- The users’ perception of differences in noise levels was not statistically significant. Users in both samples of buildings perceived of slightly too much noise from various internal sources (e.g., conversations, telephones) (p. 140).
- For the sustainable buildings, all of the factors in the satisfaction category showed a significant improvement over the conventional buildings. Occupants of sustainable buildings perceived that they were 4 percent more productive than did occupants of conventional buildings. The improvement in perceived health among occupants in conventional buildings (3.29 on the 7-point scale) in comparison to occupants in sustainable buildings (4.25) was also statistically significant (p. 143).
STUDIES ON THE INCREMENTAL COSTS TO DESIGN AND CONSTRUCT HIGH-PERFORMANCE OR GREEN BUILDINGS
Costing Green: A Comprehensive Cost Database and Budgeting Methodology
L.F. Matthiessen and P. Morris. Davis Langdon Company, Los Angeles, Calif. 2004.
Matthiessen and Morris 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 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. They noted that the non-LEED buildings all would have earned some LEED points by virtue of their basic design, but sustainability had not been the intent. Among their conclusions were the following:
- Many projects achieve sustainable design within their initial budget or with very small supplemental funding. This suggests that owners are finding ways to incorporate project goals and values, regardless of budget, by making choices.
- Each building project is unique and should be considered as such when addressing the cost and feasibility of LEED. Benchmarking with other comparable projects can be valuable and informative but not predictive.
- There was no statistically significant difference [in cost per square foot] between the LEED and the non-LEED seeking buildings. The cost per square foot for the LEED-seeking buildings was scattered throughout the range of costs for all buildings studied, with no apparent pattern to the distribution. This was tested statistically using the t-test method of analyzing sample variations.
- Cost differences between buildings are due primarily to program type.
- There are low-cost and high-cost green buildings.
- There are low-cost and high-cost non-green buildings.
- Comparing the average cost per square foot for one set of buildings does not provide any meaningful data for any individual project to assess what—if any—cost impact there may be for incorporating LEED and sustainable design. The normal variations between buildings are sufficiently large that analysis of averages is not helpful.
- Closer examination of the non-LEED and LEED buildings suggests that for any building there are usually about 12 points that can be earned without any changes to design, due simply to the building’s location, program, or requirements of the owner or local codes. Up to 18 additional points are available for a minimum of effort and little or no additional cost required.