Module 3 - Points to Ponder

What drives a project team’s decision about floor-to-floor height?

From a developer’s perspective?

• A developer would want the minimum floor-to-floor height.
• Extra height doesn’t increase the number of units that can be sold, but it does increase material costs, which lowers profit margins.
• Shorter floors can also let a developer fit more floors within a height limit, which means more units on the same site.

From a designer’s perspective?

• A designer would value higher floor-to-floor heights because they make an apartment feel much bigger and improve quality of life in the space. T
• aller ceilings also allow taller windows, which bring more natural light deeper into the unit and, for a site like mine across from Golden Gate Park, frame the views better.

From an engineer’s perspective?

• An engineer would want to maintain structural integrity while leaving enough room above the ceiling for ducts, pipes, and other building systems.
• In my class on energy efficient buildings, we have been discussing how a building’s volume and envelope affect its energy use.
• Taller floors mean more air to heat and cool and more exterior wall area losing heat, which increases energy demand. More volume also means the HVAC system needs larger equipment and ducts, which adds cost and takes up space.
• Taller ceilings can also cause thermal stratification: warm air rises and collects near the ceiling instead of where people are, which wastes heating energy. On the other hand, taller spaces have real benefits. Taller windows let daylight reach deeper into the space, which reduces the need for electric lighting, and taller rooms can help with natural ventilation because hot air rises and can leave the building, which helps with passive cooling.
• So an engineer has to balance these tradeoffs to find a height that supports both the structure and the building’s energy performance

From a builder’s perspective?

• The builder would also likely want the minimum floor-to-floor height, because more height means more material, more cost, and more chances for construction errors, since there is more building to put up.
• Shorter floors can also speed up construction and make it simpler to repeat the same floor layout up the building.

Total carbon can now be estimated before materials are specified.

How much confidence should a team place in that number at this stage?

• Not a lot. There are still a lot of variables that need to be considered, and not all of the features are set in stone yet.
• I haven’t finalized things like the structural system, the specific materials and where they come from, the foundation, or the facade assemblies, and all of those can change the number a lot.
• At this stage I think the estimate is more useful for comparing options, like one material against another or one massing against another, than for giving an exact total.

Which decision made this week has the largest effect on it?

• This week the most important decisions were finalizing the number of floors and making sure the balconies line up, which I did by adjusting the balcony layouts.
• The number of floors has the biggest effect because it sets the total floor area and how much structure and foundation the building needs, and those drive most of the embodied carbon.
• Lining up the balconies matters too. When balconies stack vertically, the structure is simpler and needs less material than when every balcony is in a different spot and needs its own support.

How would you present it to a client without overstating its precision

• I would give the client a range instead of one exact number, and I would round it so it doesn’t look more precise than it is. I would also compare it to a baseline, like a typical building of the same size, so the number has context.
• I would be clear about the main assumptions behind it and explain that the number will change as we choose materials and develop the design.
• Mostly I would present it as a tool for making better decisions now, not a prediction of what the final building will be.

At some point a conceptual model has to stop being conceptual.

How do you know when a proposal is resolved enough to move into Revit?

• I think a proposal is ready for Revit when the big decisions have stopped changing.
• That means the massing, height, and footprint are stable, the site strategy is set (for me, the U shape facing away from the noise), the structural grid and floor heights are chosen, and the analyses are confirming the design instead of still changing it.
• Another sign is when I want to add features that Forma doesn’t have, or when Forma technically has them but they take a long time to place manually because they aren’t as developed, or there aren’t enough options.
• Once the questions I need to answer require more detail than Forma can show, like walls, assemblies, and rooms, it’s time to move.

What is the cost of moving too early? Of moving too late?

• Moving too early can lead to jumping ahead to things like room layouts before the bigger design is settled. That can cause mistakes that would have been easy to avoid, and it means spending time detailing parts of the design that might still change.
• It also makes it harder to quickly test different options, because the model is more detailed and harder to adjust. Moving too late means problems with the structure, circulation, or code might not show up until the design is already locked in, which leads to rework and schedule pressure.
• My carbon and energy estimates would also stay rough for longer, since Revit is where I can start getting more specific.

Which parts of your Forma model do you expect to survive the handoff?

• I expect the structure and dimensions to survive, along with the footprint and the overall U-shaped massing, the height and number of floors, the floor-to-floor heights, the building’s orientation on the site, and the general split of spaces.
• The facade strategy and window-to-wall ratio should carry over as the design intent, even if the exact panels don’t.
• The results from my analyses, like solar, noise, and carbon, will also carry over because they guided my decisions.
• What probably won’t survive are the exact facade panel geometry and the simplified surfaces, since those will be rebuilt as real walls, slabs, and assemblies in Revit. In a way, the handoff is partly a rebuild, not just a direct transfer.