that they were 4 percent more productive than did occupants of conventional buildings. The improvement in perceived health among occupants in sustainable buildings (4.25) in comparison to occupants in conventionally designed buildings (3.29) was also statistically significant.
Widener (2009) found that most of the 21 LEED-certified projects in Illinois were not tracking health-related benefits. Survey results related to occupant overall satisfaction with building comfort (light level, noise, temperature, air quality/ventilation) were available for 11 LEED-certified projects. Widener found that, overall, occupant satisfaction was high, with the highest-rated categories being lighting and air quality/ventilation. The lowest-rated category was temperature.
Studies that seek to compare the difference in design and construction costs, the so-called first costs, or the “green premium,” between high-performance or green and conventional buildings typically discuss four different types of costs: (1) the baseline costs of the project itself; (2) the marginal capital costs of some (but not all) green improvements to the project itself, such as more expensive technologies or materials, which may be offset by savings in other systems; (3) the soft costs associated with additional documentation, analysis, and evaluation, such as energy modeling; and (4) the direct costs associated with third-party certification. Those studies, however, use different methods to define the comparison group. The different methods result in different types of findings. Some studies are specific in evaluating the cost of individual green strategies on a given building, in effect using a hypothetical baseline model for the self-same building, much as energy models do. Studies conducted for the GSA and the Indian Health Service (IHS) to look at the cost differential between LEED-certified and non-LEED-certified buildings used this approach (SWA, 2004; IHS, 2006). Caprio and Soulek (2011) looked at the cost-effectiveness of various energy efficiency improvements in Army standard designs. Others reference building budgets, asking whether the green project cost more than budgeted or anticipated for the conentional equivalent; Kats (2010) used this approach. Two studies by Mattheissen and Morris (2004, 2007) used the population approach, aiming to identify whether the population of green buildings was distinguished by cost when compared to the building stock in general. The latter approach is typically used in valuation studies that identify whether green buildings sell or lease for more than the building stock in general. The different methods for calculating incremental construction costs are valid, but should not be combined.
Matthiessen and Morris (2004) undertook a study with the goal of comparing construction costs of buildings where LEED certification was a primary goal to the costs of similar buildings where LEED was not considered during design. The authors studied 93 non-LEED-seeking and 45 LEED-seeking buildings for which data were gathered from the database of the Davis Langdon Company. All costs were normalized for time and location to ensure consistency for the comparisons. Among their conclusions were the following: