Whole-Life Carbon and Circular Design in Saudi Building Projects: Keeping Design Intent Intact from Brief to Handover

A carbon calculation can be sound when it is prepared and outdated a few months later. Usually the arithmetic is not the problem; the building around the calculation has changed. Quantities grow, products are substituted, environmental declarations arrive after purchasing decisions, and claims of adaptability or reuse lose the details that once made them credible. This paper examines how whole-life carbon and circular-design intent can survive those ordinary project changes in Saudi building delivery. I carried out a purposive integrative review of peer-reviewed research, lifecycle-assessment standards, circular-design guidance, professional carbon methods and current Saudi policy, code and rating-system sources. Across these sources, the same continuity problem recurs: early comparisons use provisional information, while later commercial decisions are made when options are fewer but product evidence is stronger. In response, I develop a decision process built around six live control questions, four project checkpoints, a Carbon and Circularity Decision Register and five levels of evidence maturity. It connects the approved baseline with design commitments, supplier information, substitutions, the installed building and the record left for future maintenance or change. It does not replace whole-life carbon assessment, competent design or building regulation. The proposal is conceptual and has not been tested against a Saudi project dataset or benchmark. Its value lies in making carbon, adaptability, durability and future material value traceable through delivery rather than leaving them as concept-stage intentions.