International Construction Specialty Conference of the Canadian Society for Civil Engineering (ICSC) (5th : 2015)

An empirical study on the sustainability of panelized residential building construction in Canada Li, Hong Xian; Yu, Haitao; Gül, Mustafa; Al-Hussein, Mohamed; Chmiel, Dawid Jun 30, 2015

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5th International/11th Construction Specialty Conference 5e International/11e Conférence spécialisée sur la construction    Vancouver, British Columbia June 8 to June 10, 2015 / 8 juin au 10 juin 2015   AN EMPIRICAL STUDY ON THE SUSTAINABILITY OF PANELIZED RESIDENTIAL BUILDING CONSTRUCTION IN CANADA Hong Xian Li 1,4, Haitao Yu2, Mustafa Gül3, Mohamed Al-Hussein1 and Dawid Chmiel1  1 Hole School of Construction Engineering, Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada 2 Landmark Group of Builders, Canada;  3 Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada; 4 ho8@ualberta.ca Abstract: Panelized construction offers benefits to the construction industry including energy savings and reductions in carbon emissions and waste. This research addresses the sustainability of panelized residential construction during the framing phase, which consists of panel fabrication in the plant, transportation to the site, and on-site assembly. This study is conducted in collaboration with Landmark Building Solutions (LBS), a panel manufacturer in Edmonton, Canada. Two tasks with respect to assessing the sustainability of panelized construction are carried out in this research: (1) The positive impact of panelized construction on the construction schedule is evaluated by utilizing archived schedule data. In this task, the cycle time of framing for panelized construction is investigated; the results are compared with those of conventional stick-built construction, and the impact of framing cycle time on on-site winter heating is addressed. (2) The benefits of panelized construction are measured in terms of construction waste reduction by quantifying the recyclable and non-recyclable waste. The results are compared with those of the stick-built method, and the impact on embodied emissions in material waste is addressed. The primary data source is archives of the industry partner, including accounting records and construction records. A literature review and comparison are carried out to provide the necessary context for achieving the research objective. The preliminary results support the sustainability of panelized construction compared with the conventional stick-built method. 1 INTRODUCTION  Off-site construction has received wide attention due to benefits such as accelerated schedule, improved quality, decreased material waste, and sustainability in terms of energy savings and emission reductions. This research aims to evaluate the sustainability of panelized construction in terms of construction cycle time (operational carbon emissions from the construction process) and construction waste (embodied carbon emissions of materials). The carbon emissions are neutrally indexed in order to evaluate construction sustainability. Construction carbon emissions associated with construction, it should be noted, comprise operational emissions from the construction process and embodied emissions of materials. Operational emissions refer to the emissions from construction activities, while embodied emissions are indirect/upstream emissions associated with the building materials used, such as manufacturing of the equipment used in production or transportation of raw materials. In specific, these include emissions from the following: (1) extraction of raw materials; (2) raw material transportation to material processing plant; (3) building material manufacturing in plant; (4) building material transportation 009-1 to the site; (5) construction on site; (6) operation and maintenance; and (7) demolishing, disposal, or recycling (Inui et al., 2011). The entire process is known as “Cradle-to-Grave”, and the corresponding emissions are referred to as “Cradle-to-Grave” emissions, among which those phases from raw material extraction to material leaving the manufacturing plant are specified as “Cradle-to-Gate”, including emissions from stages 1 to 3. “Cradle-to-Gate” is the domain most commonly used, and the one used in this study.  