Marignane: Clay Soil, Subsidence and Cracks – Official Data

The geological and climate context of Marignane

Marignane combines two handicaps: well-mapped clay ground and a substantial Cat Nat record. The GASPAR database lists 12 drought decrees (full list below) and 11 flood decrees, i.e. 23 Cat Nat decrees. On the weather side, the finding fits: three dry years in a row (2020, 2022, 2023), then 2024 back up to 747 mm (+33%) – precisely the scenario that puts foundations to work around the airport plateau and the étang. If your house is in this sector and it is cracking, it is probably no coincidence: here is what to check, and in what order.

Cassini Expertise, an independent building expert, handles drought-related cracks and damage in Marignane and across the whole of the 13. This page sets out the commune’s official data, with nothing glossed over – keep it handy if you have to deal with your insurer or a notaire.

Marignane: drought, clay and cracks – what the official data says

Yes. The GASPAR database (decrees published in the Official Gazette since 1982) counts 23 natural disaster decrees for Marignane. The useful point: note the period or periods that match the appearance of your cracks – that document is what conditions any compensation.

• 12 drought decrees (differential ground movement linked to clay shrink-swell)
  • event of 01/05/1989 (decree of 30/06/1994)
  • event of 01/01/1992 (decree of 12/06/1998)
  • event of 01/01/1998 (decree of 12/03/2002)
  • event of 01/01/2002 (decree of 25/08/2004)
  • event of 01/01/2007 (decree of 07/08/2008)
  • event of 01/07/2007 (decree of 07/08/2008)
  • event of 01/01/2016 (decree of 25/07/2017)
  • event of 01/07/2016 (decree of 22/02/2018)
  • event of 01/01/2017 (decree of 10/07/2018)
  • event of 01/01/2018 (decree of 16/07/2019)
  • event of 01/04/2022 (decree of 22/07/2023)
  • event of 01/04/2023 (decree of 18/06/2024)
• 11 flood and storm decrees

Each drought decree covers a precise window of time: if your house’s damage can be tied to a recognised period, Cat Nat compensation is conceivable – provided the claim was declared in time. Otherwise, the route of a claim against the seller for hidden defect or fraudulent concealment remains: see below.

What the official clay mapping says

The GéoRisques platform (BRGM) classifies Marignane at high exposure to clay shrink-swell, with some sectors at medium exposure. You can check the exact exposure of your plot on georisques.gouv.fr before any purchase or insurance declaration – this is the benchmark level used by insurers and notaires.

This ranking complements the decree history above: the hazard tells you what can happen, the decrees tell you what has already happened. A house in a “high exposure” area that has been through one or more dry summers carries a risk of damage that is all the better documented – to be monitored as a priority.

Why every file in Marignane is read through its local context

In Marignane, field experience shows cracking profiles closely tied to the local topography: between the foothills dominating the town to the north, the plain near the Étang de Bolmon and the residential quarters that have spread since the 1970s towards the shore, the building stock rests on heterogeneous clay soils whose behaviour varies sharply from one plot to the next. The Provençal villas and estate bungalows built during the great subdivision waves of the 1970s-80s, often founded on shallow, lightly reinforced footings, are particularly exposed to differential settlement when the swelling clay contracts during summer drought – a phenomenon frequently observed in this sector where the mistral quickly dries bare soils. The many pines and cypress hedges on property boundaries, planted for wind protection, deepen this clay shrinkage further by pumping the residual moisture around the foundations, creating suction zones well known to local building professionals. More recent constructions, from the urban renewal operations and the new programmes near the airport, generally benefit from better-dimensioned foundations – but the older stock in the centre and the historic bungalow quarters remains the most vulnerable, combining sensitive clay soil, undersized old foundations and tree cover close to the bearing walls.

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

The weather archives for the area cover 35 complete years (1991-2025). The driest ever recorded: 2017, with 395 mm over the year, against a local average of 614 mm. 2022 ranks as the 8th driest year out of 35 (445 mm against an average of 614 mm); 2023 follows in 2nd place (405 mm).

This ranking gives the true measure of the recent sequence: when the years 2020-2023 crowd into the top of the drought table, the clay has not had time to rehydrate between episodes – the classic scenario for delayed cracks. The reverse is just as instructive: a very wet year following an exceptional drought causes abrupt swelling of the ground.

