Building information modeling
Building information modeling is the practice of representing a building as a 3D model that carries the data of every element in it, and it is the technology that changed architecture from a set of drawings into a shared model of the building. A BIM file holds the wall, the beam and the duct as objects with properties, and from those objects the 2D drawings, the quantity take off and the clash check are all generated, so the model is the single source of truth for the project. This page defines the method, its levels from 2D to 5D, and the role it plays in a building project.
What the model holds
What the model holds in building information modeling is the geometry of the building plus the information about each part of it, and that is the difference between a BIM file and a 3D model. A wall in the model is not just a shape but an object with a thickness, a material, a fire rating and a cost, and the same is true of the window, the door and the duct. The discipline of architecture is the one that fills those properties, because the design decisions live in the data, and the model is where the decisions of the building are stored in a form the whole team can read. The Building materials and technology section of this site is where those material properties are defined, and the model is what carries them from the design into the construction.
The levels from 2D to 5D
The levels from 2D to 5D in building information modeling are a scale of how much the model does, and the number of the level names the extra dimension the model adds to the 3D geometry. At level 2 the model is a 3D shape, at level 3 it is a 3D model shared by all the teams and coordinated, at level 4 the schedule of the construction is added, at level 5 the cost and the quantity are added, and the talk of a 6D adds the life cycle carbon of the building. The levels are a convention, not a law, but they give a shared word for what a project expects of its model, and the more levels a project works at, the more the model is doing the work of the building. The AI in architecture page of this site is where the model at these levels is checked automatically, because the data in the model is what the AI reads.
The role of BIM in a building project
The role of BIM in a building project is to be the coordination layer that every team works in, and it is where the clashes are found before they are built. The architect, the structural engineer and the mechanical engineer each work in the same model, and a clash, such as a duct that runs through a beam, is flagged by the software and fixed in the file instead of discovered on the site, where the fix costs a multiple of the model cost. The method changed the sequence of the building, because the systems are coordinated in the model before the first element is cut, and the construction team builds from drawings that are generated from the coordinated model rather than from 3 sets of drawings that were checked by hand. The discipline of architecture is the one that leads the model, and the project manager reads it for the schedule and the cost, so the building information modeling file is the document that the whole project turns on.
Why it changed the practice
Why it changed the practice of architecture is that building information modeling moved the work from drawing to modeling, and the model is a richer object than the drawing. A drawing shows the building from one side and at one moment, and the model holds the building in full and lets the team count, check and price it without redrawing. The change was gradual, because the first models in the 1990s were a 3D shape over the 2D drawings, and the method only became the base of the project when the data in the model was rich enough to be counted and priced. The advantage is not speed alone but a shared understanding, because the 3 parties read the same file and the data is the same for all of them, and that is what removes the errors that a set of separate drawings carries. The practice of the discipline of architecture is now built around the model, and the drawing is the output, not the work, and that is the change that building information modeling made in the building of a building.