Alabaster grew quickly along the I-65 corridor south of Birmingham, and most of its housing is recent enough that the foundation problems here look quite different from those in the older cities closer to town.
Newer Slabs on Graded Ground
The bulk of Alabaster’s residential building is from the 1980s onward, and slab-on-grade dominates. A slab is a simpler structure than pier-and-beam, but it is also less forgiving: there is no crawl space to get under, no easy access for inspection, and when a slab cracks the damage is telegraphed straight into the finishes above it.
Subdivision development on rolling Shelby County ground meant substantial cutting and filling to create buildable pads. Fill that was placed and compacted properly performs well. Fill that was rushed, or placed over organic material that later broke down, consolidates over the following years and takes the slab corner with it.
The tell is a slab that has dropped at one corner or along one edge, showing as diagonal cracking above door and window openings, doors that bind at the top, and tile grout cracking in a straight line.
Limestone and Shelby County Ground
Parts of Shelby County sit over limestone, and limestone dissolves slowly in groundwater over geological time, producing the voids and irregular bedrock surfaces associated with karst terrain. Sinkholes are an occasional occurrence in the county.
This is worth stating carefully rather than dramatically. The overwhelming majority of foundation movement in Alabaster is ordinary clay behavior and poorly compacted fill, and treating every crack as a possible sinkhole would be alarmist. But if a depression appears in a yard, if a slab drops suddenly rather than gradually, or if there is any circular pattern to the movement, that is a matter for a licensed geotechnical engineer before any repair contractor starts quoting piers.
Repairs on Slab Foundations
Where a slab edge has settled, underpinning with push or helical piers along the affected footing is the usual approach, transferring the load to competent material below the problem layer.
Where an interior section of slab has dropped, polyurethane foam injection beneath the slab can lift and support it without excavation, and is considerably less disruptive than breaking out concrete.
Where the problem is plumbing rather than soil, the leak has to be found and repaired first. A slow leak under a slab keeps the soil beneath it soft indefinitely, and piering around an unrepaired leak is money spent to no purpose.
Drainage on a Graded Lot
Modern subdivisions are graded to move water toward streets and swales, and that system works until it is interrupted. Extensions, patios, retaining walls, sheds and landscaping added after the fact routinely block a drainage path that the builder engineered. When water is standing beside a house in Alabaster, something has usually been changed since it was built, and finding that is cheaper than any structural repair.