Modern Slab on Ground Design & Construction

I am occasionally told that they do not build houses like they used to. It is true of houses and foundations that they are not built the way they were built in the past. Today, houses are built much, much better.

Foundation design before 1980

As recently as 1980, almost all homes in Texas were built on foundations that were designed to transfer loads from the house to the supporting soil in a way that no excessive settlement would result. Today, slab foundations on expansive soils are still designed to restrict settlement, but in addition, they are designed to be stiff enough so that they normally experience only cosmetic distress or minor functional distress.

Foundation design after 1980

Today, slab foundations on expansive soils are still designed to restrict settlement, but in addition, they are designed to be stiff enough so that they normally experience only cosmetic distress or minor functional distress.

To give you a sense of the difference consider the following. It was not that long ago that it was common for slab-on-ground foundations to have stiffening beams that were as shallow as 16 to 18 inches deep and they were often spaced as far apart as 20 feet. Today, the standard practice is for stiffening beams to be at least 24 inches deep. That is a huge change because the stiffness of a stiffening beam is proportional to the depth raised to the fourth power.

Instead of 20 feet apart, they are rarely further apart than much over 11 feet.

These two factors alone make a typical slab-on-ground foundation approximately ten times as stiff as the typical slab-on-ground foundation as recently as the late 1970s. This is a huge difference.

Better concrete quality and finish work

But there is more: the concrete we use today is of a higher, more consistent quality. Inspection is more consistent and rigorous. Even the finish work is much better quality than it was in the 1970s.     

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