Working link to your Revit cloud model in Forma Data Management.
Working link to your Individual Forma Board
*Individual Forma Board is shared with everyone on the teaching team
DF sheet set at D size, 30 by 42 inches, six sheets. Delete any blank sheets.
Screenshot of your Insight result alongside your Week 3 Forma result.
Week 4:
Week 3:
Design memo of 300 to 400 words: what survived the handoff, what you rebuilt, what assembly choices you made and why, and where Revit and Forma disagreed.
What survived the handoff
The basic massing and structure.
What I rebuilt
- Stairs. The stairs came in from Forma with two railings, so I rebuilt them in Revit with one.
- Shafts. I rebuilt these in Revit.
- Commercial base. I had to re-export from Forma. Forma modeled the commercial level as a basic building and the residential floors as a line building, so Revit treated them as separate elements.
Assembly choices
Baseline wall (R-19): clapboard, air barrier, ½" plywood, 5½" glass fiber batt, vapor retarder, ½" gypsum.
More Sustainable wall (R-33.2): clapboard, 3" wood fiber board, air barrier, ½" plywood, 5½" dense-pack cellulose, vapor retarder, ⅝" gypsum.
I chose the more sustainable wall for these reasons:
- Performance: Studs cover 20–25% of the wall and conduct heat about three times faster than insulation. The continuous wood fiber board covers them, so the wall performs at about R-28 effective, nearly double the baseline's roughly R-15.
- Materials: Cellulose is mostly recycled newspaper, and wood fiber board is made from wood waste and stores carbon. Glass fiber requires high-temperature melting.
- Right-sized: An R-40 version with 5" of board saved only about a quarter as much heat loss as the step from R-19 to R-33. Using 3" of board cut board use by 40% and kept the walls thinner.
- Moisture and air: The vapor-open wood fiber lets the wall dry outward and keeps the sheathing warm, which reduces condensation risk in San Francisco's foggy climate. Dense-pack cellulose fills the gaps batts leave, which cuts air leakage.
Tradeoffs: The walls are 3â…›" thicker and cost more upfront. Wood fiber is also combustible, so on a 6-story building it may need fire approval or a switch to mineral wool.
Roof (R-33): white TPO, ½" stone wool cover board, 7½" tapered stone wool, vapor retarder, 6⅞" CLT. This matches the wall R-value. Stone wool is noncombustible and holds its shape under solar racking, and the taper drains water. The white TPO reduces heat gain and keeps the panels cooler. The CLT stores carbon and can be left exposed as the top-floor ceiling.
Where Revit and Forma disagreed
- Stairs: The two-railing stairs from Forma had to be rebuilt in Revit with one railing.
- Material data: Revit first reported the baseline wall at R-43.4 because of an unrealistic batt conductivity. I corrected the value to 0.28 btu·in/(hr·ft²·°F). Revit's outputs are only as reliable as its material data.
Carbon and Energy: Forma vs. Revit
- Revit estimated 1,068,272 kgCO₂e of embodied carbon, 64% less than Forma’s 2,955,997. This is likely because Revit uses my actual assemblies (cellulose, wood fiber, CLT), while Forma uses default materials.
- Forma also modeled the windows as basic double- or single-pane glazing, which I wouldn’t use in this building, so even the week 4 Forma results don’t reflect my actual window design.
- Concrete slabs on grade are still the largest source, at about 330,000 kgCOâ‚‚e, so a low-carbon concrete mix is the next improvement to make.
- Revit’s energy use intensity was about 54% higher than Forma’s (44.76 vs. 28.98 kBtu/ft²). Cooling accounts for 21.54 kBtu/ft² of it, nearly half the total. That’s surprising in San Francisco, where summers are cool and foggy and many homes have no air conditioning. The likely causes are my large window area letting in solar heat, and my highly insulated, airtight envelope.
- To elaborate on this, heating is only 2.26 kBtu/ft², which shows the envelope works but now holds too much heat. To reduce cooling loads, I plan to use triple-pane, low-SHGC glazing to limit solar heat gain, add exterior shading on the south and west faces, and include operable windows so cool, foggy outdoor air can provide natural ventilation instead of demanding cooling from an AC system.