Grasse: Clay Soil, Subsidence and Cracks – Official Data

Why every file in Grasse has to be read through its local context

In Grasse, we work in a particularly exposed area – and once you know the terrain, you quickly understand why. The commune climbs through very marked relief: the hills of old Grasse, the slopes overlooking the Siagne and Grand Vallon valleys, and the more recent neighbourhoods that spread towards the plain and the heights of Saint-Jacques or Plascassier. This rugged topography pushed 1970s-80s developers to build villas and Provençal bastides on shallow foundations, often terraced or on cut-and-fill platforms, without always taking into account the clayey nature of the marly subsoil typical of the Grasse hinterland. The more modern estates, built during the 2000s property boom on the last sloping plots available, did not always benefit from thorough soil surveys, which explains heightened sensitivity to clay shrink-swell (RGA – retrait-gonflement des argiles). Vegetation also plays a significant role: pines and olive trees planted near homes, with their powerful root systems, dry out the clay locally during summer drought, deepening differential settlement under building corners. We are regularly called out for stair-step cracks on the façades of hillside villas – the classic sign of a clay ground working through the wetting-drying cycles of the Grasse climate.

Drought in the rear-view mirror: 35 years of measured rainfall

Weather archives for the area cover 35 complete years (1991-2025). The driest ever recorded: 2017, with 507 mm of rain over the year, against a local average of 917 mm. 2022 ranks as the 3rd driest year out of 35 (636 mm vs a 917 mm average); 2023 follows in 4th place (654 mm).

This ranking gives the true measure of the recent sequence: when the years 2020-2023 all sit near the top of the dry-years table, the clay has had no time to rehydrate between episodes – the textbook scenario for delayed cracking. The reverse is just as telling: a very wet year following an exceptional drought triggers abrupt swelling of the ground.

Damp, water ingress and rising damp in Grasse

Damp in a wall can have four causes – rising damp, water ingress, condensation or a leak – and the treatments are completely different depending on the origin.

In Grasse, between the sloping ground of the old centre, the stone walls and the damp hillside climate, we regularly meet owners who have already called in a treatment contractor. They were diagnosed with rising damp and offered resin injections running to several thousand euros. Our advice: not so fast. A damp patch at the base of a wall is not always rising damp.

The 4 causes and how to recognise them

• Rising damp: moisture climbs from the ground into a wall with no waterproof barrier. Low band-shaped marks, efflorescence (saltpetre), deterioration of render at the foot of the wall, often in the older houses of Grasse with no damp-proof course.
• Water ingress: water enters from outside (roof, cracked façade, terrace, gutter). Localised marks, often rain-related, that can appear high up.
• Condensation: excess indoor water vapour with poor ventilation. Mould in room corners, on glazing, typical of poorly aired or over-insulated homes.
• Leak: a defective pipe or drain. A one-off mark, sometimes evolving, with no link to the weather or the ground.

The trap of the diagnosis sold by the treatment contractor

A contractor selling injections has a direct interest in diagnosing rising damp, even when the real cause is water ingress or condensation. The result: a costly and ineffective treatment – the damp comes back a few months later. A reliable diagnosis rests on a moisture measurement through the thickness of the wall and an analysis of the building and the site, with no conflict of interest with the sale of a treatment.

Before starting works in Grasse, request an independent diagnosis via the contact page. To go further, read the damp guide for the 06, 83 and 13.

Grasse: drought, clay, cracks – what the official database says

Your house is cracking in Grasse? You are not an isolated case: the GASPAR database lists 7 drought decrees (full list below) and 23 flood decrees, i.e. 30 natural disaster (Cat Nat) decrees in the commune. The rainfall fits the scenario: four dry years in a row (2020 to 2023), then 2024 climbs back to 1,214 mm (+43%) – the very alternation that puts foundations to work in this town perched on its hills.

Cassini Expertise, an independent building expert, handles cracks and drought-related damage in Grasse and throughout the 06. This page brings together the commune’s public data to help you work out whether your cracks are linked to this phenomenon, and what to do next – with no sales talk.

Natural disaster decrees in Grasse: the official record

According to the GASPAR database (decrees published in the Journal officiel since 1982), Grasse has recorded a total of 30 natural disaster (Cat Nat) decrees. If your cracks appeared during one of these periods, note the date of the event: that is what counts for a declaration, not the date you first noticed the crack.

