A SYSTEM FOR ESTIMATING RESIDENTIAL CONSTRUCTION AND DEMOLITION DEBRIS

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1 A SYSTEM FOR ESTIMATING RESIDENTIAL CONSTRUCTION AND DEMOLITION DEBRIS Authors: Ali Touran, James Wang, Christoforos Christoforou, Nasiru Dantata (Northeastern University, Boston, Massachusetts) ABSTRACT This paper describes a computerized estimating system that can be used to quantify the weight of wood, gypsum drywall, roof asphalt shingles, and carpet waste generated from new construction and demolition activities in residential construction projects. The system s main input is the housing permit statistics, usually available from various States websites. An interface is also created between a GIS system and the estimating module that allows the user to generate a spatial distribution of construction and demolition debris over a region. KEYWORDS: Construction and Demolition Debris; Building Permits; Estimating System; Residential Construction; GIS Interface INTRODUCTION The management of Construction and Demolition (C&D) debris has been a focal point in the planning efforts of Massachusetts Department of Environmental Protection (MADEP). In the agency s solid waste master plan, MADEP has set a goal of reducing non-municipal solid waste by 88% by 2010 [1]. As a step towards achieving this goal, MADEP is now planning to implement a complete ban on the disposal of unprocessed C&D debris in December of Northeastern University, under a research contract with MADEP is studying the potential impact of such policies on contractors and processors in the State of Massachusetts. As part of this effort, we are interested in quantifying the volume of several C&D materials (specifically wood, asphalt shingles, carpet, and gypsum drywall) generated in building construction every year in Massachusetts. The four items mentioned, have been selected by the State as items of high priority and it is believed that they constitute the largest share of C&D debris (especially volume wise) generated in residential construction. Furthermore, it is understood that most of the ABC (asphalt, brick, and concrete) debris are already recycled and the State intends to focus on items that are not being recycled extensively. The C&D data reported by the states in the Northeast is at aggregate levels without breakdown according to source or type. As an example, the State of Massachusetts estimates that in 1999, approximately 4.7 million tons of C&D debris was generated in Massachusetts, out of which about 20% was disposed in landfills [1]. In a recent CMRA (Construction Materials Recycling Association) meeting in November 2002 at Hampton, New Hampshire, representatives from various New England States reported approximate estimates of the total C&D waste generated in their respective States. In almost each case, they cautioned about the accuracy of the figures and further, no breakdown of the waste according to type and source was offered.

2 Efforts have been made in the past to estimate volume of various C&D debris. At the national level, the report by Franklin Associates [2] is noteworthy. This report was prepared with the support of the USEPA and provides a methodology for estimating the volume/tonnage of construction and demolition debris. While the general methodology is sound, the sample data used to estimate the waste volume is very limited. The volume (weight) of the samples is then used to estimate the quantity of C&D waste at the national level. Probably the most detailed analysis of the volume of C&D debris is the report by Reinhart, et al. [3] which discusses various approaches in quantifying the volume and tonnage of construction and demolition wastes in the State of Florida. The report correctly notes that construction practices in Florida are different from many other parts of the country (notably Northeast in our case). As an example, the extensive use of concrete blocks in Florida is not typical of residential construction practices in northeastern United States. Also, in the Northeast one expects to see a lot more demolition projects compared to Florida where the mean building age is younger than much of the nation [3]. Developing an estimating system for C&D debris that depends on routinely collected data can assist the planning and implementation of C&D policies. Given the scope of our project, we did not embark on methods that required extensive field data collection and sampling. As an alternative, we decided to make use of the existing data. For many years now, various towns and cities report the number of building permits issued. The proposed system estimates the C&D debris volume based on the number of building permits issued by Massachusetts towns. The permit data is routinely collected and can be accessed conveniently via Internet. The proposed system can then be used for various planning purposes by allowing analyst to conduct sensitivity analyses and to estimate potential tonnage diverted from landfills or directed to processing units. Market development for recycling C&D debris will depend to a large degree on the availability and consistent flow of recyclable C&D materials for foreseeable periods. Also, the decision to adopt different engineering practices, such as deconstruction, may depend on the volume of recyclable C&D materials available. APPROACH Our objective is to estimate the quantity of the following four C&D materials: wood (lumber and engineered wood), drywall (gypsum boards), roof asphalt shingles, and carpet [4]. The source of C&D debris resulting from building construction can be traced back to the following activities: (1) new construction, (2) demolition, and (3) renovation and repair projects. These projects can be classified as residential or commercial. In this paper we focus on debris generated from new construction and demolition in residential projects only. One can find the Commonwealth of Massachusetts building permit statistics at the following website: In this website, the number of building permits issued every year in various cities and towns is reported. Building permits are broken down into single unit, two-unit, three or four-unit, five or more units. Each of these potential construction projects generates C&D debris. As an example, an estimator factors in around 10% of wood to account for possible waste [5]. A waste factor of 5% for drywalls and 5% to 8% for asphalt shingles has been suggested [6]. Values of 5% to 15% waste have been suggested as estimates of construction material waste in new projects. In case of demolition projects, without source separation efforts,

