Less is More…more or less

When we ask users how they model and define their Revit assemblies (walls, floors, roofs) most will tell us that their libraries are made up of complete assemblies created from inside to outside.
As we move away from traditional ‘model to get the drawings’ workflows and begin to create models that are shared and leveraged beyond our own needs as architects, we start to realize that our initial approaches might need to be re-examined. For the purposes of this exercise we’ll use walls but the same principles apply to any assembly.

Thinking of a wall as a complete assembly from inside to outside seems like the logical choice but when you consider all factors a real case can be made for breaking things down a bit. It may seem counter intuitive to suggest modeling more individual walls to achieve greater flexibility but the numbers bear this out. We’ll get back to the numbers in a moment.

Look at the image below and, although a little extreme, it illustrates the difficulty when we consider how many variables affect an assembly as it moves through a building.

The core structure of a wall may have many variations of interior finish or exterior cladding. An exterior structural concrete wall might have a variety of cladding materials or systems applied to the face of the concrete. At the same time a number of interior conditions are encountered along that wall as it moves from room to room in the interior. Various combinations of furring, strapping, both insulated and non-insulated, plumbing chases, various code and structural needs come together to create a mind boggling number of variations. This doesn’t even take into account the ‘Z’ factor of various finishes not going the full height of a wall.

If we look at it in terms of a matrix that shows a series of cores and a variety of cladding/finish conditions we begin to see just how many ‘complete’ assembly types would need to be created to accommodate all conditions. The list of assembly types would be vast and users would probably find it difficult to locate the correct assembly for placement in the project and managing this library becomes cumbersome. In addition, every time a new cladding/finish material is introduced; it raises the possibility that multiple new whole assemblies will be needed.
Concrete walls at the structural core of a residential tower
Interior Finish/Cladding
Exterior Finish/Cladding
Furring and gypsum board
Concrete 200 mm thick
Furring and gypsum board
Plumbing chase with ceramic tile
Concrete 250 mm thick
No Finish
Wood Panel over furring (Lobby)
Concrete 300 mm thick
Insulated furring and gypsum board
Possible combinations when created as complete assemblies – A1A, A1B, A1C, A2A, A2B etc.  27 unique wall types
Number of separate core/finish/cladding assemblies to create those same 27 unique conditions – 9 unique wall types
In the breakdown scenario if a new finish is required only the finish assembly needs to be added to the library. It can then be ‘applied’ to any number of core assemblies with any number of finishes on the other side.

Simplifying the management of all these assemblies has added benefits when we look at the accuracy of our model and a truly collaborative BIM workflow. The structural consultant is generally not too concerned about the finishes on the interior face of a concrete wall but at some point they will be in control the structural portion of the wall. If the architect places the core concrete wall at the design development stage the structural consultant needs only to replace the architectural wall with his structural wall when linking the architect’s model. The same thinking would apply if interiors are a separate package from the shell building. Interior ‘finish’ assemblies can be placed on a separate workset, or in the case of multiple models, in a separate ID model with architecture linked in as a background.

From a design standpoint placeholder walls can be modeled well before design decisions are finalized. With careful consideration for location lines of placed assemblies, accommodating design variations and reacting to design changes can be propagated more quickly and more predictably.  

The contractor and sub trades can more easily schedule work by trades or discipline, assign task ID information for construction scheduling and, if desired, supplement the model with fabrication level detail.

At first glance when it is suggested that the user needs to place more walls or break down floor and roof assemblies into separate component parts there can be resistance. “If I need to place more walls, that’s more work for me!” It may appear that way on the surface but the numbers don’t lie.
Sometimes more is less!
Dimitri Harvalias


Dimitri is a Senior Technical Consultant and Revit Guru at Summit Technologies. He draws on over 35 years of practical experience in the AEC domain. His education as a building technologist and hands-on experience in all facets of design, construction contract administration and CAD management gives him a unique perspective on the integration of BIM technology solutions to the design and project delivery process.

