We have had this happen often here in AZ. Here, the problem is caused by the builder not properly compacting the soil before pouring the slab.  While in most cases it can be repaired, it is costly. They have to remove large sections of the slab and re-pour it.

It is also a disclosure item and that pretty much stigmitizes the property.  The value of these homes drops dramatically.

Yes, I JUST terminated a deal that had that very issue. The SE said that the clay soil is expanding and contracting, and the settlement crack will continue to worsen.

We even had our contractor go out to give us an estimate to repair, just in case raising the home and re-setting the foundation wasn't going to be too costly. The cost wound up being considerable and the buyers are willing to take that on.

That is a real problem that probably will need to be solved by a structural engineer.

I have seen this just a couple of times Nathan Gesner and often wondered how to deal with it properly so thank you for asking the question. I like what you said about getting it to it's maximized expanded state and then building on that... it makes sense.

wow.... since when is construction built on material that is not properly designated as load bearing.... when the ground moves, everything moves.... that's why builders use footers....

     We have areas with pipe clay... it cause major settling, cracks in the slab.  We have to call in a structural engineer and a contractor; they decide how to remedy it.

$$$ seems to be the solution in the answers: builder warranty?

Nathan, You answered your own question.  I don't have a degree in this kind of issue, and the experts matter. A

I have no experience with clay floors - I know if it were wood subflooring I would rip it out and relay the sub floor

Disclose and get it fixed.

To answer the question, photos of foundation type needed. I guess is slab- jack up house, cut through the slab, maybe mud jack,  core down, remove 3 or 4 feet of clay, stabilize the existing soil, underpin maybe, add re-bar and piers which will level it back, examine foundation walls under the soil level, come up with plan to make water flow away from house - and snow in your neck of the woods, could add french drains (cheap) could add sump pump could add the new electronic water measuring meters that ping your iphone, grout up seal up keep moisture out... But drought may have cause the clay change and may cause cracking in everything.  Think of a marble on the kitchen floor that rolls to the other side of the house.  If house has crawl space it's cheaper to fix. If basement more pricey. 1000 square feet general cost about $11000 if the walls don't crack when you jack it up. 

Here's the real pickle: If you disclose in contracts lender is going to want to see it cured. If you don't disclose buyer is in poor house if has other damage. 

Perhaps buy with construction loan and licensed contractors

I would stay away from DIY with a 203k loan it might cost more than the $30000 you can get with that FHA product.

All things are fixable, it's how much it costs and how long it takes to cure

Not an issue in my area. I am clueless on this one!

We build mostly on footing and the home is not built on slab, this is probably because of the amount of rain we get in our area.  I have lived in areas where the slab is the basis of the home.  I would run away from this house because of the problems that could come up in the process that fixing the identified problem and it could excalate.  

I have no experience with this.

Haven't run across that issue. Ours tend to be soil movement that causes cracked slabs, etc. althugh occasionall I have head of builders not correctly compacting the soil. Will be interested to hear about the solution.

We have red clay earth here, Nathan... but this is a new one on me and I wouldn't opine in your position. A structural engineer will need to provide solutions to the floor. 

What is floor made out of ? Concrete? Wood? etc?

Footers should have been dug 4' to 6' deep. If they poured during dry spell, or water is getting under house and swelling up - Could be from tree roots, improper gutter / downspout configuration, no sump pump, and no drain tile under the slab, etc. Not enough soil removed before prepping slab to pour. No expansion joint around perimiter of slab.

 Most likely demo will be required, and slab replaced. Some piers might need to be dug. We usually go 4' or more deep depending on the soil tests.

We have expansive soil also, but have not had just the floor buckle, maybe because we have basements.  Would have to listen to what the engineer had to say, and the comfort level of the buyer.    

No idea.

After the fact, only fixing the problems as far as I know (from experience).

Is it because of the weather on real wood wood climate change effects it

No experience with expansive clay. And I thought I had problems

Parked and Reading.  Interesting stuff here. 

never heard of this ?

No personal experience with this...

Nathan Gesner - a few good answers here...

we mostly have red clay and crawl space homes in my market and I've never had an issue of anything buckling beyond actual flooring (hardwoods or laminate) that had been wet or installed before having time to season in the house.

I have seen the reverse happen when soil gets so dry and settles resulting in foundation settling, slippage and cracking walls. 

They have very expensive to apply type liquid cement injected into the soil that does the expanding as well as the solidifying to cure future movement. As far as grading an existing floor, I am reminded of what gophers can do under the house if left alone. They dig up the ground until all crawl space is eliminated making you have to tunnel in and re-grade to put it all back. Some people have to cut holes in existing flooring to access

Never had this issue

We do not have expansive clay,  but do have settling issues with some homes. I have seen pilings put it as well as concrete. Cant wait to hear what your remedy ends up being