The early design stage exerts the greatest influence on a building’s whole-life carbon emissions, with architects and engineers playing a decisive role in shaping its environmental impact. However, existing studies largely rely on simulation-based sensitivity analyses to identify carbon-critical design parameters, while practitioners’ perceptions are often overlooked, potentially leading to misplaced carbon-reduction efforts.
First, this study conducted an online questionnaire survey among AEC (Architecture, Engineering, and Construction) practitioners in China and the United States, collecting 100 valid responses, including 44 from professionals primarily practicing in the U.S., 50 in China, and the rest in other regions. Participants evaluated the importance of 14 design parameters for carbon emissions using a five-point Likert scale. Then, a weighted scoring and normalization method was developed to synthesize literature findings on design variable importance, accounting for publication quality, sample size, and building type, and scaling all variables to a consistent 1–5 range. Finally, the two sets of results were compared to reveal similarities and differences.
The findings reveal cross-national and professional differences in perceptions, with architects and sustainability consultants showing distinct evaluations. More importantly, practitioners’ judgments do not fully align with simulation results, with several critical variables being either underestimated or overestimated. This divergence highlights a significant cognitive gap between research outcomes and practical applications.
Therefore, future research and tool development should more closely integrate practitioners’ perspectives and strengthen communication between researchers and designers to enhance both the scientific validity and practical operability of low-carbon design. This study provides empirical evidence and a comparative perspective for bridging the gap between theoretical carbon optimization research and early-stage design practice.