3 one can consider 100% of material as C&D debris. Unfortunately U.S. Census Bureau stopped collecting demolition permit data after Because of this, Massachusetts data on demolition permits is not reported. State of Connecticut however, reports demolition permit statistics on an annual basis. We analyzed Connecticut demolition permit data and compared it with Massachusetts. The general trend in building permits in both states is similar. Furthermore, both of these neighboring states seem to be affected by the same economic factors. This allowed us to use Connecticut data for estimating the number of demolition permits in Massachusetts. Estimating Material Quantities in New Construction We have used R.S. Means data for estimating the quantity of wood, drywall, asphalt shingles, and carpet in various residential and commercial projects [7, 8]. R.S. Means is a company that specializes in publishing construction cost and productivity data. Specifically we have used Residential Cost Data (1999) for estimating C&D waste in new and demolition projects. An example of factors used for estimating these quantities are shown in Table 1. TABLE 1 Typical factors used in the proposed estimating system * 1-story average residence 2-story average residence Wood (fbm/ft 2 ) Plywood (ft 2 /ft 2 ) Drywall (ft 2 /ft 2 ) Shingles (ft 2 /ft 2 ) Carpet (ft 2 /ft 2 ) * Based on R.S. Means Residential Cost Data (1999) and converted to quantities per square foot of gross enclosed area of the building. Using these factors, number of building permits reported for various towns and cities, and type of residential buildings (number of units per building permit), we estimated quantities for the four items mentioned in Table 1. Then assuming a waste factor of 10 to 12%, we estimated the C&D volume generated from new construction. Assumptions with regard to construction types and multi-unit permits are described in [4]. Although the U.S. Census Bureau estimates that only 98% of all building permits are actually built, we did not adjust our estimate because of other uncertainties involved in the analysis. Estimating Demolition Quantities In order to estimate demolition quantities for Massachusetts, we resorted to Connecticut s demolition permit data (Table 2). The ratio of the number of demolition permits over the number of new construction was calculated for the past few years. We assumed that the average ratio for Connecticut is valid for Massachusetts as well.

4 TABLE 2 Housing and demolition permit statistics in Connecticut No. of New Building Permits 9,349 11,863 10,637 9,376 No. of Demolition Permits 1,193 2,968 2,001 1,790 Ratio 12.8% 25.0% 18.8% 19.1% This assumption is reasonable because the housing style in two states is very similar. The economic drivers for building construction appear to have impacted both states in similar manner. As an example, Figure 1 shows variations in housing permits in Massachusetts and Connecticut during It can be seen that these numbers closely follow each other. The correlation coefficient between the housing permits in the two states during this six-year period was calculated as Total Housing Permits for Mass. and Conn Total Housing Permits Year Massachusets Connecticut FIGURE 1 Number of Housing Permits in Connecticut and Massachusetts Since both states are more or less similar in terms of population density and number of older residences, it seems plausible that the number of demolition permits may vary in similar ways. We used an average ratio of 19% (using Table 2) to estimate the number of residential demolition projects for the Commonwealth of Massachusetts. RESULTS The estimating system is developed using an Excel spreadsheet. By entering the appropriate housing statistics, the system calculates quantities (in square feet) of each of the specified material. Using appropriate unit weights for the four building materials and the number and types of residential projects reported in building permit statistics data, we estimated total tonnage of C&D debris for Massachusetts for 2000 (Table 3).

