Bridging the renovation data gap: A novel method for estimating renovation activity and rates from energy performance certificates

• Novel method for estimating renovation rates based on energy performance certificates. • Monitoring unreported renovation activities based on building stock data. • Actual renovation rates are higher than previously estimated. • Energy use of buildings labelled as unrenovated declines over time. Decarbonising the building stock is essential for achieving climate targets, with renovation strategies playing a central role. However, tracking renovation progress is challenging due to limited data—especially from unreported renovations not reflected in official statistics. This study presents a novel method for estimating renovation activity using energy performance certificates (EPCs), focusing on buildings classified as unrenovated in Salzburg, Austria. Buildings are grouped into archetypes by construction period and type (single-family or multi-family), and default heat transmission losses are calculated under various scenarios using TABULA and Austrian Institute of Construction Engineering (OIB) data. Findings reveal that actual transmission losses are 27–42% lower than expected, indicating widespread unreported renovations. Across scenarios, 45–61% of the energy savings from full renovation have already been achieved. The method also estimates renovation depth, showing that 69–89% of buildings underwent at least light renovation, 33–40% medium renovation and 8–15% deep renovation. These insights suggest that the remaining energy-saving potential is significantly lower than commonly assumed. By analysing changes in primary energy demand over time, the study estimates an average effective renovation rate of 2.3% per year from 2017 to 2024 (based on a total reduction of 18% in mean primary energy demand), with a peak of 5.1% in 2022 (90% confidence interval: 4.0–6.0%) and a drop to 1.5% in 2024 (90% confidence interval: 0.6–2.4%). With anticipated improvements in EPC data quality and coverage, this approach offers a practical tool for monitoring renovation progress, including unreported renovation activities.