responses from occupants of 475 buildings (CBE, 2012). As of 2011, the Usable Buildings database contained surveys of occupants of 500 buildings in 17 countries (Baird et al., 2012).
Studies on high-performance or green buildings use a wide range of definitions to describe the criteria/attributes of the buildings being evaluated. In some studies, green buildings are defined as Leadership in Energy and Environmental Design (LEED)-certified. In others, the green building sample may include a mix of LEED-certified buildings, LEED-registered buildings, buildings receiving industry awards, and buildings designed with energy efficiency as an objective. This variance in definitions, like the variance in baselines, makes it difficult to objectively compare the results of one study to another.
• Types of buildings and sizes. Each of the studies reviewed included a variety of building types in the sample sets for green buildings, ranging from office buildings to schools, hospitals, and laboratories to courthouses. Different building types and different building sizes incorporate different types of mechanical and other systems to meet differing needs in terms of hours of operation (24/7 or weekdays only), use, intensity of use, number of floors, and other factors. Generalizing findings across a mix of building types and sizes introduces another set of confounding factors that prevent an apples-to-apples comparison across studies.
Given those factors, the factors identified in Chapters 1 and 3, and a 6-month time frame to complete its work, the committee determined it would need to focus solely on the main purposes of the statement of task. For its evaluation of the research literature, the committee determined that it would rely on studies that met the following criteria:
• Time frame. The committee relied on studies published in 2004 or later because the first studies evaluating the incremental costs of LEED-certified buildings were published in 2004. The first evaluations of a sample of at least six high-performance or green buildings were published in 2006.
• Robustness. The committee focused on studies with clearly stated objectives, a clearly defined methodology, findings based on empirical data, and a sample size of at least six buildings. The committee relied more heavily on those studies that reported measured results for energy (utility bills) than on modeled or predicted results, because the committee believes that data from actual buildings will be more reflective of the type of results that DOD can expect from its high-performance buildings.
Because the number of green buildings is increasing each year, more recent studies can incorporate larger sample sizes from which to make comparisons. Larger sample sizes can help to eliminate some factors of bias, error, and chance that are prevalent in individual case studies, although such factors may still be present.
• Relevance to the DOD operating environment. The research literature on high-performance and green buildings includes a number of reports that analyze the market and price effects of LEED or ENERGY STAR®3-certified buildings (primarily office buildings) compared to conventional buildings in terms of rental rates, vacancy rates, turnover ratios, appraised value, and other factors (Miller et al., 2008; Chappell and Corps, 2009; Dermisi, 2009; Fuerst, 2009; Fuerst and McAllister, 2008; Fuerst et al., 2010; Conlan and Glavis, 2012; Eicholz et al., 2009, 2011). These studies are of value, particularly to the private sector and to federal agencies such as the General Services Administration (GSA), which secures commercial space for other agencies. However, because DOD primarily owns and operates its facilities for 30 years or longer, the committee did not analyze these studies in detail, because market-related factors such as rental premiums and appraised value are not directly relevant to the DOD operating
3 ENERGY STAR® is a labeling program for energy-efficient building-related products and equipment. It is not a green building certification system.