There is a global call for a paradigm shift in the construction industry towards carbon neutrality, but a scant effort has been madein practice, especially concerning circularity. This paper helps bridge the gap by introducing a parametric approach to optimize sustainable construction design. The methodology was tested on a newly constructed office building, inspired by circularity principles, in Westerlo, Belgium. The methodology consists of parametric construction-typological analysis, automated through One Click LCA software (Life Cycle Assessment) and Microsoft Excel with 21 alternate designs and 630 iterations. The parametric variations involved three key performance indicators: construction system, materials’ environmental impact, and materials; reuse of content. The environmental effects of both construction systems (i.e., structural system, foundation type, materials, and envelope details) and reused building materials content (i.e.,) were evaluated by the parametric analysis for four construction systems scenarios. Environmental impact analysis for timber, steel, concrete, and hybrid construction systems was conducted, following ISO 14040 and CEN/TC 350 standards. The focus of the whole life cycle assessment was mainly on carbon neutrality. Results indicate that using local biosourced materials, including timber, can remarkably reduce buildings’ environmental impact. The sensitivity analysis results provide hard evidence that the construction material’s weight, materials reuse potential, and construction dismantling ability are the most influential factors in carbon-neutral buildings. This paper should improve professionals’ understanding of the impact of different structural systems choices and inform building designers about the circularity potential, and carbon footprint of construction technologies.