5 TABLE 3 Estimates of Residential C&D for Massachusetts in 2000 Construction Demolition Total Wood (tons) 30,800 56,300 87,100 Drywall (tons) 20,100 38,000 58,100 Shingles (tons) 5,800 11,300 17,100 Carpet (tons) ,400 Totals for above (tons) 57, , ,700 Because the housing permit data is reported according to towns and cities, one can calculate a spatial distribution for the C&D debris generated. This becomes an effective planning tool for siting of processing plants, allocation of resources to C&D recycling effort, and conducting economic analysis for the C&D recycling activities. INTERFACE TO GIS We have created an interface between the estimating system and a GIS (Geographic Information System) that portrays the distribution of C&D debris according to Massachusetts s towns and cities. Massachusetts GIS data is available at By tying the volume of C&D generated in each town (which is a function of building permits) to the geographical location of each town, we have developed a spatial distribution of any or all types of C&D waste. Figure 2 is an example of this effort. In this example, darker shades identify areas with larger amounts of C&D debris. As an example of a typical application let us assume that a firm is interested in establishing a processing plant in a specific location in Massachusetts and is interested in the potential C&D volume in the area within a specified radius. The user can identify the location on the map and draw a circle with the appropriate radius on the map. The GIS will select all towns within the circle and the estimating system will calculate the total C&D waste tonnage and present a tonnage breakdown for various material types.

6 FIGURE 2 Distribution of C&D waste (wood, drywall, shingles, and carpet) in Massachusetts Towns in 2000 CONCLUSION AND FUTURE WORK Establishing prudent policies for C&D recycling and planning for the reduction of landfill disposal require reasonable estimates of C&D quantities. The estimating system developed in this work is important because it provides a systematic tool that allows rapid estimation of items of interest in the C&D waste stream. The estimate is a function of building permit statistics, widely available and routinely reported for various states throughout the country. The estimate can be prepared for various periods and locations by using appropriate building permit data. The next logical step in this effort is the verification of the estimates prepared. Unfortunately we are not aware of any source of data in Massachusetts or Connecticut on any of the building materials that we are estimating with this system. Landfill records are not sufficiently specific to allow verification of the wood or drywall quantities. Methods of direct measurement and sampling seem to be reasonable approaches that will help in verifying the system s results. Another important step is to estimate the quantity of C&D resulting from repair and renovation work. Detailed data on repair and renovation projects is collected by American Housing Survey and reported on the web page of the U.S. Census Bureau [9]. We are currently developing estimates of C&D for repair, remodeling, and renovation projects based on these statistics.

7 ACKNOWLEDMENT This project is funded by a grant from the Massachusetts Department of Environmental Protection. This support is gratefully acknowledged. We are also indebted to James McQuade and Peter Allison for their advice and contribution to this endeavor. REFERENCES 1. Beyond 2000 Solid Waste Master Plan, Executive Office of Environmental Affairs, Department of Environmental Protection, Commonwealth of Mass., December Franklin Associates, Characterization of Building-related Construction and Demolition Debris in the United States, prepared for the United States Environmental Protection Agency, June Reinhard, D.R., T. G., Townsend, H. Heck, S. Chakrabarti, K. Cochran, and S. Medeiros, Generation and Composition of Construction and Demolition Waste in Florida, Annual Report, State University of Florida, June Christoforou, C., A Systems Analysis Tool to Assist Decisions in Construction and Demolition Waste Management, MS Thesis, Northeastern University, June Reiner, L. E., Methods and Materials of Residential Construction, Prentice-Hall, Inc., 1981, p Dagostino, F.R., and L. Feigenbaum, Estimating in Building Construction, Prentice- Hall, Inc., 1999, p. 256 and R.S. Means, Square Foot Costs, 17 th Ed., R.S. Means Co., Inc., Kingston, Mass., R.S. Means, Residential Cost Data, 18 th Ed., R.S. Means Co., Inc., Kingston, Mass., U.S. Census Bureau, American Housing Survey,