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Geotechnical diagnosis of building estate to limit the risk of damage due to climatic variations

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29Oct. 2020
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The Elan law of November 23, 2018 created a new mandatory diagnosis since January 1, 2020 when selling a building estate: a soil study to secure the construction of individual houses.

The Elan law of November 23, 2018 created a new mandatory diagnosis since January 1, 2020 when selling a building estate: a soil study to secure the construction of individual houses.

Why a soil study?

The obligation to carry out a soil study is based on the observation that drought-related sinister, already significant, are expected to continue to increase with climate change. These sinister are caused by the phenomenon of shrinkage and swelling of clay soils, which affects the integrity of buildings, following droughts followed by rainy episodes. This problem particularly affects individual homes, which often have lighter foundations than collective buildings.

Every year 20,000 to 30,000 individual houses are built on clay areas without suitable foundations according to the French Insurance Federation.

The geotechnical study must make it possible to inform a buyer of the potential risk of the estate and transmit the study to the builder for the latter to propose adapted technical solutions.

  • by informing the buyer of the potential risk.
  • by informing the builder to whom the soil study should be given. The builder must then obligatorily propose adapted technical solutions.

The content of the soil study

The geotechnical study is said to be "preliminary" when it identifies the geotechnical risks of a site and defines general construction principles to prevent the risk of ground movement due to drought and soil rehydration.

The geotechnical study is called "design" when it considers the location and characteristics of the building. The purpose of the soil study is then to determine, based on an identification of the geotechnical risks of the site of implantation, the constructive prescriptions adapted to the nature of the soil and the construction project.

Geographical areas concerned by the soil study

The geotechnical study is necessary for an estate located in a risk zone, in practice a clay soil zone. A map of exposure to the phenomenon of differential ground motion is available on http://www.georisques.gouv.fr/.  It distinguishes the zones more or less exposed.

  • high exposure;
  • medium exposure;
  • low exposure;

A soil study is mandatory in areas where the risk exposure is qualified as medium or high.

In the geographical areas subject to geotechnical study, are concerned:

  • sales of construction free estates that can be built on for the construction of individual houses (building estate);
  • contracts for the construction of individual houses (CCMI).

The soil study was to be mandatory for estates sales and CCMIs signed on or after January 1, 2020.

The geotechnical study is valid for 30 years if no soil remediation has been carried out.

The geotechnical design study considering the location and characteristics of the building is valid only for the project for which it was carried out.

Apart from any legal obligation, it is always recommended to carry out a soil study before starting a home construction project.

On July 22, 2020, three decrees were issued to specify the exposed areas, define the content of the geotechnical studies as well as the specific construction techniques. All the measures set up by these texts apply to sale and construction contracts concluded as of January 1, 2020.

Sources:

Articles L112-20 et suivants du Code de la construction et de l'habitation  ;

Décret n° 2019-415 du 22 mai 2019 ;

Décret n° 2019-1223 du 25 novembre 2019 ;

Dossier sur le site du ministère en charge du logement et sur le site des consultations publiques ;

Rapport fait au nom de la commission des affaires économiques sur le projet de loi Elan par Mme Dominique Estrosi-Sassone

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