Soil De-impermeabilization: Definition, Challenges, and Regulatory Requirements in France

Soil De-impermeabilization: Definition, Challenges, and Regulatory Requirements in France

What is soil de-impermeabilization?

Definition and distinction from de-artificialization

De-impermeabilization refers to the process of removing or replacing an impermeable surface with a permeable or vegetated surface, thereby allowing water to infiltrate the soil once again.

It differs from de-artificialization in the strict sense, which involves restoring land to its natural or semi-natural state. Under the ZAN Act, de-impermeabilization contributes to counting “de-artificialized” areas as long as it results in effective renaturation.

What types of surfaces are affected?

• Parking lots (paved or concrete)
• Roads and sidewalks
• Roofs (replaced with green roofs)
• Courtyards and open spaces (government offices, schools, hospitals)
• Industrial and logistics zones

Why sealing the ground is problematic

The Water Cycle and Runoff

Natural soil absorbs between 50% and 90% of rainwater. Impermeable soil absorbs between 0% and 10%. This excessive runoff is one of the main causes of urban flooding.

Contribution to heat islands

An unpaved surface absorbs solar radiation and releases it at night in the form of heat. The difference in surface temperature between an asphalt parking lot and a green space can reach 20°C to 25°C on sunny days.

Loss of biodiversity and carbon sequestration

Sealed soil is dead soil. Removing the seal, followed by restoration, allows the soil’s flora and fauna to gradually recover. Living soil can sequester between 0.5 and 3 tons of CO2 per hectare per year.

The regulatory framework in France

The ZAN Act and the goal of Zero Net Land Conversion

The Climate and Resilience Act (2021), as amended by the Act of July 20, 2023, sets two objectives:

1. Halve the rate of land conversion over the 2021–2031 period
2. Achieve Net Zero Land Conversion by 2050

Requirements in urban planning documents

Local Urban Planning (PLU) and Territorial Coordination Plans (SCoT) must incorporate ZAN objectives, including an assessment of impervious surfaces, reduction targets, and concrete measures to restore permeability.

The Surface Biotope Coefficient (SBC)

The CBS measures the proportion of areas conducive to biodiversity on a plot:

• Natural soil = coefficient 1.0
• Green roof with slabs = 0.5
• Green roof = 0.7
• Waterproof area = 0

Methods of de-impermeabilization

Demolition and restoration

The most radical approach: removing impervious surfaces and replanting. It is the most environmentally effective option, but also the most expensive.

Permeable pavements

Permeable pavers, stabilized gravel, and porous concrete: these materials allow for traffic or parking while restoring partial permeability to the ground.

Gardens, swales, and green spaces

Creating swales, rain gardens, or green spaces in place of paved areas is effective and beneficial to the local environment.

How can we measure and monitor the loss of soil permeability in a given area?

Key indicators

• The imperviousness rate: % of impervious surface area
• Vegetation cover rate: % of soil covered by vegetation
• The CBSh: a composite index that incorporates the quality of habitats for biodiversity

The Value of Aerial Imagery

High-resolution aerial imagery makes it possible to map these indicators across an entire region in just a few days, without the need for field surveys. Netcarbon analyzes these images to produce maps at the parcel level.

Who are the stakeholders involved?

De-impermeabilization applies to: local governments (roads, schoolyards), developers (green roofs in new construction projects), public housing providers (residential courtyards), infrastructure companies (parking lots), and businesses (courtyards and parking lots).

Would you like to know the level of carbon sequestration in your region or on your property? Netcarbon can map it in just a few days, without the need for field surveys. Request a demo.