What BIM is

Building Information Modelling is a way of working in which a project is described by shared digital models that carry both geometry and information. A wall in a BIM model is not just two lines; it knows its material, thickness, fire rating and cost.

Because each discipline, architecture, structure, plumbing, electrical and HVAC, models in 3D, their models can be combined and checked for clashes before anything is built. Drawings and quantity schedules are generated from the model, so they stay consistent when it changes.

Linking the model to the schedule gives 4D simulations of the construction sequence; linking it to costs gives 5D estimates. After handover, the information supports facility management, which is the start of a digital twin.

Collaboration needs rules: who models what, to which level of detail, in which file formats, and through a common data environment. ISO 19650 sets out such an information management framework internationally. Open formats such as IFC let different software exchange models.

BIM is not a single piece of software. It is a process supported by many tools: authoring software for each discipline, model checkers, scheduling and estimating tools, and viewers for site teams on tablets. Its benefits depend on agreeing early what information each party must deliver and when, which is the purpose of the employer's information requirements and the BIM execution plan. On infrastructure, the same ideas apply to roads, railways, tunnels and utilities, often combined with survey data and GIS.