Comparing Climate and Cost Performance of On- and Off-Site Concrete Facility Construction Projects: A German Case Study

Selecting a reinforced concrete construction system is usually justified either economically or environmentally, and the two perspectives are rarely derived from the same project data. It therefore remains unclear whether the cost-optimal and the carbon-optimal choice coincide, and whether the differences between the systems are large enough to be distinguished from the uncertainty of the underlying assumptions. This study addresses that question for a real industrial building in northern Germany. Cast in situ, fully precast, and semi-precast systems were compared for the walls, slabs, and beams of a technical building, using contractor cost calculations and supplier quotations for the direct construction costs, and project-specific material quantities with generic emission factors for the construction-phase embodied carbon (modules A1–A5 of the European Norm EN 15978), both based on identical functional units. The direct costs differ substantially: the semi-precast double wall was 27.2% and the filigree slab 50.3% cheaper than their cast in situ equivalents, the fully precast wall and slab were 46.0% and 62.7% more expensive, and precast beams were 15.4% cheaper. The embodied carbon results differ by at most 5.1% between any two alternatives, and a one-at-a-time sensitivity analysis over ten parameters shows that this difference is not robust, since its sign changes within plausible parameter ranges; the cement content of the plant concrete is the dominant uncertainty. Material production accounts for 87% to 94% of the total in every case. The choice of construction system is therefore primarily an economic decision, whereas embodied carbon has to be addressed through material-related measures rather than through the construction method.