Module 4 - Points to Ponder

Submitted For

How much detail should you include about wall, floor and roof composition at different stages?

Conceptual design

Preliminary design

Exterior and interior wall locations and the core (stairs, elevators, shafts) need to be established.

Floors: Generic floor slabs at each level.
Roof: A generic roof with the basic shape, showing where it sits relative to the top floor.

Design development

This is the stage where composition such as layers, materials, and approximate thicknesses, should start to be developed
Walls: Start to develop the composition

Structure, insulation, sheathing, and exterior cladding, with approximate layer thicknesses and target insulation values.

Floors: Develop the structural system (concrete, wood, steel) and add layers like underlayment, finishes, and acoustic insulation between units.
Roof: Develop the main layers

Structure, insulation, and waterproofing. Also consider drainage and any green roof or rooftop layers.

Construction documentation

All compositions should be completely developed, with specific materials and products
Walls: Completely developed

Every layer, material, thickness, and specific manufacturer product defined, plus fire ratings and connection details.

Exact slab thicknesses, finishes, fire and acoustic ratings, and specific products.

All layers, slopes for drainage, flashing details, membrane specifications, and specific products.

Many manufacturers provide Revit families for their products.

What is the advantage to the manufacturer of giving them away?

If people have the manufacturer’s products in their design, they are more likely to use them in the actual physical building. This results in higher sales and a larger profit.

What is the benefit to you of using them over the generic library families?

It’s possible to get very specific and make the model as close as possible to real life. As we observed this week, the real-life families carry accurate dimensions and performance data.
Beyond that, they also allow clean and concise documentation of all aspects and products. In turn , this streamlines communication between different teams.

At what point does it become appropriate to switch from generic to manufacturer specific?

I think it is best once the concept and design of the building are in place, usually in design development. At that point you can start to solidify the specific products that will make up the design you constructed. Switching too early locks you into products before the design is settled.

Your Carbon Insight Analysis result did not main Revit did not match your Carbon Analysis in Forma Building Design.

What accounts for the difference?

Forma works mostly from the massing and fills in default assemblies and benchmark values.
Revit’s Carbon Insight has the ability to use walls, floors, and roofs I actually model, with their real material quantities.
Not sure if they do, but its possible the tools use different carbon factor databases.
It’s also important to acknowledge that since some of my Revit assemblies are still generic, that also affects the result.

Which number would you show a client, and how would you explain the gap?

I would show the client both numbers as a range instead of one exact value.
First, I would lead with the Revit number since it reflects the current, more developed design.
Then, I would explain that each tool makes different assumptions, so the numbers are estimates rather than exact predictions. They are most useful for comparing design options and seeing which direction lowers carbon.
I believe that as the design and products get finalized, the estimate will become more reliable.

Does a more detailed model automatically produce a more trustworthy prediction?

No. More detailed does not mean more trustworthy or accurate. A detailed model can still be built on wrong assumptions or inaccurate data, and both Revit and Forma have their own variables they analyze and account for. The best check is comparing against known real-life values from actual buildings.