Decision-Support Tool for Assessing the Environmental Effects of Constructing Commercial Buildings

Construction of commercial buildings consumes significant amounts of energy and produces lots of emissions and waste. Where should environmental improvement efforts be focused during design and construction? The Construction Environmental Decision-Support Tool allows designers and industry practitioners to quantify energy use, emissions, and waste generation rates due to the construction phase of commercial buildings. A case study of the Bren School at the University of California, Santa Barbara, and several relevant construction scenarios are analyzed. When considering the complete building over its entire life cycle, the construction phase comprised 2% of energy consumption, 1% of $\mathrm{C}{\mathrm{O}}_2$ emissions, 7% of CO emissions, 8% of $\mathrm{N}{\mathrm{O}}_x$ emissions, 8% of $\mathrm{P}{\mathrm{M}}_{10}$ emissions, and 1% of $\mathrm{S}{\mathrm{O}}_2$ emissions. This is due to the dominance of the long-term use phase $\left(50\text{years}\right)$ compared to a relatively short construction phase $\left(2\text{years}\right)$ . Scaling up to the national level, however, construction impacts of projects are significant. In each of the categories studied (temporary materials, equipment and materials transportation, equipment use, waste generation), there are actions that can be taken by designers and builders to improve construction phase environmental effects. In structural frame construction, particular areas of concern include material and equipment selection and temporary material use. Energy use and air emissions are primarily due to equipment use, which accounts for at least 50% of most types of emissions. The major contributors are concrete mixer trucks, concrete pumps, cranes, and air compressors. A single feasible decision, such as using a concrete mixer truck with a $335\mathrm{hp}$ engine instead of one with a $565\mathrm{hp}$ engine (but having the same capacity) would reduce total construction energy demand by 12%, and the emissions of CO, $\mathrm{N}{\mathrm{O}}_2$ , $\mathrm{P}{\mathrm{M}}_{10}$ , $\mathrm{S}{\mathrm{O}}_2$ , $\mathrm{C}{\mathrm{O}}_2$ , and HC by 3, 12, 8, 10, 12, and 10%, respectively. The use of significantly older equipment can have a formidable effect on construction phase emissions. In general, equipment larger that $175\mathrm{hp}$ made prior to 1996 tends to have significantly greater emissions of HC, CO, and $\mathrm{N}{\mathrm{O}}_2$ than more recent models. The majority of waste generated during construction of the structural frame consists of concrete and wood.