Foundation and structural terms in Miami

Oolitic limestone

The rock most of urban Miami-Dade sits on, made of tiny rounded grains of calcium carbonate cemented together. It is soft enough to cut with hand tools when freshly quarried, which is why so many older Miami walls and houses are built from it, and it is riddled with solution voids of varying size. Its top surface is not flat, so two footings 30 feet apart on the same house can be bearing on very different things.

Miami Rock Ridge

The low ridge of limestone that runs roughly parallel to the coast through eastern Miami-Dade and carries most of the county's older urban development. Ground east and west of it is generally lower and softer. Being on the ridge does not guarantee shallow rock under a particular footing, but it makes it much more likely.

Muck (organic soil)

Partly decomposed plant material that accumulated in former wetlands. It has very low bearing capacity and it keeps compressing under load for decades. Where a Miami-Dade neighborhood was built by filling over wetland, pockets of muck below the fill are a common reason a footing keeps settling long after construction.

Fill

Imported soil or crushed rock placed to raise a site to grade. Properly placed fill is put down in thin lifts and compacted, and its density is tested. Fill that was pushed in and levelled without that process keeps consolidating under load, and a footing bearing on it goes down with it.

CBS construction

Concrete block and stucco, the dominant way South Florida single-family homes are built. Concrete masonry units are laid up, cells containing reinforcement are grouted solid, a poured tie beam runs around the top of the wall, and stucco covers the outside. It is durable and storm-resistant, and it is also stiff, which is why differential settlement shows up as clean stair-step cracks through the mortar joints.

Tie beam

The continuous reinforced concrete beam poured around the top of a block wall, tying the walls together and providing the anchorage for the roof structure. Because it is a horizontal exterior concrete element, it is also one of the elements where spalling shows up first on older coastal buildings.

Tie column

A reinforced concrete column cast into the block wall, usually at corners and at either side of large openings. Together with the tie beam it forms the frame that holds a CBS wall together under wind load.

Slab on grade

A concrete floor slab cast directly on prepared ground rather than on a suspended structure. Essentially all Miami houses are built this way, since a high water table rules out basements. The slab edge is normally thickened into a footing that carries the wall above.

Monolithic (thickened edge) footing

A slab and its perimeter footing cast in one pour, with the concrete deepened around the edge where the wall lands. Common in Florida residential construction. It behaves as one piece, so a footing that drops at one corner drags the adjacent slab down with it.

Differential settlement

Settlement that is uneven across a structure. Uniform settlement, where the whole building goes down together, causes very little damage. Damage comes from one part going down while another does not, which forces the structure to bend. This is why the relevant measurement is not how far the house has settled but how much elevation differs across it.

Underpinning

Extending or supplementing an existing foundation so its load is carried by deeper, more competent material. In practice this means installing piers beneath a footing and transferring load onto them with brackets. The word covers helical piers, resistance piers, micropiles, and grouting.

Helical pier

An oversized steel screw, a shaft carrying one or more helix plates, wound into the ground by a hydraulic torque motor. Installation torque correlates with capacity, so the installer can verify each pier as it goes in. Useful where there is limited headroom and where load has to be supported before the structure is in place.

Resistance pier (push pier)

A steel tube driven vertically into the ground in short sections, using the weight of the building itself as the reaction force, until it will not advance further. Because the structure provides the reaction, each pier is effectively load-tested during installation. Better suited to heavier structures than to light ones.

Micropile

A small-diameter drilled and grouted pile with steel reinforcement down its centre. Drilling means it can pass through obstructions and get into rock, which is useful in Miami where the limestone surface is irregular. More expensive per pier than driven or screwed alternatives.

Compaction grouting

Injecting a stiff, low-slump grout under pressure to densify loose soil and fill voids in place. Rather than carrying the load on a pier, it improves the ground the footing already sits on. Well suited to washed-out zones and loose fill, less suited to deep organic layers.

Polyurethane foam injection

Two-part polymer injected through small ports beneath a slab, expanding on contact to fill voids and lift the slab. It cures within minutes, weighs a small fraction of cementitious grout, and does not wash out. The standard method for slab lifting where the underlying ground is marginal.

