Inspecting Residential Lot Drainage in Areas with Expansive Soils

by Aaron Miller, Certified Master Inspector®


Nowhere is proper lot drainage more important than in areas where home and business building foundations are constructed on expansive clay soils. Proper foundation performance demands that soil moisture be controlled and moisture equilibrium be maintained under and around not only slab-on-ground and pier-and-beam foundations, but also more sophisticated structurally supported (piered) slabs. 

Expansive soils contain a variety of minerals, such as smectite clays that are capable of absorbing water. In Texas, for example, these are primarily vertisol clay soils containing montmorillonite that form deep cracks (desiccation fissures) in drier seasons or years. When they absorb water, they increase in volume, and, inversely, the soil’s volume decreases with drying. Expansions and contractions of 10 to 25% are not uncommon. This change in volume, especially if applied differentially (as opposed to uniformly), can exert enough force on the foundation of a building that has been improperly designed and constructed to cause significant and costly damage.

Properly constructed deep foundations can be built that will successfully resist the seasonal movements of expansive soils. Properly piered foundations, be they pier and beam (a raised foundation with a crawlspace, cast-in-place concrete perimeter/grade beam, and interior piers or piles), or structurally supported (piered) slab on ground, can function well without being unduly influenced by soil moisture content.  (Note that these types of foundations are not to be confused with pier-and-post foundations, which incorporate wooden posts.)

Today’s more common slab-on-ground foundations have footings that rarely exceed 30 inches in depth. In many areas, the depth of the expansive soils’ zone of influence can exceed 10 to 20 feet. There are areas in the Dallas-Fort Worth area where drillers do not reach solid substrate (usually shale) for 40 feet or more.

It is a popular myth that homeowners can prevent foundation failure by watering the foundation or the lawn around its perimeter properly and not allowing the soil to dry out or standing water to pool.  While that’s generally good advice for arid regions, it’s a flagrant oversimplification because even the best engineers at Texas A&M University can’t tell us how to achieve it.

Despite expertly installed and programmed automatic sprinkler systems (to include those designed specifically for foundation support), the soil around foundations can dry out faster on sunny or steeply sloped sides of a house than on the shaded or lesser sloped sides. Then one must also consider trees and other landscaping adjacent to the foundation that can use a significant amount of water and contribute to soil desiccation. So, in reality, it should be the responsibility of the builder—and not the homeowner—to prevent foundation failures by designing, building and landscaping them correctly in the first place, but this almost never happens.

The plain truth is that it costs more to build sound foundations on expansive soils. Part of the cost is for the professional skill and judgment needed. Experience also shows that the cost of repair is much higher than the cost of proper initial design and construction, and the results are less satisfactory. Furthermore, in arid regions where droughts are annual and water conservation is mandated, it makes no sense for homeowners to expend billions or trillions of gallons of precious water (and the dollars they represent) in an attempt to compensate for the builders’ lack of proper building practices—all in the name of increased profits.


Topography is a field of geoscience focused on the study of the surface shape and features of the Earth. This practice was once strictly under the purview of surveyors, with their optical transits or theodolites atop wooden tripods, together with their linemen and range poles. Today, you are more likely to see robotic total-station theodolites, real-time kinematic GPS stations, and other sophisticated and computerized geographic information system (GIS) equipment.  Some firms are exploring the use unmanned aircraft vehicles (UAVs) or drones. Regardless of the tools used, the task is to measure the contour of the surface of the Earth in any given area and to record this information, usually in the form of topographic maps. Such maps can be utilized by end users for any number of reasons, not the least of which is designing a building’s site lot drainage.

Inspectors may wish to perform some research prior to inspecting a property built on expansive soils.  One task is to ascertain the area or subdivision’s drainage patterns. Using Google’s USGS Topographical Maps site, one can easily determine the area’s drainage patterns, something that may not be so obvious when you are standing in front of a house or commercial building.

Soil Types and Characteristics

There are many different soil types in any given area and all have uniquely different characteristics. Another aspect of an inspector’s optional research prior to conducting an inspection can be to attempt to make at least an approximate determination of the type of soil underlying and, consequently, affecting the building to be inspected. This used to be a daunting task that required locating a printed copy of the United States Department of Agriculture (USDA) soil survey for the area in question. Now, such information is readily available at the USGS website.

