Moving plumbing in a post tension slab

[bradpac]

Looking at moving a toilet and possibly sink in our bathroom remodel. We have a post-tension slab, house is built in 1988. The toilet will move about 6 ft over from it's current position, which puts it on the other side of our main sewer line from where it is now. The water lines themselves will just be extended through the walls or attic.

I'm getting bids from plumbers, but would like a little knowledge, is it ok to punch holes in the slab big enough to do all this moving or would it be better to tunnel underneath and worry about the excavating and back fill? We are on black dirt on the east side of central Texas, expansion and contraction of the soil is a big deal, not sure i want to disturb it as our house seems to be holding up pretty well.

Also, out of curiosity, what happens if you break one of the cables in a post tension slab?

 

[sixty4]

We used to do that sort of thing in malls. However we always had the floors xrayed because hitting one was an enormus cost to repair.

 

[kaymccampbell]

You do not want to cut the cables in that slab. Moving a couple inches is not a big deal, 6' is. You need to locate the cables from the perimeter of the slab, or get it xrayed or radared or scanned somehow. Sometimes there is a tell on the outside of the slab to show where the ends of the cables are. Most folks with PT slabs learn to live with where the underground services are located, or shell out.

 

[Balvar24]

We used to do that sort of thing in malls. However we always had the floors xrayed because hitting one was an enormus cost to repair.

This.

 

[ConCretin]

Hitting a PT cable isn't likely to cause it to explode out of your floor as some people believe but it is potentially hazardous especially on the outside at the anchor locations. If a cable breaks, parts and pieces could come shooting out. You definitely want to locate the cables before starting and avoid them. If you have access to the slab edges, you might be to locate the patched pockets where the cables terminate at each end.

If PY slabs are common in your area, you should ba able to find people experienced in working around them. Good luck.

 

[bradpac]

If you have access to the slab edges, you might be to locate the patched pockets where the cables terminate at each end.

If PY slabs are common in your area, you should ba able to find people experienced in working around them. Good luck.

The entire outside of the foundation is smoothed out with mortar or whatever to make it look good. This type of foundation wasn't really a thing around here until the mid 90s-2000s. This is probably one of the first houses around with a post tension slab in our area, so not a lot of remodels done on them yet. But I've got a couple of contractors that say they have done the jobs before and checking references, leave it up to the experts for sure, and make sure they have insurance before they start jack hammering.

 

[66cj225]

Wow, hope the contractor doesn't 'end game' his insurance.

 

[kaymccampbell]

Unless you are looking for a drawn out remodel, make sure he can demonstrate his detection equipment to your satisfaction.

 

[rjacobs]

Find post tension cables...

Bore hole to avoid them...

I wouldnt want somebody just jack hammering away when they could bore a nice clean hole to put the toilet drain down through.

And as far as how to connect it to the main sewer line... tunneling under the house will be the best choice to do that IMO. It shouldnt be hard to back fill and pack it tight so you dont get any settling, shifting, etc... Its pretty common in Texas to tunnel under a house.

 

[Jeffh40]

No jack hammering. Hire someone to core a hole after the slab has been X-Rayed and the cable identified.

There is over 33,000# of tension in those cables. Cutting one is likely to kill someone if they are in the vicinity of the end of the cable.

 

[stillnostrebor]

Hitting a PT cable isn't likely to cause it to explode out of your floor as some people believe but it is potentially hazardous especially on the outside at the anchor locations. If a cable breaks, parts and pieces could come shooting out. You definitely want to locate the cables before starting and avoid them. If you have access to the slab edges, you might be to locate the patched pockets where the cables terminate at each end.

If PY slabs are common in your area, you should ba able to find people experienced in working around them. Good luck.

Great answer.

I work in the prestressed industry, so am quite familiar with pre and post tensioned systems. "No" to random jack hammering or especially sawing/core drilling. "Yes" to pre-locating the strands/cables and insuring that you are not cutting them unknowingly. Depending on if the strands are in a grouted sleeve, or an open sleeve with only mechanical vises, the amount of "holy ****" that ensues will vary. If they are solid grouted sleeves they will not explode or anything, but you will lose some/all effectiveness of the strand depending on design. Open (ungrouted) sleeved strands should not be cut unless you enjoy getting the **** scared out of you at best, or getting someone at the restraint point hurt at worst. After either drama you still have the issue of having compromised the reinforcing in your slab.

You can cut fairly close to them in most cases, which will minimize the amount of soil disturbance you have to endure. You just need a good plan of attack.

Hire someone that knows how to locate, and how to work with post -tensioned strands. Get COIs from them with you as additional insured before they start, and do your renovation.

 

[bradpac]

I appreciate all the good advice. Knowing where the cables are is the first thing I need to make sure they can do, then we can talk about method of the moving. Bored holes with tunneling underneath for the actual pipe moving sounds like the best method.

 

[SALIV8]

Can you move the walls around and leave the slab? Might be cheaper.

 

[bradpac]

Can you move the walls around and leave the slab? Might be cheaper.

Yes, this is a remodel, basically the house was added onto before we got it and the present master bedroom is pretty small compared to one of the added rooms, so we are looking to relocate the entrances to the bathroom to make the new room a master. We already have a plan for keeping the plumbing as-is, just means a longer walk to get to the toilet from the bedroom, basically you walk beside the water closet and come into the bathroom from the back side of it, which in the middle of the night is not preferred. If we could move the toilet further back and come in right where it's at instead of having to walk around it that would be preferred.

We shall see what some of the contractors I have coming out tell me. Right now apparently everyone is busy, it's hard to find someone to even give me a bid.

 

[JSCH]

Having read all the dangers and limitations and extra costs regarding moving plumbing in a bathroom on a post tensioned slab, I may have a different option to relocate the sink and shower to make the room actually work for our needs. The existing shower drain is under the shower, as expected, and down into the slab. The sink drain runs into the wall after the p-trap and then down into the slab. We need to flip the location of these two so the shower can be in a location where it can be larger.

We are lucky to have a 10' ceiling. I am thinking of building the shower on a raised platform (just high enough to allow the drain plumbing to run above the floor) and then connect into the wall to the existing drain that is currently used for the sink. If a step is needed to get into the shower that can be done. On the other side, we can have the sink drain, after the appropriate trap of course, into the drain in the floor formerly used by the shower. The pipe run might have tu be a bit creative, but it would be entirely within the vanity cabinet and we could use some carpentry to actually hide if from view as needed. All supply lines come down from the ceiling so we should be fine with those.

Does the sound like a rational plan to get the bathroom as it would work without having to deal with the limitations, extra cost, and risk that the post tensioning presents? Oh, and we were planning on retiling the floor and walls as needed anyway.

 

[nadogail]

Are you suggesting a Sewer Lift Pump?

 

[JSCH]

Nope. instead of dealing with the post tension bars and digging into the slab for the drain under the shower in the new location, thinking it might be much simpler to virtually run the drain line on top of the foundation and reaching the wall then connecting into the drain that the sink used to drop into. By putting the floor of the shower 6-8 inches above the foundation, there would be room under it for the almost horizontal drain run.

 

[flat350]

Running the shower drain above the floor, the p-trap will determine the floor height, a 2" trap will be tough to fit in 6". Running the new lav into the old shower drain you'll have a double trap it you put one at the sink location too.