Why are there so many slab foundations in Houston?

Over the years, this is a question that we have been asked repeatedly. Slab foundations are widely used throughout the South. There are several reasons for this:

  • First, slab foundations are cost effective. When you build a slab foundation, the surface of the slab becomes a floor, a floor that cost nothing over and above the cost of the slab.
  • Second, slab foundations can be engineered to perform adequately in expansive soil areas. This is not true of what are called block and pad foundations, foundations that are common in Houston and all through the South prior to WWII.
  • Slab foundations can be constructed very quickly using hand-tools and hard working, but relatively low skilled labor.

Another question: why are there no basements here?

The real question is: why do houses in the Northern states have basements? The answer is simple: any house foundation must be founded below the depth at which the ground will freeze. If it is founded above that level, when the ground freezes the soil will push the foundation upward. This situation can result in severe damage to the foundation and to the house.

In many areas of the country, the ground routinely freezes to a depth of six to eight feet or more. If you have to go that deep to place the footings, it costs only a mall amount to leave the hole open and construct walls to make a basement.

In much of the South, specifically including Houston, the ground never freezes to a depth of more than six inches or so. This is why you do not see very many basements in Houston.

One more question:  Why were slab foundations not used before the end of WWII?

This is an interesting question. Before the late 40s and early 50s there were no ready-mix concrete trucks anywhere in the South, certainly not in Houston. Any concrete used in the construction of a house had to be mixed on site, or delivered to the site as a finished product.

For example, with a block and pad, the concrete blocks and pads could be made elsewhere and delivered to the site. The driveway concrete would have to be mixed on site. If you drive through older Houston neighborhoods, you will often see what we call ribbon driveways: the driveway consists of two strips of concrete.

The introduction of ready-mix trucks into the Houston market changed the economics of using concrete on site. The cost plummeted and the quality became much more consistent. The old block and pad method could not compete against slab foundations.

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