BIM Basics

Robert Grupe / March 2016

Q: I’m considering working on a project where the construction documents require LOD 350. What is meant by that?

A: The design team and owner of that particular project have decided that design and ensuing construction will be done in a “Building Information Modeling” environment. From a very simplistic standpoint, BIM is the linking of information to a three-dimensional representation of that information. A more precise definition of BIM can be found in “The Contractors Guide to BIM, Edition One” from Associated General Contractors of America. It states that “a Building Information Model is a data-rich, object-oriented, intelligent and parametric digital representation of the facility …” Putting that in the perspective of an interior partition, the object can be seen as the wall itself, and the information component is all the data that relates to that wall. That would include the performance of the wall, meaning the fire, sound, structural and aesthetic features of the wall. The information then could provide detailed information on all the components that comprise that wall, including (but not limited to) the gypsum panels, framing members, insulation and even fasteners. Beyond that level of information, working in a BIM environment can provide data on scheduling and cost. During the natural course of the evolution of a project, more information becomes known. For example, depth of the stud may change, or the wall itself is moved. The BIM model has the capability or intelligence to update.
    
The term LOD means “level of development,” or it is sometimes referred to as “level of detail.” However, there is a significant difference between the two concepts. Level of detail is how much information is included whereas level of development is how much thought has gone into the information. By definition, there are essentially five levels of information. The specification that is often used to determine LOD comes from BIMForum, whose mission is to facilitate and accelerate the adoption of building information modeling in the AEC industry. It is co-sponsored by AGC and the American Institute of Architects, plus it works in a collaborative manner with other organizations such as National Institute of Standards and Technology and National Institute of Building Sciences. LOD is defined by BIMForum as,“The LOD Specification is a reference standard that enables practitioners in the AEC industry to specify and articulate with a high level of clarity the content and reliability of BIM data at various stages in the design and construction process.” The specification divides the data into six levels, each with a three-digit descriptor starting with 100, meaning these are the levels: 100, 200, 300, 350, 400 and 500.
    
Stepping back to the original analogy of the wall, the concept of LOD can be better understood when relating the wall to the different phases of construction. During the “feasibility” or “schematics” phase, very little information is known. In the case of the wall, it’s merely a line on a piece of paper. It is understood that there will be a wall in an approximate location. Materials, finishes and even spatial relations are not yet identified. Moving into the next phase, “design development,” more information has come to light. This pushes LOD to level 200.
    
At Level 200, the design calls for it to be a gypsum wall, as opposed to masonry. The overall wall thickness is set. Layouts, locations and wall heights are still flexible. Elevations are still somewhat approximations, but rough locations for doors and punched openings have been established. In some projects, this is when the project goes out to bid. In theory, at this phase, the architect’s budget estimate is accurate, derived in part from the BIM model.
    
As the project enters the construction documents phase, the wall should enter Level 300, a pretty close representation of the intended wall. Information is available at the wall interface with other building elements. Items such as back blocking are included as well as stud size.
    
Level 350, referring to the original question, has the wall almost ready for fabrication. Stud sizing, wall supports and possible kickers are called out. Required openings in the wall for mechanical, electrical and plumbing services are included. The type of interior cladding is specified.
    
Level 400 is that next step where fabrication or installation can occur.
    
Level 500 has all the elements field verified and can be considered the “as built” model. In theory, this is the level of model that is a deliverable to the owner for subsequent operation of the facility.
    
The above has been a simplistic glimpse of only one aspect of BIM. A contractor should think through the implications before entertaining any idea of entering into this world as a business venture. The concept that BIM is a process and not just a technology is very true. Understanding the contractual differences and insurance requirements is very important.
    
There is a lot of help available for the contractor who chooses to move into BIM. More information on LOD can be found at www.bimforum.org. In order to clarify this and other concepts of BIM, AWCI is set to launch its BIM—Doing It Right® education program by the end of this year.

Robert Grupe is AWCI’s acting director of technical services. Send your questions to grupe@awci.org, or call him directly at (703) 538.1611.