LOD Specification Enhances Communication In BIM Projects


Awareness Of Detail Levels Leads To More Accurate Bids And Better Use Of Resources


The key to a successful construction project is clear communication from the initial design by the architect, through completion by the contractors. While Building Information Modeling (BIM) can serve as the communication tool between the different parties involved in a project, the transfer of information via BIM is not always seamless.

“Modeling can be very precise, but it is only effective if everyone understands the level of precision that they are receiving,” says Dmitri Alferieff, senior director of virtual construction for Associated General Contractors of America. Because people have different perspectives and different expectations, it is important to define the intent of the information in a model as it is passed from one party to another, he says.

“If the model is passed along to a person or team within the same company, there is no problem understanding the information, because they understand how the information is meant to be used, but if the model will go from an architect to a contractor, there is a need to define the purpose of the information in the model,” he says. “For example, an architect may place a table and chairs in a model to illustrate the vision for the room’s use, but there is no expectation that the contractor place a duplicate of the table and chairs in the room.” However, without a clear, universally accepted definitions of the levels of development that the model portrays, the contractor doesn’t know if the model shows “a” table and chairs, “the” table and chairs, or “this size” table and chairs, which can lead to confusion, extra time and additional cost.

In 2011, the BIMForum initiated a working committee to develop the Level of Development (LOD) Specification as a reference for practitioners in the AEC industry to articulate with a high level of clarity the content and reliability of Building Information Models at various stages in the design and construction process. The LOD schema is developed under a joint licensing agreement between AGC and the American Institute of Architects (AIA). The working group is comprised of volunteers who represent architecture, engineering, construction and other related fields. The first LOD Specification was released in 2013 and is enhanced and updated each year. The levels include:

  • 100 – basic concept design that describes geometry only
  • 200 – schematic design that includes approximate sizes and quantities
  • 300 – detailed design that includes accurate models and drawings with precise quantity, size, shape and location identified
  • 350 – construction documentation that includes detail and elements that show how building elements interface with various systems
  • 400 – model elements are presented as specific assemblies, with complete fabrication, assembly and detail information in addition to precise quantity, size, shape and location
  • 500 – model shows constructed assemblies for maintenance and operations in addition to actual and accurate size, shape, quantity, location and orientation


When the working group is focusing on a specialty area, contractors or suppliers with that expertise are invited to participate to make sure their perspective is reflected in the LOD guidelines, says James Vandezande, AIA, current BIMForum chair and senior principal and chief technology officer for HOK.

“The 2018 version adds details to our sections on vertical transportation systems such as elevators and escalators,” he says. “We brought in manufacturers of every system to provide input.” It is the perspective of designers, engineers, construction companies and suppliers on the specifications that makes them valuable, he adds.

“The expectations of designers and engineers differ from the expectations of people on the fabrication and construction side of a project, so the LOD Specification is increasingly important as the model and information moves downstream,” says Vandezande.

While the guidelines are designed to improve communication, they are not prescriptive, he points out. “We want them to be flexible so that the designer can create custom plans with LOD specifications that set the same expectation for each system as it is handed to the next level.”

David Francis, chief technology officer at ICT Tracker and formerly an MEP manager at a mechanical contractor firm, has been a member of the LOD Specification working group since its inception.

“It is important that designers and contractors have ground rules – clearly defined expectations that enable them to identify costs that should be included in bids,” he says.

When a contract outlines the level of development for models for each phase, everyone in the project realizes a reduction in costs, explains Benjamin Crosby, director of BIM for Yates Construction Company, a TEXO member.

“LOD defines how much work needs to be done at each stage of the project,” he says. As an example, he shares the story at one architecture firm when an employee misunderstood the level of detail needed and spent 30 to 40 hours modeling the pins inside locks, when all that was needed was a count and description of where locks were located and how many keys would be needed.

“When everyone in the process understands the ground rules, costs can be better managed, and BIM will generate savings,” he adds.

Yates Construction was an early adopter of BIM and the LOD Specification adds to the ability to clearly communicate with other parties in the project, says Crosby. “BIM shortens project timelines and is especially helpful on design-build projects that involve a number of different contractors, engineers and architects.”

One of the enhancements to LOD Specification is the addition of more graphics to illustrate the differences between levels, points out Crosby. “Initially, the specifications were described in detail, but no or few graphics were used. The illustrations make the differences in levels of development even clearer.”

Contractors need to be careful if the project is defined as an LOD 300 model throughout the project,” says Francis. “There is no situation in which the BIM model is at level 300 or 350 for all designers and contractors at every phase of the project.” Knowing what level of detail will be provided allows the designer and contractor to determine how much additional labor will be needed to add the details necessary for the project.

Pete Carrato, Ph.D., P.E., consulting engineer and Fellow Emeritus of the Bechtel Corporation, a member of BIMForum, agrees that understanding the LOD of the BIM model in a project is critical.

“When contractors are told that they will bid on a BIM job, they better ask for the LOD level of the model that they will be given,” he says. “Contractors need to remember that different phases of construction will have different LOD levels.” For example, concrete might be at the 300 level, but HVAC is at 200, he points out. This information is necessary so contractors can plan time and costs.

Familiarity with the LOD Specification and use of BIM really depends on the size and sophistication of the contracting company as well as geographic location, points out Carrato. “West Coast companies adopt technology faster than other regions of the U.S., and Europe is ahead of North America,” he says. “Also, contractors working on extremely complex industrial or healthcare facilities are more likely to rely on BIM than those constructing a midrise office building.”

As the use of BIM becomes more prevalent, trade contractors also need to become familiar with LOD, suggests Crosby. “Although BIM provides the greatest cost benefit to owners by reducing the overall cost of construction, mechanical, masonry and plumbing contractors can also rely on LOD specifications to help them produce more accurate bids, better plan labor costs and minimize rework on a project,” he explains. “If a subcontractor can reduce costs by 10 percent, the bid can be reduced by 5 percent and the contractor still makes a greater profit.”

Reprinted with permission from Constructor, January/February 2019, a publication of the Associated General Contractors of America.


Leave A Reply