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BIM Detailing

3D MEP Modeling

This article assumes a basic working knowledge of what BIM is and how it is used in the construction industry. To learn more about BIM, please read our article, What Is BIM.

What Is BIM Detailing?

BIM detailing is the process by which both graphical and non-graphical information are added to an existing building information model to communicate further information about the project.

At the outset of every project using BIM, a desired level of detail (LOD) for the model is determined and communicated to all project members. LOD is defined by the model’s purpose. If the model is intended for conceptualization and basic visualization, it will require fewer fine details (such as structural connections or pipe fittings) to be modeled in full detail. Modeling more detail than necessary slows project workflow and should be avoided.

On the other hand, if construction or as-built documentation is to be produced from the model, then these finer details must be modeled with accuracy. In this case, detail drawings and other supporting information will supplement the model in the construction documentation. General non-graphic information such as codes data and schedules are included here.

Once construction is set to begin, much of the detailed non-graphical information, such as fabrication instructions and model/manufacturer data, is incorporated into the model and documentation.

The required LOD increases over the project’s life as it develops from the conceptual stage to the design, construction, and operation stages. This means that BIM detailing is involved throughout the project life cycle and is key to its advancement. As the preliminary model’s details are continually refined and verified, a reliable design is eventually chosen, and construction begins.

If future phases or projects are planned, the model details can be updated post-construction with field-verified measurements and component locations. The result is a model that serves as an excellent basis for existing conditions of any future work. An accurate as-built model is also quite useful for facility management personnel as well as the other stakeholders, as all have a vested interest in the successful operation of the building.

Fabrication Drawings

BIM Level of Detail (LOD)

To promote consistency across the AEC industry for defining and communicating desired levels of detail, the LOD Specification was developed by the American Institute of Architects and BIMForum. This is commonly used as a guide in the industry. The specification outlines 6 levels of detail:

100: Model elements are graphically represented with generic shapes and symbols rather than a representation of the object’s actual appearance. Location and orientation are approximate. Dimensions are either approximate or not included. Non-graphic data/information about the element aren’t attached. This level is generally used for preliminary and conceptual design of the structure.

200: Model elements are graphically represented with generic and approximate quantities, shape, location, dimensions, and orientation. Non-graphic data/information may or may not be attached. This level is generally associated with the schematic design of the structure.

300: Model elements are graphically represented with specified shape, location, dimensions, orientation, material, and quantities. Non-graphic data/information may or may not be attached. This level is generally associated with the design-development stage of the project.

350: Everything in 300, plus the interactions and connections of building elements with the rest of the model/structure are also specified. Non-graphic data/information may or may not be attached. This level is generally used to achieve the level of detail needed to produce construction documentation.

400: Everything in 350, with the addition of detailing, fabrication, assembly, and installation information. Non-graphic data/information may or may not be attached. This level is used once construction is actually set to begin, and the fabrication, assembly, and installation information is required to proceed.

500: An as-built model. All model elements are field-verified in terms of shape, location, dimensions, orientation, quantities, and connections/interactions. Non-graphic data/information may or may not be attached.

It is crucial to define this LOD at the beginning of the project, and at which points in the project life-cycle the LOD will increase. The numbered levels don’t necessarily need to correlate to a specific project stage. What’s important is that the required level of detail is clearly understood by all stakeholders at each stage. This ensures that all scopes of work are well-defined and don’t include unnecessary work.

The BIM Detailing Process

Once the LOD is determined, the building and its elements are modeled approximately using the BIM software’s generic model components and symbols. The LOD can be increased from this point in two ways: using existing content or creating new model components. A combination of the two is often used.

Most BIM software programs provide a content library containing models of common building components and connections available to load directly into the model. These pre-modeled components may or may not provide the LOD necessary for the project. Pre-modeled components can be acquired outside of your BIM software’s native content library if necessary. Open-source content libraries and downloads for pre-modeled components are widely available, as well as content for purchase.

If a suitable pre-modeled component is not available, the component is either modeled in-place or using another compatible 3D modeling software and then loaded into the BIM. Some BIM programs have better functionality for modeling in place than others, for which it is better to model a component in a compatible program designed to create detailed 3D models. This component model is then loaded into the BIM and placed appropriately. At this point in the detailing process, construction documents are produced as the model now includes full details of each building component and its connections.

When construction commences, fabrication and installation information are included in the model using whatever combination of methods provide the clearest and fullest instruction. These methods include:

  • General notes and descriptions of the installation and fabrication processes
  • Dimensioning with fabrication tolerances
  • Exploded assembly diagrams
  • Isolated isometric views for systems
  • Bills of materials
  • Model and manufacturer information
  • And more

Modern BIM software programs have a plethora of output capabilities to provide the most possible information about the project at any time. Effective BIM detailing makes the most of these tools to drive efficient construction through reduced ambiguity and better understanding of the project for all stakeholders.

To achieve level 500, field measurements of the finished structure are taken using laser scanning and other measurement/positioning tools. The precise positional data of the actual building components is used to then update the model to reflect the as-built structure. This type of model is then used as a basis for existing conditions for any future work.

BIM Detailing Keys

The most important thing to focus on for effective BIM detailing is the current objective of the model. The objective changes throughout the project life cycle. Communicating an appropriate required level of detail to meet the objective drives project efficiency. Defining this level of detail requires discretion, and it is as important to get this right as any other part of the BIM detailing process. Modeling too much wastes valuable time, while not modeling enough results in uninformed decisions. Proper time and model management allow the BIM detailing process to advance the project efficiently with adequate information.

If you’d like to learn how MLP Consulting’s BIM detailing services can help your project, call us at (602) 296-4090. Or, complete our contact form and someone on our team will call you as soon as possible.