The shape of a city is not an accident. Behind every street layout, every building height, and every green space lie political, economic, and regulatory decisions that shape the daily lives of millions of residents. In France, the trajectory towards zero net artificialization (ZAN) has imposed, since 2021, a profound overhaul of how urban structures develop, balancing constrained densification and the redevelopment of brownfields. This regulatory framework reshuffles the cards of urban planning and questions the relevance of inherited models.
Urban Brownfields and the ZAN Trajectory: The Lever Ignored by Traditional Urban Planning
Discussions about urban forms often focus on the opposition between dense cities and sprawling ones. Recent planning documents tell a different story, one of available land shifting towards already artificialized sites.
The Climate and Resilience Law of 2021, supplemented by the ZAN Law of 2023, sets a goal of zero net artificialization of land by 2050. Regional assessments must be submitted to Parliament between January and June 2027. In several intercommunalities like Cœur de Flandre agglo and Flandre-Lys, urban planning documents already impose reductions of over half in land consumption compared to the decade 2011-2020.
This constraint redirects the production of housing and service spaces towards brownfields, whether they are former industrial sites, logistics hubs, or decommissioned gas stations. To better understand the different urban structures according to Encherimmo, it is essential to place each morphology in this context of dwindling virgin land. The elevation of existing buildings and the conversion of vacant offices become concrete alternatives to peripheral expansion.
Urban Density and Quality of Life: A Relationship More Complex Than a Simple Ratio
Linking density and discomfort is a persistent shortcut. Density measured in terms of the number of housing units per hectare says nothing about the height of buildings, the presence of inner courtyards, or access to nearby green spaces. Two neighborhoods with the same density can offer radically different living environments depending on their morphology.
The model of suburban fabric, with its row houses of two to three levels, produces significant density while preserving access to land for each housing unit. Field reports diverge on this point: some residents find a compromise between privacy and community life, while others point out the lack of sound and thermal insulation in these older constructions.
What Built Form Changes for Mobility
A compact urban fabric mechanically reduces distances between housing, services, and jobs. Urban morphology directly conditions the mobility needs of residents. A neighborhood organized around a walkable center generates fewer motorized trips than a residential subdivision served by a single departmental road.
On the other hand, densification without anticipating public transport creates saturation situations. Increasing the number of housing units in an already under-equipped area for bus lines or bike paths merely shifts the problem from sprawl to congestion.
Urban Forms and Construction Costs: The Hidden Arbitration of Local Authorities
The choice of an urban structure has direct budgetary consequences for local authorities and developers. Water, sanitation, and road networks cost proportionally less in dense fabric than in suburban expansion, where each new subdivision requires additional kilometers of pipelines and roads.
The conversion of brownfields, while reducing artificialization, poses an inverse cost problem. The decontamination of an old industrial site, soil studies, and compliance upgrades represent high initial investments. Available data do not consistently conclude that conversion is economically advantageous compared to new construction in expansion areas. The equation depends on the level of contamination of the site, its location, and the pressure of the local real estate market.
Densification of Existing Residential Areas
Several local authorities are experimenting with parcel division in residential areas, allowing for the construction of a second housing unit on a plot originally intended for one. This approach meets several simultaneous objectives:
- Producing additional housing without consuming agricultural or natural land, in line with the ZAN trajectory
- Making existing networks (water, electricity, roads) already sized for the neighborhood more profitable
- Providing aging homeowners with a source of income or a suitable housing solution on their own land
Field reports indicate that social acceptability remains the main barrier. Existing residents often perceive the densification of their neighborhood as a degradation of their living environment, even when new projects respect existing dimensions.
Sustainable Development in France: What RE2020 Changes for Built Forms
The environmental regulation RE2020, which is gradually applied to new constructions, modifies material choices and thus the possible architectural forms. The increased use of wood and lightweight metal structures opens up possibilities for elevating existing buildings whose foundations would not support additional reinforced concrete.
This regulatory evolution also favors rehabilitation operations rather than demolition-reconstruction. Adapting an existing building to current thermal standards consumes less carbon than building a new one, provided the load-bearing structure allows it. Town centers and medium-sized cities, where old buildings are often underutilized, are prime candidates for this type of intervention.
The convergence between ZAN, RE2020, and pressure on the housing market outlines an urbanism where the shape of cities is negotiated as much in existing floors as on empty plots. Local authorities that anticipate this triple constraint by identifying their convertible brownfields and elevatable buildings now have a concrete advantage over those waiting for the regulatory deadlines of 2027 and 2050.
