It’s been more than a decade, however; the building and construction industry across the globe is still struggling to get clarity about the applicability and usefulness of Level of Development (LOD). Well, I would take up the opportunity to put across the facts in a holistic manner for the benefit of one and all. Also would appreciate, if some of the readers, across USA, Europe, Australia and Middle-East, who would want to give their inputs/suggestions, to whatsoever knowledge sharing that I attempted.
LOD - Level of Development Basics:
The measure of confidence and reliability of information at various stages is what LOD is all about. LOD filled a void and enabled project teams, those downstream particularly to understand the content and reliability of the model data may receive; but this was at the inception stage.
But the scenario changed with its wide acceptance as a standard of reliability and integration within 3D models and Building Information Modeling, fondly known as BIM. This is since when it is largely exposed to a wide plethora of interpretation associated to its applicability and usefulness.
A detailed LOD specification document published by the BIM Forum, derived on basis of AIA G202-2013 Building Information Modeling Protocol Form document, was then simplified to clarify the LOD concepts by objects and their attributes by BIM support service providers for their audiences including Architects and MEP & Structural Engineers, Land Surveyors, Real Estate Developers, Facility Managers, Consultants, General Contractors, Sub-Contractors and many more. Since then, it has been adopted by several as a default industry standard and used to design and derive contracts.
The role and use of LOD is been used, intentionally or unintentionally due to lack of knowledge, to mask the bigger challenges associated with building model data exchanges. Now a days building models are often inaccurately defined as LOD 200 or LOD 300 instead of defining the “objects a building model contains” of a particular LOD level. AEC industry needs to come to a consensus on how to exchange data effectively and consistently – across project phases – discipline to discipline basis, for geometric and non-geometric.
And it’s not that these misinterpretations are just at the level of building construction projects such as Airports, Hotels & Resorts, Hospital Building, Residential & commercial Property, Retailers, Institutional buildings etc. It has its impact even on BIM for infrastructure projects for Road, Rail, Bridges, Ports, and Tunnels etc.
BIM deliverables adapt to Level of Development (LOD – 100 to 500) with explicit state of clarity and dependability. These advancement models work for different phases of configuration, design, 3D visualization, construction-caliber quantities, scheduling, estimations, on-site production control and fabrication.
Let’s have a look at various LODs for different levels as stated by AIA:
- LOD 100: A conceptual model where parameters like area, height, volume, location and orientation are defined.
- LOD 200: A general model where elements are modeled with approximate quantities, size, shape, location and orientation. We can also attach non- geometric information to the model elements.
- LOD 300: Accurate modeling and shop drawings where elements are defined with specific assemblies, precise quantity, size, shape, location and orientation. Here too we can attach non- geometric information to the model elements.
- LOD 350: Includes model detail and element that represent how building elements interface with various systems and other building elements with graphics and written definitions. It was introduced specifically for construction coordination (clash detection etc.). It is elementarily LOD 300 with model elements added such as gusset plates, support hangers, and other components necessary to make sure the functional (LOD 300) stuff can actually be installed in the space available.
- LOD 400: Model elements are modeled as specific assemblies, with complete fabrication, assembly, and detailing information in addition to precise quantity, size, shape, location and orientation. Non- geometric information to the model elements can also be attached.
- LOD 500: Elements are modeled as constructed assemblies for Maintenance and operations. In addition to actual and accurate in size, shape, location, quantity, and orientation, non-geometric information is attached to modeled elements.
Regrettably, Levels of Development are more often been defined by reference to level of detail, which are deceptive enough as a very detailed object can be placed into the model, but it may be the wrong object or the wrong size.
The correct way of looking at or interpreting it; is to consider it to be a concept where the sum of different aspects (daic) that defines the information and geometry of each element, including:
Level of accuracy (LOa):
There are chances that a highly detailed object for finalizing the choice of construction or product as part of the design, but is of the wrong size, and hence; model development is required. I.e., you can place a highly detailed air conditioning unit in the model at an early stage to represent the approximate footprint of the final air conditioning unit, but you may encounter a situation when the same capacity unit could perhaps differ in size by 100mm or more.
Once the final product selection is made, then only the accuracy of the object is and should be determined. Considering the issue of tolerance as a part of this concept is advisable. Need of the hour is to understand that a plasterboard wall will not have the level of tolerance alike a factory assembled piece of laboratory equipment.
Level of information (LOi):
It is also fondly referred to as LOD. It needs to first define as to what all information is supposed to be supplied with each element, in order to achieve TRUE BIM, enabling its use in 4D and 5D or Facilities management. The same information can also be linked to costing information derived at the beginning of the design or the engineering information vital for further analysis.
Level of coordination (LOc):
Though not defined as a part of LOD, it certainly refers to the level of coordination with several model elements. I.e., a highly detailed window can be placed in an “architectural wall”; however, there are chances that though the window contains the correct information for a specific LOD, it might not be coordinated with the structural opening in the “structural wall”.
These specifications are meant to explain the LOD framework and standardize its applicability and usefulness, making it more fruitful as a communication tool.
It nowhere mentions what level of development is to be reached at what point during a building construction project, however; it leaves a specification of the model progression to the user of the document for future references – if required. Before concluding let’s have a look at the primary objectives:
- Assist BIM team including the owners, to specify BIM deliverables and also to specify what all is included as BIM deliverable.
- Assist design managers in explaining their teams about the required information and details that needs to be provided at various junctures in the design process.
- Provide standard as reference points by contracts and BIM execution plans.
Nowhere, do I claim that it could and should replace the project BIM Execution Plan (BIMXP), instead it is intended to be used along with such plans. It will provide means of defining models for particular information exchanges, milestones in design work plan and, of course the deliverables for specific functions as well.
About the Author: Gaurang Trivedi is engineering consultant at TrueCADD. Besides, donning multiple hats, as a website manager and marketing in charge, he also oversees the editorial content, coordinating and managing the website, its news sections, blogs and social media promotions as well.