In recent project audits and reviews I noticed a few projects that had disconnected and un-parametric elements and objects to represent very simple model elements. A toilet, for example, with a separate drafted floor plan and 3d/elevation view.
It was explained that this was done to show the manufacturers specific dimensions, shape and style in plan. Although there are ways change or override an objects plan symbol to show exactly what is perceived as necessary, this raises a much bigger question. What really is necessary in a drawing/model element? We may want a plan symbol or elevation of an element to match identically to a manufacturers drawing, but is that really necessary? I would say an exact graphic representation to a manufacturers spec is very low on the priority list for a BIM element, at least in most cases.
So what are the priorities for a BIM element? We can assign a hierarchy of what a BIM element should represent to better understand.
- A BIM element needs to be parametric with a single element representing all views. Without this criteria being met before all else, the drawings are prone to redundancies and inconsistencies, and we loose almost all efficiencies of a BIM model and BIM process.
- A BIM element should match the overall size of the manufacturers specifications. This ensures that critical clearances and space requirements of a specific model element are met. This is overall dimensions; because a basic 3D cube with an associated plan symbol may meet criteria #1 and would be far superior to disconnected 2d plan and elevation views of an element.
- A BIM element should be placed in the correct location as its overall dimensions relate to the space it will be installed/built in. It should be in the correct location in plan, elevation and 3d views to show its relationship to all other model elements.
After these criteria are met, an element will be consistent in all views, it will be easily managed, maintained and edited, it will represent the correct size and represent the design intent. Anything else a model element requires is not a project need, but simply a “want” of the designer.
What does this all mean? Simply that in most cases we do not need a manufacturers specific element. Rather we need a generic element that represents the manufacturers size and the designed location of an element.
The toilet, as in the initial example, could be a basic out of the box ARCHICAD toilet that was set to the manufacturers size and placed correctly in plan. This would be enough to convey the design intent and document the building sufficiently.
There may be some obvious additions to the hierarchy above, but rarely if ever should these take priority over the needs of a BIM element.
- Elements that are not part of the documentation, such as furniture or decoration used for visualization only may not require much thought towards what the plan or elevation views look like, but only need to show a quality 3d view. Elements that are placed only for BIMx or renderings would be a waste of time to build a correct plan symbol and parameters for listing into the element.
- Elements that require a manufacturers specific appearance to properly leverage a models visualization to make selections. Appliances and plumbing fixtures may meet this exception, but these elements should also be modeled so that their plan symbol, elevation view and 3d representation may meet the BIM element criteria above.
- An element that needs a higher level of accuracy to show relationships to finishes may require additional criteria, but may not ignore the top 3 criteria listed above. For example, a wall mounted faucet may need to show relationship to grout joints. So an additional element criteria would be manufacturers detailed dimensions. For this type of element all other criteria must be met; which means a custom object would need to be built or downloaded to maintain the integrity of the model.