Why targeting matters more than volume in building renovation policy

A new study from Eurac Research's Institute for Renewable Energy, published in the journal Buildings, models the residential building stock of South Tyrol under three different renovation strategies. The findings: concentrating deep renovation on the segments of the building stock with the highest energy demand delivers substantially larger reductions than spreading lighter interventions across the entire stock, even when a comparable amount of public investment is involved.

The study, led by Dario Bottino-Leone together with Giulia Paoletti, Alexandra Troi, Edoardo Carangelo, Flavia Trovalusci, Roberto Lollini, Daniel Herrera-Avellanosa and Wolfram Sparber, combines three elements: a review of European renovation policies and their implementation lessons, ten semi-structured interviews with experts from energy and housing policy, and a typology-based model of South Tyrol's residential buildings, built from census and provincial floor-area data together with representative energy demand values from the SINFONIA project and earlier South Tyrolean research.

The baseline model estimates the province's residential stock needs approximately 1,990 GWh a year for space heating and domestic hot water. A relatively small share of the stock accounts for most of that demand: four priority clusters, rural single-family houses built before 1990 and urban multi-family buildings and apartment blocks from 1945-1990, make up 56% of residential floor area but nearly 59% of baseline energy demand.

The researchers compared three static end-state scenarios rather than a renovation timeline: a deep renovation of those priority clusters, a medium-depth renovation of the same clusters, and a light renovation spread across the entire residential stock.

Under the model's central assumptions, deep renovation of the priority clusters would cut the stock's annual energy demand by about 704 GWh, or 35%. Medium-depth renovation of the same clusters would achieve an 18% reduction, while light renovation applied stock-wide reaches about 15%, despite covering far more floor area. The comparison also holds on cost-effectiveness: the deep, targeted scenario requires the largest upfront investment (an estimated 2.1 billion euros, against 1.2-1.3 billion euros for the other two) but comes out lowest in cost per unit of energy saved over a 30-year horizon.

"Renovation rate alone doesn't tell you whether a renovation programme is actually working," said first author Dario Bottino-Leone. "It measures how many buildings are touched, not how deep the interventions are or whether they reach the buildings that account for most of the energy demand. In our model, four building segments make up little more than half of South Tyrol's residential floor area but nearly 60% of its heating and hot water demand. That's why a targeted deep renovation of those segments outperforms a much larger, shallower renovation campaign spread across the whole stock, and does so at a lower cost per unit of energy saved."

The full paper, "Targeted Retrofit Strategies for Residential Building Stocks: Integrating EU Policy Lessons and Scenario Modelling in South Tyrol," is open access in Buildings