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15 February 2022
Sharply increasing damage and an unsuitable prevention and
compensation regime
The shrinkage-swelling of clay soils, or the shrink-swell phenomenon, consists of a series of
movements caused by variations in the water content of clay soils. Known in France for more
than 30 years, it has damaging consequences for housing that give rise to compensation,
included since 1989 in the natural disaster regime, known as “Cat Nat”. This phenomenon
has attracted recent attention from the public authorities due to the growing magnitude of
the risk and the related claims and also because of the increase in dissatisfaction expressed
by the exposed populations. Referred to by the National Assembly Public Policy Evaluation
and Audit Committee concerning the prevention and compensation of damage caused by
the shrink-swell phenomenon, the Court of Accounts conducted an investigation taking into
account the history of the issue and above all, more recent parliamentary and
administrative work. The report that is being published today shows that as the
phenomenon is evolving, its management is increasingly being called into question. In view
of this situation, the Court recommends promoting preventive measures and reconsidering
the compensation regime.
A long-standing phenomenon, with compensation included in the natural disaster regime
The shrink-swell phenomenon is the result of the combination of a geotechnical situation and
a series of climatic episodes: on certain clay soils, a series of wetting periods and drying
periods can cause damage to buildings. The Court notes that the implementation of
preventive measures was delayed and remains insufficient today. Knowledge of the
phenomenon, although long-standing, was not accompanied by any effective prevention
policy until the entry into force of the French Act of 23 November 2018, known as the ÉLAN
Act, which set out construction rules for high-risk areas.
A foreseeable increase in the shrink-swell phenomenon, with an increasingly contested
management strategy
Taking into account the reasoning and recommendations formulated last March by the
General Council for the Environment and Sustainable Development (CGEDD), the General
Inspectorate of Finance (IGF) and the General Administration Inspectorate (IGA), the Court
analysed the strengths and weaknesses of the compensation regime. Integrated into the
natural disaster regime, the current rules would be sustainable if the damage caused by the
shrinkage-swelling of clay soils was, in the medium term, constant in terms of its frequency,
severity and financial impact. However, the extent of the effects of climate change and the
various forecasts and projections made, in particular by the french public reinsurance group
(CCR) and the French Insurance Federation (FFA), show that this is not the case. Indeed, since
1989, the shrinkage-swelling of clay soils has accounted for 36% of the claims observed for
natural disasters and half of the most expensive events recorded over the same period.
Originally limited to certain regions, it now affects all areas of metropolitan France and more
than half of the stock of single-family homes. All of the studies undertaken recognise that the
costs associated with the shrink-swell phenomenon will increase sharply over the next 30
A more appropriate prevention and compensation system is needed
Based on the natural disaster regime, the compensation mechanism for damage linked to the
shrink-swell phenomenon is currently reaching its limits and should lead the public authorities
to question its very classification as a natural disaster. The spread of the phenomenon across
metropolitan France, its intensity and its social and financial consequences require that the
responses provided by the public authorities be adapted. In this report, the Court’s
recommendations focus on informing purchasers of potentially exposed properties,
monitoring the effective implementation of the construction provisions in the Élan Act and,
for buildings built before 2020, developing research into effective remedial measures. The
Court believes that if compensation continues to fall under the natural disaster regime,
significant changes will need to be considered, following thorough impact assessments.
Read the report
Emmanuel Kessler
Head of Communications
01 42 98 55 62
Julie Poissier
Head of press relations
01 42 98 97 43
Cour des comptes
Cour des comptes