What distinguishes a slab-on-grade foundation from a crawl space foundation for inspection purposes?

The practical difference between these foundation types, from an inspection standpoint, is access. A crawl space lets the inspector see the underside of the floor, the framing, the ducts and — critically — the drain, waste and supply piping, so leaks, corrosion, improper slope and damage are directly observable. A slab entombs all of that in or beneath concrete. Plumbing leaks under a slab therefore develop invisibly and are usually detected only indirectly, through unexplained warm spots on the floor, elevated water bills, the sound of running water with fixtures off, or eventual moisture at the slab edge. That limitation belongs in the report, because a client comparing two houses should understand that one of them offers no way to see a whole category of components.

A slab encloses the under-floor plumbing so it cannot be observed, while a crawl space allows direct visual access to piping, framing and ducts. That difference in what can be inspected is the practical distinction for the report.

Slab-on-grade foundations place the floor directly on prepared soil with perimeter footings or thickened edges. Under-slab plumbing is inaccessible, so leaks are inferred from indirect evidence. Crawl spaces provide access to piping, framing and ducts within the limits of clearance.

Concrete Hides the Plumbing. A crawl lets you look; a slab makes you infer. Say which house you are in.

Know the indirect indicators of a slab leak: warm floor areas on a hot-water line, running water with all fixtures off, unexplained usage, and moisture at the slab perimeter.

• •Failing to state the under-slab plumbing limitation in the report
• •Believing slabs are built without footings
• •Treating foundation type as a limit on structural capacity