Earlier this week saw the release of the new LOD Specification developed by various members of the AIA. The Level of Development (LOD) Specification is a reference that enables practitioners in the AEC Industry to specify and articulate with a high level of clarity the content and reliability of Building Information Models (BIMs) at various stages in the design and construction process. With much debate surrounding the current definitions of LOD Spec in the UK, this document may be used as a reference or used to help develop a clearer and well defined LOD in the UK. This document is well worth a read through to get a good idea of what should be included in a BIM deliverable at what stage of the project. Thanks for all the effort put in from those involved writing this document.
“The Level of Development (LOD) Specification is a reference that enables practitioners in the AEC Industry to specify and articulate with a high level of clarity the content and reliability of Building Information Models (BIMs) at various stages in the design and construction process. The LOD Specification utilizes the basic LOD definitions developed by the AIA for the AIA G202-2013 Building Information Modeling Protocol Form and is organized by CSI Uniformat 2010. It defines and illustrates characteristics of model elements of different building systems at different Levels of Development. This clear articulation allows model authors to define what their models can be relied on for, and allows downstream users to clearly understand the usability and the limitations of models they are receiving.
The intent of this Specification is to help explain the LOD framework and standardize its use so that it becomes more useful as a communication tool. It does not prescribe what Levels of Development are to be reached at what point in a project but leaves the specification of the model progression to the user of this document. To accomplish the document’s intent, its primary objectives are:
To help teams, including owners, to specify BIM deliverables and to get a clear picture of what will be included in a BIM deliverable
To help design managers explain to their teams the information and detail that needs to be provided at various points in the design process
To provide a standard that can be referenced by contracts and BIM execution plans.
It should be noted that this Specification does not replace a project BIM Execution Plan (BIMXP), but rather is intended to be used in conjunction with such a plan, providing a means of defining models for specific information exchanges, milestones in a design work plan, and deliverables for specific functions.
In 2011 the BIMForum initiated the development of this LOD Specification and formed a working group comprising contributors from both the design and construction sides of the major disciplines. The working group first interpreted the AIA’s basic LOD definitions for each building system, and then compiled examples to illustrate the interpretations. Because BIM is being put to an ever increasing number of uses, the group decided that it was beyond the initial scope to address all of them. Instead, the definitions were developed to address model element geometry, with three of the most common uses in mind – quantity take-off, 3D coordination and 3D control and planning. The group felt that in taking this approach the interpretations would be complete enough to support other uses.”
via LOD | BIMForum.
Download the 2013 LOD Specification here: http://bimforum.org/wp-content/uploads/2013/08/2013-LOD-Specification.pdf
When designing Revit families, you have to always keep in mind the level of detail you are putting in to your families, and the affect this will have on the performance of your project. When you have a large project with numerous families you may notice that your Revit starts to run slower, even when you are doing tasks unrelated to the detail of the project e.g. printing. One of the reasons for Revit “under-performing” could be the visibility settings setup or level of detail of families in a project.
It is very important when creating your families to keep this in mind, and to set up visibility settings for each one as you make it (One for coarse, medium and fine levels of detail). Once it becomes a habit to do this it is a quick process. Although going through all your old families and tidying them up may be a large job if they have not been designed correctly in the first place.
The idea is simple, how you decide to implement and set rules for detail is your decision. For this example, I am going to take one of the furnishings in the default Revit library called: Dresser – Detailed.rfa. Despite the name, this is a fairly simple and “undetailed” family – but for example purposes it will work just fine.
Open the family in Revit – by default the family does not have any visibility settings applied aside from the default sketch for plan view. We now want to begin to setup the family so it is suitable for each level of detail in the project. First thing you want to do is to decide how you want the family to be split up, for this example I am not applying any rules, just setting it up with 3 levels.
As you can see in the image above, I have selected the drawer fronts of the desk, selected visibility settings in the Mode tab and unticked Coarse and Medium. This means that when you are in a Revit project, the draws will not show up unless it is set to Fine detail.
Go through the rest of the family and split the elements up in to levels. When I am working in Revit 90% of the time I am working with Coarse detail set as this will leave only the bare bones of my families – just for a geometrical representation. I have found that switching from Coarse to Fine significantly slows down my projects, especially when I have a huge projects with thousands of families.
Above you can see how I have set out my desk family with 3 different levels of details. For a family which is as simple as the above desk, creating 3 distinct levels of details like this may be slightly over the top. In a normal case I would have kept Medium & Fine detail at the same level due to the lack of difference between them.
Although for representation purposes you wouldn’t want to have displayed the desk on the right in any sort of small scale elevations where you can actually see the details of it – It comes in useful for example in a 1:200 cross section where the desk would only be printed as a small block of colour, but Revit still has all those details stored in it when you zoom in – Therefore using resources which do not need to be used.
This is not only a good exercise to implement in all your future Revit families, but is well worth doing on old families which you regularly re-use. You will notice a increase in performance on large projects where you have the same families repeated hundreds of times.