LOD is a means of defining the extent to which model elements have been developed, from conception in the mind of the designer through to their construction and operation. Level of Development is a conceptual framework that attempts to address the fact that model elements develop at different rates during the design process. LOD describes the relative development of individual model elements in their journey from conception to realisation. Locating an element on this evolutionary scale indicates how much it can be relied on for decision making purposes. LOD is a metric that allows project programmes and deliverables to be more clearly defined. As an industry standard, it aids communication and coordination between project stakeholders. It follows that LOD should only be used to describe model elements, not models as a whole.
LOD is a valuable project management tool. When documented in an LOD Table, it can serve the following purposes:
- As a common reference for stakeholders planning model development.
- For recording agreements made about model deliverables.
- For planning and coordinating project resources.
- For communicating project requirements to team members and organising their workflows.
- For monitoring progress against the project program.
LOD is worthless without clear definition of the model’s purpose or intended uses. The resources devoted to developing and maintaining LOD Tables should be proportional to the degree that they assist management of the project.
When implementing LOD on projects it is recommended that existing standards defining model element geometry and data content are referenced and an existing LOD Table format used to document the LOD values required for each element at nominated project milestones.
Differences between BIM and traditional paper-based methods
Paper-based documents usually offer plenty of visual clues about the precision and completeness of a design and its component parts. Sketch designs are often freehand and final working drawings are heavily dimensioned, annotated and cross referenced.
BIM, however, generally provides fewer visual clues about the relative development of model elements. Elements of identical appearance can contain very different amounts of information. One may contain nothing of significance, and another a treasure trove of information including manufacturer, model number, serial number of the installed unit, commissioning and maintenance history, etc. More significantly, geometry and data give no indication of how well developed each element is for its intended purpose, how much the author expects others to rely on them or whether they are likely to change. LOD spells this out.
|LOD 100||Conceptual||In LOD 100 elements are represented graphically with a symbol or generic representation. It is the basic level of element representation. Information of model element such as cost per square metre can be derived from LOD 200 onwards.|
|LOD 200||Approximate Geometry||LOD 200 Model Elements is represented in model with approximate quantities, sizes, locations, shape and orientation. It can be said that the elements are represented in the model as a generic system.|
|LOD 300||Precise Geometry||The model elements in LOD 300 are embodied as a specific system, object or assembly with accurate measurements of size, shape, orientation, location and shape.|
|LOD 400||Fabrication||LOD 400 includes everything consisting in LOD 300 along with detailing, fabrications, assemble and installation information. LOD 400 contains high level of detailing of model elements which is extensively used by all stake holders for efficient project management.|
|LOD 500||As-built||LOD 500 is done for the as-built structures wherein the elements in the model are field verified represented accurately in terms of shape, size, location, quantity and orientation.|
Coordination and LOD
Proper coordination of building elements is obviously a crucial part of the design and construction process. One of the significant benefits of MEP BIM Services is the ability to identify collisions or clashes between building elements during the design process so they can be resolved prior to construction. Avoiding having to resolve these problems on site can result in significant time and cost savings.
There is no point commencing detailed clash detection in the early stages of a design because so many elements are loosely defined and in a state of flux – a lot of effort would be wasted. On the other hand, it is important that potentially significant coordination problems are identified as early as possible so they can be rectified. Major clashes in a well-advanced design are always more problematic and time-consuming to resolve.
If LOD and coordination are parallel considerations of model development, how do you relate the two, and how do you specify the appropriate degree of coordination required at different stages? A metric for coordination similar to that for LOD, and a way of relating them, would be useful.
Principles of Planning Model Development
Broader, overarching aspects of a design need to be resolved before attention is shifted to more detailed aspects. The overall size, layout and form of the building needs to be well defined before the design of the structure and construction system can be progressed. The layout of fixtures, fittings and equipment in internal spaces must be defined before services can be planned in detail, etc.
Identify and rank building elements with regard to the impact changes to them have on other elements, particularly those that are the responsibility of other disciplines or Model Element Authors (MEA). For example, changing the location of a power outlet and associated cabling is less problematic than rerouting a main air supply riser. Therefore, a higher LOD would be assigned to the air supply riser at an earlier project phase than power outlets.
Differentiate elements that have more constraints affecting their placement from those with less. For example, waste pipes have to be arranged so that uninterrupted falls are maintained to risers, smaller gas and water supply pipes can be routed with much greater freedom. So, in a design development context it generally makes more sense to focus on resolving the wastepipe layout before the supply pipe layout. Likewise, large penetrations in the structure need to be located and sized accurately before small ones.
Further to the above, cast-in, embedded or recessed model elements connected to services need to be assigned a higher LOD at an earlier project phase than surface mounted or loose items not connected to services.
Highlight elements that are shared between Model Element Authors or where responsibilities shift from one party to another. Team protocols for these items may need to be defined in more detail.
Identify systems and elements that are contractor-designed (Design and Construct). The LOD of these elements at given project milestones will be determined by contractual expectations, e.g. D & C of mechanical services based on schematic design, D & C based on performance criteria only (no schematic design).
The development of information associated with a model is as important as the development of geometry and needs to be planned with care and discipline to maximise the benefits of BIM. Assess the information needed to provide the deliverables specified for each project milestone and create a plan for adding and managing this information at the model element level.
Conclusion This blog highlights how LOD a valuable project management tool and gives a short bifurcation between the different LODs. For model development, proper planning has to be taken into account and some keys strategies and mentioned above. The development of information associated with model elements is as important as the development of geometry, and is integral to its LOD. The intention of a LOD is to provide clarity and certainty about what is expected of everyone involved in a model’s development, so they can plan their work with confidence. We at Tesla Outsourcing Services have experience of providing BIM Modeling Services with different Level of Development ranging from LOD 100 to LOD 500.