How do I know if a crack is dangerous?

A through-crack (visible on both sides of the wall), wider than 2 mm, or stepping diagonally from a window corner is potentially structural. An expert measures the opening with a crack gauge and analyses the pattern to determine the cause.

My cracks open in summer and close in winter: is that serious?

This is typical of clay shrink-swell movement. The soil swells with moisture and contracts during dry periods. This cyclical movement can progressively damage the foundations. Document it with dated photos and crack-gauge monitoring.

My insurer refuses to cover my cracks: what can I do?

If your municipality has been declared a natural drought disaster area, you are entitled to compensation. An independent expert can document the link between the drought and your cracks with measurements and an enforceable report.

Can I patch a crack myself?

Not before identifying the cause. Patching hides the problem without solving it. If the crack keeps moving, it will reopen. An expert first determines whether the crack is active or dormant, structural or cosmetic, then advises you accordingly.

Article

Structural vs Surface Cracks: Diagnosis and Expert Assessment in PACA

14 September 2026

Structural cracks: when should you worry?

structural vs surface cracks diagnosis and expert assessment in PACA - Cassini Expertise — Cassini Expertise – independent building expert

Cracks in a building are a frequent source of concern for property owners. Not all of them warrant an expert assessment, but some require prompt intervention. Distinguishing between structural cracks (affecting the soundness of the structure) and surface cracks (cosmetic) is essential for determining the severity of the issue and the appropriate course of action.

Classifying cracks by severity

Building experts generally classify cracks according to their width (opening):

Microscopic cracks (< 0.2 mm): Not a concern, purely cosmetic. Seen on renders and paintwork.
Fine cracks (0.2 to 1 mm): May indicate slight differential settlement. Monitoring is recommended.
Medium cracks (1 to 3 mm): Often caused by ground movement or construction defects. Technical assessment advised.
Wide cracks (> 3 mm): Indicative of structural disorders. An expert assessment is essential.
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Causes of structural cracks

Structural cracks can have multiple origins:

Ground movement: Differential settlement, expansive clays, shrink-swell, drought/natural disaster.
Design flaws: Undersized foundations, missing expansion joints, poor allowance for loads.
Construction defects: Poor concrete placement, insufficient reinforcement, absence of tie beams.
Weather-related stress: Freeze-thaw cycles, excessive heat, humidity fluctuations.
Abnormal loading: Nearby works (foundations, excavations), operational overloads.

Technical diagnosis of structural cracks

The independent expert applies a rigorous methodology to diagnose the origin of the cracks:

Topographic survey: Level measurements to detect settlement.
Crack monitoring: Tracking crack evolution over time (progressing? stable?).
Core sampling: Analysis of concrete quality and reinforcement.
Geotechnical investigations: Soil study (pressuremeter tests, boreholes).

Structural cracks and legal warranties

Structural cracks fall under the 10-year statutory warranty (décennale) from the date the building is handed over. If the origin is a hidden defect affecting the soundness of the structure, the builder is required to repair it at their own expense. In the event of a dispute, an independent expert assessment can determine:

Whether the crack is structural or superficial.
Whether the origin lies with the builder, the design, the loading, or the soil.
The liabilities involved (builder, architect, engineering firm).
The cost of repairs (local repair or underpinning).

Surface cracks: treatment and prevention

Surface cracks, while less serious, still deserve attention:

Renders: Cracks caused by excessive thickness, rapid drying, or the absence of a base coat. Localised repair.
Paintwork: Cracks caused by inadequate surface preparation or application on a damp surface.

Cracks in the PACA region: specific factors

The geological and climatic context of the PACA region favours the appearance of cracks:

Expansive clays: At-risk areas (Var plain, Grasse region). Ground movement that can crack foundations.
Seismic zones 3-4: Seismic accelerations that can cause cracks, even moderate ones.
Mediterranean rainfall: Significant fluctuations in soil moisture.

Frequently asked questions about cracks

Does every crack warrant an expert assessment?
No. Only wide cracks (> 3 mm), those that are actively progressing, or those accompanied by other issues (a sticking door, cracked glass) require an expert assessment.

Does a structural crack always fall under the 10-year statutory warranty?
Yes, as soon as it affects the soundness of the structure or renders it unfit for its purpose, even if it appears several years after handover.

How much does an independent expert assessment for cracks cost?
The cost varies according to the complexity of the building and the extent of the investigations: from €1,200 to €3,500.

For cracks anywhere on the French Riviera, our independent expert assessment can help you determine the severity of the issue and the liabilities involved. Cassini Expertise covers the entire Alpes-Maritimes and Var departments.

Water infiltration: diagnosis, expert assessment and solutions in the Alpes-Maritimes and Var

📅 Updated on 31/07/2026 – By Cassini Expertise, independent building expert covering the Alpes-Maritimes & Var. Free quote: 04 22 46 06 04.

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.