When performing a comparative LCA of structure only, how do you address functional equivalency? For example, do you include all the other “stuff” needed to make a steel structure functionally equivalent to a concrete structure, like connection materials and fireproofing? Or for a timber structure, including the acoustic build-up?
Follow up question to this would be what good workflows have been established to capture this “stuff” if not modeled in a structural Revit model.
Hi Lauren,
Yes, I’d expect those things you list to be included. Fireproofing has a noticeable impact on embodied carbon and should be included if code requires it for steel, and the concrete topping for shear and acoustical mat on mass timber should be included if they’re likely to be needed.
I have heard the contractors often estimate secondary steel by adding 10% to the primary steel estimate early in design, so that might be a good way to cover that. In Tally you can add a multiplier to each assembly if you want.
-Kjell
Hi Lauren,
From my point of view, you should allow all the aspects you have mentioned i.e. fire protection and acoustic.
The comparison should be a like-for-like.
Mirko
I also add steel fireproofing as part of the structure.
This is a great question! Our firm is proceeding with the policy: Only include items we designed. A full LCA will require each discipline to contribute.
But how about CMU? Say a steel office building with a CMU facade. Us engineers specify the f’m, but it’s not technically structuarl, and we don’t model the walls in our revit models.
Is the CMU part of the “structural system LCA”? Will engineers reporting to SE 2050 include the CMU-based emissions? CMU impact can be significant.
Important to be consistent for establishing benchmarks.
Lauren - FYI for the Embodied Carbon Intensity Diagrams on the se2050 website we included a 2" concrete topping in the mass timber scheme because we know that it is needed in the floor package. It’s one of those tricky things because it’s not truly structural, similar to Solomon’s CMU example.
Another secondary impact of structural systems is the change in floor height. Structural steel for example often requires more floor height than CIP concrete for a like ceiling height… I don’t know where to draw the line, but the impacts on the facade can be significant. Impacts to interior partitions shafts etc also influence, but likely to a lesser extent.