About Annex 75

Buildings are a major source of greenhouse gas emissions and cost-effectively reducing their energy use and associated emissions is particularly challenging for the existing building stock, mainly because of the existence of many architectural and technical hurdles. The transformation of existing buildings into low-emission and low-energy buildings is particularly challenging in cities, where many buildings continue to rely too much on heat supply by fossil fuels. However, at the same time, there are specific opportunities to develop and take advantage of district-level solutions at urban scale. In this context, the project aims to clarify the cost-effectiveness of various approaches combining both energy efficiency measures and renewable energy measures at the district level. At this level, finding the balance between renewable energy measures and energy efficiency measures for the existing building stock is a complex task and many research questions still need to be answered, including:

  • What are the cost-effective combinations between renewable energy measures and energy efficiency measures to achieve far-reaching reductions in greenhouse gas emissions and primary energy use in urban districts?
  • What are the cost-effective strategies to combine district-level heating or cooling based on available environmental heat, solar energy, waste heat or natural heat sinks, with energy efficiency measures applied to building envelopes?
  • How do related strategies compare in terms of cost-effectiveness and impacts with strategies that combine a decentralized switching of energy carriers to renewable energy sources with energy efficiency measures applied to building envelopes?
  • Under which circumstances is it more appropriate to use available renewable energy potentials in cities at a district level, under which circumstances are decentralized renewable energy solutions more advantageous, in combination with energy efficiency measures applied to building envelopes?


The project aims to investigate cost-effective strategies for reducing greenhouse gas emissions and energy use in buildings in cities at district level, combining both energy efficiency measures and renewable energy measures. The objective is to provide guidance to policy makers, companies working in the field of the energy transition, as well as building owners for transforming cost-effectively the city's energy use in the existing building stock towards low emission and low energy solutions.

Given the limitations due to available financial resources and the large amount of investments needed to transform the cities’ energy use in buildings, the identification of cost-effective strategies is important for accelerating the necessary transition towards low-emission and low-energy districts.

The planned project focuses on the following objectives:

  • To give an overview on various technology options, taking into account existing and emerging efficient technologies with potential to be successfully applied within that context, and how challenges specifically occurring in an urban context can be overcome;
  • To develop a methodology which can be applied to urban districts in order to identify such cost-effective strategies, supporting decision makers in the evaluation of the efficiency, impacts, cost-effectiveness and acceptance of various strategies for renovating urban districts;
  • To illustrate the development of such strategies in selected case studies and gather related best-practice examples;
  • To give recommendations to policy makers and energy related companies on how they can influence the uptake of cost-effective combinations of energy efficiency measures and renewable energy measures in building renovation at district level, and to give guidance to building owners/investors on related cost-effective renovation strategies.

Accurate understandable information, guidelines, tools and recommendations will be provided to support decision-makers from public and private sectors in making better decisions and choose the best options that apply to their specific needs.