Carbon accounting and reporting will likely become necessary for various key industrial sectors due to government regulations and policies. The U.S. Environmental Protection Agency is in the process of finalizing the power-plant carbon rules. Working towards a regional carbon trading scheme, the state of California will soon require annual carbon emission reporting of compliance that covers 85% emission sources and industry sectors. While the construction industry has the third highest greenhouse gas (GHG) emissions among all US industry sectors, emission estimates are dramatically different from construction activities primarily due to the complexity of construction activities and the lack of carbon accounting standards. This paper presents a framework of carbon accounting for construction projects. The paper compares existing enterprise carbon accounting standards and evaluates their applicability at the project level. A life-cycle project carbon accounting protocol is developed that follows a bottom-up approach and covers emissions from site-preparation, material manufacture, on-site construction, waste management, operation and environmental mitigation. With detailed discussion on calculation methods for example emission sources, the protocol provides a guideline for construction professionals to identify possible alternatives in terms of CO2 emissions and form a complete list of baseline candidates.


As one of the greatest challenges of our time, climate change has increasingly become a top priority for governments, businesses, and general public. According to the Environmental Protection Agency (EPA), the construction sector has the third highest CO2 emissions among all industrial sectors. Construction site activities alone contribute approximately 1.7% of total U.S. emissions, or 6% of national industrial carbon emissions (Truitt, 2009). Additionally, a great amount of construction materials are being consumed every day, which produce a magnitude of CO2 emissions due to embodied energy. For example, approximately 110 million tons of cement is used every year in the construction indsutry (Horvath, 2004). Embodied emissions from cement manufacturing and processing represent 58.7% of the construction site emissions estimated by the EPA (Hanle et al., 2004). Considering the fact that 54% of energy consumption and 32% of CO2 emissions are directly or indirectly related to facility construction and operation, the construction and facility management industry will be one of the major sectors that should take more environmental responsibilities and comply with stringent emission standards (Horvath, 2004).|

Commitments and efforts to reduce CO2 emissions must be based on accurate emission inventory accounting and analysis. In the power and manufacturing industries, Life-Cycle Assessment (LCA) methods have been developed to establish the emission inventory baseline, including Economic Input-Output LCA (EIO-LCA), and hybrid LCA (Seo and Hwang, 2001; WRI, 2005; ISO, 2006; Ochoa et al., 2008; Sharrard et al., 2008; Yan et al., 2010). These models will need to be adjusted and refined to suit for construction projects given the unique nature and complexity of the construction sector (Truitt, 2009). Especially, Construction managers today face a rapidly evolving and often bewildering array of competing standards, approaches and regulations. They require practical approaches to quantifying CO2 emissions, both for voluntary disclosure and management as well as to meet emerging reporting requirements and regulations. Existing studies on calculating CO2 emissions in construction projects, however, cover disparate emission sources and produce distinct estaimates on similar projects. This is well demonstrated by the emissions estimates ranging from 300-1500 tons of CO2 emitted from constructing one lane-mile asphalt pavement (Encord, 2010; Miller-hooks et al., 2010; Cass & Mukherjee, 2011). It is urgent for the construction industry to establish a consensus on the boundary, process, methodology, and reporting requirement to develop emission inventory for construction projects and organizations.

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