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View Full Version : Conventional Slab Vs Post Tension Slab


hyperlitejb
09-15-2011, 11:36 AM
Buddy is looking to build a house, and looking for opinions on his slab options. Any advice for him?

TexMax
09-15-2011, 11:40 AM
Pier and beam ;)

http://discussions.texasbowhunter.com/forums/showthread.php?t=219613

Double Rods
09-15-2011, 11:51 AM
I wouldn't put a post tension slab under a doghouse! Go with conventional.

125Dad
09-15-2011, 12:14 PM
I wouldn't put a post tension slab under a doghouse! Go with conventional.

Why do you say that ?


I would have a structural engineer design one after a soil report was done.

glpoe1
09-15-2011, 12:19 PM
Why do you say that ?


I would have a structural engineer design one after a soil report was done.

Post Tension is the only way we can keep a house foundation together in some parts of Snyder. The conventional slabs crack due to the soil being to unstable around here. I have aconvention slab for our new house but we are on a calechie hill (rock). Have that engineering study done, you won't regret it.

Saxet Nomad
09-15-2011, 12:21 PM
I wouldn't put a post tension slab under a doghouse! Go with conventional.

I've heard this with many builders when we were building a few years ago...

Bily Lovec
09-15-2011, 12:21 PM
Pier and beam ;)

http://discussions.texasbowhunter.com/forums/showthread.php?t=219613

FOR THE WIN ;)b

125Dad
09-15-2011, 12:28 PM
Post Tension done right Is the best way IMO.

froghunter
09-15-2011, 12:54 PM
i would put piers under a convetional slab.

i have seen post tension slabs fail. i have even seen one that literaly broke in half. i may just be old school but i would not go with post tension. i would also highly recomend an engineer as well.

Snakelover
09-15-2011, 12:59 PM
I would have a structural engineer design one after a soil report was done.^^^This.^^^

I had my house built in 1998. Soil tests were done and a foundation engineer was consulted. I got a post-tension slab with beams and piers. My area is known for expansive soils and notorious for foundation problems. I may be the only person in Rockwall that has a house as old as mine and still no cracks in the drywall. ;)b

ZZ Pops
09-15-2011, 01:50 PM
I certainly agree with those who recommend hiring an engineer to assess the soil conditions and then design an appropriate foundation. It could be the best money ever spent.

Another thought:
Several years ago, I worked for an engineering testing firm, mostly designing and testing concrete. That job was a real eye-opener for me, especially as it related to the actions of concrete suppliers and foundation builders, and the quality, or lack of it, applied to the construction of private home foundations. Some concrete workers had no concept at all of the importance of mixing and proper handling of ready mix - mostly, they tried to do a job that finished well. Meaning that it looked good. Some mix plants had minimal ethics and would send out mixes that were almost worthless - after all, who would know the difference?

I suppose the message here, is that the type of foundation is important, but any can fail if improperly constructed or made of weak material. If I were building a home with a concrete foundation, I'd insist on strict specifications and include a requirement that the concrete be properly tested.

lameduck
09-15-2011, 01:58 PM
Buddy is looking to build a house, and looking for opinions on his slab options. Any advice for him?

I see you are in Hockley, is this where he is going to build?

125Dad
09-15-2011, 03:03 PM
I certainly agree with those who recommend hiring an engineer to assess the soil conditions and then design an appropriate foundation. It could be the best money ever spent.

Another thought:
Several years ago, I worked for an engineering testing firm, mostly designing and testing concrete. That job was a real eye-opener for me, especially as it related to the actions of concrete suppliers and foundation builders, and the quality, or lack of it, applied to the construction of private home foundations. Some concrete workers had no concept at all of the importance of mixing and proper handling of ready mix - mostly, they tried to do a job that finished well. Meaning that it looked good. Some mix plants had minimal ethics and would send out mixes that were almost worthless - after all, who would know the difference?

I suppose the message here, is that the type of foundation is important, but any can fail if improperly constructed or made of weak material. If I were building a home with a concrete foundation, I'd insist on strict specifications and include a requirement that the concrete be properly tested.

Very true I hierd a third party to do test on my concrete to make sure it was all done to spec's. The Builder hated me. But my house did not a have a crack in the sheetrock when i moved out 10 years later.

Bill M
09-15-2011, 03:17 PM
Why do you say that ?


I would have a structural engineer design one after a soil report was done.
I agree with this also except that if the soil sample and report is done by an engineer, they may recommend a compacted pad to build the conventional grade beam slab on. Post tension for the most part isn't recommended by engineers around here.

Extremebowman
09-15-2011, 03:39 PM
All good responses above. Best way is to engage a local engineer that knows local soils. Ask him for his preferred soils lab and go from there. There are numerous variables to be considered. I wouldn't get hung up on the type or what others say, I would follow the guidance of the Engineer.

hyperlitejb
09-15-2011, 03:41 PM
I see you are in Hockley, is this where he is going to build?