• 7 drought decrees (differential ground movement linked to clay shrink-swell)
  • event of 01/07/2003 (decree of 27/05/2005)
  • event of 01/01/2007 (decree of 07/10/2008)
  • event of 01/07/2007 (decree of 07/08/2008)
  • event of 01/07/2017 (decree of 10/07/2018)
  • event of 01/01/2018 (decree of 17/09/2019)
  • event of 01/04/2022 (decree of 03/04/2023)
  • event of 31/03/2023 (decree of 23/09/2024)
• 23 flood decrees and storm

Each decree covers a precise time window: if your house’s cracks date from a recognised period, Cat Nat compensation is on the cards, provided you declared the claim to your insurer within 30 days of the decree being published. If that deadline has passed, or if the period is not covered by any decree, the remaining route is a claim against the seller for hidden defect (vice caché) or fraudulent concealment (dol) – see below.

The official clay shrink-swell exposure rating

The GéoRisques platform (BRGM) classifies Grasse as high exposure to clay shrink-swell, with some sectors at medium exposure. Before buying or starting works, check the zoning of your exact plot on georisques.gouv.fr: this is the reference level used by insurers and notaires. Another point to check on the same platform: Grasse is classified at radon potential class 3 – a separate issue from cracks, but one that warrants a measurement if you spend time in a basement or on the ground floor.

This zoning completes the decree record above: the hazard level tells you what can happen, the decrees tell you what has already happened. If your house is in a high exposure area and has been through one or more dry summers, the risk of damage is all the better documented – a point to verify before works or before signing.

Forty years of decrees: Grasse’s complete timeline

Each line = an event recognised by a prefectoral decree published in the Journal officiel (GASPAR database):

• 🔵 11/1982 → 11/1982 – Cyclones / Storms (decree of 15/12/1982)
• 🔵 10/1987 → 10/1987 – Floods (decree of 02/12/1987)
• 🔵 09/1992 – Floods (decree of 19/03/1993)
• 🔵 10/1993 → 10/1993 – Floods (decree of 19/10/1993)
• 🔵 02/1994 → 02/1994 – Floods (decree of 12/04/1994)
• 🔵 06/1994 → 06/1994 – Floods (decree of 29/06/1994)
• 🔵 01/1996 → 01/1996 – Floods (decree of 02/02/1996)
• 🔵 10/1999 → 10/1999 – Floods (decree of 03/03/2000)
• 🔵 11/2000 → 11/2000 – Floods (decree of 19/12/2000)
• 🔵 11/2000 → 11/2000 – Floods (decree of 29/05/2001)
• 🔵 12/2000 → 12/2000 – Floods (decree of 29/08/2001)
• 🔵 11/2002 → 11/2002 – Floods (decree of 02/04/2003)
• 🔴 07/2003 → 09/2003 – Drought (RGA – clay shrink-swell) (decree of 27/05/2005)
• 🔵 09/2005 → 09/2005 – Floods (decree of 10/10/2005)
• 🔴 01/2007 → 03/2007 – Drought (RGA – clay shrink-swell) (decree of 07/10/2008)
• 🔴 07/2007 → 09/2007 – Drought (RGA – clay shrink-swell) (decree of 07/08/2008)
• 🔵 10/2010 → 11/2010 – Floods (decree of 30/03/2011)
• 🔵 11/2011 → 11/2011 – Floods (decree of 18/11/2011)
• 🔵 11/2012 – Floods (decree of 20/06/2013)
• 🔵 06/2014 – Floods (decree of 02/10/2014)
• 🔵 09/2015 → 09/2015 – Floods (decree of 18/11/2015)
• 🔵 10/2015 – Floods (decree of 28/10/2015)
• 🔴 07/2017 → 09/2017 – Drought (RGA – clay shrink-swell) (decree of 10/07/2018)
• 🔴 01/2018 → 03/2018 – Drought (RGA – clay shrink-swell) (decree of 17/09/2019)
• 🔵 11/2019 → 11/2019 – Floods (decree of 28/11/2019)
• 🔵 09/2020 – Floods (decree of 23/11/2020)
• 🔴 04/2022 → 09/2022 – Drought (RGA – clay shrink-swell) (decree of 03/04/2023)
• 🔴 03/2023 → 06/2023 – Drought (RGA – clay shrink-swell) (decree of 23/09/2024)
• 🔵 03/2024 → 03/2024 – Floods (decree of 05/06/2024)
• 🔵 10/2024 → 10/2024 – Floods (decree of 30/10/2024)

How an expert reads this: 7 droughts and 23 floods. Clusters (several decrees close together) mark crisis periods – the summer sequence of 2022-2023 is the best recent example. An owner whose damage dates from a covered period has a solid Cat Nat file; outside a covered period, the route is a claim against the seller.

