Introduction

Historic buildings are among the hardest buildings to renovate. Improving energy performance can affect historic materials; conservation measures can limit accessibility; and a technically effective solution may prove too costly to maintain. Unlike in a conventional building, mistakes can be difficult—or even impossible—to reverse. The principle behind the Herit4Ages approach is therefore simple: listen before you touch.

The challenge is significant. Around 85% of EU buildings were constructed before 2000, while an estimated 75% have poor energy performance. Europe therefore needs to accelerate renovation while protecting its historic building stock. For heritage buildings, this means understanding how each building actually behaves before interventions are made—and considering energy performance, conservation, accessibility and cost together.

_{Figure 1. The DTE brings together Heritage Building Information Models (HBIM), live monitoring data and specialised tools in one shared digital environment.} 
 

The Herit4Ages project is developing a Digital Twin Ecosystem (DTE) to support this approach. Led by IDP, the DTE brings together Heritage Building Information Models (HBIM), live monitoring data and specialised tools in one shared digital environment, hence a DTE. Rather than simply creating a digital replica, it connects information about the building so that it can be analysed and used to support renovation decisions. At the heart of the DTE are six Heritage-Centric Tools, each looking at a different part of the renovation challenge.

1. Is the building at risk? The Smart Monitoring and Preventive Conservation tool, developed by FSMLR, uses discreet sensors to track conditions such as temperature and humidity and identify potential risks to the building and its historic materials.
2. What are the environmental impacts? CETIM's LCC/LCA Tool looks at the environmental footprint and life-cycle impacts of the renovation solutions developed by the project, helping users consider their wider environmental consequences.
3. Will the renovation actually improve energy performance? The Energy Efficiency Optimisation Tool, developed by the Tyndall National Institute and the University of Bologna, combines information about the building with monitoring and energy simulations. It can be used to compare different retrofit options and check whether expected improvements are achieved after installation.
4. How will the building be maintained? The Operation & Maintenance Optimisation Module helps users plan maintenance, assign responsibilities, and keep track of tasks and costs, supporting the building throughout its life rather than stopping at the end of the renovation.
5. Does the solution make financial sense? The Financial Management Tool brings together investment and running costs, energy savings, and other economic factors, helping users understand the longer-term financial implications of different renovation choices. It crosses energy efficiency optimisation (energy consumption reduction) thanks to the installation of insulation panels against their installation and Operation & Maintenance costs (CAPex & OPex), leading to a return on investment (RoI) calculation, aiming at improving Heritage Owners/Managers’ decision-making.
6. Can everyone use the building? The Architectural Barriers Identification Tool, developed by the Warsaw University of Technology and called 'Universal Design' within the DTE, helps identify accessibility barriers and consider how different users experience a building. It also includes an audio navigation function for blind and low-vision users and follows WCAG 2.2 accessibility guidelines.

The strength of the system lies in connecting these different perspectives. The building model acts as a common reference point, linking monitoring data, technical information, simulations and maintenance records to specific spaces and elements. Energy performance can therefore be considered alongside conservation risks, environmental impact, accessibility, maintenance and cost, rather than assessed separately.

_{Figure 2. Screenshot of the DTE.} 

This is the central idea behind the Herit4Ages approach: listen before you touch. By bringing together what can be observed in the historic fabric, what can be measured through monitoring, and what can be explored through digital models, the DTE helps create a clearer picture of a building before decisions are made. 

For heritage renovation, where every intervention can have lasting consequences, that insight can be the first step towards protecting the past while preparing buildings for the future.