Fine cracks appear on the walls then widen, lengthen, and end up endangering the very structure of the buildings. Eleven million houses in France are threatened by clay shrinkage-swelling (RGA), a phenomenon which is increasing with global warming.
The fifth measure, out of 51, of the third National Plan for adaptation to climate change presented Friday by Prime Minister Michel Barnier and the Minister of Ecological Transition, Energy and Climate, Agnès Pannier-Runacher, plans to “protect the population of disorders on buildings linked to the shrinkage-swelling of clays”.
Known by its acronym RGA, the phenomenon has become a “national scourge” with the multiplication of periods of drought and episodes of extreme rain due to climate change, according to Sébastien Leroy, the mayor of Mandelieu-la-Napoule (Alpes Maritimes) , who launched a cry of alarm in 2023 before the Association of Mayors of France.
Soils, when clayey, shrink in dry periods and swell in wet periods, which causes cracks, especially for buildings without a suitable foundation or structure. The risk ranges from an unsightly crack to a dangerous decree.
Climate change, by accentuating episodes of drought and precipitation, intensifies this phenomenon, explains Cerema, public technical expert for the management of the transition of cities and territories.
The second cause of compensation in France
Nearly half of the 11 million buildings concerned were built after 1976, according to the Ministry of Ecological Transition. RGA has thus become the second cause of compensation in France behind floods, according to France Assureurs.
According to forecasts from the Central Reinsurance Fund (CCR), losses resulting from RGA are expected to increase by 44% per year by 2050 if average temperatures in France rise by 1.5 degrees compared to pre-industrial times. . And therefore much more if we have to adapt to an average increase of 4 degrees.
Compensation for damage is provided under the “natural disasters” regime. To be eligible, the area where the damaged building is built must have been recognized as affected by a “natural disaster”. But many requests for recognition of loss are unsuccessful.
In total, 84% of municipalities in France have more than 50% of houses exposed to clay zones, according to the “reference for the resilience of buildings to natural hazards” published last September.
The public site Georisks has listed the risk areas, and publishes a map of France commune by commune, in conjunction with the BRGM.
The plan presented on Friday mainly provides for strengthening prevention for new constructions in order to mitigate the cost of subsequent damage, regular updating of the exposure map taking into account episodes of drought from 2025, and better information individuals on the quality of houses.