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In many parts of the country a post tension slab is used where the soil is considered unstable or poorly compacted. It may be used for that in Tucson, but in most cases it is considered to be a superior foundation for a Tucson home.
If you see a Tucson home with a post tension slab it shouldn’t raise a red flag, just the opposite it is a desirable foundation for a Tucson home. Why? because of our pesky neighbors the subterrainean termites.
Post tension slabs have cables running both directions through the concrete spaced approximately 3 feet apart. They are in a slip cover which allows for tension to be put on the cables once the slab is poured and has cured to a certain point.
Tensioning the slab keeps it from cracking. The end result, it becomes one large slab held together as a single unit.
This picture was taken after a cable was tensioned. The cable is a spiral and the tensioning is done inside the slab. Once it is tensioned the cable excess is cut off and the hole is sealed with concrete.
Cracks in foundation slab can invite subterranean termites or other things that might invade the home through those cracks. It also means you should never have to worry about your foundation suddenly cracking and ruining your floor or cracking any tile. There is a peace of mind when you have a post tension slab foundation.
There are no special concerns when laying tile on a post tension slab. I’ve laid tile in two homes with post tension slabs. I have also drilled small 1/4″ wide and 1″ deep holes for anchors when installing a transition strip between rooms.
The one thing you don’t want to do is drill large holes that might sever one of the cables or compromise the integrity of the slab tension. If there is a need to do so for remodeling purposes, it is important that the exact location of the cables be determined and plans made accordingly. You never want to break a cable in a post tension slab or drill a large enough hole to cause damage to the foundation which is under pressure.
A post tension slab will usually have a stamp located by the garage entry either just inside the garage door our just outside the garage door.
It is rare to see cracks in a post tension slab. If there are cracks, they should be hairline cracks only; anything larger you should consider having a structural engineer check into the foundation.
Personally, I like a post tension slab and always look for this stamp when considering purchasing a property.
While having my house treated for Termites a helper drilled a 1/2 inch hole through the outside coener of the post tension slab. There is no apparant damage to the concrete. What would you recommend I do if anything?
Thank you!
Fritz
Fritz,
I’ve never heard of them drilling in the actual slab. They usually drill around the outside of the slab in the concrete around the slab, driveway, walk, patio, etc that aren’t a part of the slab.
Even in the slab a 1/2 hole should cause no damage to the slab. Damage is usually caused when drilling holes large enough to accommodate a plumbing move and break a cable.
From what you describe there isn’t anything you need to do. If it were my house I wouldn’t worry about it.
I purchased a home 6 months ago in the Phoenix area and I have 11 tiles that have cracked in the last month or two. When I first noticed the cracks, there were 5 or 6 in 3 different spots, and now the cracks are in 5 different spots ranging from 1 to 4 tiles long. 4 of the 5 cracks start from an outside edge of the house and there is a corresponding crack in the slab…which is post tension. There is also one other crack in the slab that I can see, but there is carpet at that area so I cannot tell if the crack is growing like the others appear to be. The builder is coming to “check it out”, but I would like to educate myself a bit so I can tell if they are really taking care of any problems there are. These cracks seem to go against everything else I have read about post tension slabs. Any advice?
Michelle,
It was good to speak with you on the phone. This does go against everything I’ve read and experienced with a post tension slab as well.
Have a structural engineer take a look at this is probably the best way to get a better handle on what is going on. But you are very right this is not normal behavior for a post tension slab.
Hi!!! We are building a house its almost finished. when we cleared our land they our preferred trees to be at least 10 feet from the house. Most of them are. there are 2 in question. a small oak tree about 4 feet from house i guess its about 8 ft tall maybe 15 inches circumference??? and a much larger oak about 8 feet fom the house this is a fairly large oak tree…. we are thinking about cutting down the one thats about 4 feet from slab??? do you think thats the best thing to do??? the slab was poured about 2 months ago. it is a post tension slab. is it worse to cut down the tree after the slab is poured???? or better in the long run to do it??? thankyou for your help.. would you suggest cutting one or both down????
Kathleen,
Oaks are typically very slow growing trees. They add a lot to the natural cooling of your home by providing shade and the evaperative cooling effect under their branches.
Personally, I would leave them both. If at some time in the future you see roots near the foundation looking intrusive then you could remove the tree, but being an oak, that could take 30 to 40 years or more.
You can always remove them later. They will provide more benefit than deficit. Being post tension they won’t crack the foundation even if they do grow under it. But as I said above it will probably be many many years before it would become an issue and there is a good chance it never will be an issue.
I would love to have trees like those near a new home. Enjoy them.
I was doing a little research on post tension cables breaking as ours snapped a couple of years ago. I thought you might be a great person to ask this. We are getting our house ready to sell and I wanted to know if that is something I need to disclose on the seller disclosure form. The foundation was under warranty and was repaired (with an engineers approval). My concern is, the home builders rep actually told me there was no need to disclose the information as there was really nothing wrong with the slab itself.
I would appreciate your input!
Thanks
michelle,
You must disclose this. Disclose exactly what happened, what repairs were made and the engineers approval of the repairs made. This way you have disclosed, and provided documentation the issue was resolved.
The rule of thumb is always disclose, disclose, disclose.
