Embodied carbon decisions in early design
The structural system, the massing, and the materiality of a building are often determined before there's BIM. Early phase carbon assessment keeps these early decisions on track.
Which decisions get made before there’s BIM?
Long before there’s a BIM model, a design team usually settles the big moves. It decides whether to keep the existing building, how much floor area to build, and how much of it goes below grade. It picks the structural system and the grid. It sets the massing and the materiality, including how much of the facade is glass.
Each of those decisions sets how much material the building needs. The facade is specified per square foot of wall, and the massing sets how many square feet of wall there are. The structure is designed floor by floor, and the massing sets how many floors there are, how tall each one is, and how many sit in a concrete box underground. When the client signs off on a scheme, the team has committed to much of the material in the building, months before anyone writes a specification.
When does carbon assessment usually happen?
Conventional carbon assessment usually happens at the end of design. A life cycle assessment needs a bill of materials, and a bill of materials comes from a design that is mostly done. The report arrives in design development or later and describes decisions the team made before there was a BIM model. By then, changing the answer means redrawing the building.
C.Scale started in 2020 as a research fellowship at EHDD, to find a path to Climate Positive on every new project the firm took on. The question was whether early phase carbon assessment could keep the earliest decisions on a project on track, when data is scarce and the potential to cut emissions is highest. The first real test was the proposal for the AIA’s national headquarters, and the detailed assessment near the end of construction documents landed within 5% of the proposal-stage estimate.
What does it cost to change course early?
Changing course early costs very little when the change is planned. RMI’s study with Skanska found embodied carbon reductions of 19 to 46 percent in a mid-rise office, a multifamily building, and a tilt-up building, using low-cost and no-cost measures that added less than one percent to construction cost. Those measures only work if they’re on the table early. Early phase carbon assessment keeps them there, while they’re still cheap to adopt.
What does early phase carbon assessment need to do?
It has to keep pace with the design. In C.Scale a project starts from six inputs (name, year, location, use, number of levels, and area), and the model builds a whole life carbon baseline from them. A team can have the baseline and three scenarios in about ten minutes, in the same week it is testing massing options.