The foundation is the structural base that transfers a building's load to the ground. It is the part you never see, but everything depends on it. Get the foundation wrong and the building will crack, settle, or worse.

There are two main types. Shallow foundations — spread footings, mat slabs, and grade beams — sit near the surface and spread loads over a wide area. Deep foundations — piles, caissons, and piers — reach down to stronger soil or bedrock when the surface soil cannot carry the load.

Soil conditions determine the choice. Sand, clay, rock, and groundwater each behave differently. Geotechnical engineers test the soil and recommend a foundation type. In earthquake zones, foundations must also resist lateral forces. In flood zones, they may need to be elevated.

Waterproofing and drainage are critical. A foundation that sits in water will fail. Drain tiles, sump pumps, and waterproof membranes keep the basement dry and the structure sound.