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Crack monitoring is the most reliable method for objectively tracking crack evolution and establishing a link with clay shrink-swell subsidence (RGA). It involves installing measuring gauges (crack meters) across the cracks and taking regular readings of their width.
How does it work?
A crack meter is a graduated gauge glued on either side of the crack, with a fixed index and a mobile index. The distance between the two indexes measures the crack width to within 1/10th of a millimetre. Periodic readings (every 2 weeks to 1 month) allow an evolution curve to be plotted.
Interpreting the results
- Stable crack: no significant variation over time → likely not linked to clay subsidence (RGA)
- Cyclical crack: widens in summer (drought) and closes in winter (rain) → RGA confirmed
- Progressive crack: continuous worsening → structural defect requiring urgent works
Duration of monitoring
Crack monitoring generally runs for 6 to 12 months, to cover at least one full seasonal cycle. The longer the monitoring period, the more robust the data for the expert assessment.
Equipment used and measurement reliability
The mechanical crack meter (Palmer type) remains the benchmark for reliable, low-cost monitoring, with accuracy to a tenth of a millimetre. For complex defects or high-stakes buildings (apartment blocks, public venues), optical or digital monitoring (connected sensors) allows more frequent remote readings – useful when site visits are impractical or when the evolution needs to be precisely dated for a legal case file.
Where to place the crack meters
Choosing the measurement points is critical: target the most representative cracks (the widest, the through-cracks, those on load-bearing walls) rather than multiplying gauges on superficial cracks. An expert typically installs between 3 and 8 crack meters depending on the size of the building and the spread of the defects, together with a dated photographic survey and a floor levelness check (laser level).
Crack monitoring and CATNAT or decennial liability claims
Crack meter readings are a central piece of technical evidence in a CATNAT drought claim or a decennial liability claim: they objectively demonstrate that the defect is evolving (and therefore active) – a point insurance experts often require before agreeing to any compensation.
FAQ
Can monitoring be paused and resumed later? Technically yes, but an interruption weakens the consistency of the evolution curve presented in the expert report; it’s best to set up a regular reading protocol from the outset.
Who has to pay for crack monitoring? Without an amicable agreement with the insurer or builder, it falls to the property owner, but the cost can generally be recovered as part of a compensation settlement or a favourable court ruling.
Cassini Expertise – Crack meter installation and monitoring across the Alpes-Maritimes (06), Var (83) and Bouches-du-Rhône (13). Request monitoring →
Installation protocol and reference standards
Fitting crack meters must follow a rigorous protocol to ensure the measurements are valid. Installation should be carried out by a qualified expert who cleans the crack, fits the gauges according to best practice, and precisely records the initial positioning. The crack monitoring method follows the framework set out in EN 12188:2007 (test methods for determining crack depth), complemented by the recommendations of AFNOR standard NF P 18-419 on monitoring and interpreting cracks in building structures. These references ensure the traceability and admissibility of the results before a court or an insurance company.
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📅 Updated on 26/07/2026 – By Cassini Expertise, independent building surveyor covering the Alpes-Maritimes (06) & Var (83). Free quote: 04 22 46 06 04.
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Frequently asked questions
How do you measure crack evolution?
To measure how a crack evolves, a crack meter (or crack gauge) is fixed on either side of the crack. The gap between the two parts is read regularly, which allows variations to be tracked over time. It’s important to record the date and conditions (temperature, humidity) at each reading to correctly interpret the results.
How much does a crack meter cost?
The price of a crack meter varies depending on the type and precision. Simple direct-reading models cost between €10 and €50, while electronic crack meters with data logging can exceed €200. For professional use, a higher budget should be expected, but for homeowners, a manual crack meter is usually sufficient.
What’s the difference between an active and an inactive crack?
An active crack changes over time – its width or length increases – while an inactive crack stays stable. This is determined through regular measurements over several months. If the readings show a significant variation (for example, more than 0.5 mm), the crack is considered active and requires monitoring or repair work.
Survey carried out by Frédéric Faucouneau, independent building expert – Antibes, Alpes-Maritimes (06), Var (83), Bouches-du-Rhône (13). Find out more
📅 Last updated 02/11/2026 - Cassini Expertise, independent building expert – departments 06, 83 and 13.