Trending to Assemblies

Traditional construction documents were drawings and specifications - both published in paper form. The industry is trending to more electronic means of representing the construction contract requirements. Building information models are touted as the repository of all the data required to complete construction projects. But…

There is always a "but." In discussions with many architects, I keep hearing that the architects want to work in the model generically for as long as possible. This is contrary to what is perceived as the industry trend of embedding data in the model. There is a workable balance that can be used today - allowing the model to remain generic while still defining the assemblies comprising the model.

Data need not be embedded directly in the building model to be available and useful. However, for convenience the model objects should be capable of being linked to the data describing the model object.

One to Many

Specifications systems such as Speclink-e with Linkman-e and e-SPECS establish links between model objects and construction specifications. The links rely on the model object identifying specific materials forming the object. Model objects are three-dimensional assemblies, not singular materials. So a single model object will have multiple materials and therefore multiple links to multiple specification sections to describe the single model object.

Establishing these links between the model object and the specifications requires decisions - perhaps many decisions - about the components required for each object. During early design stages, architects are generally not ready to discuss individual material selections. For instance, when architects place the first exterior wall in the model, it is unlikely that the complete construction will be known. What may be known is that the wall is expected to be about 15 inches thick. The decisions about the cladding, cavity, insulation, weather barrier, and backup construction will come later, much later.

One to One

The lack of specific product selections when placing that first exterior wall object in the model does not prevent data development describing the object. The model object "Exterior Wall" can link to an assembly description via the "B2010 Exterior Walls" UniFormat assembly code contained in the Revit family properties window.

So what can be said of a generic wall assembly without knowing the components? Plenty! Think performance. What must the exterior wall do?

  • Enclose the space
  • Resist wind loads
  • Resist air infiltration and water penetration.
  • Resist thermal conductance
  • Limit outside sound transmission
  • Provide daylighting and views

The performance for each of these attributes can be defined to meet the owner's project requirements, well before the designed solution is known.

Specifiers Can Manage Data

There is no need to embed the data in the model. Simply link the model object to the file containing the data. That file can be the Preliminary Project Description (PPD). PPDs are arranged by UniFormat, just like the model objects to describe the functional elements of the project systems and assemblies.

Once the model is linked to the description in the PPD, then the PPD can make the final link to the material specifications. Let the specifier control this final linking. It's what specifiers do now, so there is no need to change. Ultimately, the material specifications may become standard documents and the project specific information will be contained in the PPD. Let the building model and the PPD work together and keep the linking simple.

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