Building Codes

Current building codes contain much information regarding the need for (and, to a certain extent, the prescriptive measures for) providing proper lot drainage and grading on residential and commercial building sites. Inspectors wishing exceed their SOP to provide their clients with more information can familiarize themselves with these codes.

Though it used to be an expensive undertaking to purchase all of the necessary code publications in their print form, the International Code Council (ICC) has made their residential and commercial building codes available to the public online. Many larger municipalities have put their subdivision drainage requirements on their city websites.

The International Residential Code (IRC) addresses lot grading and drainage in several sections of Chapter 4 and, when faced with expansive soils, the IRC directs you to Chapter 18 of the International Building Code (IBC). Most of these citations address grading and drainage from the perspective of how they affect foundation design and construction and, thus, performance. This is of paramount importance but not the only consideration to take into account.

Health Issues

Standing water on the lot of a building site is not just unsightly or inconvenient; it is also a health hazard. It provides the perfect breeding ground for mosquitoes. These creatures carry many diseases, not the least of which is West Nile Virus.

Your local pesticide applicator will gladly sell an environmentally-disastrous poison misting system that will not only kill everything in sight, but also cost several thousand dollars. Regardless, you will not get rid of mosquitoes until you get rid of the conditions that attract them.

Most municipalities and homeowner associations prohibit public-nuisance conditions on building sites. Once cited, failure to correct the ponding water may result in hefty fines.

Mold growth in the crawlspaces of pier-and-beam foundations is another health consideration that should not be overlooked.

Inspection Basics

The grading and drainage improvements of the soil on a building site should not allow water to pond in any location or for any length of time. In order to achieve proper drainage, it is necessary to consider many things.

Are adjacent lots higher? If so, are swales or mechanical drainage provisions present to manage the water draining from these lots to the lot you are inspecting?

Does the house have gutters around the perimeter? If not, why not? If so, are the downspouts of sufficient length? Do they terminate at swales or mechanical drainage provisions in order to manage the water falling from the roof?

If the property is designed with swales for drainage, are the swales properly sloped so that they remove the water from the lot to an approved municipal drainage location? This can be ascertained by measuring the length and slope of the swales with a tape measure or measuring wheel and laser level.

If the lot is equipped with mechanical drainage provisions, are they of the proper type?

The rule of thumb for grading requirements around the perimeter of a foundation is a 6-inch drop in elevation in the first 10 feet out from the foundation. For lot and swale slope, look for a 1/4-inch drop per linear foot.

Are there indentations in the lot surface that will allow for ponding water during periods of heavy rain or sprinkler use? These can usually be easily observed.

Are there municipal or subdivision drains on or near the lot? If so, do the homeowners know their functional history?

Is the house built on a creek or ravine lot? Are there erosion concerns?  It’s a good idea to recommend to your clients that they gather as much information as possible from previous owners, surveyors, municipal department personnel, homeowners’ association representatives, and neighbors regarding water flow, flooding, etc.

Are there retaining walls on the lot? Do they appear to be properly constructed and performing well? Do they have drainage provisions to prevent the hydraulic pressure in the embanked soil from damaging the walls?

Is the elevation of the finish floor of the house higher than the street level, as required by the IRC?

Litigation Considerations

Home inspectors in Texas represent liability-assuming entities designed to protect the interests of real estate brokers and their agents. If that sounds like hyperbole, consider that the Texas Real Estate Commission does not require brokers or agents to purchase professional liability (errors and omissions) insurance policies, but does require this of inspectors. In fact, no state-licensed profession in the state of Texas is required to be so insured other than home inspectors.

In the case of pier-and-beam foundations with crawlspaces, poor lot drainage can lead to excess moisture or even standing water under houses. This can cause mold growth, which is both a health hazard and a threat to a building’s finished surfaces and structure. Standing water under a house can also contribute to rot in the substructure and attract wood-destroying insects, such as termites and carpenter ants. It also provides a much-needed source of moisture for rodents and other unwanted pests.

Inspectors are not the only ones likely to be sued over poor lot drainage. Homeowners are often sued when their lots drain onto neighboring lots and cause a nuisance. Allowing ponding water that attracts mosquitoes can also lead to litigation by neighbors or their homeowner’s associations.

