I had an unusual situation… an older house built around 1950 with an addition built later maybe 10-15 years ago. no one knows. The addition is on a “floating slab” as far as i can tell. I stuck a rod down where the footers should be and i can stick it right under the slab. its about 5" thick. it appears to have compacted limestone under it. the client wants my opinion. I personally think it will not heave or settle more than it already has but i don’t want to put that in a report just as i wouldn’t want to say the house wont move even on a proper foundation. my location is Indiana and frost line is 30" below grade. anyone ever run into a similar situation?
Footings (not footers) are a necessary component of any building foundation. I would guess that this is an unpermitted addition, and you should not endorse it regardless of your observations or opinions as to its stability.
what is the difference between footers and footings anyway?? i hear them both used for the same reference and you can even google either and get results… thanks Jeff
Many 3 season cottages up here are placed on floating slabs. Most have 12 in. of clear crushed stone under. From a structural point of view I have found its not the “settling” that is of concern as much as the uneven settling. The house has ‘finished’ its settling whereas the addition may continue to. I have even found (my brother in in demolition) that floating slabs with very good installed drainage, over time, loose the ability to drain water due to silting. In all my designs I am very careful of separating the compacted stone from the soil with a German made silt barrier (from our Green Roof practice). It is a geotextile about 3/8 in, thick. That does not help you here however. Any slab can be made not to break from uneven settling. My concerns would lean towards the connection of the addition to the older home. Are they extra secure? If not as the slab ‘floats’ the forces on the attachments are huge --easily generated 1000-2000 lbs bending and 1500 -2000 lbs shear and 900 to 2000 tensile - few fasteners or combination of fasteners in typical construction can withstand these loads. More ofter than not I look for interior and exterior vertical patches or mouldings covering separating seams between the addition and the home… The roof flashing is the second largest problem I have seen. As the outer edge of the slab settles two things happen at the same time. The inner edge of the slab is forced into the foundation wall of the home damaging it and acting as a pivot point or ‘turning moment’ on the addition and pulling the top of the addition roof away from the home.
Terry Ethridge
Footings spread the vertical loading of the foundations over a wider area thus reducing the weight per square foot. Better with 2 or 4 re-bars. I believe the term “footers” (rarely used up here) refers to the thickening of a floating slab around the edges and under interior load bearing partitions to add strength and prevent cracking. Also better with 2 or 4 re-bars.
there are no interior signs of any movement at all. inspectapedia says absent footings may or may not be a defect depending on design and soil conditions
i happen to have a structural engineer i work with on my day job and he says although not likely, the danger exists every winter that heaving will take place.
Mostly just a “pet-peeve” of mine. The term “footer” is widely used and recognized, but technically incorrect.
Floating slabs are often acceptable, but are generally much more than 5" thick. Also, depending on your seismic zone, caissons will often be used to prevent lateral displacement of a floating slab.
Personally, I have never seen a “floating” slab-on-grade that was less than 10" thick.
In my area, if the addition is attached to the original structure it has to have a four foot frost wall on top of footing. It also must be pinned to the foundation of the original structure.
i set 10’ diameter tanks - 30’ tall on a floating slab just a few weeks ago… i was quite surprised that the engineer didnt require footings- it was just crushed stone… we tore out 3’ thick concrete where the old ones were… i aint no engineer so its hard to argue.
i backed out of making any kind of statement to the buyer btw… i wasnt about to put my *** on the line but was hoping to point him to some links to read by people more qualified.
Requirements for residential foundations are different than those for “pads” and other non-habitable construction. You cannot compare a tank-pad with a residential foundation.
The “addition” to this home was probably built over a patio slab, which (at least in CA) is an unacceptable practice.
Vintage foundations (stone and rubble) had no footings. Footings developed shortly after the advent of brick foundations. However, not all foundations require true footings. For instance, pre-cast foundation walls sit on crushed stone… no footing.
In your specific situation, the best advice you can offer as an inspector is to stay away from the engineering determination, and recommend having the client research whether the addition is registered with the township, if the plans were approved, and whether it was ever inspected. The rest goes beyond any reasonable SOP, and may get you into trouble. They can also hire a licensed PE/SE for further investigation.
Photos from a borescope could be somewhat helpful, but will likely be inconclusive.
Footers relate to a single footing under a post, in pier, post and beam style construction but not only. A per-say 3 by 3 foot square filled 10 inches high, with cement and the post being on top center. It stops the post from being thrust into the ground under loads…
Footings encompass the total diameter '‘but not always’'of the home and again are 24 inches wide minimum and 10 inches high and sit under the foundation some times connected to the foundation with rebar for stability. Please understand my dimensions are imaginary to give an visual effect.
You should be able to google footings and foundations for examples.
Homes with out footing or footprints are old or not well designed.
You can rent a tool that will see frenchdrains and footings. In my area anyway.