Li et al. (2014) quantified and compared the direct (construction operation) and indirect (embodied) emissions from panelized and stick-built construction, and concluded that the use of the panelized construction method reduces overall emissions by 42.76% compared to the stick-built method. They also found that on-site winter heating accounts for 34% and 50% of the measured emissions for the panelized and stick-built methods, respectively. The key aspect of panelized construction that leads to reduced emissions from on-site winter heating is the reduced cycle time of construction. Panelized construction is also proven to reduce wood waste from construction. Mah (2011) investigated the waste generated from the framing of residential buildings, and found that an average of 1,400 kg of waste is generated from the framing of a single-family home using the stick-built method, among which 89% is wood waste. Monahan and Powell (2011) investigated panelized timber frame construction, and found that there was a 34% reduction in embodied carbon when compared to traditional construction methods. In this research, to further investigate the benefits of panelized construction, the construction cycle time and generated waste associated with panelized construction are studied and compared with those associated with the stick-built method.  This research uses a case study to investigate differences in operational (direct) energy and emissions between the two methods with regard to winter heating. This case study is unique in that it reveals differences between the two methods specifically in a cold weather climate. Further investigation leads to a greater understanding of the differences in methods with respect to winter heating and waste, using environmental metrics such as embodied energy and embodied emissions as the indices. Embodied energy and emissions are summations of all the energy and emissions related to all materials, transportation, and construction up to the framing stage, i.e., the energy expended and emissions emitted from the upstream of the framing stage along the value chain.  2 RESEARCH OBJECTIVE  The aim of this research is to address the sustainability of panelized residential construction in the framing phase in terms of construction cycle time and construction waste. The research objective encompasses the following two tasks: 1. Evaluate the benefit of panelized construction in terms of construction schedule: In cold regions, on-site winter heating is a primary contributor to energy consumption and carbon emissions. Construction cycle time, in turn, is the determining factor for on-site winter heating duration. In order to assess the benefits of panelized construction, the average framing cycle time of panelized construction is evaluated based on archived construction records, the results are compared with those of stick-built construction, and the impact of framing cycle time on on-site winter heating is addressed using operational (direct) and embodied energy and emissions. 2. Measure the benefits of panelized construction on construction waste: Material waste is another important factor influencing the sustainability of construction. In this study, the waste generated with the state-of-the-art technology is categorized into recyclable and non-recyclable and then quantified. The results are compared with those of the stick-built method and the impact on material embodied energy and emissions is addressed. To achieve the research objective, the required data is obtained from: (1) the industry partner’s operation records for 2013, including accounting and construction records, and (2) construction schedule records for January, 2011 to April, 2013. A literature review and comparison are also carried out. 009-2 3 CONSTRUCTION CYCLE TIME  Corresponding to the manner in which the current state-of-the-art technology is utilized, the milestones in the residential construction schedule are date to field, framing start, siding start, drywall boarding, finishing stage 1, and possession date. Based on the construction schedule records for January, 2011 to April, 2013, the cycle times of panelized and stick-built construction are given in Table 1, Figure 1, and Figure 2.  Table 1: Cycle time of panelized and stick-built construction Construction Method Construction Cycle Time (Calendar Days) Date To Field – Framing Start Framing Start – Siding Start Siding Start – Drywall Boarding Start Drywall Boarding Start – Finishing Stage 1 Start Finishing Stage 1 Start – Possession Date Total Stick-built 35.8 51.2 19.0 59.0 42.8 207.8 Panelized 36.8 27.2 33.8 23.7 69.5 191.0  Sample Size Stick-built 84 70 59 34 20  Panelized 75 67 57 63 61     Figure 1: Stick-built construction cycle time profile Figure 2: Panelized construction cycle time profile The cycle time comparison between panelized and stick-built is graphically represented in Figure 3. Regarding construction schedule, the main difference between panelized and stick-built construction, which has to do with the construction technology used, is the span from framing start to siding start; other schedule differences are primarily determined by the business process and coordination of residential construction and are not specifically tied to either panelized or stick-built construction. Regarding the identified span during which there is a notable difference between the two construction methods, panelized construction is associated with a 47% reduction in duration from framing start to siding start compared with stick-built, as shown in Figure 3. 