Rebar Slab on Grade or Post-Tension foundation???

[ama481]

We are looking at building a 2 story 30x40 brick detached garage and I am getting bids from 2 separate builders. One builder wants to do a rebar reinforced slab on grade concrete foundation. The other builder wants go with a post-tension concrete foundation. We are pretty much located on solid rock in Midlothian, TX. Should I be concerned with going the rebar reinforced slab on grade? Are there any downfalls going with it over the post-tension slab?

Thanks in advance!

 

[Youngandfree]

What's your local building inspector like?

 

[Rusted Nut]

I have done a lot of PT decks, unless there is a very real compelling reason for a PT, go with slab on grade, even with piles and/or grade beams. PT is expensive and seldom done on grade. Ask contractor why they are recommending PT.

 

[Hopey]

Are you sure about the soil conditions? Usually when there is a high percentage of clay (like most of Texas), that together with precipitation and high summer temperatures cause a lot of soil shifting and foundation issues- that’s usually when they suggest post tension slab. Suggest you get soil analysis done before choosing a foundation.

 

[egdede]

Ditto the first 2 replies.

 

[bb29510]

they are both good, solid rock, good

 

[ConCretin]

The only reason for post tensioning in a slab is unstable soli conditions such as expansive clay. If the soils under your slab are expanding and contracting with weather conditions a normal slab on grade, which depends on the ground for support will fail.

The fact that one of your contractors even does post tensioning suggests there is a need for it in your area. Was your reference to 'solid rock' metaphorical or are you actually on ledge?

Rebar and PT are similar in that they hold the concrete together so that cracks don't open up and displace whereas PT prevents cracking in the first place.

 

[pima67]

Another aspect is what floor finish you will want such as stained/colored concrete or carpet throughout. Ours is a PT slab with tile in parts (thinking about removing carpet and staining the concrete). PT "eliminates cracking after the tension is applied. Visited the house during construction and never saw anything but small shrinkage cracks (I think you call them}. For some strange reason they did the rounded V shaped groves in garage floor which is part of the PT slab. Maybe as a parking aid? Did have a thin crack in the garage where the 2 "steps" met. Filled it with thin set and wait of a month or two to see if the crack would reappear. Applied Rustoleum 2 part epoxy over the 2 steps later. Never saw the crack again. No cracks at the bottom of the Vs either.