Level of Detail
Level of Design / Development / Detail (LOD) is the overall state of your information model at a particular point in its design process. This includes not only graphical objects, but also the data associated with the objects. Your model should develop over time from a very coarse design to the record drawings and as-builts. This process has been distilled down into five distinct categories as formalized in the AIA E202 contract document.
At the core of the five layer LOD is the concept of model progression. It is important to realize that the model will not progress at the same rate for all elements and that not all elements will be present in all levels. For example, fittings on mechanical systems may only exist in level 400 while core structural elements may progress through all 5 levels.
Specific disciplines will also progress through the process at different rates. It is very common to have structural steel reach 400 level before all mechanical has reached 300 level. The entire team must recognize this and plan accordingly, making sure objects do not make it to the field if their final design will be influenced by objects not yet defined in the model. For example, steel must not be released from the 300 level before mechanical loads are known. This is not to say that mechanical must be complete to the same level, only that the loads needed to calculate the steel are true. As the model progresses from conceptual through as-built, ownership of graphical objects and their associated data may pass from one group to another. This may also involve the transition from one data format to another. It is critical that data fidelity be maintained through this process.
It is critical to have a clear definition of what is included in the information model at different points in a project's life-cycle. Understanding expectations, roles, and responsibilities is one of the most important aspects of a successful BIM-based project. To assist in this, GSA has developed several resources:
- Basic Definitions of Level of Detail (listed below)
- Detailed Object Definitions (under development)
Detailed definitions of the development of individual objects through the design life-cycle.
Assignment of the responsible party to each object across the five phases of development.
A list defining what can be done with the model at each phase of development (e.g. level 400 models may be used for exact pricing)
LOD 100 - Conceptual
LOD 100 is the beginning of a project and may not be a part of many brownfield projects. LOD 100 is very similar to the traditional conceptual design phase. During this phase, a model will be at its most primitive. The building will be sited and roughly sized, a basic site layout may exist, and some very preliminary analyses may be performed. These analyses could include whole building energy analysis, conceptual cost based on cost per square foot, and preliminary whole site construction phasing.
In some cases there may be no model data associated with LOD 100. There may only be analysis data and 2D CAD data or even hand sketches. LOD 100 is often done by GSA personnel or a different Architect than the LOD 200 level and above. When possible, any model data should be created with the understanding that it will need to move to a BIM design tool. For example, if the future design (200 & 300) will be completed using Revit, a tool which is compatible with Revit should be considered for 100 level massing, modeling and analysis.
LOD 200 - Approximate Geometry
LOD 200 is similar to schematic design and design development. It is the phase that will transition the conceptual massing model and associated data into a model ready for the creation of construction documents. This is one of the longest phases that any model will go through as it encompasses both the traditional schematic design as well as design development efforts.
At the conclusion of this 200 level, a model will contain the approximate quantity, size, location, and systematic relationships of most objects that will eventually be installed. The data about all objects will be preliminarily filled in with basic information. Although specific object information may not yet be available, at a minimum space claims for each object or system should be accounted for.
Preliminary high level coordination should be happening throughout this stage. Coordination should be focused on planning and not hard clashes (e.g. vertical space allotment for utilities not pipe-on-pipe collisions). This coordination should be cross discipline and be handled in the project coordination meetings as defined in the project's BEP.
LOD 300 - Precise Geometry
LOD 300 similar to construction documents, the phase where a design begins to accurately resemble what will be installed. Specific elements are confirmed as 3D object geometry. Object dimensions, capacities, and connections defined.
At the conclusion of 300 level, a model will contain the accurate quantity, size, location, and systematic relationships of all objects that will eventually be installed. The data about all objects will be filled in with all basic information. No space claims or rough shapes should exist for any object that will be installed (space claims to protect space for code compliance or similar will still be present).
Individual object level coordination should be happening throughout this stage. Coordination should be focused on major hard clashes (e.g. pipe-on-pipe collisions). The AE and Constructors should be involved in the coordination meetings at this point.
LOD 400 - Precise Geometry
LOD 400 is achieved when fabrication and assembly can be driven directly from the model. For most object types, the level 400 information model is created solely by the trade partners with input from the AE. It is common in this stage of development for the design information model to go dormant as fabrication models are derived from them on a different CAD platform. The tools required for fabrication level models are not the same that are needed for design or as-built models.
A key difference of LOD 400 is trade scheduling. At 100 through 300 levels, different trades are completing the stages at different times. For example, structural steel and foundations will often be at least one level above the other trades, followed by architectural elements and lastly by MEP. In LOD 400 this will change and all disciplines will align instead by physical area, such as by floor.
Coordination must continue through out the 400 phase. All parties should be included in this coordination and no fabrication should begin until the entire team agrees that an area is ready. The end result of level 400 coordination will be installation certainty.
LOD 500 - As-built
LOD 500 is the post construction as-built stage of a project. This is the final first cost stage of any project. At the conclusion of the 500 level. the model is handed over to the building's Facility Manager. The process of creating a 500 level model will often involve the integration of the 400 level fabrication model data into the 300 level model.
At LOD 500, the model will contain all building elements. They will be geometrically accurate while not showing excessive fabrication level detailing. For example, duct work will be sized correctly as installed but will not have flanges modeled. Objects will contain their actual record costs (data), purchase documentation (link), commissioning data (link), maintenance requirements (link or data), object specific data (e.g. fan CFM) as well as any other data relevant to the life cycle management of the building. Refer to the GSA Standards for specifics on the implementation of the COBie format.