Florida Building codes.

[Ralph Stakely]

Ok guys, or Jerry
Today I was watching a TV program called 100 Day Dream House.
Premise is that they can build a house from open lot to finished in 100 days.. No matter. Nothing to do with question.

My question is: this particular house was being built in Florida, on sand.. The lot was "leveled" smoothed and a concrete slab was poured directly on top of the sand.
The contractors put up the form boards on the sand.. I saw nothing of a footing or any sort of foundation.
The slab was poured and then concrete block walls were built on top of this slab. And from there the house was finished.
Granted, the slab was 6 to 8 inches thick. I also saw no wire mesh or metal rods to strengthen the slab.
Were my eyes deceiving me, or is this ok in Florida.?
Even my Boss (wife) said, " Hey aren't they supposed to have a foundation under that slab?" She was even the one that said, "Why don't you get on your inspectors site and ask your friends."

Curiosity got the best of me.

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[Jerry Peck]

My question is: this particular house was being built in Florida, on sand.. The lot was "leveled" smoothed and a concrete slab was poured directly on top of the sand.
The contractors put up the form boards on the sand.. I saw nothing of a footing or any sort of foundation.
The slab was poured and then concrete block walls were built on top of this slab. And from there the house was finished.
Granted, the slab was 6 to 8 inches thick. I also saw no wire mesh or metal rods to strengthen the slab.
Were my eyes deceiving me, or is this ok in Florida.?

Ralph,

The answer is; yes, no, maybe ...

The typical construction here is Florida (where the 'frost depth' is probably at about 2000 feet up) is "concrete slab on ground", aka "slab on grade" ... and therein (that last term) creates part of the problem - which I thought went away in the years following Hurricane Andrew (August, 1992) and especially 'went the way of the dinosaur' with the statewide adoption of a Florida Building Code, starting with the 2001 Florida Building Code (which was not effective until 2003, but that's another story).

The minimum depth to the bottom of the footing is the same as elsewhere - 12 inches below frost depth. Being as there is 'no frost depth', the frost depth is "0", i.e., at grade.

Now back to "slab on grade" ... and that sticky tricky word "on" ... even with "concrete slab on ground" (but "ground" does not indicate the same thing as "grade" does) - slab ON grade ... no problem ... AS LONG AS the bottom of the footing is 12 inches below frost depth, i.e., 12 inches below grade.

Back to your question: IF the slab was actually only "The lot was "leveled" smoothed and a concrete slab was poured directly on top of the sand.", then that is not as required by the Florida Building Code, Residential (we basically have the various codes, based on the various ICC codes, with one- and two-family and townhouses being under the FBC-Residential).

The proper (required) way would be for the bottom of the footing to be 12 inches below grade on virgin soil or on compacted fill (once soil is disturbed, it is required to be compacted to density prior to being used to support structures. Now, if ... IF ... if that "sand" was leveled off, and a footing dug down 12 inches, with the bottom being compacted (try digging just to 12 inches and not having to add fill and level it out --- compact that soil under the footing); then the form boards set in place (the slab will be at least 6 inches, likely more, above final grade, making the "thickened edge slab", where the thickened edge includes the footing, with fill in the center area ... compacted ... to provide for a 4 inch slab --- yeah, yeah, 4 inches and 12 inches does not equal 12 inches below grade to the bottom of the footing and 6 inches above grade to the top of the slab; then the plumbers, and others as needed, come in and dig out for their below slab piping, then clean fill is again added and compacted; then a vapor barrier is installed; then the concrete slab is poured and finished.

WWM? Not required if fiber reinforced concrete is used, some contractors use WWM, some use fiber reinforced concrete, some use both 'just to make sure'.

Steel reinforcing (rebar) in the footing is required.

Good contractors will pour a recess around the edge of the slab (require when concrete block is being used), advantageous when frame walls are being used - the recessed edge places the bottom of the wall below the level of the interior slab, leaks are now given a seepage joint to leak outside instead of inside. You'll get varying opinions on the recess for frame construction, from 'I've never seen that', to 'I've only seen that on concrete block construction', to 'hey, great idea'.

Back in the late 1970s, in Gainesville, Florida, I was one of many (I recall there being 300-400 people working on the house that day) who constructed a house in 11 hours, poured the slab, painted, carpeted, and totally finished (of course, though, the carpet had to be pulled out to let the concrete slab finish curing and letting the moisture out of the house), but the house 'was completed' in time. But that's another story.