BIM: The Challenge of Modeling Existing Conditions
by John M. Russo, AIA
The first thing an architect or engineer will request when contracting with an owner to create design drawings for renovation work are record drawings, commonly referred to as “as-builts.” However, it’s not uncommon to find that drawings don’t exist, or that the drawings that are available have not been kept up to date or validated and can’t be relied upon. It is at this juncture that an existing conditions as-built must be performed. Many times this is done in 2D, but it is becoming ever more common for designers to request this information in 3D.
When complex building geometry such as curved, non-planar surfaces is involved, it can be much more difficult to document with the required degree of dimensional accuracy. This is never more evident than when it comes to creating a three-dimensional existing conditions model or an existing conditions building information model (BIM). Fortunately, today’s technologies are making it much easier to document and represent these complex building systems in 3D and, as a result, are improving the process of design and construction for renovation projects.
Frequently, people are turning to 3D laser scanning to capture complex existing conditions. Laser scanning can capture the most complicated geometries easily and quickly. However, processing a point cloud into an accurate three-dimensional model can sometimes seem like a daunting task. Even seemingly simple geometries can be a challenge to model given the limitations of the BIM authoring software. What should take a matter of minutes can often take hours to create. And when there are dozens of such conditions on a project, it can leave the modeler, the project manager and the client frustrated with the time required to complete the model.
The length of time needed to create the model usually depends on the required level of detail and accuracy. For example, is there a need for an exact profile of a piece of molding, or can it be represented with a basic shape? If the profile is needed, it must first be extracted in 2D from the scan data and brought into the modeling program to be turned into a profile sweep. Will it suffice to use a generic family to represent an object, or will a custom family be required to show an adequate level of detail? When the software isn’t cooperating to show things as they really are, what methods can be used to finesse the software? These are questions commonly faced by modelers when trying to build a model and meet a deadline.
It is very important that the client understand that there is no “easy button” when it comes to modeling existing conditions in 3D. While the tools now exist to capture and create accurate representations of real-world conditions, there are still many challenges to overcome. Adequate time must be factored into the modeling process. However, having an accurate representation of the existing conditions will help all parties relying on the data make better decisions. This, in turn, will result in fewer change orders, fewer delays and lower risk for all stakeholders.