Qs about home addition's foundation (percentage, legal, inspector, room)

[Johnny Northside]

The subject home is a postwar brick colonial in a northern climate (near suburbs of Chicago) ... There is some question about whether the home addition (family room that is semi-open to the dining room, added in the past 10-15 years) is built on an excavated foundation/footing below the frost line or on a concrete slab. (Many homes of this style and vintage in the area originally featured a screened porch in the location where the addition now stands)

So the question is twofold:
1) Trying to determine whether there is a foundation -- my understanding is that a normal home inspection does not include anything below grade. So where to turn to get an inspection and determine a) presence of foundation; b) cost to repair/upgrade the foundation if it is found to be deficient.

The second question requires a more pragmatic/practical response, in the event no new foundation/footing can be found:
2) How many/what percentage of home additions such as these are built on concrete slabs or similar "non-conforming" footings, and what are the "probable" consequences of such a condition. I understand that a foundation that does not reach the frost line is against the local building code, but I also realize that the code often goes beyond the practical application in many situations. I know that at minimum it would be more difficult to heat/cool this area, but in this particular situation, my past experience and knowledge are lacking as far as the probability of greater structural issues down the road.

[middle-aged mom]

I'll PM you with my guy, a home inspector who is also a structual engineer.

[rubytue]

Go down to the county permit office and check out the permits. The permit should show the type of foundation for the addition and if it passed its inspection. I've found the inspection office is generally helpful and will talk with you about what it means if they just went over the slab. Plus, since they local, they will have the most accurate information. If you don't find a permit, its not a legal addition and you can bet that its not on a proper foundation.

[chet everett]

I have owned little homes on slabs that were fine, as long as the footings are appropriately sized / done properly their is really nothing to be concerned with.

To determine if the footings are where they are supposed to be I would NOT rely on any records -- even if the municipality still has the original permits there is no guarantee that is how things were done "in the field".

You need a inspector that has the knowledge and experience to do some literal digging -- best case scenario they can get a spade do and verify the footings at a couple of corners. Typically you would select an engineering firm that can also design a solution if they discover problems...

If there are improper footings there may already be evidence of the concrete heaving away or toward the other portion of the structure. This can be corrected with "mud jacking" in most cases, and if that is not feasible other types of poured foundation repairs / reinforcements can be done. The costs vary widely, depending on how much concrete is needed, access issues, and even liability factors.

If I understand correctly, the seller has no knowledge of how the "pad" was built, but I think that it would be a far bet that even MANY pads intended for only a patio do in fact have appropriate footings. Those they do not rarely remain level over more than a few freeze/thaw cycles...