there are two types of piers that, if installed properly, provide excellent results. These two types of piers are:

• Drilled, concrete pier A drilled concrete pier is an excellent pier when the bottom of the pier is either firmly implanted in “bedrock” or is belled out to a diameter of 2.5 times the pier shaft diameter. For example, if a pier has a 12” shaft diameter, then the bottom of the pier will be belled out to a diameter of 30”. This bell provides an excellent anchor for the pier. This pier is typically installed to minimum depths of 12 to 15 feet below the surface (unless “bedrock” is encountered first). As stated previously, the depth varies as a function of the actual onsite soil conditions. The drilled, belled, concrete pier offers excellent protection against further foundation settlement and/or upheaval of the pier. (however, no pier system installed under an existing foundation can prevent the foundation from lifting up off of the pier. Note that all warranties of the various foundation repair companies only warrant against future settlement.)

• Steel pipe pier (piling) There are several advantages of a steel pipe pier: it can be installed in some locations where it is not possible to install a belled concrete pier; it’s installation is usually more “friendly” to the landscaping around a foundation; often it can be driven to depths deeper than other types of piling systems; and it is not as susceptible to upheaval as some of other types of piers

 It should be stated that the above comments are general in nature and are based on years of experience and observations.  It is important that the engineer consider many factors when developing a solution to a foundation problem.  Actual onsite conditions, climate changes, soil reports, house structure, landscaping, and budget may dictate a different pier strategy/design. This is why it is recommended that an independent, experienced, structural engineer be consulted prior to conducting foundation repairs.

Homeowner Maintenance

In order to reduce the effects of seasonal foundation movement, it is important for a homeowner to maintain the soil at a constant moisture around the foundation, throughout the year. This is done by ensuring that water will run rapidly away from the foundation during times of excess rain and by adding water to the soil during times of drought.

During the drier times of the year, the soil around the house can be watered by means of a soaker hose or a lawn sprinkler system. If a soaker hose is used, it is recommended that the hose be placed around the outer perimeter of the foundation at a distance of 1 ½ to 2 feet away from the foundation.  Of course too much of a good thing can be harmful, so it is important to realize the goal is to maintain the moisture level, not drench the ground around the house.

Another factor is to realize that because of environmental considerations, some sides of a house may not require as much watering as others. For example, evaporation is usually more intense on the south and west sides of a house (unless these areas are shaded and protected from the wind).

Drainage Conditions

One method to both reduce the effects of the foundation movement and help preclude significant upheaval from occurring is to ensure that there is good drainage around the foundation – the surface of the ground should not allow water to pond within 8 to 10 feet of the foundation. Another good idea is to make sure all rain gutters have adequate downspouts so the gutters do not overflow during a heavy rain.  Furthermore, all downspouts should either be terminated in a buried drain pipe or positioned such that the water is deposited several feet (8’ or so) away from the foundation into an area where the water will drain rapidly away from the foundation. 

Finally, where possible, the ground surface (including flowerbeds) should be sloped at a minimum rate of 5% (i.e. 3 inch drop over a 5 feet distance) away from the foundation for the first 5 feet all around the foundation. At this point (5 feet from the foundation) the ground surface should slope adequately to drain the surface water away from the house. Again, do not allow water to pond within 8 to 10 feet of the foundation. Drainage swales should, if possible, have longitudinal slopes of at least 2% (i.e. 6 inches over a 25 foot distance) or a 1% minimum slope (3 inches over 25 feet).