Lies, Damned Lies and Statistics: How Important are LEED Buildings in Reducing US Greenhouse Gas Emissions?

I was intrigued by last week’s USGBC tweet (August 30th) referencing the impact of LEED buildings on US greenhouse gas reductions. They point to a chart from a 2011 report on Greenbiz.com (chart at p. 30), reprinted by the World Resources Institute in a recent blog post. Here’s the chart:

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Rob Watson wrote the 2011 report. Rob is widely know as the “father of LEED” and is a very smart guy, but he's also a very strong LEED partisan. His 2011 report, based on 2010 data, projected more than a five-fold increase from 2011 to 2020 in the impact of LEED buildings on reducing US greenhouse gas emissions. (The analysis was detailed and careful, but still made many wild assumptions based on limited data to reach its conclusions.)

Let’s take a look at the real numbers. By 2015, LEED had certified about 3.6% of the total nonresidential floor area in the US, per my book Reinventing Green Building. Assuming that commercial and industrial building operations make up about 19% of US greenhouse gas emissions and that LEED buildings cut energy use (and therefore in most cases greenhouse gas emissions) by 25%, that number would indicate a greenhouse gas reduction from LEED certified buildings of about 0.17% in 2015, about half of the total estimated in 2011. (It’s useless to try to add certified LEED homes and apartments to this total, since the total certifications to date are about 100,000, or 0.07 percent of 133 million US residences).

Annual LEED certified building area growth in the US has pretty much flatlined since 2015, so we can assume that 2020 numbers will be about five years worth of 2015 numbers. The 2015 numbers can be found in my 2016 book, Reinventing Green Building, at page 228 (in Table 3).

By taking the 2015 number of 500 million sq.ft. of LEED certified nonresidential projects, and projecting it for five years, we get a total LEED-certified area of 2.5 billion sq.ft., over the five-year period. In a total US commercial building stock in 2020 of about 90 billion sq.ft., this represents about 2.8% additional square footage. Applying the same math gives an additional 0.14% of US greenhouse gas emission reduction (2.8 x .25 x .19).

So adding up the two totals, we get a projected 0.31% reduction in US greenhouse gas reductions from LEED buildings by 2020, about one-sixth the projected amount! (To be fair, Watson’s 2011 analysis did attempt to count carbon emissions from reductions in auto commute trips caused by LEED urban design standards, but that was and is wildly conjectural. He also counts GHG reductions from onsite renewable energy use, but the fact is that LEED buildings get very little operating energy, on average, from on-site solar power.)

There are certainly issues with this analysis, not the least of which is that no one really knows if LEED buildings reduce energy use by 25%. There hasn’t been a serious (i.e., third-party) study of the long-term energy performance of new LEED buildings since one by the New Buildings Institute in 2008, to my knowledge.

And of course, we don’t know that LEED buildings are performing better, on average, than non-certified new buildings, and by how much. Increasing ASHRAE energy efficiency standards, new state buildings codes such as CalGREEN, and other variables are pushing energy use lower each year, bit by bit.

I don’t want to suggest that LEED buildings are not valuable in their own right or are not more energy-efficient than conventional buildings. I also don’t want to suggest that the green building movement hasn’t helped reduce overall building energy use by demonstrating what is possible on a “conventional” building budget, by encouraging architects, engineers, builders and owners to adopt new approaches and aim to achieve far lower building operating energy use.

The key lesson is to take all of these estimates with a grain of salt and to apply some rudimentary analysis to any claims of the carbon-reduction effectiveness of green buildings, absent any more convincing data.

Don’t you think that an organization such as USGBC that has been pushing “green buildings for all in one generation” for the past ten years should be more serious about analyzing the effectiveness of its certifications?