Local rainfall: the trigger

Annual rainfall recorded on the Grasse weather grid (Open-Meteo data):

• 2019: 1,209 mm · 2020: 715 mm · 2021: 670 mm · 2022: 636 mm · 2023: 654 mm · 2024: 1,214 mm
• Average over the period: 849 mm/year, driest year: 2022 (636 mm)
• Four deficit years in a row: 715 mm in 2020, 670 mm in 2021, 636 mm in 2022, 654 mm in 2023
• Then 2024 bounces back to 1,214 mm, i.e. +43%

Clay shrink-swell plays out in two stages. First the drought dries the clay at depth: the ground shrinks, the first cracks appear. Then the rain returns and abruptly rehydrates the ground: swelling, fresh differential movement. If your house sits on shallow foundations – the norm for 1970s-2000 construction – it takes the hit first, with a 12 to 24-month lag after the dry episode. A crack appearing today may therefore date from a dry summer one to two years ago.

Cracks in Grasse: the tell-tale signs

Here is what to look at in your home before calling anyone:

• A stair-step crack, passing through the wall, wider than 2 mm
• A crack that evolves over time: fit a plaster tell-tale or take a dated photo, and re-measure 2-3 months apart
• Associated signs: doors and windows that stick, floor tiles splitting diagonally, render coming away
• A house on clay ground, a tree closer than 10 m, an out-of-service drain or gutter

With 7 drought decrees recognised in Grasse, as soon as several of these signs build up, do not rush to fill them in: have a survey carried out before any repair, and before signing a purchase or a sale. Filling in too early robs you of the evidence if the crack keeps evolving.

Buying or selling a cracked house in Grasse: what the law says

Between the recent decrees and the volume of transactions, plenty of properties change hands with damage passed over in silence. If you are buying and discover cracks after the sale, two levers are open to you:

• Hidden defect (vice caché, Article 1641 of the French Civil Code): serious cracks, not visible at the viewing, predating the sale → you can claim a price reduction or cancellation of the sale, within 2 years of discovery
• Fraudulent concealment (dol, Article 1137): the seller knew and concealed the damage → cancellation and damages, within 5 years; the commune’s GASPAR decree record then supports your file

In both cases, have the damage precisely dated by a survey before consulting a French property lawyer: this is what turns a suspicion into an admissible file.

How a drought/clay survey works in Grasse

If you call us, here is what happens in practice:

• Technical visit: crack mapping and classification, width measurements, functional damage
• Context: the clayey nature of the ground, the commune’s Cat Nat record (7 drought decrees), local drought episodes
• Costing of works: underpinning, injections, drains – with several scenarios to suit your budget
• A written report you can pass on as it stands to your insurer or your lawyer

For an on-site survey: building expert in Grasse.

Independent expert, with no ties to any repair company – our report leads to no construction contract. Request a visit in Grasse – see also our complete RGA and Cat Nat guide for the 06, 83 and 13.

Soil surveys on clay ground: what the regulations say

The requirement for a preliminary geotechnical survey has applied since 1 October 2020 (ELAN law, art. 68); the new exposure map of 1 July 2026 widens its scope. This requirement, introduced by the ELAN law no. 2018-1021, article 68 (decree no. 2019-495 of 22 May 2019), applies particularly to Grasse (high exposure under the BRGM classification).

