The aim of this study was to identify, structure, and empirically validate a systematic repertoire of elementary form-transformation rules that accurately depicted sketch-based architectural design processes and can be directly implemented in computational environments. To address the lack of a systematically organised, detailed repertoire of shape transformation operations in architectural design research, 48 shape rules were developed through literature review and refined through empirical observation of sketching sessions conducted by two experienced architects. The rules were assigned to two operational categories (Plastic, Structural), one meta-category (Figurative), and 14 rule classes. Protocol analysis confirmed that the repertoire captured the full range of observed form manipulations across 23 sketches and 267 coded transformations, with high intra-coder reliability (Cohen’s Kappa: 0.85-0.87), confirming the robustness and clarity of the proposed classification. Structural rules made up 74% of the observed transformations, highlighting the predominance of configurational exploration in early-stage design, whereas Plastic and Figurative rules accounted for 15% and 11%, respectively. Statistical analyses, including principal component analysis and hierarchical cluster analysis, showed a consistent bipartite structure across both designers: structural rules formed a distinct cluster, while plastic and figurative rules grouped, with PC1 explaining 97-99% of the total variance. The practical significance of this research lies in providing a transparent and reusable transformation framework that supports the analysis of architectural sketching behaviour and facilitates the development of rule-based computational design tools
architectural sketching; form manipulation; shape grammar; protocol analysis; design cognition
Received 14.10.2025, Revised 14.10.2025, Accepted 24.02.2026 Published 26.03.2026
Retrieved from Vol. 12, No. 1, 2026
https://doi.org/10.56318/as/1.2026.55
Pages 55-66