© CML Municipality of Lisboa

A green make-over for heritage buildings

Today, when mayor Fernando Medina climbs the remarkable central staircase of the historical Paços do Concelho City Hall, he can enjoy a renewed thermal comfort while still admiring the work of architect José Luís Monteiro.

Over a hundred years old, Lisbon’s city hall is an iconic building that reflects the image of Lisbon, and of liberal and republican Portugal. It is home to the mayor’s office, and it is used for city council meetings, as well as high-level receptions of national and international delegations. As it both counts as a service building and as a cultural heritage site, the challenge to renovate it improving its energy efficiency was considerable, but the Lisbon team was up for the task.

A tricky job

According to the European Commission, at least 35% of buildings in the EU are 50 years or older, and Europe’s historic buildings are well-known for not being very energy efficient. They consume large amounts of electricity to light spacious rooms and hallways, and receive expensive bills for heating, or cooling, while lacking proper insulation. The Commission also found that service buildings, such as Lisbon’s city hall, are on average 40% more energy intensive than residential buildings.

Such numbers make it evident that it is crucial to find energy efficient solutions for such buildings to make a significant contribution to reaching the EU’s new target of a 55% reduction in emissions by 2030 – part of the Renovation Wave Strategy. However, as some of these buildings are protected, owners have to overcome additional barriers such as strict heritage codes that make them tricky to renovate.

This is an issue that the ROCK project has raised in its ‘Recommendations to decision and policy makers’, calling for creating a balance between flexibility and regulation. Based on the experiences from the project, which Lisbon is also part of, cities must be allowed to balance protection and preservation of cultural heritage with flexibility and innovation, and decisions should be based on impact assessments and stakeholder participation.

A quest towards sustainable heritage

In the quest to renovate Lisbon’s city hall, multiple stakeholders were involved to find the right balance. The Lisbon Municipality, in charge of the renovation project, together with the Energy and Environment Agency, Lisboa E-Nova, overall coordinator of the implementation tasks of the Sharing Cities project, coordinated their efforts with Portugal’s Directorate-General for Cultural Heritage, charged with protecting the country’s historic treasures. With the help of digital models of the city hall created by the Technical University of Lisbon, they discussed solutions and found agreements.

“The process was an interactive process between the team and all the national stakeholders, mainly the National Directorate for Culture and Heritage,” explains Eduardo Silva, project manager at Lisboa E-Nova. “In some cases, it took two years to find an agreement. It wasn’t an easy process, but we have provided solutions to ensure that these measures are possible to be implemented in these buildings.”

It wasn't an easy process, but we have provided solutions to ensure that these measures are possible to be implemented in these buildings
— Eduardo Silva, project manager at Lisboa E-Nova

Typical renovations aiming at increasing the energy efficiency of a building would start by working on insulation, but insulation material would have ruined the iconic facade of the city hall, and was too complex to be integrated indoors within richly gilded walls and ceilings. This left the windows and doors to improve. Again the standard go-to solution, double-glazed aluminium or PVC windows, would not work for the city hall as the 100 windows could only be restored, so the final choice fell to renewing the existing wood frame and adding a thicker single glaze.

While the installation of the new heating, ventilation and air conditioning system, and the replacement of the 2,000 chandelier light bulbs with Light-emitting diode (LED) technology were not contentious, the installation of solar panels spurred more negotiations.

“The National Directorate was very worried about the visual impact that this technology could bring in terms of several panoramic views we have in the city,” says Eduardo.

The project team procured panels in darker colour to better blend with the roof tiles, and they carefully and strategically positioned them for sensible architectural integration.

“This was a very important step to show also to the National Directorate that intervention is possible without undermining the visual impact of the panoramic views,” confides Eduardo.

Intervention is possible without undermining visual impact
— Eduardo Silva, project manager at Lisboa E-Nova

“A continuous work on reducing non-technical barriers to the installation of solar systems in these roofs is at stake,” says Deputy Mayor, José Sá Fernandes “so that the goals of the Lisbon Solar Energy Strategy are fulfilled, as well as the vision of an energy-poverty free city.”

View of Lisbon City Hall solar panels © CML Municipality of Lisboa

Results in compromise

At this point, the renovation of Lisbon’s city hall might sound like a long list of compromises, so can the building still deliver on the promise of more energy efficiency? The short answer is yes.

The analysis is not definitive, and the final impact of the renovation will be clearer in a few more years of monitoring, but the numbers so far are promising. The energy consumption went from 493.72 MWh annually in 2016, before the renovation started, to 246.93 MWh in 2019, after all solutions were implemented, a 50% decrease equivalent to 84 tons of CO2 emissions reduction.

“Of course it’s much easier to implement these measures in other buildings,” admits Eduardo “for heritage buildings the work is much more expensive, not only because of the technical solutions that have been implemented, but considering all the procedures the companies had to follow to ensure the correct implementation of the different measures.”

The good news however is that Lisbon’s payback time is around 10 years for the €420 thousand invested by the city, with an additional €168 thousand EU funding received through the Sharing Cities project.

Who’s next?

“Thinking Lisbon Solar City implies proactive involvement of architects, urbanists, heritage authorities and citizens in a continuous dialogue and collective action to facilitate the sensible realisation of the city decarbonisation goals,” says Deputy Mayor, José Sá Fernandes.

To cities that are planning similar historic renovations, Lisbon suggests starting with a building assessment clearly laying out the baseline energy performance, along with what can be done and what the cost savings would be. Cities should also involve all national engineering or heritage authorities from the get-go to avoid bureaucratic surprises, and to ensure all procurement requests have the right details and restrictions.

“The lessons learnt with the City Hall energy renovation should also inform wider interventions in the built environment,” says deputy Fernandes “notably residential buildings sited in heritage protected areas.”

The lessons learnt with the City Hall energy renovation should also inform wider interventions in the built environment
— José Sá Fernandes, Lisbon deputy mayor

Cities who are interested in pursuing quality interventions in cultural heritage can also get involved in the new peer-learning programme Cultural Heritage in Action – a call for participation will be published soon. As one of its focuses, the programme believes that quality interventions in cultural heritage “are essential if we want to bequeath our heritage to future generations – they are the outcome of multiple factors including aesthetics, habitability, environmental friendliness, accessibility, integration into the surrounding environment and affordability.”

There are many paths to achieving both heritage conservation and sustainable living, and many of our cities are already taking these steps, who will join next?

Find out more about the Lisbon renovation within Sharing Cities here and here

Read Culture Heritage in Action’s catalogue of good practices here

Wilma Dragonetti Eurocities Writer
in numbers:
  • 50%

    decrease energy consumption
  • 84 tons

    of CO2 emissions reduction
  • 10 years

    payback time
  • €420 thousand

    invested by the city