I have built only on deep foundations on undisturbed soil or sand. I know the foundations are level at the start as the carpenters always shoot a transit across the corners and shim if necessary; contrary to what one might think, poured concrete doesn't totally level itself at the top.

Even though they "save" somebody money, slabs are a poor foundation choice in expansive soils. As the linked paper notes, "[t]he best way to avoid damage from expansive soils is to extend building foundations beneath the zone of water content fluctuation."

Where I build, the builder must warranty structural damage for seven years. Were that in place in your jurisdiction, perhaps you'd see a lot fewer slabs being built.

Slab Uplift (From linked reference)

Here is a link that might be useful: Foundation Damage from Expansive Soils

This post was edited by worthy on Mon, Jul 15, 13 at 13:50

This is also a major problem here in DFW.
One way to avoid this is to start off with concrete piers down to bedrock and then install concrete beams + slab on top of the piers and void boxes between the beams to de-couple from the soil. This is usually done for high end builds because it is a bit more expensive. But less pricey and disruptive than installing helical steel piers after the fact...

I think your engineering company failed to engineer correctly. Unusually wet or dry years should have been accounted for.

Can you tell if the slab is sinking by examining your house. Is it leaning now? Are the windows still level?

Unfortunately, in this area, nobody builds anything except concrete slab foundations so it is impossible to find anyone with any expertise in anything else. In fact, 99 percent of foundations in this area are "post-tension slabs" and builders screw them up with regularity. For that reason, we insisted on a more costly steel rebar reinforced slab and had it engineered by the most reputable engineering firm in our area.

The area is old ranch land and probably 50 years ago someone had dug a stock pond toward the back side of our property. The remnants of that stock pond are still visible. However, the land been sitting fallow for at least 20 years before we started building on it. (The development was first opened in the late 1980's and we bought out lot in 2001.) Over the years, this lot had grown a pretty extensive crop of trees. There were a couple of large trees with trunk diameters of about 20 inches located just about where the garage ended up going. In retrospect, I suspect, the disturbance caused by their removal may have exacerbated the problems caused by our drought conditions.

I don't think the engineering company failed to engineer the slab correctly. After cutting down the trees and pulling out the roots, I think my builder failed to properly recompact the ground under the garage slab area before laying out the slab foundation and the engineer who came out to approve the setup before the concrete was poured had no way of knowing that two large trees with extensive root systems had been removed or just how well the ground was/was not re-compacted after their removal.

Yes, the garage slab is definitely sinking on one side and the garage is leaning toward the west. The windows on the north and south sides of the garage are no longer level.

As far was we can tell, the house portion of the slab has not moved.. at least not by a significant amount. However, the entire slab (house, connecting porch, and garage) were poured as a single unified structure (monolithic slab) and the connecting screened porch area (which has a deck overhead) has several very wide cracks running running completely across it (N to S) that appear to extend thru the complete thickness of the slab. I suspect that the reason the house slab hasn't been affected is because the slab basically broke across the screened porch area which allowed the garage to move separately.

As for warranties, Texas requires that builders provide a 10 year warranty on foundations. However, by filing bankruptcy, our builder discharged all his warranty obligations to us and to all of his other home-building clients... including those required by statute. In other words, a warranty - regardless of whether it arises by contract or by statute - is not worth a penny once your builder files bankruptcy.

And bankruptcy laws are FEDERAL so they override any attempt your state might make to force builders to continue to honor their statutory commitments.

Soils tests are critical in areas of expansive soils so that the architect and engineer know the parameters for foundation design.

Generally speaking, there are two options for foundation design for single family residences in such conditions:

--Piers and grade beams, where the piers are driven or drilled to refusal (not necessarily to bed rock, since there may or may not be any bed rock) and continuous grade beams are poured in place on the piers;
--Mat slabs, where the concrete slabs and reinforcing are designed to "float" on the expansive soils and have sufficient overall resistance to offset normal differential settlement or heave.

There's nothing that will resist a sink hole.

For those building in areas of expansive soils, there's simply no short cut for an experienced soils engineer and structural engineer for proper foundation design under such challenging conditions.

Bevangel, I'm sorry to hear about the problems. Thank you for sharing your experiences, I hope for the best possible outcome for you.

