SB meaning in Real Estate ?

A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the boiler, water heater, breaker panel or fuse box, car park, and air-conditioning system are located; so also are amenities such as the electrical distribution system and cable television distribution point. In cities with high property prices, such as London, basements are often fitted out to a high standard and used as living space.

In British English, the word basement is used for underground floors of, for example, department stores, but the word is used only with houses when the space below the ground floor is habitable, with windows and (usually) its own access. The word cellar applies to the whole underground level or to any large underground room. A subcellar is a cellar that lies further underneath.