Savigny-en-Revermont (France) (AFP)

Here, a crack burst the plaster and a flap threatens to collapse. There, the walls are open to let the light through. Thousands of homes have suffered from the drought of 2018 and the phenomenon is now spreading to areas never before touched.

"It's a house that's almost a hundred years old and that (had) never moved," says Christelle Chaloyard, in Savigny-en-Revermont (Saone-et-Loire). "At first we did not worry too much", but the walls are now crisscrossed, sometimes several centimeters wide.

This house "is worth nothing". "We will not be able to (sell) it, keep it to renovate, it's our memories that fly away," says the 43-year-old woman, who grew up in this house located away from the village, where his father lives alone today.

Savigny-en-Revermont is one of the 262 municipalities of Saône-et-Loire where the state of natural disaster was recently recognized by the government because of the drought of 2018. Throughout France, more than 3,000 municipalities are concerned.

Involved: the movement of clay soils, which swell with moisture at the end of winter and which, from spring and summer, will shrink under the effect of lower rainfall and increase in heat.

- Geographic expansion -

"These last three, four years, we had almost every year episodes a little hot and dry," says Sebastien Gourdier, geotechnician of the Bureau of Geological and Mining Research (BRGM).

The regions affected by the "shrinkage-swelling" of the clay soils are not always the same, continues the specialist: "In 2017, it was the south of France and the PACA region, in 2018, rather the center and the is (from the country) and the south of the Ile-de-France. "

A key for homeowners, problems of airtightness or water, loss of value of homes, and often expensive work, according to the geotechnician, but a risk of collapse that remains according to him very rare.

For thirty years, "the south-west of France is not badly touched" by decrees of natural disaster, but "we saw appear requests of recognition in previously hitherto rather spared regions", as the Great East or Burgundy-Franche-Comté.

Geographical expansion likely to last, according to the expert of the national geological service: "there are many uncertainties, but the trends are in the direction of an increase in the frequency of these episodes of drought or the duration of these canicular episodes ".

The significant number of communes affected in 2018, if it can still evolve, already makes it a year comparable to the severe drought episode of 2003.

- Micropiles -

For Sandrine Orts, departmental referent of the "Forgotten of the heat wave", an association that defends in 22 departments the owners of damaged houses, the decree of natural disaster is only a first step.

"We will be able to call the insurance, make the declaration", but "it is not a long calm river: the insurance will send an expert to see the damage, to say if it is (caused by) drought or not ".

The association recommends that the owners concerned require a so-called "G5" soil study, which requires a durable repair without being limited to superficial repairs.

The works often cost tens of thousands of euros and sometimes exceed the price of the house. In some cases, the expansive resin injection will be sufficient to consolidate the foundations.

In others, more severe, it will install micropiles under the foundations, kind of piles consisting of a metal frame in which one sends a grout of cement, up to 18 meters deep.

For new buildings, a mandatory geotechnical study is provided for in a law of November 2018, which is supposed to help to take better account of the clay composition of soils.

But according to a Senate report on the subject dated July 3, "at present, no penalty is put in place in case of non-completion of this geotechnical study."

© 2019 AFP