Whether trying to meet sustainable design requirements set by a code, standard, or rating system, does it ever feel like your projects have a way of gravitating toward the minimum threshold set by the requirements? Whether code-compliance, LEED Platinum, net zero, or anything in-between, when I have conversations about green building design and construction, I frequently hear accounts of teams contending with the minimum thresholds set for projects.
I wanted to test this hypothesis, so I examined the final LEED certification scores for 30,000 random and anonymized new building projects going back four years. The results were fascinating.
Examining the mean, median and mode
Examining the mean, median and mode of the LEED project scores tells a fascinating story.
The mean (i.e., the average value) for each certification level were three to six points higher than the minimum required for certification.
The median (i.e., the central number of the data set) for each certification level told a similar story, ranging between two and five points above the minimum.
The mode (i.e., the number in a data set that occurs most frequently) was very close to the minimum points required for Silver (+1 point), Gold (+0 points), and Platinum (+3 points). Interestingly, the mode for basic certification was 48 points, just two shy of Silver.
So, what does it all mean?
Figure 1: The mean, median, and mode for 30,000 LEED certified projects organized by certification level. Figure courtesy of author.
Holding the line in the sand: balancing requirements and resource capitals
From my own professional experiences, I'll offer a simple anecdotal explanation based on basic design principles. I am an architect, but I think this explanation carries over into any design/engineering/construction endeavor.
I think it is a simple matter of the accountability brought to bear on a team when minimum requirements are set. The proverbial "line in the sand." There is never a perfect design and although a design/engineering/construction team can claim to have achieved an "optimized" design, such a design solution does not truly exist—the reason being that no design is perfect; one can theoretically continue improving a design in perpetuity because there are always more improvements to identify and further develop. In practice, an owner establishes (or is otherwise obliged to meet) requirements for a project's design and/or performance. If the person(s) communicating the owner's project requirements does so clearly and effectively, the project's design/engineering/construction team can develop a solution that meets all those requirements without completely expending the time, monetary, and other resource capitals allocated. By this measure a team could claim a successful design—and a successful project.
However, if a project team starts designing to exceed the owner's project requirements arbitrarily then those held accountable to the time, money, and other resources spent toward the project may assert that too much is being spent—now the notion of "optimization" becomes quite relative.
Stated differently, optimizing a design will take as long as time, money and other resource capitals allow.
So back to the LEED score data. Following the logic above, one could suppose that every LEED certified project started with a LEED certification requirement. Big stretch, right? However, it is the specific project requirements that drive the design/engineering/construction effort on the project. Arbitrarily going beyond the set project requirements when time, money and other resource capitals are at stake—in the eyes of some stakeholders that is the opposite of optimization.
The data offered here seems to exhibit simple design requirements/constraint math. One very interesting observation is that the mean, median, and (especially the) mode are much higher in the basic certification range than the others. One could speculate why this is the case—perhaps more basic certified projects started with an endeavor to achieve LEED Silver but settled due to project constraints—but more data would be required to understand why the basic certification tier exhibits these higher scores. When it comes to the more challenging and expensive pursuits of Silver, Gold and Platinum, outcomes gravitated toward the minimum thresholds.
The big take-away: when it comes to meeting challenging sustainable design objectives, explicit minimum project requirements make all the difference. The line in the sand (as frustrating as it can be at times) matters.