The single most useful question in UK subsidence is also the one most "free surveys" answer with a guess: is the movement active right now? A crack that exists today and a crack that is growing today are completely different problems. The first one is a historical record. The second is a live structural issue. The only way to tell them apart with confidence is a proper monitoring programme run over a full season of British weather.
What crack monitoring actually involves
Monitoring is a disciplined sequence of measurements taken across the same crack at the same locations, with the same instruments, over a defined period. The classic UK programme runs twelve months, because clay-shrinkage subsidence in the South East, the most common cause nationally, is driven by the seasonal wetting and drying cycle, and only a year of readings captures the full picture. Shorter programmes (six to nine months) are sometimes appropriate where the trigger is specific and recent (a known drain failure, for instance), but twelve months remains the gold standard for an open diagnosis.
The instruments we use
- Avongard plate telltales. The familiar two-piece plastic gauge bonded across the crack. Cheap, hard-wearing, accurate to within a millimetre. Ideal for monitoring opening and closing of a single crack on a single plane.
- Vernier crack gauges. Where a sub-millimetre reading is needed, a digital vernier reads to 0.05mm and replaces visual estimation with an instrumented measurement.
- 3D monitoring studs. For complex situations, corner cracks, party-wall cracks, three-dimensional movement, we install pairs of survey studs and measure with a micrometer caliper in three planes.
- Tilt and level monitoring. Where a façade may be rotating, optical or digital levels record reference points to millimetre accuracy.
- Reading interval. Typically monthly, with a fresh baseline at install and a final reading at programme close. Readings are taken at the same time of day and recorded with weather and ambient conditions noted.
How a monitoring report reads
At the end of the programme you receive a monitoring report from a chartered engineer, with the full reading dataset, a graphical record of movement at each location across the year, a comparison to the seasonal weather context, and a clear professional judgement on one of three outcomes:
- No significant movement. Readings within the noise floor of the instruments. The cracks are historical. The recommendation is cosmetic repair (filler and decoration) with no further structural action.
- Seasonal but stable. Cracks open and close with the weather cycle but return to the same baseline. The property is moving within its normal range. Repair is cosmetic; no underpinning is warranted.
- Progressive movement. Cracks open across the year with no return. The movement is active and a structural response is warranted, usually after a confirmed cause investigation identifies the trigger.
Why monitoring saves money
Monitoring is invariably a fraction of the cost of the intervention it most often makes unnecessary. Full residential underpinning runs into five figures, sometimes well into them. A monitoring programme that concludes "seasonal but stable", by some distance the most common outcome, has just saved you the underpinning cost. A programme that concludes "progressive movement" gives you incontrovertible evidence to support an insurance claim, which the insurer is statistically far more likely to accept on a properly-monitored property than on a property where the contractor argued for underpinning from the first visit.
Monitoring as insurance-claim evidence
Where your insurer has accepted a subsidence claim, monitoring data is the evidence pack that determines the proportionate response. A clean monitoring record showing stable readings will often steer an insurer away from traditional underpinning and toward the smaller-scope cause-removal intervention (drain repair, root barrier, resin injection) that the Financial Ombudsman has consistently endorsed. Monitoring data is also the primary evidence in challenges to insurer-led decisions to underpin.
When monitoring is not the right answer
Monitoring is the wrong choice in two situations: severe, plainly progressive damage (BRE category 4 or 5, cracks above 15mm and visibly growing within weeks) where the situation is structurally unstable and requires immediate engineering input; and time-pressured transactions, where the parties cannot wait twelve months for a verdict. In both cases the right response is the formal structural engineer's report plus a focused investigation.
How to start a monitoring programme
Most monitoring programmes follow on from a subsidence survey. The survey identifies the cracks that warrant tracking and the right instruments for each. Monitoring can also be commissioned standalone, typically for second-opinion purposes alongside an existing insurer's report. Send us your photographs and recent survey or insurer correspondence through the booking form and we will quote a fixed monitoring fee.