With all of that in mind, improper lot drainage that can instigate foundation distress, cause a public nuisance, be a factor in lot erosion, subject a house to flooding, contribute to persons contracting life-threatening diseases, play a part in mold growth, attract termites and carpenter ants, provide attractive harborage for rats and mice, rot the understructure, etc., may seems to be somewhat important, if one wishes to avoid lawsuits.

Referrals to Other Professionals

Home inspectors are not experts in every aspect of residential or commercial construction. In fact, other than those who are licensed in other trades or professions, we are strictly generalists.

Specifying lot drainage corrections can sometimes be simple and straightforward. Often, though, it requires a level of expertise that can only be conveyed by other professionals with extensive experience in this field.

The type of professional to refer a client to regarding the specification of lot drainage can vary from a licensed landscape architect to a licensed stormwater engineer. Some circumstances may also call for consultation with an attorney specializing in drainage disputes. Recommend that your clients seek out such professionals, should the need arise.

Personal Experience

I have encountered thousands of lots that required drainage improvement. Most were in the minor-to-moderate range of difficulty regarding remediation. I recently encountered what was perhaps the worst situation I have ever seen.

The house was in a very pricey neighborhood in one of the cities located in my service area. The 1-acre lot alone was valued at $1.5 million. The lot sloped toward the house so that there was a 10-inch drop in elevation from the street level to the finish floor level of the pier-and-beam foundation. The lots to the north and east were significantly higher than this lot. The backyard had been graded in a bowl shape, with a swale leading to the center of the west lot line. At that point, I observed what appeared to be a municipal drainpipe in a makeshift catch basin.

The owner reported that the area flooded every time it rained. He had photos of his grown son in water to the top of his fishing waders that was ponding in the backyard after a recent rain. He also told me that the drainpipe on the west edge had been installed by the builder when the subdivision was first developed. It was not in a municipal easement, but passed beneath the six properties from this house to the cross street at the west end of the block.

He attempted to get the city engineering department to run a sewer camera through the drainpipe to ascertain its condition and terminus to no avail. All such cameras were truck-mounted and there was no access to the backyard by vehicle.

The owner had bids from several contractors to correct the drainage. The most reasonable of these included a 7-horsepower electric pump, along with hundreds of feet of PVC drainage pipe costing around $25,000. Since most rain occurs with lightning, and this area is known for power losses during such storms, a generator would be required to ensure the pump’s operation during power outages. This increased the price by another $7,000.

I was not certain that this would work and had him contact the city. The municipal stormwater engineer stated that such a massive amount of water being pumped onto the city street might cause a public nuisance. The homeowner’s association agreed.

The owner was getting ready to sell this property in an attempt to downsize. The house was 60 years old and, due to the size of the lot and local property values, it was considered a tear-down. Builders who had responded to his call for bids on the property had reduced their bids substantially due to the drainage problem. Beyond the demolition, they would be required to bring in truckloads of engineered soil in order to build up the lot for new construction. That soil would then need to be mechanically compacted to the density of the native soil.

Any builder would then still have to install extensive underground drainage provisions in order to accommodate drainage from the height lots to the north and east. All of this additional work meant a $150,000 decrease in offers to purchase the property.

Fortunately, I encountered this situation late in my career. I covered all the bases in my report to include referring the client to stormwater engineers I have worked with in the past. Can you imagine if a prospective buyer walked into a similar deal where the property owner was less than ethical or the buyer’s inspector was a Realtor’s ally?


Drainage and grading are important aspects of property inspections. For that matter, all aspects of inspections require due diligence on the part of inspectors (and their clients). Due diligence is simply the care that a reasonable person exercises to avoid harm to others and their property. It requires that you be proactive in your thoughts, research and education, and in the development and maintenance of your professional integrity, including being honest and fair in your dealings with clients.


― Warren Buffett


About the Author

Following six years in the U.S. Army, Aaron D. Miller began work as a general contractor in the residential building and remodeling industry in 1975, until becoming a full-time home inspector in 1997. A member of InterNACHI and a Certified Master Inspector®, Aaron is also a TREC-Licensed Inspector and Professional Instructor, a Master TPREIA Inspector, and an ICC-Certified Residential Inspector in five areas.  He is a native of Dallas and has lived in the Dallas suburb of Garland for the past 15 years. A full list of his extensive professional credentials can be found on his website at

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Soils and Settlement
Moisture Intrusion
Soil Contamination Inspection

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