Bridging the digitalization gap in nZEB renovation: a systemic barrier assessment framework for smart deep energy retrofits

The integration of smart technologies in deep nZEB renovation projects is often hindered by systemic barriers that limit the achievement of expected operational performance. While buildings may comply with energy requirements at the design stage, they frequently underperform in terms of adaptive control, data-driven optimization, and interoperability. This discrepancy is conceptualized as a digitalization gap—a lifecycle-accumulated divergence between intended smart readiness and realized digital capability. This study addresses the identified research gap by proposing a Systemic Digitalization Gap Propagation Model (SDGPM) combined with a Digitalization Gap Index (DGI). The objective is to develop a framework that captures how digitalization barriers emerge, propagate across lifecycle phases, and accumulate into measurable performance constraints, and to assess its applicability through exploratory validation. The methodology integrates lifecycle-based barrier mapping, root-barrier identification, and expert-based multi-criteria assessment. The framework was applied to a typical public building, identifying 64 barriers, including 7 root barriers that generate 57 derived and emergent constraints. Results show that derived barriers dominate the system (70%), suggesting strong cross-phase propagation effects. Root barriers—particularly those related to data governance, digital architecture planning, and organizational competence—exhibit the highest systemic influence. Exploratory validation through two public buildings renovation case studies demonstrated a 27–32% reduction in the digitalization gap and provided preliminary evidence that early-stage digital planning and organizational capacity significantly decrease the number of root barriers and mitigate barrier propagation. A sensitivity analysis further demonstrated that the principal conclusions of the proposed framework remain robust under alternative Barrier Severity Score (BSS) weighting schemes. The proposed framework provides a replicable approach for assessing digitalization gaps and supports the transition from nZEB compliance toward digitally enabled, high-performance, and environmentally optimized buildings.