Retrofit zero energy projects

How can Europe’s existing building stock be upgraded to ‘nearly zero energy’ buildings by 2050?

Author: Alex Rathmell

06 October 2020

The RenoZEB prototype facade solution installed in Bilbao, Spain

The RenoZEB prototype facade solution installed in Bilbao, Spain IMAGE © IGNACIO TORRENS

Long before the discussion of a green post-COVID economic recovery, governments across Europe had already been directed to develop long-term decarbonisation strategies for buildings, via Article 2a of the European Commission’s Energy Performance of Buildings Directive, Long Term Renovation Strategies pp. 7-10.

In practice this means that by 2050, most of Europe’s existing building stock will be upgraded to ‘nearly zero energy’ buildings (nZEBs). The question currently being asked is how this unprecedented transformation can be cost-effectively delivered.

The European Commission’s vast Horizon 2020 science and innovation funding pot has mobilised a number of projects to develop technical and market-based solutions. These are typically delivered by consortiums of private and academic organisations from across at least three member states. Some projects are focusing on technological aspects, while others concentrate on mobilising finance and developing new business models.


One project that is aiming to tackle a whole range of interrelated technical and market barriers is RenoZEB, running from 2017-21. The project is ambitious, aiming to unlock the nZEB renovation market by harnessing the anticipated uplift in property value that renovated buildings will experience. This will be achieved through a new systemic approach to retrofitting, including innovative integrated façade components, processes and decision-making methodologies embedded in new software tools, and a BIM-based collaborative online environment to bring together all value-chain actors in the renovation process.

The project, a consortium of 19 organisations from across the EU, is developing cost-effective plug and play façade solutions that will be deployed in a set of real and virtual demonstrators.

Two real buildings in two distinct climatic zones will be refurbished to demonstrate the RenoZEB solution: A 1960s-constructed, municipal-owned apartment building in Durango, northern Spain, and a largely owner-occupied apartment building dating from the 1980s Võru, Estonia. Before either of these real buildings are refurbished, the technologies and processes are being tested at the KUBIK facility in Bilbao, Spain.

“The project is ambitious, aiming to unlock the nZEB renovation market by harnessing the anticipated uplift in property value that renovated buildings will experience”
Virtual environment

In order to prove replicability in other countries and markets, the whole approach will also be validated in a virtual environment using models of real buildings from Bulgaria, Italy and Greece, allowing additional climatic zones to be considered. These virtual demonstrators are also an opportunity to test the solution in other building types, and will include a multi-tenant office building (Greece) and a shopping centre (Italy), as well as an additional residential building (Bulgaria).

The project is a recognition that deep retrofits – defined in RenoZEB as renovations that deliver energy savings of 60% or more and integrate on-site renewables – are a very different proposition to the energy efficiency projects that have gone before. Deep retrofit projects have to incorporate multiple technologies to achieve this level of energy demand reduction, as no single measure can achieve the necessary impact. Buildings are visually transformed by the process, which often involves a new façade or other external insulation measure, but changes also take place beneath the surface as mechanical and electrical systems, controls and building fabric are treated or replaced in a single hit.

This involves a disparate collection of professionals – architects, surveyors, building services engineers, product specialists, contractors, financiers – collaborating towards a common goal, but the goal itself is an integrated system that must perform as planned in order to meet the needs of residents and achieve the required level of decarbonisation.

Collaborative endeavour

The RenoZEB project is a collaborative endeavour, with consortium partners working across national borders and language barriers, and embracing a range of organisation types and cultures. These working arrangements, not to mention the restrictions on travel and in-person meetings imposed by the COVID-19 outbreak, mean that the use of virtual development environments and collaboration platforms that can effectively convey complex technical concepts has become essential. For some time, digital technologies have been changing the art of the possible, but projects like RenoZEB are now forcing these approaches into the mainstream.

RenoZEB’s funder, the European Commission, is looking for replicable, scalable and sustainable solutions that can accelerate the annual rate of building renovation from the present 1.2% to the 2.9% needed to reach 2050 targets. Much attention is being paid to the transition to prefabricated construction and integrated panel and façade systems, which shift some of the complexity of nZEB design away from the construction frontline to an offsite factory, allowing economies of scale to be realised in the process.

“The RenoZEB project is a collaborative endeavour, with consortium partners working across national borders and language barriers”
Mass customisation

But renovation contractors need to know how to specify and install these new solutions, which represent a radical departure from current techniques. One size does not fit all – really this is about mass customisation rather than mass production – and poor implementation will seriously compromise the performance of the finished building, so this must be monitored carefully. RenoZEB partners are developing collaboration platforms and resource libraries that can be easily adopted by contractors, and training resources covering deployment of off-site-built retrofit modules, maintenance and end-of-life planning.

Work has been going on at a local level in Spain and Estonia for over 18 months to engage residents, building their acceptance and enthusiasm. Concurrently, detailed building surveys have informed the development of BIM-based digital models, hosted in a new collaborative development environment created by CYPE software. The RenoZEB integrated façade system, developed and manufactured by Focchi, will eventually be specified directly from such BIM models, which will be generated using a simplified building survey process, intended to be faster and easier than a conventional building survey.

Thermal performance

When installed, the façade modules form a new outer wall to the building, dramatically improving thermal performance while integrating new services such as photovoltaic panels, ventilation, roller shutters, and communications devices to interface with other building systems. The primary modules – those featuring glazing or features such as photovoltaic – are designed first, then secondary, opaque modules are integrated. Each module is designed to be plug and play, fitting to pre-installed brackets and seamlessly integrating with other panels.

The RenoZEB approach is user-centric, so the renovation balances the user’s individual comfort preferences with the need to reduce the overall energy use by over 60%. The resident will benefit from hugely improved control of their environment, harnessing natural daylight, better ventilation, air quality and precise temperature control. In practice this means the retrofitted facades are laden with Internet of Things sensors, and a new communications gateway is installed as part of the refurbishment. Some residents will even be monitored using wearable devices, with smart software tracking their metabolic data to check their comfort level.

Real performance data

Scaling RenoZEB-type solutions to a continent-wide scale requires massive collection of data on real performance. Gone are the days when the retrofit industry can rely on deemed savings or calculated values. The new generation of nZEB buildings uses active technologies responding to occupants’ behaviour and requirements, live monitoring and continuous optimisation, which in turn will calibrate and refine the models used to design future renovation solutions.

Thus, once the retrofits are installed later in 2020, a cascade of performance data will follow. The consortium will use this to retro-commission the technologies, evaluate the conditions for residents, and estimate the uplift in property value. During this monitoring phase, the project consortium will concentrate on the finance and business models that will allow RenoZEB technologies to be commercialised, contributing to the scale-up of deep retrofit across Europe.

Deep-retrofitting an Estonian apartment block

One of the first RenoZEB projects is a 1,300m2, 16-apartment block in Võru in the south of Estonia. Built in the late 1980s, the building is now in need of refurbishment, and participation in RenoZEB follows several years of engagement between the Tartu Regional Energy Agency – a partner on the RenoZEB project – and the building’s owner. Apartments are individually owned, meaning direct engagement with residents has also been essential.

The building construction is primarily clay brick, which will be augmented with a complete façade system, incorporating triple-glazing, to achieve an overall U-value of 0.18W/m2K. This radical improvement in insulation, replacement of the heating system and the introduction of mechanical ventilation and heat recovery, will reduce overall energy demand by around 60%. When the refurbishment takes place later in 2020, occupants will benefit from lower heating and hot water costs, better indoor air quality, greater control over their environment, and an uplift in property value.


Related competencies: Sustainability

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