Land in Florida, especially South Florida, is comprised of loose, sandy soil, and low water tables. That, plus the area’s proximity to the Gulf and Atlantic Ocean have always made it a difficult place to build on. That’s why almost all South Florida buildings (including condos and community associations) are set on concrete slabs, rather than the type of below-ground foundations used further inland or in different geologic regions.
“Due to Florida’s geological history, the type of shallow surface soils that support our buildings are relatively loose sands, clays, and decaying organic material,” says David Bodzenski, vice president of operations of NSquare Inc., a foundation contractor in Naples. “When you’re dealing with a multifamily or condominium, you are going to have to use a deep foundation and then you pour the slab on that to connect.”
According to David Bryant, a registered structural engineer with Certified Structure & Foundation Inc., in Melbourne, concrete foundations traditionally consist of three parts.
“You start with footings, which are wide areas of concrete at the base of foundation walls responsible for spreading the weight of the building evenly into the soil to prevent cracks. Then, foundation walls are usually eight-inches or thicker and extend from the top of the footings to the base of the building. Finally, a slab, poured inside the foundation walls forms the floor or subfloor of the building and can support interior partitions.”
The Monolithic Slab
Ever since the mid-’60s, the slab of choice in South Florida has been the monolithic slab, in which the slab and the footing are one and the same, with the footing at the perimeter of the slab and under any load-bearing walls being turned down a little deeper than the floor area.