the lowest cost. For buildings achieving 35 to 60 percent energy savings, each increment of energy saved came at an increasingly higher cost (plug load reduction, small-scale renewable energy, building orientation, site-specific design).

Widener (2009) found wide variation among the 15 Illinois LEED-certified projects that submitted information on construction costs. Widener concluded that similar to conventional buildings, the variation in construction costs for the LEED-certified buildings may be attributed to principal building activity and the individual project’s goals and specifications.

The Kats (2010) finding that the median premium is 1.5 percent, as compared to a notional budget, is not incompatible with the IHS finding that adding green features to a reference conventional building results in a premium of 1 to 8 percent, nor is it incompatible with the Matthiessen and Morris (2004) finding that there was no statistically significant difference between the LEED-seeking and non-LEED-seeking buildings.

CONCLUSIONS

The committee did not identify any research studies that met its criteria and that conducted a traditional benefit-cost analysis to determine the long-term net present value savings, return on investment, or long-term payback related to the use of ASHRAE standards 90.1-2010 or 189.1-2011, the LEED or Green Globes green building certification systems, or the LEED Volume certification program.

The committee did identify 15 studies that compared the energy use of high-performance or green buildings to conventional buildings. Those studies incorporated different methods, baselines, types of buildings, and sample sizes; some applied to large areas of the country, and some were specific to regions or states. Despite these variations, the 13 studies that measured actual energy used (not modeled energy) found that high-performance or green buildings, on average, used 5 to 30 percent less site energy than conventional buildings.

There was also some evidence that high-performance or green buildings used less water than conventional buildings, with average water-use reductions in the range of 8 to 11 percent.

On a building-by-building basis, however, not all green buildings achieved energy or water savings in comparison to conventional buildings. Because there was significant variability within sample sets in terms of the types, numbers, and locations of buildings, the committee could not determine with certainty why individual buildings succeeded or failed to meet the average. For those studies that looked at buildings certified at different levels of LEED, the evidence that is available is inconclusive regarding whether LEED-Silver-certified buildings outperformed LEED-certified buildings, or whether LEED-Gold buildings outperformed LEED-Silver buildings.

There was also suggestive evidence that operations and maintenance costs may be lower for green buildings, but the very limited sample size leaves the analysis results outside the range of certainty. The three studies evaluated all included utility costs (energy and water) in operating costs, so it is not possible to determine how significant the other factors were in total operating costs.

Additionally, there was suggestive evidence that high-performance buildings result in improvements in some aspects of indoor environmental quality (air quality, thermal comfort, and overall satisfaction with workspace).

Regarding the differences in costs to design and construct green buildings in comparison to conventional buildings, the studies reviewed used different methods to identify those costs. The results from the studies indicated that design and construction cost (variously defined) would range from 0 to 8 percent higher for green versus conventional buildings, depending on the method used to calculate the costs and the type of building.



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