Soil level and slab

I have a home with approximately 20” of slab showing before the grade. There are cracks in the area that would indicate that the slab is not being properly supported.
I know 4-6” of visible slab is ideal, but what is the maximum amount of visible slab before it is not being properly supported?
The builder is telling them 24”. Any help is appreciated.

No photos?

Photos and where you are located would be helpful.

He’s located in Fart Worth, Texas.

Questions in bold, italic above.


Fort Worth, Texas

Answers in BOLD

Based on your pictures provided what makes you believe this brick/stone separation has been caused by foundation movement?

What diagrams are you speaking of? What technical specification states that with more than 6" of foundation displayed the foundation is not being properly supported?

I asked “How is a slab supported?” and not “How is this slab supported?”.

This question is the same as before.

Then why are you attempting to quote design factors for a foundation?

The pictures here do not support this report from the owner. The pictures here display an apparent proper slope that has possibly subsided very slightly but not from “steep” to what it is now.

Then why are you attempting to quote design factors for a foundation?

This is an example of a diagram of how this slab should be constructed.
These diagrams don’t show that having 20” above the grade is proper construction. That’s my question. At what point is the foundation not properly supported? I cannot find anything on the subject. If I just go by the diagrams, I have to assume anything more than 6” is unacceptable.
I’ve closed the report on this with some help I received yesterday. I’m going to try and move this from the “emergency” forum to the regular. Since this is clearly a discussion that needs to be had.

Your illustrative graphic indicates “minimum” distances for the noted elements. That being the case it could be a high as 48-inches or virtually almost any height if the property grade needed or demanded it.

Read Manny’s information carefully … he is trying to help you out here.

I’m not from Texas, can’t say I’ve ever done any concrete flat work other than walkway or patio that wasn’t frost proofed. That is probably a monolithic pour, if it was two separate pours (foundation and slab) you would see clear indication of a cold seam. I suspect the brick veneer return has separated due to expansion of the framing. Probable moisture intrusion causing expansion and not enough gap between the brick and sheathing

If “anything more than 6" is unacceptable” then this foundation is in a world of hurt :slight_smile:

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Glad to hear you say that and yes let’s discuss. My questions were meant to illicit thought on the subject. I know they tell Inspectors in training that “We only do a visual inspection” but that is only to indicate we are not required to go beyond a visual nature and do not perform destructive inspections. However a “Visual Inspection” is more than just listing what we see but also making sense of it many times when possible and referring them to the appropriate professional when not possible and the issue is significant. That’s what our clients are paying us for and anything less is not providing a service to them.

First read the caption of the diagram as it says a lot. Be careful about using any textbook, CodeCheck, or other diagram as an authoritative source on foundations. I’ve performed many pre-pours and the caption of that diagram is so true and what you see there does not follow many engineered plans. In our area foundations are designed by PE’s with that requirement in every jurisdiction I’ve inspected. No matter what you read the PE trumps it all but most, if not all, do use the various standards. Because of the issues we have with foundations here I do recommend you perform a lot more reading so as not to get caught with your pants down and standing in front of TREC. There is so much free information on the WEB it is simply incredible! Other information does come at a price but in this profession those prices are some times well worth it and even some of that information is found where it should not be (:wink::wink:). These are some sources I would recommend you review, mull through, digest, and think of how it is done here.

Obviously the IRC AND IBC (IRC will reference it for foundations built on expansive soils) which are available for free viewing on the ICC WEB site.

In Texas you’re lucky to have the Foundation Performance Association which has a TON of great information completely free.

Most newer and many older foundations are Post Tension design. The Post Tension Institute sets the standards and many PE’s also use and reference them in plans. The standards book is really small, easy reading, and well worth paying for. If I am correct the INACHI convention this year has PTI on site for their Level I certification training. I would expect they will be providing some worthwhile training.

The American Concrete Institute sets the standards for concrete usage in foundations. Unfortunately they sell their standards and they are not cheap! However some of the older ones are available in various places and some large concrete associations write White Papers based on the ACI standards. Between the two you can get some really good information from them.

Next let’s look at your situation. I’ll try to cut to the meat of it. First Nolan has already very succinctly described how high can the perimeter foundation beam be. What matters is the beam extension amount under the soil. We have no freeze zone so by building codes that can be as little as 12" below soil. However typically it is 18" - 24" below soil level here or whatever the PE calls for in the design.

Looking at your pictures I see no real foundation distress but I do see indicators that the foundation form boards were intentionally set that high. The first indication is in your very first picture if you look at the right side foundation wall, below the water heater TPRV and pan drains, and near grade. From brick to near grade the wall is about as smooth as possible after pulling form boards and has a tell-tale line about center point. The line is where the form boards were stacked and concrete seeped into the joint. Below the WH TPRV/pan drain you can see where concrete is protruding irregularly from the wall. When the form boards were set on the original grade they did not pack any openings at the bottom edge to help prevent concrete from seeping out like they should. It won’t typically cause a structural issue but more of a nuisance one if the owner wants to create a garden or other such thing. However it is a really good indication for us where digging for the perimeter beam started. If you want to probe for foundation depth I carry a mechanics flathead screwdriver with a 12" shank just for that purpose. You can also use a T-Probe like this one which comes in handy for all kinds of probing when needed. Obviously use caution you don’t hit irrigation lines or other buried items.

Another indicator is the termination points for the TPRV and drain pan. Look at how low down the foundation side they are. They could have been replaced with longer ones but I seriously doubt it.

And of course the last indicator is the coloration of the concrete itself. It’s fairly uniform from brick to grade whereas had grade been high and subsided or changed as the owner states then I would have expected the concrete to have some discoloration to it.

RE my question about load paths for a structure was intended to illicit a little research that can help with the question of if there is sufficient foundation perimeter beam under the soil. It is a BIG description that I won’t rehash but the foundation must be able to support both vertical and lateral loads from the structure above. If you Google “Vertical Load Path” and “Lateral Load Path” you will find a whole lot of information to read. Essentially though if this foundation was created with proper perimeter and interior grade beams, and as others pointed out if it was properly reinforced (rebar, PT Cables), and no other loading issues are visible then we have no other choice but to expect the structure including its foundation is properly supported.

With the exception of the one brick under the house number sign all I see is separation of brick and stone at mortar joints. BTW that brick is easy to crack (looks like Boral brick) and I see isolated brick cracks like that frequently with no mortar damage around it. So what caused the separations? Don’t have a clue since we were not there but Joseph has a very good possibility with framing expansion. Another has to do with the separation at that door trim brick where it is wider at the top and ends part way down. That might be caused by an undersized header. Did you see any header bowing?

Basically we can’t offer much insight since were were not there. Looking at the narrow view of the interior and entry lip of the garage I see no apparent damage of the slab. Also the garage looked packed with belongings and views blocked which obviously left you in a lurch as I expect there was very limited visibility to look for other signs. Hopefully your report made note of that?

Do you have any other questions the members can help with? It’s a great topic to discuss. Also you need to be careful about making any engineering calls as that can place you in front of TREC in a heart beat!


That’s an awesome pic!! Was that a flood zone construction?

No, not a flood zone, just a Texas Hill Country home on a sloped lot.

I’ve done concrete in CA, CO, and Utah, and I’ve never seen anything like that.

Here’s a couple more from around my area:

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Mike, can you explain what they are? Looks like a raised concrete floor.

Those are all Slab on Grade (SOG) foundations on sloped or uneven lots. The photos are all from . Go to the Project Portfolio tab then the Residential tab to view more. Some are post-tension, some are rebar/steel mesh reinforced.