A Comparative Life Cycle Assessment of Mid-rise Office Building Construction Alternatives: Laminated Timber or Reinforced Concrete

The objective of this project aimed to quantify and compare the environmental impacts associated with the construction of a mid-rise office building. Two alternative scenarios were considered; a traditional cast-in-place, reinforced concrete frame and a laminated timber hybrid design, which utilized engineered wood products including glulam and cross-laminated timber (CLT). The study boundary was cradle-to-gate and encompassed the structural support system and the building enclosure. A case study building; Discovery Place – Building 12, was selected to represent a typical five-storey office building constructed in North America. Floor plans, elevations, material quantities and design loads associated with the concrete-framed building design were obtained from issued-for-construction engineering drawings. A functionally equivalent, laminated timber design was then conceived, based on the requirements outlined in CAN/CSA-O86-01. Design values for locally produced CLT panels were established from in-house material testing results. A life cycle assessment of CLT, manufactured in British Columbia with mountain pine beetle killed wood, was developed based on primary inventory data collected from a pilot-scale manufacturing facility. Life cycle inventory and impact assessment data for building materials was obtained from secondary sources including BEES® 4.0, ATHENA® EcoCalculator, CORRIM, and the US LCI. TRACI, an impact assessment characterization methodology, was employed to translate inventory flows into environmental impact indicators. The environmental comparison of building design alternatives was based on 11 impact categories. The results concluded that the laminated timber building design was associated with a lower environmental footprint in 10 of 11 categories. At a minimum, the heavy timber design demonstrated a 14% improvement, when considering acidification potential. At a maximum, the timber design exhibited a global warming potential that was 71% less than the concrete design. Fossil fuel depletion was the only category where the concrete design was superior, displaying a 6% advantage over the timber scenario. The cumulative embodied energy of construction materials was also calculated; with results estimating energy contents of 116 and 66 terajoules for the timber and concrete designs, respectively. The concrete building acquired 20% of its energy from renewable sources, whereas in the timber-framed case, renewables accounted for over 60% of the combined feedstock and process energy.

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Life Cycle Sustainability Assessment

Author Adam Robertson
Institution University of British Columbia
Advisor Dr. Frank Lam & Dr. Ray Cole
Expected graduation 2011