Skip to content
The AIA Trust home

BIM Definition and Planning

What is BIM?

The National Institute of Building Sciences (NIBS) defines BIM as, “a digital representation of physical and functional characteristics of a facility. As such it serves as a shared knowledge resource for information about a facility forming a reliable basis for decisions during its lifecycle from inception onward.”

Accordingly, this digital database contains much more information than text and lines. Rather, it can render intelligent data which includes product data and other specification information, 2D drawings, 3D images, image animation, and elements of time/scheduling (known as 4D) and cost elements (known as 5D).  

The data for 4D and 5D are typically produced by the contractor. For the purpose of this white paper we will address BIM only as it relates to the products of service produced by architects and their consultants (3D) whose responsibilities do not include time/scheduling or cost data.

Since we call building information modeling BIM, the term “BIM model” may appear redundant to some. However, for clarity we will refer to the “BIM model” when we address the 3D model in this paper.

BIM Planning

Since it is more efficient for all members of the project team to be working on the same BIM model, it makes sense to first get everyone on the same page. This can be managed with a planning document referred to as a BIM Execution Plan or a BIM Protocol Manual.

The intent of the BIM Execution Plan or BIM Protocol Manual is to provide a framework that will allow the owner, architect, engineers and contractors to undertake BIM technology in a collaborative manner to enable faster and more cost-effective project delivery. Naturally, when this can be accomplished, management of risks are improved as well. Many organizations who have subscribed to BIM project delivery have developed their own internal management document. A BIM Protocol Manual prepared by the firm Ayres Saint Gross is available with this paper.

The plan establishes a baseline of services and expectations of those involved in development of BIM for a project. It addresses the intended and allowable use of the model and establishes guidelines and protocols for file sharing and other elements of work flow within the project team. The plan can include collaborative process mapping in the form of a narrative matrix that describes the activities of the owner, architect, engineers, contractors and even the commissioning agent from Conceptualization/Program of Requirements through design, agency coordination/buyout, construction and facility management as applicable to the project.

The plan typically includes a Model Element Table – Level of Development (LOD) which addresses the level of development of BIM components and deliverables and the points which design consultants and contractors will be engaged.

An excellent example of a document used to develop the Model Element Table is the Level of Development Specification (see This specification utilizes the basic LOD definitions developed by the AIA for AIA Document G202-2013, Building Information Modeling Protocol Form, and it is organized in CSI Uniformat 2010.

The LOD Specification “…defines and illustrates characteristics of model elements of different building systems at different Levels of Development. This clear articulation allows model authors to define what their models can be relied on for, and allows downstream users to clearly understand the usability and the limitations of models they are receiving.”[1][Bold added]

Levels of development are defined in the LOD Specification to establish a clear limitation on the complexity of the completed model. An abbreviated narrative description of the “Fundamental LOD Definitions” are:

  • LOD 100 – Massing, including location and orientation
  • LOD 200 – Generalized systems or assemblies, approximately quantified and located
  • LOD 300 – Specific assemblies, accurately modeled
  • LOD 350 – 300 combined with other building systems
  • LOD 400 – Specific assemblies, accurately modeled and detailed so as to be suitable for fabrication
  • LOD 500 – Accurate, as-constructed actual assemblies

The LOD Specification may also provide graphic depiction of the Model Element definitions. A more precise level of detail is established through images representative of the level of intended completion of the details in the model.

The objective of establishing a clear definition of the Model Elements is to allow for independently generated details from the various design disciplines (and from trade contractors if they are involved in pre-construction) that have the same level of completion and complexity and will effectively work together as a unified Building Information Model. From a risk management standpoint, the definition establishes finite service deliverables and responsibilities as well as a consistent expectation among the team players.

The BIM Execution Plan should also include a File Naming Structure for each individual model file, narrative descriptions of Analysis Models, and a description of the Clash Detection Process. The more that can be defined and described in the BIM Execution Plan, the less likely for a misunderstanding or a failed expectation.

Numerous guides and descriptions are available such as that offered by Penn State University, available at


‹‹ back to SUMMARY | top of this page | on to next section