In France, more than 10 million homes threatened by clay shrinkage-swelling (RGA) due to climate change

The fifth measure, out of 51, of the third National Plan for Adaptation to Climate Change (PNACC-3) presented on Friday by Prime Minister Michel Barnier and the Minister for Ecological Transition, Energy and Climate, Agnès Pannier-Runacher, plans to "protect the population from damage to buildings linked to the shrinkage and swelling of clays".

Known by its acronym RGA, the phenomenon has become a "national scourge" with the increase in periods of drought and episodes of extreme rainfall due to climate change, according to Sébastien Leroy, the mayor of Mandelieu-la-Napoule (Alpes Maritimes), who had sounded the alarm in 2023 before the Association of Mayors of France (AMF).

Soils, when clayey, shrink in dry periods and swell in wet periods, which causes cracks, especially in buildings without a proper foundation or structure.

The risk ranges from unsightly cracks to a danger order.

Climate change, by accentuating episodes of drought and precipitation, intensifies this phenomenon, explains Cerema, a public technical expert for the management of the transition of cities and territories.

Nearly half of the 11 million buildings concerned were built after 1976, according to the Ministry of Ecological Transition.

The RGA has thus become the second cause of compensation in France behind floods, according to France Assureurs.

According to forecasts by the Caisse Centrale de Réassurance (CCR), claims 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 the pre-industrial era. And therefore by much more if we have to adapt to an average increase of 4 degrees.

Compensation for damage is provided under the "natural disaster" scheme. To be eligible, the area where the damaged building is built must have been recognised as having been affected by a "natural disaster". However, many requests for recognition of damage are unsuccessful.

In total, 84% of French municipalities have more than 50% of their houses exposed to clay areas, according to the "benchmark of resilience of buildings to natural hazards" published last September.

The public website Georisques has listed the risk areas and publishes a map of France by municipality, in conjunction with the BRGM.

The plan presented on Friday mainly provides for increased prevention for new constructions in order to reduce the cost of subsequent damage, regular updating of the exposure map taking into account drought episodes from 2025, and better information for individuals on the quality of houses.