No, he is building in Alleyton, right outside of Columbus.

cosmiccowboy
09-15-2011, 04:11 PM
As others have said, it depends on the soil. In my opinion Post tension slabs are better in expansive clay soils. When I was in home building after college I built literally hundreds of homes with both types of slabs. There is nothing wrong with post tension IF the cables are placed correctly and IF they aren't moved or displaced in placing the concrete and IF the finishers don't add too much water to the mix to drag it. Conventional slabs are probably a little more forgiving on finisher error/negligence.

firemanjj82
09-15-2011, 04:36 PM
Engineer told me that post-tension in the expansive soil that I'm in is second only to a piered slab, with piers down to rock. I built mine over a year ago and they did post-tension and the only shifting I notice is in the corner joints of door trim. I have only had one crack and that was in a sheetrock seam. The big thing in my area is just making sure the foundation is watered. That's why I have a sprinkler system.

Dusty Britches
09-15-2011, 04:42 PM
I would have a structural engineer design one after a soil report was done.

;)b

And if the engineer designs it, their license is on the line if something goes wrong - provided it was built to their specs.

LFD2037
09-15-2011, 05:14 PM
I have post tension. Built 7 years ago. I have ZERO cracks anywhere in my sheetrock. There is about a 2.5" gap between my slab & the dirt. Gets like that every summer and never a problem. Plus it came w/a 10 year warranty. I have that crappy black soil that shifts a LOT. Right now I have dozens of monster cracks in my yard 1/2' wide & very deep. I say post tension for the WIN!!!!!!!

kaizen
09-15-2011, 05:31 PM
Most folks don't want to pay for extra $3500 for the soil testing or the extra $ for the engineer to design it. Without the soil testing, the engineer is just making an educated guess. I've designed a bunch of commercial/industrial foundations and few houses pads. The real issue is $ vs potential problems. Can he live with a few drywall cracks, may be some cracked brick under a window? No. what if he can save $7000 in fees and another couple thousand on the foundation? Tough consideration when it comes to writing the checks.

kaizen
09-15-2011, 05:37 PM
;)b

And if the engineer designs it, their license is on the line if something goes wrong - provided it was built to their specs.

That's why engineers don't line up to design house foundations or perform inspections for home loans. The liablity is elevated compared to fees involved. Of course if the engineer doesn't have liablity insurance, It's really a mute point. Problems that arise from foundation design are usually a difference in expectation and not an issue of competency which is what the Texas Board of Professional Engineers is concern about.

Draco
09-15-2011, 09:35 PM
If a conventional slab is designed and poured correctly. It doesn't even need dirt under it to hold the house and not crack. You would just need columns at the corners and beam crossings.

Atfulldraw
09-15-2011, 09:51 PM
I certainly agree with those who recommend hiring an engineer to assess the soil conditions and then design an appropriate foundation. It could be the best money ever spent.

Another thought:
Several years ago, I worked for an engineering testing firm, mostly designing and testing concrete. That job was a real eye-opener for me, especially as it related to the actions of concrete suppliers and foundation builders, and the quality, or lack of it, applied to the construction of private home foundations. Some concrete workers had no concept at all of the importance of mixing and proper handling of ready mix - mostly, they tried to do a job that finished well. Meaning that it looked good. Some mix plants had minimal ethics and would send out mixes that were almost worthless - after all, who would know the difference?

I suppose the message here, is that the type of foundation is important, but any can fail if improperly constructed or made of weak material. If I were building a home with a concrete foundation, I'd insist on strict specifications and include a requirement that the concrete be properly tested.

As others have said, it depends on the soil. In my opinion Post tension slabs are better in expansive clay soils. When I was in home building after college I built literally hundreds of homes with both types of slabs. There is nothing wrong with post tension IF the cables are placed correctly and IF they aren't moved or displaced in placing the concrete and IF the finishers don't add too much water to the mix to drag it. Conventional slabs are probably a little more forgiving on finisher error/negligence.

The weakest link here is the cheapest guys on the site -- the finishers. First thing they want to do is add water to the mix to make it easier to work. I liked to stand next the the water valve on the truck to make sure that didn't happen :)

My finishers used to hate me :o

I never used a post tension slab that I didn't also use a pump truck and test cylinders out of each truck on site. Unfortunately, the thrust of the pump truck will displace the cables. I used to make sure my post tension company had a rep on site the day of the pour to make sure the cables stayed where they were supposed to.

They used to hate me too. :cool:

Reaper
09-16-2011, 08:36 AM
engineer's report is the way to decide, its an avoidable risk

Booger74
09-16-2011, 09:06 AM
;)b

And if the engineer designs it, their license is on the line if something goes wrong - provided it was built to their specs.

^^^^This^^^^;)b