Construction costs comparison between green and conventional office buildings

The actual construction cost of certified green office buildings in New Zealand is compared with conventional buildings. Although a large body of research exists on the financial and environmental benefits of green buildings, there is little evidence on capital cost implications for building green. This study serves as the first empirical study to analyse detailed cost plan data in New Zealand to quantify the impact of green building on construction cost. Data from 17 Green Star NZ v1-certified office buildings were paired with a set of modelled cost estimates derived from the Davis Langdon Blue Book and the Rawlinsons New Zealand Construction Handbook (the authoritative published sources for New Zealand construction cost data). The paired data were analysed across five panels using the non-parametric Wilcoxon matched-pairs signed ranks test. When benchmarked against the modelled costs, green building construction costs were higher on average, but the difference was not statistically significant. This was true across all five panels tested: the entire green building dataset, mid-rise buildings, high-rise buildings, 4 Green Star-rated buildings, and 5 and 6 Green Star-rated buildings. Each panel featured buildings that were above comparative costs as well as several whose actual costs were below modelled estimates.