009-3   Figure 3: Cycle time comparison between panelized and stick-built construction Construction cycle time has a major impact on on-site winter heating in cold regions. In cold regions, winter heating accounts for the largest portion of energy consumption and carbon emissions during the framing phase. On-site propane heaters operate 24 hours a day, 7 days a week, and are refilled by a 5-ton truck every 3 days on average in winter. The heating season in Alberta is about 6 months in duration, i.e., winter heating is occurring 50% of the time. However, the nature of panelized construction shifts many outdoor construction activities to a more efficiently heated indoor environment, which markedly reduces the use of on-site winter heaters. As well, panelized construction reduces on-site assembly cycle time, thereby reducing winter heating time.  The common practice within the residential construction sector is to install a 100,000 Btu propane heater in the basement once the foundation has been backfilled. The hourly propane consumption is calculated as Equation 1, and the diesel consumption of the truck carrying out the propane refill is assumed to be 20 L per instance.   Where: Ph is hourly propane consumption (L/hr); CC is converting coefficient from BTU to MJ, 0.0010551; HV is heat value of propane, 25.3 MJ/L (Natural Resources Canada, 2010);  Based on the above calculation, the assumption regarding propane tank refilling, and the recorded cycle time, propane and diesel consumption per house is calculated for panelized and stick-built construction as shown in Table 2. Furthermore, to measure the impact of using the panelized construction method on winter heating, (as a result of improving the productivity of the process and reducing the idle time between framing and the downstream construction activities), the winter heating period for the purpose of comparison is defined as the span from framing start to siding start. The propane and diesel used for winter heating entails: (a) operational energy and emissions, which can be calculated using Equations (2) and (3), and (b) embodied energy and emissions, which can be calculated by means of Equations (4) and (5). 009-4 [2]  [3]  Where: E is operation energy (MJ); CO2 is CO2 emissions (kg); F is the amount of Fuel (L); HVF is heat value of fuel: the HV of propane is 25.3 MJ/L (Natural Resources Canada, 2010), and the HV of diesel is 38.68 MJ/L (National Energy Board, 2015); EF is the operational emission factor of fuel: the EF of propane is 1.51 kg CO2/L and the EF of diesel is 2.663 kg CO2/L (Environment Canada, 2013)   Where: EE is embodied energy (MJ); F is fuel consumption (L); EF is the embodied energy factor: the EF of propane is 26.44 MJ/L, and the EF of diesel is 45.7 MJ/L, ECO2 is embodied CO2 emissions (kg); EEFF is the embodied emission factor of fuel: the EEFF of propane is 0.22 kg CO2/L and the EEFF of diesel is 0.57 kg CO2/L (Energetics, 2013).  The operational energy and emissions of winter heating calculated based on the above methodology are shown in Table 2, and the embodied energy and emissions are shown in Table 3. Table 2: Operational energy and emissions of winter heating   Winter Heating per House % of Houses Need Winter Heating Emission Intensity (kg/ft2) Energy Intensity (MJ/ft2) Cycle Time (Days) Total Propane Consumption (L) Diesel Consumption for Refill (L) CO2 Emissions (kg) Energy (MJ) Panelized Construction 27.2 2722.2 181.3 4,593 75,943 50% 1.44 68.13 Stick-Built Method 51.2 5124.1 341.3 8,646 142,952 50% 2.70 241.41 Table 3: Embodied energy and emissions of winter heating   Winter Heating per House % of Houses Need Winter Heating Emission Intensity (kg/ft2) Energy Intensity (MJ/ft2) Cycle Time (Days) Total Propane Consumption (L) Diesel Consumption for Refill (L) CO2 Emissions (kg) Energy (MJ) Panelized Construction 27.2 2722.2 181.3 707 80263 50% 0.22 25.08 Stick-Built Method 51.2 5124.1 341.3 1331 151083 50% 0.42 47.21 4 CONSTRUCTION WASTE  Construction waste is another important metric of construction sustainability. Based on the assumption that the net materials used in a house are the same for both the panelized and stick-built methods, the waste difference determines the difference in embodied emissions of materials between panelized and stick-built methods. The wood waste of panelized construction consists of waste generated in the plant 009-5 and waste generated on site. The on-site waste accounts for only a small proportion (0.036 in this case) of the overall waste for panelized construction, so only the wood waste generated is considered in this research. To measure the sustainability of panelized construction, the waste generated is collected by reviewing accounting records, as shown in Table 4; Figure 4 shows the amounts of wastes shipped out from the manufacturing facility in 2013.    