Economic robustness of staged renovation in an existing nonresidential building: An anonymised analysis of cost boundaries and financial sensitivity

An energy renovation can show a large calculated demand reduction while remaining financially sensitive to cost allocation, energy prices, and realised savings. This paper investigates that distinction through an anonymised secondary analysis of one complete nonresidential energy consultancy report. Four cumulative renovation packages are examined, with particular attention to the difference between total project expenditure and the additional expenditure assigned to energy improvement. Reported values are normalised by conditioned net floor area. The complete package combines approximately EUR 347.3/m² of total investment with EUR 184.3/m² of energy-related additional expenditure and first-year modelled energy-cost savings of EUR 8.63/(m² year). These imply simple paybacks of approximately 40.2 and 21.3 years, respectively. Neither is identical to the report's 27-year payback, which belongs to its separate economic calculation. A transparent screening model is introduced using a 30-year horizon, end-of-year savings, explicit discount and escalation assumptions, and no grant. At a 5.5% discount rate, the complete package's additional-cost net present value changes from about minus EUR 58.8/m² with constant savings to plus EUR 16.7/m² with 4% annual savings escalation. Under the latter assumptions, the break-even savings-realisation multiplier is about 0.917. Consequently, a modest reduction in realised monetary savings removes the positive margin. These are deterministic stress tests, not forecasts or reconstructions of the original software's full cash flows. The study demonstrates why reported profitability should be accompanied by explicit counterfactual maintenance costs, consistent financial conventions, and a plan for verifying realised performance.