Post tension slab?

[Kit Williamson]

Building a new 2 car garage with guest quarters above. One builder wants to do a post tension slab that costs more. Another builder thinks that is overkill for a detached garage but will do it if we wish. Ask.com seems to agree with the second builder. The second builder is going to use rebar. Any thoughts?

 

[72Anthony]

They are common in the Houston area with all of the track/mass production builders. As I understand it, it costs a little less per square foot than a conventional slab: less steel and labor with placing and tying all the rebar.

Not sure what the soil conditions are like in your area, but here soil borings are done an engineered foundation with a professional engineer's seal is required.

A conventional slab is easier to deal with if you ever need to drill or cut into you slab: lift or monorail install. However with a post tension slab, you can see where the cables are on the outside edges of the slab: after tensioning and securing the cables, they are covered over with cement/grout. You will see 4-6 inch diameter patches every 4 feet or so. The cables usually run in both directions.

 

[Dug W.]

I'm from Northern California and I haven't seen any post tensioned slabs for a garage or home build but I think in areas where the soil is more expansive that it might be necessary. I would think you'd want a soils engineer to do some borings to determine the re-enforcing you need. How is your house built? Is your current garage or an exposed concrete post tensioned?

 

[BigBoyinMS]

You also have another choice but it seems not as well known. Do a search for "wafflemat foundation'. Supposedly less labor to make it less costly but also advertised as never having a structural failure.

 

[brownbagg]

it all depends on your soil, if you have good soil then a plain slab with no rebar is all you need. It all depends on your soil report

 

[ddawg16]

I lived in Texas until recently....I would never have a post tension slab again. Your basically depending on the tension of the cables to keep you slab intact. My mom still lives there and one corner of her house as dropped about 4" because the soil eroded out from under the corner. The tension cable is keeping it together...but didn't stop it from cracking and dropping.

Foundations are one of those things that are hard to go back and fix after the fact.

Better to do it right from the beginning.

I'm researching it now where I live.....the local code here requires a 24" deep footing about 16" wide....with plenty of rebar. I can't imagine building a slab without rebar.....sounds pretty short sighted.

With a footing....less chance the soil can get washed out under it.

 

[Kit Williamson]

Thanks guys. Great info. The second builder does plan to reinforce with rebar. From what i am seeing that seems to be the way to go in my situation. Just waiting for a bid from one more contractor.

 

[Norcal]

I lived in Texas until recently....I would never have a post tension slab again. Your basically depending on the tension of the cables to keep you slab intact. My mom still lives there and one corner of her house as dropped about 4" because the soil eroded out from under the corner. The tension cable is keeping it together...but didn't stop it from cracking and dropping.
Foundations are one of those things that are hard to go back and fix after the fact.

Better to do it right from the beginning.

I'm researching it now where I live.....the local code here requires a 24" deep footing about 16" wide....with plenty of rebar. I can't imagine building a slab without rebar.....sounds pretty short sighted.

With a footing....less chance the soil can get washed out under it.

That sounds like a drainage issue, get water running the wrong way & all sorts of bad things can happen.

 

[bobscogin]

One builder wants to do a post tension slab that costs more. The second builder is going to use rebar. Any thoughts?

A post tension slab shouldn't cost more. If the beam/footing cross sections are optimized for post tensioning, the slab will likely require less concrete. I'd be inclined to go with conventional steel reinforcing, but in the end, it's more about the quality of the workmanship than the type of reinforcing.

Bob

 

[mebuildit]

We are getting ready to build a new house and detached shop. The contractor will only do post tension slabs. I've personally never dealt with them here in Az. He said that he can give a better warranty from the house moving or cracking.
I was just worried about drilling a hole in the concrete and hitting one of those cables. He said that as long as you don't hit a cable you will be fine. So we are going to have him do the post tension slabs.

 

[HAY YOU]

I’ve never heard of PT slab for residential use. On every concrete building (story job) is post tensioned & there is still rebar in them along with every concrete bridge job. Did my first PT story job over 30 years ago. Building hasn’t fallen yet.