Slab on grade foundations

What method do you use to inspect a slab on grade foundation? If there are no obvious signs of problems like uneven door frames or tilted floors what else can you do to collect information?

I have a 100’ liquid digital level

More like checking floor vents if embedded and nearby trees.

When I was younger we used an EDM and would shoot all the corners of the building and compare it with a bench mark and a topo. But that is a little outside of the average home inspection

I do a visual inspection of the ext and int of the
I also do NOT use the term ‘cracked slab’
Find a GOOD inspector to shadow and he/she
will give you some good info.

Call it what it is…monolithic.
Without x ray vision I can’t see nothing but concrete…Huh?

Sorry for being so short Michael.
I did a ride along with a struct’ Engineer and
HE advised me to never use the term ‘cracked foundation’ as
many see that as a failed foundation.
He gets atleast 1 call a month from a realtor because
an Inspector used those words.
He said and showed me the main concern is the active area of the slab, outer
most 10 Feet of slab as it exibits the most
issues from moistire.
“concrete cracks”


Just report what your saw and any restrictions that prevented your from observing the entire slab. Typically you only see the portion exposed between the siding and ground on the outside. Carpet and other flooring prevents a visual inspection on the interior portion. Taking elevations without knowing the elevations at the time of construction is just an exercise in collecting useless data, unless its for documentation for comparison in the future. One exception would be if the slab is completely exposed with visible cracks that occurred after construction. A scaled drawing with elevations and visible cracks together with other supporting data such as drywall or brick veneer cracks may provide enough information to conclude that a low spot was the result of settlement versus poor workmanship when pouring the floor. Keep in mind post tension slabs can settle without creating large cracks. Providing elevation data also puts you in a position to answer the questions; is the elevation difference significant?, is it a structural concern?, should it be repaired? Answering these questions is outside the SOP and answering them incorrectly can cost you $$$. For example you scared the buyer and the seller sues you for working outside the SOP and possibly practicing engineering without a license.

And that’s covered with flooring. So when the customer asks, “hows the foundation?” what can you answer? I suppose without it being out of level or visibly cracked there’s not much to observe.

Travis - thanks for the advice on avoiding the words “cracked foundation.” I’ll add that to my file of buzz words to not say.

Randy - I understand the danger of making definitive statements that exceed the SOP but there must be some cases where advising review by a structural engineer is warranted without exceeding the SOP right? I guess I’m trying to determine when that is without sounding alarms.


You can say:

  • I saw no visible evidence the foundation was not performing as intended.


  • I saw visual evidence x, y,& z that may indicate a settlement and/or a structural concern that may need further investigation by a foundation contractor or structural engineer.

It’s the buyer’s job to decide what to do with that information. Don’t let them put that monkey on your back.

Very good advise folks. Thanks Randy.


You can only report what you can see. If you feel unevenness when walking the floor, out of square doorways, unusual cracking in the stucco or drywall, then that’s what you report and recommend further evaluation by the appropriate expert. You certainly don’t need to break out the water level.