Marignane: 23 Cat Nat decrees since 1982, in chronological order

Each line = an event recognised by an interministerial decree published in the Official Gazette (GASPAR database):

• 🔵 11/1982 → 11/1982 – Cyclones / Storms (decree of 18/11/1982)
• 🔵 11/1982 → 11/1982 – Floods (decree of 18/11/1982)
• 🔴 05/1989 → 12/1991 – Drought (RGA – clay shrink-swell) (decree of 30/06/1994)
• 🔴 01/1992 → 12/1997 – Drought (RGA – clay shrink-swell) (decree of 12/06/1998)
• 🔵 09/1993 → 09/1993 – Floods (decree of 11/10/1993)
• 🔵 10/1994 → 10/1994 – Floods (decree of 21/11/1994)
• 🔵 08/1996 – Floods (decree of 01/10/1996)
• 🔴 01/1998 → 06/1998 – Drought (RGA – clay shrink-swell) (decree of 12/03/2002)
• 🔵 09/1998 – Floods (decree of 21/01/1999)
• 🔴 01/2002 → 06/2002 – Drought (RGA – clay shrink-swell) (decree of 25/08/2004)
• 🔵 09/2002 – Floods (decree of 17/12/2002)
• 🔵 12/2003 → 12/2003 – Floods (decree of 12/12/2003)
• 🔵 09/2005 – Floods (decree of 10/10/2005)
• 🔴 01/2007 → 03/2007 – Drought (RGA – clay shrink-swell) (decree of 07/08/2008)
• 🔴 07/2007 → 09/2007 – Drought (RGA – clay shrink-swell) (decree of 07/08/2008)
• 🔵 09/2009 – Floods (decree of 10/12/2009)
• 🔴 01/2016 → 06/2016 – Drought (RGA – clay shrink-swell) (decree of 25/07/2017)
• 🔴 07/2016 → 12/2016 – Drought (RGA – clay shrink-swell) (decree of 22/02/2018)
• 🔴 01/2017 → 06/2017 – Drought (RGA – clay shrink-swell) (decree of 10/07/2018)
• 🔴 01/2018 → 03/2018 – Drought (RGA – clay shrink-swell) (decree of 16/07/2019)
• 🔵 11/2019 → 11/2019 – Floods (decree of 12/12/2019)
• 🔴 04/2022 → 09/2022 – Drought (RGA – clay shrink-swell) (decree of 22/07/2023)
• 🔴 04/2023 → 06/2023 – Drought (RGA – clay shrink-swell) (decree of 18/06/2024)

How an expert reads this: 12 droughts and 11 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.

Damp, water ingress and rising damp in Marignane

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.

You are seeing damp marks in Marignane and looking for a solution. Before signing a resin-injection quotation or having a ventilation system installed, you first need to understand where the problem comes from. The four causes are treated in radically different ways, and confusing one for another means spending several thousand euros for nothing.

The four causes and how to recognise them

• Rising damp: groundwater climbs into the walls by capillary action. Marks low on the wall, saltpetre, render degrading over 50 to 80 cm.
• Water ingress: water penetrates from outside (roof, façade, defective seals). Localised stains, often linked to rain, that gradually spread.
• Condensation: humid indoor air condenses on cold walls. Mould in room corners, in bathrooms, streaming windows.
• Leak: defective pipe or drain. A pinpoint stain, often near a kitchen, bathroom or water riser.

The trap of the diagnosis sold by the treatment contractor

In Marignane as elsewhere, many damp-treatment companies offer a “free quotation” that systematically concludes rising damp, whatever the real cause. Why? Because it is the most expensive service they sell: resin injection, tanking, drainage. The problem is that if your damp actually comes from a roof leak or a ventilation defect, the injections will achieve nothing and the damp will return – after several thousand euros invested.

An independent diagnosis, with no commercial interest in selling the treatment, is the only way to identify the true cause before committing to works. Ask for an independent diagnosis in Marignane to avoid this trap, and see our damp guide for the 06, 83 and 13 to go further.

Why do cracks appear several months after the drought?

Annual rainfall measured on the Marignane weather grid (Open-Meteo data):

• 2019: 672 mm · 2020: 424 mm · 2021: 684 mm · 2022: 445 mm · 2023: 405 mm · 2024: 747 mm
• Average over the period: 562 mm/year, low point in 2023 (405 mm)
• Three dry years in a row: 424 mm (2020), 445 mm (2022), 405 mm (2023)
• Rebound in 2024 to 747 mm, i.e. +33%

The shrink-swell cycle plays out in two stages: the drought dries the clay at depth (shrinkage, first cracks), then the return of the rains rehydrates the ground in one go (swelling, differential movements). If your house was built between 1970 and 2000 on shallow foundations – the case for most villas in the sector – expect cracks to appear 12 to 24 months after a dry episode, not immediately: that is normal, and it helps date the loss for your file.

