Juan Álvaro Alayo grew up in the Ensanche de Bilbao in the 60s and 70s. After studying, he moved away from his city, worked in England, and eventually came back home, more or less, because his current home is a few kilometers away from the Ensanche. Far enough to mythify the setting of his childhood and study it obsessively.
"In my square kilometer, 60,000 people lived in 1975," recalls Alayo, a professor at IE University and an international consultant for urban projects. "Imagine that in my parents' house, there were nine of us, including siblings, parents, and the housekeeper, and it was not exceptional. How many families like that are left in Bilbao? Very few. I have calculated that if in 1975 I moved within a radius of 400 meters from my building entrance, in other words, a five-minute walk, I had a circle of 6,000 homes and 200,000 square meters of commercial space. Those 200,000 square meters are equivalent to a large mall, mind you. And in 6,000 homes, with four or five residents per home, we get 26,000 people."
We all idealize the past, but Juan Álvaro Alayo speaks of that hyper-populated world as a lost paradise where a family had almost all its needs met within a short walk, where the slightly rich and the slightly poorinhabited the same streets and shared codes and interests, and where children were educated nourished by the infinite and complex stimuli of a real city. The longed-for 15-minute city of 2025 was the five-minute city in 20th-century Spain.
And no, it was not an ideal world because it lacked green areas and the air quality was poor... But it is impossible not to long for its virtues now that the Abando neighborhood, the Ensanche de Bilbao, has 23,785 inhabitants (Eustat data for January 2024) in an area of 1.17 square kilometers; the Barrio de Salamanca in Madrid, 27,019 inhabitants per square kilometer, and L'Eixample in Barcelona, 36,023. Right in Barcelona, on the border with L'Hospitalet, there is another even more crowded square kilometer, a piece of city that houses 53,119 people and is the most densely populated place in the European Union. Its center, more or less, is halfway between the Collblanc and Santa Eulàlia stations.
"Nowhere in Europe are there square kilometers as dense as those we have in Spain," says Alayo. "Some neighborhoods in Paris are comparable but always below. And the most urban areas of the United Kingdom and Germany have half the density."
Alayo explains that there is a measure more important than inhabitants per square kilometer: the coefficient of square meters built per square meters of surface. "In the 20th-century expansions, there was a ratio of up to five to one. In the developments of the last 25 years, we are at 1.2 meters built per square meter of surface. And 1.2 is no longer an urban measure, if anything, it is peri-urban."
Now comes the paradox: the good apartments in the old expansions are much more expensive than their modern and spacious equivalents in the paus. Spaniards still prefer the noisy and solid streets of their parents.
The debate on city density has become relevant for many reasons. First, due to the alarm over housing inflation: this year, the average price per square meter of residential property in Spain exceeded the previous record before the 2008 crisis. Second, because the housing deficit in Spain has become a chronic problem: Spain built 90,000 new homes in 2024, but the demand entering the market each year is three times higher. And third, as a consequence of all the above, after 30 years of housing policies based on large new urban land operations, the feeling is one of exhaustion. The paushave offered great apartments for several generations of middle-class professionals, but have not facilitated access to housing, not even for their children. And Spanish cities, reduced in density, have become segregating, lonely, bland, and expensive to maintain in their infrastructure. Who wouldn't want to live on Ercilla Street in Bilbao.
Earlier this month, the Popular Party, one of the main promoters of new land policies during these 30 years, presented the Zaragoza Agreements, a housing, city, and energy efficiency program that caught attention for its anti-squatting proposals. However, perhaps more interesting is the fine print: the third point of the document talks about streamlining and loosening height regulations in residential buildings. Faced with the housing crisis, the PP is advocating for the first time to densify cities.
Paloma Martín, senator and Deputy Secretary for Sustainable Development of the PP, explains that their proposal is not so much aimed at bourgeois expansions but at working-class neighborhoods from the 50s, 60s, and 70s, full of now obsolete housing and trending towards marginalization. "In Spain, we have a very aged housing stock," she states. "50% of homes have accessibility issues, and 75% were built before the European energy efficiency directive came into force. We have entire neighborhoods of three or four-story buildings, poorly insulated apartments, without elevators, and with communities that do not have the economic capacity to modernize."
The Popular Party proposes enabling these communities to build upward, to increase heights and occupy vacant spaces, thus becoming promoters of new housing to finance their modernization. In this way, the popular party argues, declining neighborhoods will attract new residents and higher-quality commerce, and coexistence within them will be revitalized.
"There are experiences that have already worked through public housing companies like the one in Madrid. What we want is for the private sector to be able to do the same," says Martín, recalling that the Spanish government committed to the European Union to rehabilitate 85,000 homes per year with PERTE housing funds, but in 2023 only 37,700 files were processed. "Densifying is building a city. If we manage to improve these neighborhoods with better housing, the result will be more security, more economic activity, and more cohesion."
