Reuse of reinforced concrete (RC) components reduces construction’s environmental impacts and waste. Rather than crushing the concrete of an obsolete structure, its components are saw cut and later reassembled in a new structure. The theoretical feasibility of this method is demonstrated through a case study: the design of a residential building structure that reclaims cast-in-place RC components from two 60-year-old office buildings scheduled for demolition. Parts of the source buildings are allocated to an optimal position in the target building using an algorithm that minimizes the need for strengthening. Construction details are developed for the slab-wall connections and the bracing system. An alternative conventional cast-in-place RC design is proposed for comparison, as well as a hybrid design balancing environmental and cost savings with technical readiness. The assessment of the designs confirms that reusing RC components allows saving up to 75% of greenhouse gas emissions for similar costs, as long as demolition and disposal of obsolete source material are considered.