Concrete Slabs

Thickness, reinforcement and the extent of site preparation determine the price, and all three follow from the load the slab will carry. A shed pad and an ADU foundation at identical square footage are not comparable in cost.

Excavation is the factor most often underestimated. Ground that must be excavated, hauled off and replaced with imported base costs more than ground that can be cut and compacted in place. See digging and grading for that stage. Estimates are provided on site at no charge.

The most common type in this region is a slab on grade: concrete placed directly over prepared ground, generally with a thickened edge or a separate perimeter footing to carry the walls. Where the thickened edge and the slab are placed as a single pour, it is described as a monolithic slab.

The other types in general use are stem wall foundations, in which a short wall sits on a footing and the slab is poured within it, and suspended slabs, which span between supports rather than bearing on the ground. Most residential flatwork, from shed pads to garage floors, is slab on grade.

Four inches is standard for most residential slabs, including shed bases, garden pads and standard garage floors. Five to six inches with heavier reinforcement is specified where vehicles, equipment or stored weight are involved, and commercial floors may be thicker again.

Thickness is one of several factors. Reinforcement, base preparation and joint layout contribute equally to performance. A thick slab over a poor subgrade will still fail.

Cement is a single ingredient. Concrete is the finished material: cement, sand, aggregate and water, generally with admixtures. Cement is the binder that holds the other components together and is not a material a slab can be poured from on its own.

The terms are used interchangeably in general speech, and a cement slab and a concrete slab refer to the same thing in ordinary usage. The distinction becomes relevant when specifying a mix.

Neither is universally preferable, as they suit different conditions. A slab on grade is poured directly over prepared ground, requiring fewer steps and no crawl space, with the finished floor close to grade. A raised foundation on stem walls or piers provides a crawl space, which keeps plumbing and wiring accessible and accommodates a sloping lot more readily.

Slab on grade is the standard choice for new residential construction on level ground in this region, and for garages, shops and ADUs. Site conditions generally determine the decision: lot gradient, drainage and soil type.