Clay shrink-swell: what should you check before buying a house?
Check the clay shrink-swell exposure map on Géorisques: it rates each area as low, medium or high exposure. Since the January 2026 update, the medium and high zones cover 55% of mainland France and around 61% of detached houses. For an existing house nothing is required at sale: look at the cracks and ask about past claims; for building land in a medium or high zone, the seller must provide a preliminary soil survey.
The phenomenon in two sentences
A clay soil shrinks when it dries and swells when it gets wet again. These repeated movements shift shallow foundations, especially those of detached houses, and eventually crack the walls.
Dry summers make the problem more frequent. Trees close to the house, which draw water from the soil, and poor drainage of rainwater make the movements worse.
Other data often matter for the same house, such as radon, cavities and earthquakes and whether a house is in a flood zone. You can see how a dossier sets them out register by register in the sample dossier.
Reading the exposure map
The map, drawn up by the BRGM (the French geological survey) and published on Géorisques, was updated in January 2026; an order of 9 January 2026 gives it regulatory force. The new zoning applies to sale agreements and deeds for building land and to detached-house building contracts signed since 1 July 2026.
It has limits: it rests on geological maps at 1:50,000. A pocket of clay can exist in an area shown as outside any zone, and a plot in a medium zone can turn out to be barely sensitive. Only a soil survey settles it at plot level.
The ELAN law: the soil survey
In medium or high exposure zones, articles R132-3 to R132-8 of the Construction and Housing Code impose two things:
- on the sale of undeveloped building land, the seller has a preliminary soil survey carried out, annexed to the sale agreement or deed;
- to build a house, the client follows either the specific construction techniques set by order, or those of a design-stage soil survey.
For a house already built, the sale does not require a soil survey. If you plan an extension, the architect or builder will tell you whether a survey is useful.
Extending a house: declaration or permit
Cracks: what to look at during the viewing
- Stepped or diagonal cracks, especially at the corners of openings, rather than fine render cracks.
- Doors and windows that stick, loose tiles, a floor slab that lifts.
- Recently filled cracks, and trees planted close to the walls.
- Invoices for underpinning works, if there were any.
A crack alone does not tell you its cause. A building surveyor or a soil engineering firm can assess it; it is up to you to decide whether to bring one in before the compromis.
Negotiating a house price with facts
Natural disasters and insurance
Drought damage is only covered by the natural disaster guarantee if an order recognises a natural disaster for the commune and the period. The list of those orders is on Géorisques. The state-of-risks report from the seller must show the property’s claims paid on that basis.
Also ask whether a claim was made and refused, and whether works were done with the payout. A repaired house still under a ten-year builder’s guarantee is not the same as a cracked house with no file.
For one address, ScanAdresse shows the clay exposure level, the commune’s natural disaster orders and the other Géorisques hazards, with the source and date of each item.
Frequently asked questions
Is a soil survey required for an existing house?
No. The ELAN obligation covers the sale of undeveloped building land and house building in medium and high zones, not the resale of a house.
Does a high zone make a house unsellable?
No. More than half of detached houses are in a medium or high zone. What matters is the condition of the building, the foundations and the claims history.
How do you know whether the commune had a natural disaster order?
The orders are listed by commune on Géorisques, with the type of event and the dates.
Can you add a condition to the compromis?
The parties can agree conditions precedent. Drafting them is the notaire’s job; the notaire tells you what is possible in your case.
Sources
- Géorisques: clay shrink-swell
- Géorisques: risks near me
- Construction and Housing Code, art. R132-3 to R132-8
- Service-public.fr: state-of-risks report
ScanAdresse is a private service by SRI Group BV (VAT BE1037052239), not connected to any public authority: it brings together public data, with the source and date of every item.
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