Empty homes have become one of Europe's preferred climate solutions. Faced with housing shortages, rising construction costs, and growing pressure to reduce emissions, policymakers are increasingly turning their attention to what already exists: empty flats above shops, offices that may never be fully occupied again, and houses with more space than their residents use. This shift is welcome. Reusing buildings generally requires fewer materials, less energy, and less land than building new ones.
But there is a risk in how this agenda is being framed. In many policy discussions, the focus is no longer on sufficiency, but on the "better use of existing buildings". The phrase sounds sensible and uncontroversial, yet it strips away much of what makes sufficiency a transformative idea.
The IPCC identifies sufficiency as the first pillar of climate mitigation in the buildings sector, ahead of efficiency improvements and renewable energy. Sufficiency is about "avoiding the demand for energy, materials, land, water and other natural resources while delivering wellbeing for all within planetary boundaries". It combines two objectives: a social floor below which nobody should fall, and an ecological ceiling that society cannot collectively exceed.
The idea of "better use" captures neither. Instead, it turns housing into a productivity question: how can we generate more housing from the existing stock? This is essentially an efficiency approach applied to buildings. And the benefits of efficiency improvements are often limited by rebound effects. Bringing an empty building back into use does not automatically reduce environmental pressures if new developments continue to spread across farmland, demolitions continue, and living space per person keeps increasing.
In that case, reuse simply adds more floor space to an already expanding system. The key question is therefore not whether an existing building can be reused, but whether its reuse avoids the need for new construction. Reuse becomes a sufficiency strategy only when it replaces new development rather than accompanies it.
Three questions need to be brought back to the centre of the European debate.
First, what are the limits?
Today, the environmental value of reuse is often measured against a hypothetical new development. A reused building is considered successful if it performs better than a newly built one. But this is a relative measure. Sufficiency requires us to ask a different question: does housing remain within planetary boundaries?
How much land can still be developed? How much carbon can still be emitted? How many materials can still be extracted?
Europe has committed to ending net land take, yet housing policies are rarely evaluated according to their contribution to this objective. Success is still largely measured by the amount of housing delivered. From a sufficiency perspective, housing policy should instead be judged by its ability to avoid the need for new construction altogether.
Second, wellbeing for whom?
Justice sits at the heart of sufficiency. The environmental challenge is not simply that Europe uses too much housing space and too many resources. It is that housing resources are distributed profoundly unequally.
Discussions about "under-occupied" homes often focus on older people living alone in family houses. They are easy to identify, highly visible in statistics, and often have limited ability to resist public scrutiny. Yet, this focus raises an uncomfortable question: why do housing policies so often start with those who have a spare room rather than those who own multiple homes?
The same cities that contain underused dwellings also contain overcrowded flats, waiting lists for social housing, young adults unable to leave their parents' home, and people experiencing homelessness. These realities are connected. Under-occupation, overcrowding and homelessness are not separate problems. They reflect the unequal distribution of access to housing.
A sufficiency perspective therefore asks not only where space is unused, but who lacks access to adequate space and who controls more than they need. This shifts attention toward second homes that sit empty most of the year, investment properties kept vacant, short-term rental portfolios, and housing held primarily as a financial asset rather than as a place to live.
This distinction matters because climate transitions that fail to address inequalities rarely gain legitimacy. Asking ordinary households to adjust while leaving speculative accumulation untouched risks turning sufficiency into a burden for those with the least power and the fewest alternatives.
The question is not simply how to use housing more efficiently. It is how to ensure that everyone has access to adequate and affordable housing before some continue to have more housing than they need.
Third, what counts as success?
What we measure shapes what we value.
If success is measured in square metres delivered, then the most visible and resource-intensive interventions will always appear most successful: large conversions, extensions, and redevelopment projects.
Less material-intensive solutions tend to disappear. Home-sharing, intergenerational living, cooperative housing, and housing exchanges often avoid more demand than construction projects. They can also meet social needs that conventional housing indicators rarely capture: companionship, care, mutual support, and a sense of belonging.
Housing is not only about providing physical space. It is also about creating the conditions for security, participation, and social connection.
Policy instruments must therefore be seen as part of a wider strategy rather than as isolated measures. A vacancy tax, limits on land development, affordable housing policies, and stronger tenant protections reinforce one another. Assessing them individually misses how they work together to reduce demand and improve wellbeing.
Underlying all of these debates is a question that European housing act does not ask: how much living space is needed to ensure a good life for each of us?
Space requirements are often treated as personal preferences. In reality, they are social norms shaped by planning rules, mortgage systems, housing markets, and building standards. Across Europe, these expectations have increased steadily for decades.
As long as those expectations remain unquestioned, gains achieved through reuse are likely to be absorbed elsewhere. A square metre saved in one place can easily reappear as a larger home, a second residence, or another housing development.
Answering the question of how much is needed to ensure a good life for each of us cannot be left to markets alone. It is fundamentally a democratic question.
At the same time, sufficiency cannot be pursued through surveillance. Monitoring people through mobile phone data, social media activity, or other intrusive methods would quickly erode public trust. Instead, residents, tenants, and local communities must play a central role in deciding what constitutes wellbeing and how housing resources should be shared.
None of this is an argument against bringing empty homes back into use. On the contrary, reuse should be a central part of housing and climate policy. But its value does not lie in producing more housing supply. Its value lies in making it possible to meet housing needs while building less, consuming fewer resources and using less land.
The question, however, is not only environmental. It is political. Who benefits from the space that is freed? Who decides what counts for a good life? And whose housing needs are prioritised?
Climate justice requires more than lower emissions. It requires a fair distribution of housing opportunities, resources and environmental burdens. Reusing empty homes contributes to that goal only if it helps those who currently have too little while placing limits on those having too much. It also requires ensuring that any housing brought back into use remains affordable over time. Otherwise, public resources can end up subsidising the transfer of vacant buildings into profitable assets, while housing insecurity persists.
Community land trusts, housing cooperatives, social housing providers and anti-speculation safeguards are therefore not optional additions. They are the mechanisms through which the benefits of reuse are shared rather than captured. Without them, reuse may reduce emissions while leaving housing inequalities untouched, or even worsening them.
Europe's housing crisis and ecological crisis stem from the same belief: that every shortage can be solved by producing more. Sufficiency starts from a different principle. It asks how existing resources can be shared fairly before new resources are extracted.
Sufficiency asks not only how much housing society can build, but how to ensure everyone has access to adequate and affordable home. Unless those questions are addressed, the reuse of empty homes may improve efficiency, but it will not deliver climate justice.