Cracks in Marignane: which signs should make you call an expert

• A stair-step crack, passing through the wall, open by more than 2 mm
• A crack that is evolving over time – fit a tell-tale (a plaster band or a glass tell-tale) and check it over several months
• Disorders that often come with it: doors and windows that stick, floor tiles splitting diagonally, render that bulges
• A house on clay ground, a tree close by, failing drainage

With a record of 12 drought decrees for the commune, as soon as you spot several of these signals together, do not repair anything straight away: first have the damage recorded and dated by an expert, before any decision to buy, sell or commission works. Repairing before the survey can cost you the evidence.

Is my cracked house in Marignane compensable? Buying or selling with damage present

With the recent drought decrees and the volume of transactions under way, quite a few properties change owner with damage passed over in silence. If you are buying a cracked property or discover cracks after the sale, you have two legal levers:

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

To build your strategy, instruct a French property lawyer.

What actually happens during a drought/clay survey in Marignane?

• Technical visit: crack mapping and classification, width measurements, associated functional disorders
• Context analysis: nature of the ground, the commune’s Cat Nat history (12 drought decrees), local drought sequences
• Costing of repair works: underpinning, injections, drains – with several scenarios
• A written report you can pass to your insurer or your lawyer without rewriting

Independent expert, with no ties to any works company – and therefore no interest in inflating the repair bill. Request a visit in Marignane – see also our complete guide to RGA and Cat Nat in the 06, 83 and 13.

Soil surveys on clay ground: what the regulations say

The requirement for a prior 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 to Marignane (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: Marignane 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, counter-surveys. Request a consultation.

Frequently asked questions

Is Marignane in a clay risk zone?

The Bouches-du-Rhône is widely exposed to the clay shrink-swell hazard (BRGM mapping, available on georisques.gouv.fr). For Marignane, the 12 drought decrees recorded in GASPAR show this risk is nothing theoretical.

Can a cracked house in Marignane be covered under natural disaster provisions?

Only if the damage can be tied to a period covered by a decree (the last recognised: 1994, 1998, 2002, 2004, 2008, 2017, 2018, 2019, 2023, 2024) and if the claim was declared within 30 days. Failing that, the action against the seller remains – and dating the damage by survey then becomes the central issue.

Can the figures cited on this page be verified?

Yes: the decrees come from the GASPAR database (Official Gazette, open data sets, 2025 update), and the rainfall from the Open-Meteo weather archives for the Marignane grid. Cassini Expertise does not touch this data.

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

In the commune: recent rain (2 days ago). Rainfall over the last 30 days: 17 mm, against roughly 58 mm expected at this time of year – a 71% deficit.

A sustained deficit over this window, especially in 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: recent rain (3 days ago). Rainfall over the last 30 days: 17 mm, against roughly 58 mm expected at this time of year – a 71% deficit.

A sustained deficit over this window, especially in 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.

What is the rainfall situation today? (as at 12/10/2026)

In the commune: recent rain (5 days ago). Rainfall over the last 30 days: 74 mm, against roughly 62 mm expected at this time of year – a surplus of 19%.

A sustained deficit over this window, especially in 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.

Drought right now (as at 19/10/2026)

In the commune: no notable rain for 12 days. Rainfall over the last 30 days: 74 mm, against roughly 66 mm expected at this time of year – a surplus of 12%.

A sustained deficit over this window, especially in 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.

Water table memory: 29 years of measurements, a well-documented context

The reference piezometric station for the sector (002JNGC) has been monitoring the water table since 1998 – 29 years of records. As at 02/10/2026, the mean level over the last thirty days is 211.61 m NGF. Across the whole record, the water table has spent only 15.1% of its time below this level: a very low level, rarely reached in the station’s record.

• Last comparable episode: 03/10/2024 – 2.0 years ago
• Frequency: 64 similar episodes recorded since 1998, i.e. a return every year on average – in hydrologists’ language, a rare event
• Historical minimum: 210.96 m NGF, reached on 05/08/2017

This long memory changes how the risk is read: a low level is not merely a weather episode, it is an event whose frequency is known. For a house on clay, it is that frequency that informs the probability of further settlement – and hence the urgency of precautions.

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.