Mudjacking (slabjacking)

The older slab-lifting method, pumping a cementitious slurry through larger holes to raise a slab. Cheaper per cubic foot than foam and still appropriate for large voids over competent ground, but the material is heavy, which is a real drawback when the reason the slab dropped was weak support.

Spalling

Concrete breaking away from a surface. In coastal Miami it is almost always driven by corrosion of the reinforcement inside: rust occupies several times the volume of the steel it came from, and the resulting pressure splits the cover off. A rust stain is the early warning; a piece on the ground is the late one.

Delamination

A layer of concrete that has separated internally but has not fallen off yet. It sounds hollow when tapped with a hammer or dragged with a chain, which is how surveyors map the true extent of a spalling problem. Visible damage is usually a fraction of the delaminated area.

Chloride ingress

The movement of chloride ions from salt air, salt spray, or salt water into concrete. Once enough of them reach the reinforcement, the alkaline film that normally protects the steel breaks down and corrosion can start. The closer to the water and the thinner the concrete cover, the sooner it happens.

Concrete cover

The thickness of concrete between the outside face and the reinforcing steel. It is the reinforcement's only protection from the environment, so cover requirements are higher for concrete exposed to marine conditions. Older structures built to thinner cover requirements deteriorate faster in the same location.

Carbonation

Carbon dioxide reacting with concrete over time and reducing its alkalinity from the surface inward. Like chloride ingress it removes the chemical protection around embedded steel. In coastal South Florida chlorides usually reach the reinforcement first, but on inland and sheltered elements carbonation is the mechanism worth checking.

Epoxy injection

Filling a crack in concrete with a rigid two-part epoxy under pressure, structurally rebonding both faces so the section behaves as one piece again. It requires a clean, dry, and dimensionally stable crack. Injecting a crack that is still moving simply relocates the failure.

Polyurethane injection

Filling a crack with a flexible resin that expands on contact with water and seals against leakage. It does not restore structural strength, but it works in wet cracks and tolerates a small amount of ongoing movement, which makes it the right choice for water intrusion rather than structural repair.

Crack monitor

A simple two-plate gauge fixed either side of a crack with a graduated scale, so movement can be read directly over weeks or months. Cheap, and it answers the only question that really matters about a crack: is it still moving. Thirty to ninety days of readings usually settles the diagnosis.

Stair-step crack

A crack that runs diagonally through a block wall by following mortar joints, stepping across and up. It indicates the wall has moved along the weakest path through it. The cause can be a settled footing below, a failed lintel above an opening, or thermal movement in a long wall, and the repairs differ completely.

Seawall cap

The continuous concrete beam poured along the top of a seawall, tying the panels together and providing the finished edge. A cracked or spalled cap is often the visible symptom of something else, typically soil loss behind the wall that has removed the cap's support.

Tieback and deadman

A rod running back from a seawall to an anchor buried in the soil behind it, resisting the pressure that would otherwise rotate the wall outward. Retrofitting tiebacks is a common alternative to replacing a wall that is otherwise sound but has begun to lean.

Building recertification

The Miami-Dade County requirement that older buildings be inspected by a licensed engineer or architect and certified as structurally and electrically safe, then re-inspected on a repeating cycle. Single-family homes and duplexes are not part of the program. The inspection report lists any deficiencies and the owner or association has a defined period to address them.

Milestone inspection

A separate Florida statutory inspection requirement created after the 2021 Surfside collapse, applying to condominium and cooperative buildings of three stories or more. It overlaps with Miami-Dade recertification, and a building here can be subject to both. Confirm the current thresholds and deadlines with your local building department, since the statute has been amended more than once.

Structural integrity reserve study

A study Florida condominium and cooperative associations must have prepared for the structural elements of their buildings, setting out remaining useful life and the reserve funding required. It matters to foundation and concrete work because it is where the money for a large restoration project is supposed to come from.

Biscayne Aquifer

The shallow, highly permeable aquifer beneath southeast Florida and the region's drinking water source. It is the reason the water table in Miami sits so close to the surface, and its permeability is why water moves so freely through the ground here, which is directly relevant to how soil gets washed out from under slabs and seawalls.

More depth on most of these sits in the guides, and the Miami foundation repair guide is the place to start if you are new to the subject.