According to José Carpio, a professor at the Polytechnic University of Madrid and urban planning consultant, "any policy that talks about densification, in general, is a good idea." He continues: "In the future, cities will have to grow vertically and not horizontally after many years in the opposite direction. The key is how, because densification can also have negative aspects. If the word 'liberalize' appears, in the sense of removing restrictions and letting the invisible hand of the market act as it pleases, I start to worry."
"Cities will have to grow vertically and not horizontally. The key is how, because densification can also have negative aspects"
Carpio argues that having 3,000 apartments where there are currently 2,000 is perfectly possible and desirable in many neighborhoods in Spain, but it requires careful planning. Where do the new heights affect the sunlight of neighboring houses and where do they not? Who pays for the expansion of public facilities? What happens to schools, social security clinics, municipal sports centers? And with traffic and private transportation? Is it possible to avoid a chaotic landscape of eight-story buildings next to others of three? And how can this densification avoid becoming a speculative practice that benefits a few at the expense of others?
Juan Álvaro Alayo revisits the last question. "If we are lenient with height permits, which I think is fine, we have to consider what happens with the added value that Administrations generate for landowners. If we add up the value of all the land reclassifications that have been done in Spain during democracy, we are talking about a minimum of 500,000 billion euros. It is much more than the bailout transfer."
What remains for the common good of this more or less gifted added value? There is an intuitive answer: what remains are affordable housing units that alleviate the issue of access to housing. "It would be a bit naive to think something like that," Alayo responds. "No one has calculated how many homes would need to be built in Spain to have an impact on prices. 200,000 extra houses? We don't know because administrations cannot consider anything like that, and the private sector is not interested. In the meantime, no operation has an effect on the market. If tomorrow they release land and build 1,000 homes in front of your house, your house will not depreciate, it will appreciate because it will be in a better neighborhood, with more services."
Alayo believes that the price of housing only stops when demand collapses, not when supply surges. And he points out that there are two residential Spains. One has surpassed or is around the peak prices of 2007, but the other remains between 20% and 40% below its peaks. Fifteen provinces are in that last group, including highly urbanized areas like Zaragoza, Murcia, Almería, or Tarragona. "The housing problem in Spain will only be solved with a national plan that counteracts the trend of concentrating wealth in a few cities," he argues. "As long as half of Spain is emptying because no one wants to live there and in the other half there is not enough room for people, housing will be a problem."
What else does the success of an urban densification policy depend on? Mobility. Is that hypothetical neighborhood that goes from 2,000 homes to 3,000 doomed to perpetual traffic jams? "No, but under certain conditions," answers Iosu Ramírez, director of the planning consultancy Leber. "A denser city is more efficient. A very dense one is not much more efficient than a dense one, there are statistics that prove it, but densification always benefits efficiency because it encourages investments in public transportation and short-distance travel, on foot or by bicycle. However, just densifying is not enough. Mixed uses need to be created, so neighborhoods are not only residential but also offer work, commerce, education..."
If residents in a neighborhood with a density of 35,000 people per square kilometer have schools, offices, cinemas, and stores on their streets, high density will favor mobility because they can live without a car. But if they need to go to a shopping center for their weekly groceries and work awaits them in an office park, disaster is inevitable. "Densifying is much better than creating new land, without a doubt, but it depends on two things: high-quality public transportation and mixed land uses," Ramírez argues.
"There are experiences that can serve as a model for establishing densification areas with sustainable mobility criteria," explains José Carpio. "There is the case of transit-oriented developments (TODs) in the San Francisco metropolitan area and the Curitiba model, which focuses densification on express bus corridors."
Carpio raises more questions. "What happens to current residents while their buildings are expanded? There are cases where construction has been done on what was already built. It is possible, but I do not dare to recommend it for all cases. Another thing is what happens in recent models that left a lot of vacant open space. In the United States, in some suburban fabrics, building in the backyards of private homes is allowed and working very well. In Spain, too, there are some fabrics with excess open space. Developments during the bubble years included very generous private open spaces. It doesn't seem crazy to think about dedicating some of that space to create new buildings without disturbing the existing ones."
Ultimately, Carpio envisions a future where the direction proposed by the Zaragoza Agreements to save working-class neighborhoods from obsolescence and marginalization is also applied to middle-class developments to address their inefficiency and conformist way of life. "It sounds a bit harsh, but the reality is that an excess of green areas is killing the essence of cities," concludes Juan Álvaro Alayo. "Ultimately, a pedestrianized street or one where there is more balance between pedestrians and cars can be the best green space possible."