• What it changes for building: a soil survey is no longer optional – the ELAN law makes it compulsory in exposed zones for any sale of unbuilt land and any construction contract. Adapted foundations, ground treatment, drainage arrangements: the specifications flow directly from the survey.
• What it changes when buying a recent property: ask whether the survey was carried out and which specifications were applied. A house built without following the geotechnical recommendations on clay ground is a medium-term cracking risk.
• What it changes for sellers: the absence of a survey on a property built before the requirement is not a defect in itself – but if damage appears, a seller who knew about it and concealed it exposes themselves to a claim for fraudulent concealment (dol).
• The link with the data above: Grasse combines high exposure with a documented record of drought decrees. Building or buying here without checking the nature of the ground means building on a known and measured risk.

Cassini Expertise handles these files: compliance checks between geotechnical specifications and what was actually built, damage surveys on clay ground, second-opinion expert assessments. Request a consultation.

Frequently asked questions

Is Grasse part of the clay risk zones?

Yes. The Alpes-Maritimes is very widely covered by the clay shrink-swell hazard (BRGM mapping, consultable on georisques.gouv.fr). In Grasse, the 7 drought decrees recognised in GASPAR confirm that this risk is anything but theoretical: if your house is cracking, the clay hypothesis must be checked first.

Is my cracked house in Grasse eligible for natural disaster compensation?

Only if your damage falls within a period covered by a decree (the last recognised: 2005, 2008, 2018, 2019, 2023, 2024) and if you declared the claim to your insurer within 30 days of the decree being published. Failing that, you still have the action against the seller – and there, precisely dating the damage by survey becomes decisive for your file.

Where do the figures on this page come from?

The decrees come from the GASPAR database (Journal officiel, open data, updated 2025), the rainfall figures from the Open-Meteo weather archives for the Grasse grid, and the water table level from the ADES/Hubeau network. Cassini Expertise reproduces this data without altering it.

Drought right now (as at 04/10/2026)

In the commune: not a drop of rain for over a month. Rainfall over the last 30 days: 1 mm, against roughly 57 mm expected at this time of year – a 98% deficit.

A sustained deficit over this window, especially during the growing season, often precedes by a few weeks the drop in the water table visible above: it is the first signal owners can track themselves, before any cracks appear.

Weekly drought update (as at 05/10/2026)

In the commune: not a drop of rain for over a month. Rainfall over the last 30 days: 1 mm, against roughly 59 mm expected at this time of year – a 98% deficit.

A sustained deficit over this window, especially during the growing season, often precedes by a few weeks the drop in the water table visible above: it is the first signal owners can track themselves, before any cracks appear.

Weekly drought update (as at 12/10/2026)

In the commune: recent rain (5 days ago). Rainfall over the last 30 days: 12 mm, against roughly 69 mm expected at this time of year – an 83% deficit.

A sustained deficit over this window, especially during the growing season, often precedes by a few weeks the drop in the water table visible above: it is the first signal owners can track themselves, before any cracks appear.

Weekly drought update (as at 19/10/2026)

In the commune: no significant rain for 12 days. Rainfall over the last 30 days: 12 mm, against roughly 80 mm expected at this time of year – an 85% deficit.

A sustained deficit over this window, especially during the growing season, often precedes by a few weeks the drop in the water table visible above: it is the first signal owners can track themselves, before any cracks appear.

The water table against its historical record: what 30 years of measurements show

The reference piezometric station for the area (002FFSZ) has been monitoring the water table since 1997 – 30 years of records. As at 26/09/2026, the average level over the last thirty days is 70.81 m NGF (NGF, the French ordnance datum). Across the entire record, the water table has spent only 24.0% of its time below this level: a low level, in the lower quartile of known values.

• Last comparable episode: 30/10/2023 – 2.9 years ago
• Frequency: 19 similar episodes recorded since 1997, i.e. a return period of once every 2 years on average – in hydrologists’ terms, an intermediate episode
• Historical minimum: 65.58 m NGF, reached on 24/10/2022

This long memory changes how the risk should be read: a low level is not just a passing weather episode, it is an event whose frequency is known. For a house on clay, it is this frequency that tells you the probability of further settlement – and therefore how urgent the precautions are.

Find out more: Article 1641 of the Civil Code and the hidden defects warranty (garantie des vices cachés), explained.

Survey carried out by Frédéric Faucouneau, independent building expert – Antibes, Alpes-Maritimes (06), Var (83), Bouches-du-Rhône (13). Find out more

📅 Last updated 06/11/2026 - Cassini Expertise, independent building expert – departments 06, 83 and 13.