Foundation Failure with New Home Construction
Within 4 months of moving into their newly constructed home, evidence of foundation problems started showing in Aaron Jackson’s home in Dallas. First, he noticed the side door in his garage started getting hard to open and close. Then he started seeing some significant cracks in the garage floor.
This was unbelievable particularly since he had paid the builder extra money to include a post-tension slab to “eliminate” foundation settlement issues. Yes, this type of higher-tech slab can and does fail because the edges are not protected to prevent water from getting underneath which can then cause “heave” forces to crack the foundation.
Causes of New Home Foundation Failure
An amazing statistic comes from the Zillow Research https://www.zillow.com/advice/US/all/question-discussion-guide/foundation/ up to 15% of new homes constructed each year will have a foundation settlement issue – that’s 150,00 new homes each and every year. This is particularly a problem in areas of expansive clay soils such as many parts of Texas, Oklahoma, Arkansas, and Kansas among others.
There are a variety of factors that can contribute individually or in combination that can result in failure with a newly constructed foundation. Here are the primary factors:
- Poor Site Preparation – sometimes builders, primarily subdivision builders, fail to take geotechnical samples on each lot and thus miss important soil characteristics to properly excavate and properly design the building pad and the foundation. This includes removing all sod and organic material, layering in and compacting course stone and chips to reduce capillary action, and leaving a high and dry sloped building pad. The soil composition under every home is different and should be evaluated individually.
- Improper Concrete/Cement Mixture – the cement/concrete recipe must meet specific standards to result in a perfectly poured slab foundation. This is not always achieved either through improper ingredients or even too much or too little water during the mixing. For example, a 2017 report in Connecticut showed that pyrrhotite bearing aggregate was to blame for as many as 34,000+ homes with failing foundations.
- Improper Drainage – the interaction of water and soil is perhaps the most critical component of a stable, long-lasting foundation. Pier and beam foundations are designed such that the area under the house should be kept bone dry. Slab foundations are designed to keep the moisture level of the soil consistently moist i.e. not too dry or too wet. Ponding or flooding adjacent to the foundation will cause clay soils to expand like a sponge heaving the foundation. Drought conditions will cause the soil to shrink, resulting in settlement. Proper drainage management and maintenance is critical.
New Construction Technique for Foundations on Shifting Soils
According to a news report in the Dallas News (February, 2017) a newly developed, patented technology to address the problem of building foundations on expansive clay soils has been created. The system has been introduced by Tella Firma Foundations has been used by over 1,000 foundations constructed in the Dallas area.
“It sells piers and a lifting mechanism that allows concrete companies to elevate a foundation. The piers go down to bedrock or solid earth and then the concrete foundation is poured on top. A crew uses wrenches to raise the slab up a few inches, so it is at least an inch higher than the predicted vertical rise of the soil. That leaves a protective void for the soil to rise and fall, without moving the house. The suspended structure resembles the design of a parking garage.”
This appears to be a viable and cost-effective solution for new home builders and homeowners.