Sustainable development focuses on reducing environmental impacts throughout a project's life cycle, which includes design, construction, occupancy, and project decommissioning. This report focuses on the benefits of sustainable construction practices. To encourage contractors to use sustainable construction practices, a simple evaluation tool is proposed. The report acknowledges the contractor's role in sustainable construction and the benefits a contractor could presumably achieve through implementing sustainable construction practices. Currently, very few contractors use sustainable construction practices unless they are specified in the contract. Primary reasons for this disposition are a lack of knowledge and understanding of sustainable construction methods and a belief that sustainable construction increases costs. To overcome these barriers contractors need to be educated on sustainable construction practices and their potential benefits. Contractors could accrue several benefits from using sustainable methods, such as: savings on construction costs, increased competitiveness between contractors in sustainable construction, and reduced impact on the environment. In order to achieve these benefits, contractors need to understand what sustainable construction practices are available and how to choose the ones that will best meet their needs.
Important sustainable construction practices are: recycling construction waste; use of reusable concrete forms; use of bio-based hydraulic fluids and cleaning products; pre-planning to reduce waste; developing storm water management (SWM) plans; using bio-diesel fueled construction equipment; creating a site protection plan; and creating a construction waste and debris management (CWDM) plan. These construction practices are important because they are completely under the control of the contractor, i.e. the contractors can implement them, whether the project specifications call for them or not. Several competitive factors such as bid price, construction time, quality plan, construction program, technology plan, experience on similar projects, availability of key personnel, technology capacity, site management, and human resources can motivate contractors to implement sustainable construction practices. Any practice that improves a contractor's performance related to these factors would also improve their competitiveness and productivity.
A framework for a decision process that contractors could use to evaluate sustainable construction practices is discussed. The decision-making process is threefold - first, contractors need to be aware of the potential benefits of sustainable construction; second, these benefits need to be ranked according to importance; and finally, a process is needed to evaluate sustainable construction practices relative to the benefits. In order to evaluate sustainable construction practices, the method needs to weigh alternative construction methods with a list of criteria that would motivate contractors. To answer this multi-criteria decision making problem, an Analytical Hierarchy Process (AHP) is adopted. The AHP consists of a simple hierarchy process that allows contractors to evaluate sustainable construction methods against a set of motivating criteria. The AHP model consists of four phases:
Phase 1: Structuring the problem to build up the hierarchy
Phase 2: Collecting data through absolute scale measurement
Phase 3: Determining the priorities
Phase 4: Analysis for the solution of the problem
Figure 1: Analytical Hierarchy Process
The motivating criteria used in this study are savings on construction costs, increased competitiveness between contractors in sustainable construction, and reduced impact on the environment. The first criterion - saving on construction costs - was selected because it is generally the top concern of construction companies. Competitiveness is defined in terms of contractor's sustainable knowledge, and the final criterion - reduced impact on the environment - was selected because, by definition, the distinguishing factor of sustainable construction methods is that they have a lower negative impact on the environment. To evaluate the best sustainable construction practices, the relative importance the three motivating criteria is required. The data required to identify the relative importance of the criteria are obtained from the results of a "Questionnaire on Sustainable Construction". The purpose of this questionnaire is to determine how contractors value the different motivating criteria. Based on the results of the "Questionnaire on Sustainable Construction", relative weights (w1, w2, w3) for three study criteria are obtained. The three criteria are savings on construction costs, increased competitiveness between contractors in sustainable construction, and reduced impact on the environment. The contractors are asked to rate the relative importance of these criteria. To test consistency in the responses, the questionnaire evaluates using a Likert Scale rating of each criterion (1=extremely unimportant; 5=extremely important); a simple ranking of criteria (1=most important; 3=least important); and a pairwise comparison ("A is better than B"). The final criteria weights are determined by taking an average of these questions. Table 1 displays the results of questions in terms of percentages. Example alternative construction practices such as recycling, re-usable concrete forms, and bio-based fluids are evaluated on their contribution to each of the motivating criteria. The scores for individual construction practices are multiplied with the respective weight and a summation results in an absolute or total score for each sustainable construction practice. The best alternative construction practice is the one with the highest total score. Table 1 shows the relative importance of the selection criteria:
Results show 34%, 37%, and 29% for w1, w2, and w3 respectively. The next step is to evaluate each of these construction practices in terms of their contribution to each of the criteria. Scores (c1, c2, c3) for each construction practice are obtained through Absolute Scale Measurement. Absolute measurement is applied to evaluate alternatives in terms of their performance on each of the criteria. For this study a range of intensities is used to rate the alternatives relative to the criteria. The scale consists of three intensities (Excellent, Average, or Poor). An "excellent" rating is worth 100% of the criteria weight, "average" is worth 50% and "poor" is 25% of the criteria weight. These intensities are best determined through review of published data and expert judgment. Table 2 shows an evaluation of the alternative construction practices.
The evaluations in Table 2 are developed based on literature review and judgment of five construction experts. For this pilot evaluation, recycling would score the highest, followed by reusable concrete forms and bio-based hydraulic fluids. It should be noted that these results have not yet been validated and are provided for illustration purposes only.
The current report presents a simple approach for contractors to evaluate sustainable construction methods against a set of motivating criteria. The objective of developing a simple evaluation approach is to motivate contractors to use sustainable construction practices by supplementing information on current practices. The importance of this report is to introduce a simple approach for any construction contractor to be able to run the AHP process with her/his own set of criteria and alternatives, and be able to arrive at the best sustainable construction practices.