Figure 4: Wood product waste and other waste in plant The nature of panel fabrication in a plant provides the opportunity to optimize material usage and reduce material waste. Furthermore, several measures to reduce waste were implemented in 2012. Currently, all lumber and engineered wood for framing is precut by computer numerical control (CNC) saws, which have the ability to optimize cutting for multiple panels. As a result, the waste in the plant is less than with the stick-built method. The waste generated under the current approach is illustrated in Figure 5 to Figure 8.   Figure 5: Lumber waste at CNC sawing station Figure 6: Wood blocks from lumber cut-offs kg 009-6   Figure 7: OSB cut-offs from CNC panel saw Figure 8: I-Joist cut-offs Usually the floor joists are cut from 60-ft standard length I-Joists, which are purchased directly from manufacturers; accordingly, more than 70% of the total wood product waste generated in the plant is I-joist cut-offs. In the case of the stick-built method, I-Joists are precut by the material supplier before they are shipped to the site, and the waste in houseware is not included in the scope of the stick-built method; to be consistent for panelized and stick-built methods, it is therefore necessary to deduct the corresponding amount of waste associated with this process at the supplier’s warehouse from the waste calculated for panelized construction. Table 4 shows the adjusted waste amounts of the panelized construction method and associated embodied GHG emissions. To compare panelized with the stick-built method, the waste generated from stick-built construction is ascertained through a literature review. It is found that the construction of a single-family home in North America typically produces between two and four tons of wastes on site (NAHB Research Center, 1996; Laquatra 2005). Mah (2011) conducted an empirical study of construction wastes has been undertaken to investigate the mass and volume of waste generated during the new home construction process. His study noted that typically in stick-built construction there are three waste pick-ups, with the first pick-up coming after the completion of framing. The study included an on-site audit of the first waste pick-ups of five single-family homes under construction. On average, over 1,400 kg of total waste (wood and non-wood) had been generated at a single-family house construction site by the time framing had been completed. Almost 89% of this waste was either dimensional lumber or engineered wood products. The results of Mah’s study are consistent with those of similar studies that have been conducted around North America. Therefore, the results from Mah (2011) that on average 536 kg of lumber waste and 710 kg of engineered wood waste are generated in the framing of one house are used in this research for the purpose of comparison of between the stick-built and panelized approaches. To evaluate the impact of reduced waste on the sustainability of construction, the amount of waste is used to calculate the embodied energy and emissions of materials using Equation (6) and Equation (7). The results are shown in Tables 4 and 5.  Where: EW is embodied energy of waste (MJ); W is the mass of waste (kg); and EW is the embodied energy factor of wood product: 10 MJ/kg for dimensional lumber and 15 MJ/kg for engineered wood (Geoff Hammond & Craig Jones, 2011).  Where: ECO2 is embodied CO2 emissions (kg); W is the mass of waste (kg); EEFW is the embodied emission factor of wood product: 0.341 kg CO2/kg for dimensional lumber (Meil, 2000), and 0.576 kg CO2/kg for engineered wood (Forintek Canada Corp., 1993). 009-7 Table 4: Embodied energy and emissions of waste for panelized construction Waste Source Plant Total Equivalent Amount (30%*) Dimensional Lumber Engineered Wood Total Amount (kg) 175,981.4 703,925.6   Production Outputs (ft2) 1,216,866   Waste (kg/ft2) 0.145 0.578   Embodied Energy (MJ/ft2) 1.446 8.677 10.123 3.037 Embodied GHG Emissions (kg/ft2) 0.049 0.333 0.383 0.115 * The 30% value refers to the finding that waste in the panel fabrication plant amounts to just 30% of the waste generated by the corresponding scope of work performed on-site in the stick-built method. Table 5: Waste and embodied emissions of stick-built construction  Dimensional Lumber Engineered Wood Total Waste (kg/house) 536 710 1,246 Average Floor Area(ft2/house) 1,600  Waste (kg/ft2) 0.335 0.444 1 Embodied Energy (MJ/ft2) 3.349 6.658 10.007 Embodied CO2 Emissions (kg/ft2) 0.114 0.252 0.366 5 CONCLUSION AND LIMITATIONS This study has demonstrated that utilization of a panelized method enhances the sustainability