Impact of project lead time on construction-phase CO₂ emissions of concrete-framed apartment buildings

In recent years, the climate impacts of the construction industry and the efficiency of production have gained increasing attention, yet their relationship has remained unclear. The aim of this thesis was to examine which time-related factors influence the progression of the construction process in a concrete-framed residential apartment building, and how these factors affect site-specific carbon emissions and costs. The study was conducted empirically by combining qualitative interviews and quantitative carbon footprint calculations. The research questions focused on factors that improve workflow during the construction, their impacts on emissions and costs, and the relationship between lead time and CO₂ emissions.

The literature review addressed low-carbon construction, lean construction principles, and time-related factors influencing construction progression. The findings defined the scope of the interviews and emission calculations. The study identified eight factors that affect the temporal progression of the construction process and four mechanisms through which these factors influence emissions and costs. Results show that optimizing lead time from an emissions perspective is not a single measure, but rather a case-specific process influenced by multiple variables. Implementing takt time planning can reduce both lead time and emissions if the project participants are jointly committed. Additionally, the use of low-carbon concrete in suitable structures supports emission reductions. The findings support more systematic decision-making, in which optimizing construction duration and promoting low-carbon practices are seen as parallel and mutually reinforcing objectives.