Gibson HomeBuilders

Today’s topic is residential Basements built in Texas Part 2.
My guest today is Tom Werling with North Texas Basements, Jean Gibson, Vice President of Gibson Home Builders also Leon Campbell with the Native Shade Tree Farm.
Building Basements In Texas

Why don’t most builders in Texas, build basements? The answer is liability. Our soils in Texas are expansive and create problems not found in the northern states where basements are a common item.
You can build basements in Texas if you follow a good plan of action. The basements here may cost more than building one up north but if you scrimp on the process or leave out necessary techniques, you’re asking for trouble.

If you plan basement construction in an area that has clay in the soil, you need to take precautions to avoid structural damage to your home. So here are a couple tips to consider before you start basement construction in clay soils.
Before you start basement construction you need to know what type of soil you are building on. The U.S. Department of Agriculture has soil information on most of the United States. Soil testing can also be done so you will know what you are working with. Another important step is to make sure the ground is compacted. Failing to compact the ground properly can also lead to trouble in the future. Having a soil analysis performed for your building site is an absolute must to avoid problems
Expansive clay soils, cause structural damage to basements and home foundations when proper precautions aren’t taken during construction. When deciding to build a basement in an area that has clay soil you need keep in mind the nature of the soil that you plan to build on. Clay holds moisture and as the seasons change the amount of moisture in the soil also changes.
If you build on clay when it is holding large amounts of moisture, you can have your basement sink as the moisture content of the soil decreases. If you build while the moisture content is low, your basement may be pushed up when the moisture content increases. This can end up causing structural cracks. There are several ways to deal with the seasonal changes in the moisture content in clay when you are constructing a basement.
Before putting in the basement, you need to be building on stable ground. With clay in particular, it is important to make sure you have the ground compacted properly so you do not end up with the ground shifting under the weight of your home. It is possible to treat the soil with a lime mixture to increase stability and control swelling. Do this by removing a layer of the soil and adding several trenches under the area you want to construct your basement or foundation. Once you have the trenches in place you fill them with a lime mixture. This treatment adds about a month on the time you are going to need for construction.
Basements that are built in clay soil need to be able to breathe or move up and down slightly with the ground water in the soil. Concrete floors are not attached to the concrete foundation so that this movement doesn’t cause structural damage. To allow for this movement, all internal walls in the basement need to be “floating walls” or raised walls. Floating walls are suspended from the first floor and have a gap between the wall and the concrete floor slab. When you build in some areas you are actually required to use floating walls in basement construction. When you obtain your building permit you need to find out if this is a requirement for your area.
When basement construction includes plumbing, a reverse of this floating wall process is required. The floating walls are attached to the floor to create a solid base and the space is at the top of the wall in these cases. Expansion joints and flex lines are used for basement plumbing when working in clay soil to allow for the natural movement with ground moisture changes. Space must be left for pipes to reduce the risk of pipe breakage.

Expansive Soil
(Return to Index)
Soil is an essential component in the construction and stability of a house that is often overlooked by homeowners and homebuyers. Since the house is built on soil, structural damage to a house can occur if the soil expands, contracts or slides.
Expansive clay soils, Throughout the United States, particularly in Texas, California, Virginia and Colorado (though not exclusively in these locations), expansive or reactive clay soils are known to cause adverse effects on residential structures. Expansive soil expands and contracts due to changes in the moisture content of the soil, causing structural problems through differential movement of the structure. If the moisture content and or soil type differs at various locations under the foundation, localized or non-uniform movement may occur in the structure. This isolated movement of sections of the structure can cause damage to the foundation and framing, evidenced by cracking of the slab or foundation, cracking in the exterior or interior wall covering (indicating movement of the framing,) uneven floors and/or misaligned doors and windows. This type of movement is usually associated with slab on grade construction that is common in the previously mentioned regions of the country. However, this type of movement also occurs in structures with basements and crawlspaces.
A second effect of expansive soils is additional horizontal pressure applied to foundation walls found in basements and crawlspaces. Increased moisture in the soils adjacent to the foundation wall will cause the soils to expand and increase the lateral pressure applied to the foundation wall. If the foundation wall does not have sufficient strength, minor cracking, bowing or movement of the wall may occur. Serious structural damage to, or failure of, the wall may also occur.
A third effect associated with clay stone soil (a type of expansive soil) is the movement of soils on unstable slopes. Expansive clay stone soil, found as a layer under a more rigid top layer of soils, become unstable as the moisture content increases, allowing the clay stone and the top layers of soils to move. If the soil is located on a slope, the top layer of soil can creep (slow movement) down hill or even cause a landslide (sudden and dramatic movement). Consequently, a house with an inadequate foundation built on unstable slopes can be subject to creeping of the structure down slope, or to failure of the structure in a landslide.
Possible Solutions; 
Pre-construction solutions: Prior to building the structure, a soil test of the site should be performed to ensure the soils are stable or to determine the approximate effect the soils will have on the structure. This will assist in determining if the soils are capable of properly supporting the structure. In addition, information on the soils can ensure that the foundation is designed to withstand the effects of the existing soil conditions, and assist in the development of plans for long-term maintenance.
Post-construction solutions: For structures already in existence, several possible solutions to counter the effects of expansive soils are available. Common preventative solutions include proper soil maintenance such as maintaining a uniform and constant moisture level in the soil. This may involve introducing moisture into the soils continually and uniformly to prevent shrinking; and/or preventing excessive or isolated saturation of the soil through proper drainage and grading techniques that prevent swelling. For structures affected by expansive soils, future movement can be prevented by providing additional strength and support to the foundation. This may include various methods of underpinning (to prevent vertical movement and/or sliding) and/or reinforcing of the foundation walls (to withstand lateral pressure).