Refers to the part of a multi-tenant building that directly serves and affects all tenants.

In conventional North American practice, base buildings are constructed by speculative office building developers, leaving choice and responsibility for the reminder of the building to tenants during the fit-out phase.

The base building normally includes the building's primary structure; the building envelope (roof and facade) in whole or part; public circulation and fire egress (lobbies, corridors, elevators and public stairs); and primary mechanical and supply systems (electricity, heating and air conditioning, telephone, water supply, drainage, gas, etc.) up to the point of contact with individual occupant spaces.

Base buildings provide serviced space for occupancy; Supports are residential base building.