Turning Empty Spaces into Energy-Efficient and Affordable Homes
Before building on new land, Europe should make better use of what it already has. Across the continent, addressing the housing crisis must include the reactivation of abandoned and empty dwellings.
Miro spent two months searching for a rental apartment in Zagreb and described the experience as worse than in major global cities like London or Dubai in terms of affordability. Soaring rents, shrinking supply and sudden lease terminations are particularly affecting young families and students in Croatia.
In Athens, Eirini and Ioanna were forced to leave their homes as rent consumed an unsustainable share of their income. Students also report the near impossibility of finding affordable accommodation in university cities due to tourism pressure, short-term rentals and housing shortages.
Meanwhile, the first major survey on homelessness in Slovenia’s capital, Ljubljana, highlights that a growing number of couples with children and young adults are becoming homeless because of lease cancellations, financial hardship and lack of affordable housing.
These are not isolated cases, but clear signs that Europe is facing a severe housing crisis. The emergency became so evident that, in 2024, the European Commission appointed its first-ever Commissioner for Energy and Housing, Mr. Dan Jørgensen, who presented the long-awaited Affordable Housing Plan in December 2025, followed by a new package of measures in 2026.
Against this backdrop, many publicly funded initiatives are focusing on housing affordability. One of them is the recently launched Transforming Invisible Buildings (TIB), funded by EUKI.
From Zagreb to Athens, cities need data and strategies to tackle the housing crisis
By 2028, Transforming Invisible Buildings aims to address both energy efficiency and housing affordability by bringing vacant and underused buildings back into use. Rather than constructing new ones, we should first reactivate the 47.5 million vacant homes across the EU.
Through vacancy mapping, policy labs and capacity-building workshops, first implemented in the pilot capitals Zagreb, Ljubljana and Athens and later expanded to six additional cities, the project seeks to influence housing policies at both national and EU levels. Its goal is to integrate sufficiency principles into housing strategies and provide the scientific evidence needed to return underused buildings to the housing market.
Zagreb, Ljubljana and Athens offer strong testing grounds for vacancy mapping methodologies and advocacy approaches that could later be replicated across Europe. All three cities are heavily affected by the housing crisis and still lack comprehensive data that would support a clearer understanding of the housing situation.
According to data, electricity consumption data suggests that around 10,000 residential units in Ljubljana may be vacant. The local partner Institute for Innovation and Development of the University of Ljubljana (IRI UL) stresses that limited data availability and the absence of systematic policy tools prevent a clear understanding of the scale of underused housing. “Through TIB, IRI UL aims to help develop governance models and methodologies that can support the activation of vacant properties and better-informed policymaking”.
“Greece is one of the clearest examples in Europe of the coexistence of extensive vacant housing stock and severe housing affordability pressures,” says INZEB, the Greek project partner specialising in energy efficiency, innovative financing and energy poverty. According to the organisation, around 2.2–2.3 million dwellings across Greece are vacant or not used as primary residences. Through TIB, INZEB aims to contribute to a scalable framework for transforming inactive housing into affordable, energy-efficient homes.
In Croatia, the project partner Society for Sustainable Development Design (DOOR) points out the contradiction between the country’s high number of vacant homes and the growing housing affordability crisis. Vacant dwellings have increased by 149% over the past two decades, while the country faces a shortage of more than 236,000 affordable homes. Despite a strong political commitment and concrete initiatives to address the problem, DOOR notes that “the connection between vacancy reactivation and energy efficiency is still missing”. Through TIB, the organisation will work with the City of Zagreb to integrate at least one policy instrument linking vacant housing reactivation with energy efficiency requirements into the city’s framework by the end of the project.
Interested in learning more about the housing crisis and Transforming Invisible Buildings? If you are in Brussels from 9 to 12 June, visit the New European Bauhaus Festival and stop by our stand!