[Michael Costa]

Hey all. What is the proper way to tie a new slab or foundation (addition) to an existing post tension slab? I've seen plenty of forums/sites describing the connection of foundation to foundation but nothing regarding post tension slabs. I want to sound somewhat educated when talking with contractors. Thanks.

 

[mako1]

I have built many 20 or so story condos in Florida with post tension cables.I don't think I would trust your usual contractors advice on this subject and an engineer should be consulted.I have seen these cables snap and come up out of a 7" concrete slab like a snake.
If it's a slab on grade it makes it a lot simpler but still not something for just any contractor to deal with.

 

[Michael Costa]

Thanks. One of the things I was worried about was getting someone who tells me it's a non-issue only find out the truth when it's too late.

 

[jlhaslip]

Nope. Don't drill or cut that post tensioned slab without an Engineer saying so.
Ideally, the Engineer from the company which built them.

 

[mako1]

Any way you go there are engineering and testing firms that can come out and locate the cables.Make sure your contractor has this done before any work starts.There is an anchorat each end of each cable that has two grippers which hold the tension on the cable.These are grouted over after the pour and the grommet is removed so they have to be located by a pro.

 

[Daniel Holzman]

You may be way ahead of yourself. First you need to ask if it necessary or advisable to tie the addition foundation into the existing. In my experience, for residential work, a properly designed, properly built foundation does not need to be connected to the existing foundation. In your case, connecting to a post-tensioned slab is definitely not a simple process, as previously mentioned the cables are under serious stress, and inadvertently releasing a cable can lead to serious injury or death.

 

[Michael Costa]

There was a part of me wondering if it had to be tied in at all. After normal settling, just patch up the cracks, right? It's not like the addition would decide to move away from the house. (If so, I could add those flexible connectors that they use to join two city buses together - lol)