The reduction of the energy consumption and carbon emissions in the building sector is an important target for actions to mitigate the climate changes and different actions are being carried out to promote a transition to a low carbon built environment. However, present standards are mainly focused on new buildings which may result counter-productive in existing ones, due to their technical, functional and economic constraints.
In Europe, the latest updates in the directive on the energy performance of buildings introduced two fundamental concepts, namely the cost-optimal energy requirements and the nearly-zero energy buildings (nZEB). Although these concepts are related, the cost-optimal is focused on costs while the nZEB prioritise the energy performance and the use of renewable energy harvested on site. To understand how these two concepts can be articulated to potentiate energy savings in the Portuguese building stock, reference buildings representative of the residential building stock were analysed.
Several standards regarding energy consumption have emerged in the last decade, defining increasing requirements, and culminating with the recent emergence of the “nearly zero energy” buildings concept, as described in the Energy Performance of Buildings Directive1. However, these standards are mainly focused on new buildings neglecting, most of the time, the existing ones that represent the least efficient, the largest consumers and the largest share of the building stock.
The renovation of the existing building stock represents a huge potential in actions to mitigate climate change, not only by the improvement of the overall energy performance of the built environment but also by the reduction of resource depletion and minimization of waste production related with new construction.
In times of great transition of the European construction sector to energy efficient and nearly zero energy buildings (nZEB), a market observation containing qualitative and quantitative indications should help to fill out some of the current gaps concerning the EU 2020 carbon targets. Next to the economic challenges, there are equally important factors that hinder renovating the existing residential building stock and adding newly constructed high performance buildings.