Fill Settled under Concrete Slab

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  #1  
Old 01-28-06, 06:05 AM
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Fill Settled under Concrete Slab

Hi, we live in a newer home, and I am in the process of finishing my walk-out basement. There is no sign of settling in the house--but under the poured slab, you can see that the fill has settled considerably. It's a split level home, and the construction procedure was to dig out for the foundation walls etc, then fill the void back in and pour a 4inch slab. I can tell there is a void underneath the entire slab because of the cutout/stub out for the bathtub drain. You can see that under the slab is hollow.

The slab shows small cracks in various places, but otherwise looks like its holding up, even though it's floating in air.

What are my remedies, and is this that big of a deal? The house is still under a warranty by the builder--but the builder is playing coy about it all. He says its not a big deal--and in fact, a few of his houses have this issue, this isn't the only one.

Advice is welcome....

Bryan
 
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  #2  
Old 01-28-06, 04:13 PM
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Location: South Dakota
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Just because there is a void under the bathtub drain does not mean there is a void under the who slab. If fact I would bet there is not a very big void. It is not uncommon to leave a small void maybe a foot or 18" around those kind of drains. The reason for this is that many many times the concrete needs to be taken out for larger drains or in some cases more then one drain.
I don't know where you live, but in most areas of the country, a concrete inspection is required before the pour. Now, on the houses that I build, I always pour 6" slabs. It costs a little more, but it is alot stronger. You are going to have small cracks in concrete. There is an old saying. If you have concrete, its going to crack. Just the nature of the beast. Good Luck You could call your State Builders Board if you have real concerns.
 
  #3  
Old 01-29-06, 07:53 AM
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Void extends to the foundation Walls

Jack, thanks for the reply. I can look under the slab and with a flashlight, I can see all the way to the foundation walls. The slab is floating on air, with pea gravel on the "ceiling" and "floor" of my new "sub-basement" level. It's about a 24inch void all the way across under the slab...the pea gravel under my slab looks more level than my actual slab.
 
  #4  
Old 01-29-06, 11:03 AM
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This has me very puzzeled. I think you should get a building inspector, or a home inspector or sturctural engineer to look at this. If it is as you say, this is very uncommon. I guess my question would be what held the concrete up when they poured it ? It may cost you a few bucks to have it inspected, but it would be worth it. Don't get the builder involed at this point. Get your ducks lined up first. Let us know what the inspectors found. Good Luck.
 
  #5  
Old 01-29-06, 12:39 PM
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Fill settling...

Thanks for the reply--my theory is that the they had the fill and pea gravel up to the level of where they poured the slab, but over time, the fill settled, creating a void. Now the slab is over air.
 
  #6  
Old 01-29-06, 02:17 PM
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Not 24 inches...10inches

I mis-spoke earlier. The height from the top of the gravel to the bottom of the slab is 10inches. With a flashlight, I can see the foundation walls across the house. The slab appears to be floating on air--though I suppose it is supported by the foundation walls on the sides. My concern is whether the floor will fail at some point, or if the foundation walls are bearing a greater load that would initiate settling of the whole structure.
 
  #7  
Old 01-29-06, 02:23 PM
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I agree that your concerns have merit. that is why I suggested an inspection. Good Luck
 
  #8  
Old 01-30-06, 04:38 AM
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This is definetely odd. The foundation and slab of a home are to be built on "undisturbed" soil. There should NEVER be any settling of the earth underneath.

Do you have any cracks in your walls on the 1st or 2nd floor of your home?
Can you see any cracks in your foundation?
 
  #9  
Old 01-30-06, 05:39 AM
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No Foundation Damage

There is no foundation damage at all--and no sign of structural settling. This is common practice in my area in constructing split-level homes. Dig out the area, pour the foundation walls, then fill back in the hole to pour the slab. Many of the homes that I've been in in this area sound hollow as well--so it seems like a common occurance that the fill settles.
 
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