The story is as old as 3D modeling (which actually started in the ’80s): Project teams using a Building Information Model (BIM) must share and hand off a 3D model among architects, engineers, a general contractor, and trade subcontractors at different points in that project’s lifecycle, often with none of those parties knowing exactly what they’ll hand off or receive.
The design stages of conceptual design, schematic design, and design development, for example, do not translate easily into 3D detail or into what construction professionals call a constructability model, complete with sequencing information and details such as where a worker stands to install a system in the best way.
Architects and engineers from small firms have adopted BIM to not only provide better deliverables but also to gain a competitive advantage over other firms—some of them much bigger—that can’t provide BIM detail. But how can a small firm unlock the potential of this technology without knowing what to provide to their construction counterparts and when?
In 2008, the American Institute of Architects (AIA) released AIA E202 Building Modeling Information Protocol Exhibit, its first BIM contract document. E202 contained five different Levels of Development (LOD) of model elements. As one of the first attempts at a BIM design and construction document, these definitions included language such as “Level 100: Overall building massing indicative of area, height, volume, location, and orientation may be modeled in three dimensions or represented by other data.”
Now, in association with the AIA, the BIM Forum, a multidisciplinary group of AEC industries professionals that has organized BIM conferences for all stakeholders since 2005, has added some detail to those definitions by releasing the LOD Specification (available as a draft for download).
“The key to being able to break out of this cycle is collaboration,” says James Vandezande, AIA, a principal at HOK who served on the LOD Committee’s Exterior Building Skin Group. “It’s a stepping stone to get from document deliverables to model deliverables. This particular stepping stone is the tool that levels expectations between different stakeholders and provides an apples-to-apples comparison.”
The intent of the document, as stated, is to:
- Help teams, including owners, to specify BIM deliverables and to get a clear picture of “the reliable model elements that will be included.”
- Help design managers explain to their teams the information and detail that needs to be provided within the model during the design process.
- Provide a standard that can be referenced by contracts and BIM-execution plans.
The BIM Forum Committee that wrote the LOD specification was set up as an AEC project team with Jan Reinhardt of Adept Project Delivery, a general contractor by trade, and James Bedrick, FAIA, architect and principal of AEC Process Engineering. Together, they directed a content committee with members such as Vandezande, who worked specifically on problems detailing a building project’s exterior skin. All of the domain content members had one construction professional and one designer on them so that both sides of the equation were represented throughout the writing process.
The LOD Specification defines what should be in a model at five different levels of development:
1. LOD 100: The Model Element may be graphically represented in the Model with a symbol or other generic representation but does not satisfy the requirements for LOD 200. Information related to the Model Element (that is, cost per square foot, tonnage of HVAC, etc.) can be derived from other Model Elements.
2. LOD 200: The Model Element is graphically represented within the Model as a generic system, object, or assembly with approximate quantities, size, shape, location, and orientation. Nongraphic information may also be attached to the Model Element.
3. LOD 300: The Model Element is graphically represented within the Model as a specific system, object, or assembly in terms of quantity, size, shape, location, and orientation. Nongraphic information may also be attached to the Model Element.
4. LOD 350: The Model Element is graphically represented within the Model as a specific system, object, or assembly in terms of quantity, size, shape, and orientation and interfaces with other building systems. Nongraphic information may also be attached to the Model Element.
5. LOD 400: The Model Element is graphically represented within the Model as a specific system, object, or assembly in terms of size, shape, location, quantity, and orientation, with detailing, fabrication, assembly, and installation information. Nongraphic information may also be attached to the Model Element.
These definitions add clarity to building processes and also tell software developers and third-party content creators exactly what to put into BIM objects at the various levels, meaning less time BIM and CAD managers must spend building oft-used object libraries in-house.
The final LOD Specification document is scheduled for release to the public on July 3, 2013. For more information on Levels of Development, visit the BIMForum.