How An Inexpensive Add On to Your Light Frame Building Structure Could Really Be Like A Cheap Insurance Policy
March 30, 2009, by David JoynerThis article is to builders of light commercial buildings and residential homes practicing in areas where highly expansive clay is known to exist. As an engineer and examiner of hundreds of buildings that did not perform as intended, we have learned some things that are missing from a number of properties that could potentially save builders headaches and thousands of dollars in unexpected warranty work. If you have been active in the building industry for any length of time you have come across language in the building documents which indicate that water should be well drained from the building to avoid ponding and standing water during wet periods. This is good advice and should be heeded.
Over the years our firm has inspected hundreds of buildings and has found expansive clay soils to be a common occurrence in areas such as East Austin, Eastern San Antonio, Los Colinas, and much of the eastern portion of Texas. During periods of drought and times of torrential rains, the perimeter walls of the structures experience dramatically different atmospheric conditions (wet to extremely dry). The soil at your perimeter can go from desiccated soil to receiving all the rain which falls from the ridge to the eave deposited within 12 inches of the edge of the foundation. This is because most properties in Texas are constructed without the benefit of installed rain gutters. Rain gutters are an inexpensive long-term preventative measure to make sure that moisture content in the soils adjacent to your perimeter foundation of your building doesn't experience dramatic moisture content fluctuations.
We don't manufacture or sell rain gutters. We can easily attest to the positive experience you're likely to have by having installed them on your structure. If your geotechnical or structural engineer has recommended soil substitution at your building site, that should be all the warning you need to include rain gutters as a preventative measure on your project. You say the architect didn't specify it? We would suggest an RFI to the geotechnical or structural engineer asking if the inclusion of rain gutters would be a recommended feature to be added based on the existence of underlying expansive soils.
Some local communities are near quarries and supplies of rock and gravel are relatively inexpensive and may not be a problem to use in increasing the final floor elevation of the structure. In other communities this can be a real problem. The increased building costs brought on from obtaining and hauling building materials can increase builders cost. Builders are already faced with rising building commodity prices in the last five years. If you are one of the builders looking at site conditions that make it difficult or expensive to bring up the finished floor elevation to ensure good drain run off away from the building, we have one simple word - gutters. That’s right, one of the best things you can do to insure that the building foundation performs as the designer intended is to capture the rain water from the building and insure that it is deposited away from the foundation. In most cases the geotechnical and/or structural engineer of your project had nothing to say about whether this feature was included or not.
Expansive clay soils can cause the foundations of light weight structures to easily be pushed around by the shrink and swell forces of the underlying clay during periods of excessive moisture and drought. Why? The areas on the perimeter of a building are affected by atmospheric conditions so extreme periods of drought and the eventual wetting of the soils adjacent to the perimeter causes the edges of a foundation to drop slightly and then swell up the perimeter wall of the building. The center of the building has a vapor barrier, a floor, and a roof over it so that it's moisture content is relatively stable over the life of the structure.
The cost of one upset client over a foundation which does not perform as intended is going to be at minimum the cost of 10 to 20 simple gutter systems. Addressing foundation issues on lightweight commercial buildings and residences can be one of the more expensive fixes you will ever have to deal with as a builder.
Happy Building!!
Mr. David Joyner is a registered professional engineer and President of the Trinity Group. Mr. Joyner has over eighteen years experience in the engineering and construction industry and has maintained an engineering practice since 1993. Mr. Joyner holds a B.S. in Civil Engineering and an MBA and is currently completing his dissertation in doctoral level course work. Mr. Joyner has also been a member of the faculty at Texas State University and Saint Edwards University Graduate Studies in Austin, Texas.