According to the United Nations Environment Programme (UNEP), existing European buildings consume about 40% of the total energy consumption in Europe. For this reason, in the last decades, several energy  policies have been directed to deep renovation of the existing stock (as last 2018/844). Considering that more than one quarter of all European buildings were constructed before the 1950s, we can assume that many of them are of cultural, architectural, social and heritage values, hence in need of special attention for conservation purposes.

The main objective of Subtask C is to identify, assess and in some cases further develop retrofit solutions and strategies for historic buildings. The solutions should fulfil the conservation compatibility of historic buildings as well as energy efficiency goals towards lowest possible energy demand and CO2 emissions (NZEB). Further, the objective is to make the solutions available for comprehensive integrated refurbishing concepts and strategies.

Historic building restoration and renovation requires sensitivity to the cultural heritage, historic value, and sustainability (i.e., building physics, energy efficiency, and comfort) goals of the project. Heat recovery ventilation can contribute to the mentioned goals if ventilation concepts, and airflow distribution is planned and realized in a minimally invasive way. Compared to new buildings, the building physics of historic buildings are more complicated in terms of hygrothermal performance. In particular if internal insulation is applied, the need for dehumidification is needed for robust and risk-free future use, while maintaining the building’s cultural value. As each ventilation system has to be chosen and adapted individually to the specific building, the selection of the appropriate system type is not an easy task.

Renewable Energy Sources (RES) implementation, particularly in existing and historic buildings, can contribute significatively to the reduction of the energy requirement for thermal conditioning and electrical needs. The use of renewable solar energy systems in existing buildings is now strongly supported by the legislative European (EU) framework, which introduced specific targets to increase the share of RES, to cut carbon dioxide emissions (CO2 emissions), and to enhance the energy performances of existing buildings RES play an important role for achieving these goals in energy renovations of existing buildings, as the legislation requires to cover 32.5% of energy produced for domestic hot water, heating, and cooling by RES [1]. The EU 2030 Climate Target Plan consist among other things of an amended proposal on the draft EU Climate Law to incorporate the new 2030 emissions reduction target, considering reducing emissions (GHE) by at least 55% by 2030 as realistic and feasible objective.

The renovation of historic buildings is a complex task, as standard packages of solutions cannot be applied as in the renovation of buildings without historical significance. Each measure must be assessed on a case-by-case basis. In addition to improving energy efficiency and technical maintenance, the preservation and the  respect of the historic values must be guaranteed. The compatibility among the different measures of the renovation strategy must be carefully considered before being implemented.

Within the framework of IEA-SHC Task 59, a multidisciplinary team of experts from around the world has come together to investigate current approaches for energy retrofit of the built heritage with energy efficiency conservation-compatible measures, in accordance with cultural and heritage values, and to check and adapt the new standard EN-16883:2017 for historic buildings. This paper introduces activities within IEA-SHC Task 59 (Subtask C) focused on retrofit solutions with high impact on sustainability, energy efficiency, and the integration of renewables, which is the main goal of the solar group, focused on the integrated solar systems for historic buildings. Relying on an extensive, detailed, and accurate collection of case studies of application of solar photovoltaic and thermal systems in historic buildings, the assessment criteria of the standard have been reviewed and tailored for better solar implementation evaluation in a heritage context. All this is studied based on technical compatibility, the heritage significance of the building and its settings, the economic viability, the energy performances and indoor environmental quality and use, as well as the impact on the outdoor environment of solar renewables.

Buildings of heritage significance due to their historical, architectural, or cultural value, here called historic buildings, constitute a large proportion of the building stock in many countries around the world. Improving the performance of such buildings is necessary to lower the carbon emissions of the stock, which generates around 40% of the overall emissions worldwide. In historic buildings, it is estimated that heat loss through external walls contributes significantly to the overall energy consumption, and is associated with poor thermal comfort and indoor air quality. This paper provides an evidence-based approach on the steps required during assessment, design, and construction, and after retrofitting through a literature review. Moreover, it provides a review of possible measures for wall retrofit within the deep renovation of historic buildings, including their advantages and disadvantages and the required considerations based on context.

Historic building restoration and renovation requires sensitivity to the cultural heritage, historic value, and sustainability (i.e., building physics, energy efficiency, and comfort) goals of the project. Energy-efficient ventilation such as demand-controlled ventilation and heat recovery ventilation can contribute to the aforementioned goals, if ventilation concepts and airflow distribution are planned and realized in a minimally invasive way. Compared to new buildings, the building physics of historic buildings are more complicated in terms of hygrothermal performance. In particular, if internal insulation is applied, dehumidification is needed for robust and risk-free future use, while maintaining the building’s cultural value. As each ventilation system has to be chosen and adapted individually to the specific building, the selection of the appropriate system type is not an easy task. For this reason, there is a need for a scientifically valid, systematic approach to pair appropriate ventilation system and airflow distribution solutions with historical buildings.