We have a tension slab in a house we bought new in Dec 1999- Five years later out tiles tented up in 3 different places in the hall and entry. Customer service came to our house since we had extra tiles they were laid back down and we were told ( don’t worry it might never happen again and if it does you are under warranty). Well in December 2007 the tiles tented up in our kitchen family room and are still that way. There are not matching tiles left to replace. We do have a 10 year warranty but the builder refuses to honor it. We bought a finished landscaped model home. Now we are being told there are drainage problems that are our fault, Don’t know why but it is pretty awful to have this hole in floor. The builders rep have told us that we just have to replace the floor. We are seniors on a low income and this is a bad situation. The other tiles in house are not even anymore and can feel difference when walking on them. We have maintaned our house and yard the same as many neightbors. So my question is – Is it normal for tiles to become uneven after a period of time? And have you heard of this tenting up.?
Gail,
I’ve never heard of this in a properly tensioned slab. It definitely sounds like something is very wrong. With a post tension slab you shouldn’t even cracks. If you do they should only be hairline and never open up.
Are you sure this was a post tension slab?
Have you had a structural engineer assess the house and land?
Finally, to your question it is not normal for tiles to become uneven after a period of time in a post tension slab home.
I can’t give you advise and I’m not an attorney, but you might want to find one and a structural engineer while you are at it.
Good luck in the future I’m sorry you have had these issues with your home.
Sir: Can damage be done to a post tension slab when taking up cermaic tiles?
Peggy,
No, as long as you don’t drill or cut into the slab breaking one of the cables you can’t hurt the post tensioning.
Hi Dave,
We have PT slab and we want to add a shower to our downstairs bathroom. City said we can’t do it because we might break the cable. Do you know of anyway to solve this problem?
Thanks,
Kim
Kim,
It might not be possible. But the person I would get in touch with to find out for sure is Scott at:
SK Builders Inc.
1836 S. Research Loop
Tucson, AZ 85710
Phone: 520-749-1035
Scott is a custom home builder here in Tucson. Give him a call and explain what you want to do. Good Luck.
Dave
Hi Dave,
We have an on-going construction of a Built to Order house and noticed that there’s a portion of the house where the slab surface exceeds 3″ wide from the sidings to the edge of the foundation. So, they chip out 3″ wide & 2 ft deep(from slab surface to ground level) to level the foundation wall from the sidings. Is what they do will compromise the house foundation? Thanks in advance.
Roland
Roland,
Sorry to be so long getting back to you on this. Some how your comment got lost in the moderation cue.
I would recommend you get a structural engineer to take a look at what is happening. I can’t really tell from your description above, but a fresh set of eyes on the project seems to be a prudent thing to do.
Dave
I have a post tension slab and would like to bolt a safe into the foundation. Is that possible without affecting the integrity of the slab…? There is a raised area in the back of the garage about 3 inches which is flush with the inside of the house. Does this mean the post tension slab is deeper than that?
Thanks
Rob,
Sorry to take so long getting back to you on this, I’ve been fighting a major sinus infection for the past two weeks.
It is possible to drill into a post tension slab, but it is not advisable, especially large holes. The fear is breaking one of the cables in the slab.
The curb stop in the garage usually does not have cables running through it, but every build can be a little different.
If you want to bolt down the safe I’d drill small holes where you want it located, I’d go slow and stop the if you meet any resistance. But there are never guarantees when drilling into a post tension slab.
Dave
Hi, We moved into a Tucson home w/ a PT slab last July and have heard you should not use a drip system near the home foundation. Is this true? Thanks, Tom
Tom,
That’s a new one on me. I know that exterminators will tell you not to have your drip too close to the foundation. That is because moist soil next to the foundation attracts termites and makes it easier for them to invade the home. I can’t see a drip system harming a foundation unless there was some kind of catastrophic failure where the valves didn’t shut off and the main lines broke forcing water under the foundation for a very long period of time.
Dave
Can you tell me if in the cables for the slab run in the garage area. I am putting in a uder ground safe in the garage. Then it will be filled all around back with concrete.
Dean,
Most do. I’d proceed with extreme caution.
Dave
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Hi,
My house was built in 2007, we bought it 2 years ago. We now have a crack that runs from my kitchen to the living room and our brick has cracked at the window seal in the front and back of my house. We called the builder to look at the crack he told us it was not the foundation. I am still concerned because this crack is not a hairline crack and I have concrete chipping out where the crack is. I have stamped stained concrete floors. Should this be happening with a post tension slab?
Honey,
Did the builder come out the property and look at the foundation? If the crack is more than a hairline crack (It sounds like it is) that is not typical of a a post tension slab.
Dave
Hi Dave,
We are remodeling our front yard and today the landscaper attempted to remove our front porch and there are tension cables in it and he broke all but the one closest to the front door! We bought this house 2 years ago and were not aware of the post tension foundation. When they broke did that compromise the foundation under my house and can it be repaired safely?
Thanks so much,
Laura
Laura,
This is not good news. You need to get in touch with the builder ASAP for input from them. Getting an evaluation from a structural engineer would also be wise.
Don’t wait. I would strongly recommend no further landscaping work till this is resolved. I hope your landscaper is licensed and bonded.
I’m no expert, or engineer, I can’t render an opinion on the compromising of the foundation. But I do know you need to have this checked out right away.
Good luck.
Dave
Dave,
We purchased a home about 4 years ago with a post-tension slab. This summer during extreme drought conditions in Texas one of the cables snapped. We have noticed cracks in our drywall and crown molding along the top of our cabinets pulling away from the ceiling and wall. These conditions just so happen to be in the proximity of the cable that snapped. Do we need to have someone come look at the snapped cable? Can this be easily repaired? Please advise.
Tim,
Yes, you probably need a structural engineer to look at it. If the home is still under builder warranty you should get in touch with the builder and have them look at it.
Dave