10 Responses to Less is More…more or less

  1. Excellent post Dimitri – this is exactly the "argument" I am in the midst of getting through at work right now – having encountered the very same reservations (about "additional work") that you've noted. Good work!

  2. Hi Dimitri, I remember you well from the AUGI forum. You have never stopped writing good articles and opinions. I will have to agree with you Dimitri once more, for the simple reason it's BIM here we are talking about. That means you have a lot of INFORMATION to manage. You spent more time on the information process than in the design work. But that's the evolution. Even if this looks as a slow process , in the end you understand that you couldn't have solved the puzzle in a better and faster way. In this complex situation you have described, "more is less" definitely! Thanks

  3. Thanks for the comments. Others have argued that I'm suggesting that a simple stud wall with gypsum board on both sides should be modeled as three separate walls! Not the case at all. I'm advocating trying to find the largest common denominator here. Find the components of the assembly that will remain consistent along their length and that is your core assembly. Add finishes or cladding assemblies onto those to define the unique or intermittent conditions.

  4. Hi Dimitri,
    Yeah we have had to do this on some projects and I was starting to wonder if it might make sense to deliberately do it as a rule. It also allows for colour filters in plan to highlight plasterboard types or finishes. Still open question as to exactly what goes into each wall. For example for metal stud partitions – are the linings included in the wall with the studs, or is it actually 3 walls – linings to each side and the studs in the middle? Some partitions might have moisture resistant plasterboard one side, some might have it both sides… still not sure what the answer is!
    Guess it requires a lot of careful locking elements together and checking end join conditions, but on the plus side wall joins probably tidy up properly!

  5. Looking at this very problem at the moment, creating a magnitude of wall configuations to accomodate them.

    is it possible to look at it this way.

    a standard plasterboard wall would consist of three elements.

    1. plasterboard layer
    2. stud layer
    3. plasterboard layer

    could you model them individually? then join them together to become one wall, so that doors/windows etc.. can be added to the new combined wall and it would create the "door hole" in all "three" walls.

    thats the problem im trying to make work at the moment!! Any hints would be greatly appreciated.

  6. You could model them that way but, as suggested above, it depends what you are trying to accomplish. Why the need to model each layer separately? Are you looking for quantity information, assigning construction sequencing information to your model or what?
    In most cases, on the design side, modeling each layer as a separate wall type seems to me to be too cumbersome. The approach I describe in the post is primarily geared toward 'finishes' and cladding applied to either side of an assembly as opposed to individual wall elements.
    Find the commonalities and only break down the exceptions.

  7. Tagging them becomes a bit of a problem because wall layers are separate walls as far as revit is concerned.
    Also window/Door families need to be reworked for them to be able to have a variable "thickness" because they can cut openings in joined walls but the trim and rest of the geometry will only extend to recognize its host which can only be one wall.

  8. I wouldn't necessarily call the tagging issue a problem, just one more thing to rethink. In my experience I have never tagged exterior wall assemblies as complete assemblies. The approach would be that the whole assembly would be tagged as three different classifications of assembly. Core, Exterior cladding and interior finish. Each of these is typically the responsibility of a different trade, under a separate contract and certainly a different stage of construction. The tags could appear in the same set of contract docs or in separate views in separate bid packages.
    As for families hosted in these assemblies, I agree; some may require reworking to allow them to adapt to a joined wall condition but this would only need to be the case if the frame for the opening actually spanned or wrapped across the entire width of the assembly.
    Thanks for the feedback.

  9. Each situation is different and needs to be addressed based on what you have and what you want.
    If your project is a neighbors two car garage and the exterior wall assembly is exactly the same throughout, then I would create the exterior wall as one assembly. If it's a large commercial building with multiple cladding systems (masonry, metal panel, stucco) on a common structural core (steel, concrete, concrete masonry) I would likely create separate core, cladding and interior finish assemblies.
    If the BIM plan calls for different consultants to handle different portions of the assembly then that's another argument for separate assemblies.

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