of construction. In particular, this study has investigated the impact of cycle time savings and waste reduction resulting from panelized construction. Based on the operational data, the framing cycle time of panelized construction has been calculated, and the impact on winter heating has been evaluated. The waste generated by panelized construction has been quantified and compared with that of stick-built construction, and the impact on embodied emissions has been evaluated. The results in Table 6 and Figure 9 show that the overall energy intensity, including operational and embodied, is reduced by 202.378 MJ/ft2 using the panelized construction method, which represents a 67.77% reduction compared to the stick-built method. Table 7 and Figure 10 show that the overall emission intensity is reduced by 1.758 kg/ft2 using the panelized construction method, which translates to a 49.1% reduction compared to the stick-built method. Compared with stick-built construction, panelized construction as a sustainable construction method is demonstrated empirically to reduce energy usage and CO2 emissions. This research entails the following limitations: (1) due to the data accessibility, the data on stick-built construction waste was obtained from published research collaborated with the same industry partner, while others was archived from the industry partner’s records for this research; (2) Winter heating is a crucial issue in Canada; however, in other countries and regions, there may not exist the same issue.  009-8 Table 6: Energy comparison between panelized and stick-built construction Construction method Winter Heating Energy (MJ/ft2) Waste-Embodied Energy  (MJ/ft2) Overall Energy (MJ/ft2) Panelized 93.214 3.037 96.251 Stick-built 288.622 10.007 298.629 Reduction 195.408 6.970 202.378 Reduction % 67.70% 69.65% 67.77%  Figure 9: Energy intensity comparison  Table 7: Emissions comparison between panelized and stick-built construction Construction method Winter Heating CO2 Emissions (kg/ft2) Waste-Embodied CO2 Emissions (kg/ft2) Overall CO2 emissions (kg/ft2) Panelized 1.707 0.115 1.822 Stick-built 3.214 0.366 3.580 Reduction 1.507 0.251 1.758 Reduction % 46.88% 68.64% 49.10%  009-9  Figure 10: CO2 emissions intensity comparison References Energetics. 2009. Propane reduces greenhouse gas emissions: A comparative analysis, Propane Education & Research Council. Retrieved from http://www.propanecouncil.org/uploadedFiles/REP_15964%20Propane%20Reduces%20GHG%20Emissions%202009.pdf (Apr. 15, 2013). Environment Canada. 2013. Fuel Combustion. Retrieved from http://www.ec.gc.ca/ges-ghg/default.asp?lang=En&n=AC2B7641-1 (Mar. 12, 2013). Forintek Canada Corp. 1993. Raw material balances, energy profiles and environmental unit factor estimates: Structural wood products. Athena Sustainable Materials Institute, Ottawa, ON, Canada. Hammond, G. and Jones, C. 2011. Inventory of carbon & energy (ICE) version 2.0 summary table.  Inui, T., Chau, C., Soga, K., Nicolson, D., and O’Riordan, N. 2011. Embodied energy and gas emissions of retaining wall structures. Journal of Geotechnical and Geoenvironmental Engineering, 137(10): 958-967. Laquatra, J. 2005. Waste Management at the Construction Site, Partnership for Advancing Housing Technology (PATH). Retrieved from www.pathnet.org/si.asp?id=1069 (Apr. 15, 2013) Li, H. X., Esfahani, M. N., Gül, M., Yu, H., Mah, D. and Al-Hussein, M. 2014. Carbon footprint of panelized construction: an empirical and comparative study. Proceedings, Construction Research Congress, ASCE, Atlanta, GA, USA, May 21-23. Mah, D. E. 2011. Framework for rating the sustainability of the residential construction practice. Ph.D. thesis, University of Alberta, Edmonton, AB, Canada. Meil, J. K. 2000. A life cycle analysis of Canadian softwood lumber production. Athena Sustainable Materials Institute, Ottawa, ON, Canada. Monahan, J. and Powell, J.C. 2011. An embodied carbon and energy analysis of modern methods of construction in housing: A case study using a lifecycle assessment framework. Energy and Buildings. 43(1):179-188. National Energy Board. 2012. Energy Conversion Tables. Retrieved from http://www.neb-one.gc.ca/clf-nsi/rnrgynfmtn/sttstc/nrgycnvrsntbl/nrgycnvrsntbl-eng.html (Mar. 26, 2014). Natural Resources Canada. 2010. Gas Heating Terms and Conversions. Retrieved from http://198.103.48.133/residential/personal/gas-heating-terms.cfm?attr=4 (Mar. 11, 2014). NAHB Research Center. 1996. Construction Site Waste: A New Profit Center? Energy Source Builder #46, Iris Communications, Inc. Retrieved from http://oikos.com/esb/46/sitewaste.html (Apr. 15, 2013). National Energy Board. 2015. Energy Conversion Tables. Accessed 25th October 2014, available at: http://www.neb-one.gc.ca/nrg/tl/cnvrsntbl/cnvrsntbl-eng.html#s2ss_auto5 009-10 

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