Scary stuff, Bev. I wish you the best of luck working through it.

Question for the panel: are these compensatory measures applicable to a crawlspace foundation, or just slabs? We'll be building in the North Carolina Piedmont, home to some pretty expansive clay soil.
Should I be asking questions of my engineer/builder, or do I forget about it because we're not using a slab foundation?

FmrQuahog - Where have you heard that our clay soil here in the piedmont is pretty expansive clay soil? We haven't come across anything that lead us to believe that is the case.

(Are you originally from New England? I ask because of your log in name.)

These conditions are applicable to the soil. Foundations should be designed for soils conditions.

Forget about crawl space, slab on grade or other "normal" foundation preconceptions. Find out what your specific soils conditions are and have your architect and engineer design an appropriate type of foundation for YOUR conditions.

Tract home builders tend to just build the cheapest foundation they can. Internet plan factories don't even design a foundation for their house plans. Owners going these routes really need to do due diligence to find out what their property soils conditions are from a reputable soils engineer and then have the appropriate foundation designed for those conditions. There's nothing universal about foundations.

by filing bankruptcy, our builder discharged all his warranty obligations to us and to all of his other home-building clients... including those required by statute.

Maybe we're unique. But in Ontario, Canada the mandatory warranty programme (pdf) maintains a fund used to pay for warranty work and claims even if the builder refuses to do the work or goes bankrupt.

I don't understand the value of a "foundation level analysis". If there was excessive rainfall in the months before construction, why didn't your engineer recommend drilling or driving to firm soil instead of using a reinforced mat?

Scary stuff indeed, since you expect the professionals you hire to look out for you. It seems to emphasize the need to be proactive, learn as much as one can and continually verify the job is being done right. But even then it's not possible to stay on top of everything.
You mention wide cracks appearing. Sometimes cracks appear but the mesh or rebar in the concrete is intended to hold it together and keep it in the same plane. The presence of wide cracks indicates a lack of reinforcing metal. I hope you are not seeing a difference in height from one side of the crack to the other.

There is no substitution for footings!

@ deke: yep, transplanted South County, RI swamp yankee here!
I should walk my Piedmont clay comment back a bit. My conclusion that it's expansive comes from watching the ground pull away from the slab of my current home during the last severe drought conditions (coupla years back). The tar line was exposed by about 3 inches, complete with good-sized gaps and fissures. I've never considered a soil analysis on this home (it's a stepping stone), just recalling what I observed.

@ virgil: thanks for an excellent response, as always!

We live in an area that has a lot of clay, as well as sand. The sight we built our house on is slightly elevated from the rest of our property and has heavy clay underneath. My husband is an engineer, and because of this he engineered a concrete pier foundation himself. In 3 years we have not shifted one inch and are as solid as a rock.

Slab foundations are common in Florida. We did not remotely want one over clay. It can cause too many issues. In our area many people tried to push a stemwall foundation. We quickly rejected that as well, as we saw people having major, and very expensive issues with them in the south. Stemwalls are common "up north", and they really are for an 'up north" building situation.

There is a reason all the old, and I mean old, original Florida cracker homes are still standing. They built them on a pier foundation. Granted, some of these are brick piers, and were adjusted over the years, but we've seen a form of concrete as well. The piers also allow the home to breathe, and keeps insects under control. Termites need to build a mud tube to reach a building that is not sitting on the ground, and are easily seen.

It is also a fact that if trees are removed from the site a home is to be built on, that a waiting period has to pass. The ground settles, sometimes a great deal, if ALL the roots are not removed (hard to do) and as the roots rot the house will settle. A friend of mine in central Florida was told she had to wait a minimum of 3 years after some pines were removed. She still had the pines removed, but chose a tree free site for her home.

We've learned the hard way over the years that somnetimes what an "expert" will tell you is not always so, including engineers and builders. There is a lot of ignorance out there. We decided we would handle everything about building this home ourselves, and though stressful at times, we wouldn't have changed doing so.

This house will withstand anything except a major fire or a tornado.

I am so sorry for your home issues. It is heartbreaking. I hope you will be able to find a way to correct all this without going broke. You did the best that you thought you could do, and the so called "experts" really let you down.