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CIB Conferences

Abstract

Environmental sustainability has become a core value for many companies in the construction industry. However, while methodologies and tools for carbon accounting are available, design decisions are still primarily driven by cost rather than carbon considerations. One reason for this lies in the timing and availability of data. Cost estimates are collected early and refined throughout the design phase, which supports decision-making. In contrast, carbon data is often unavailable or difficult to gather, rarely updated, and collected late when most design decisions have already been finalized. This misalignment poses practical challenges to effectively integrating carbon and cost assessments into the decision-making process throughout the entire design phase.

This study investigates the root causes of delays and challenges in assessing a building's embodied carbon during the design development and detailed design phases and the difficulties in linking embodied carbon results to costs to support decisions. Using a residential multi-family building project as a case study, we identify key obstacles in 1) collecting Quantity Take Offs (QTO) and carbon impact factors for each building element and 2) linking carbon assessment results with corresponding cost estimates.

We found that only 11% of the building’s final carbon impact came from elements with quantities extracted from the Building Information Model (BIM), while 89% relied on 2D drawings or scattered data sources. Additionally, only 20% of the building’s carbon footprint was calculated using product-specific Environmental Product Declaration (EPD), with 80% relying on industry-average EPDs. The embodied carbon assessment was completed only during the detailed design phase, whereas cost estimates were updated in each phase. A further challenge was the misalignment between the carbon breakdown and quotes for many building elements, making it difficult to link carbon impacts with costs for effective decision-making. In addition, the final carbon assessment covered only 55% of the building’s total estimated cost, highlighting an imbalance between the possibility to estimate embodied carbon and cost.

To address these challenges, this study recommends: 1) consolidating the number data sources and standardizing quantity estimation procedures, 2) selecting building products early in the design process to use product-specific EPDs, and 3) involving general contractors and subcontractors before the design development phase to estimate quantities and align quotes with carbon breakdown. By identifying practical challenges and providing recommendations, this research takes a step toward integrating carbon considerations into design decisions to increase the chance of achieving sustainability goals.

The paper will be presented:

In-person

Primary U.N. Sustainable Development Goals (SDG)

Sustainable Cities and Communities - - Make cities and human settlements inclusive, safe, resilient and sustainable

Secondary U.N. Sustainable Development Goals (SDG)

Climate Action - - Take urgent action to combat climate change and its impacts

Primary CIB Task Group OR Working commission

TG124 – Net Zero Carbon Building Design and Construction Practices

Secondary CIB Task Group OR Working commission

W116 – Smart and Sustainable Built Environments

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