The tenant for my rental listing at 28820 N Nobel Rd in Dynamite Mountain Ranch was moving in yesterday, when I spotted this stamp in the concrete in front of the garage. The homes in Dynamite Mountain Ranch were built by DR Horton, in an area of Phoenix that has been identified as having potentially expansive soils. Expansive soils grow, or heave up beneath the home when they absorb water, and as a result, DR Horton chose to build the homes with post tension slabs. So, what are post tension slabs?

The slab foundation is the primary foundation of choice for builders in the Phoenix area, considering we don’t have much in the way of natural disasters, freezing weather, and a relatively shallow sewer table. Footings are dug along the perimeter and other load bearing points of the slab, to anchor the slab in place, and then the slab is poured over a prepared bed of crushed stone, with a network of rebar that keeps the slab together during warming and cooling cycles. The thickness of the footings may vary, depending on the structural needs of the home. Well engineered slab foundations are designed to crack at certain points, which need to be noted by tile installers, so that minor movement at this crack doesn’t break the tile above. If you are walking your home during construction and see cracks in the slab, these will likely be considered normal, so long as the crack isn’t wider than 1/4″.

A Post Tension Slab is installed similarly, except with regard to the rebar that networks its way through the slab. For a post-tension slab, the rebar is placed under very high tension as the concrete is drying. The result, is a very, very strong slab that rarely, if ever, will crack. If you are looking for the most termite proof slab, this is it. Termites often make their way into the home, through the designed internal cracks in your slab.

When I said very high tension, I wasn’t kidding. The reason a post tension slab has this stamp on it, is to alert everyone of the extreme danger of ever drilling into the concrete. For example, if you need to repair a plumbing or gas line that is within or below the slab. Or perhaps you wish to remodel a bathroom and move the location of a drain. This type of change in a post tension slab home needs to be done by a trained professional. If the rebar that is under tension is cut, it will snap like a rubber band pulled too tight, and when it does, the result will be potentially disastrous for the person that cut it. Death would not be unlikely. Serious injury is very likely.

If you are new to the Phoenix area, and are curious about this stamp in the concrete, typically near the front of the garage, hopefully this have been of some help.

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