What Is a Basement Monitoring Survey?
A basement monitoring survey (often called movement monitoring) is a precise survey that records the current position and condition of a property — usually neighbouring buildings — before basement works start, then tracks any movement (settlement, subsidence, heave, horizontal shift) during and after construction.
Surveyors install fixed monitoring targets (reflectors and markers) on walls and foundations of adjacent properties and the subject site. They take high-precision readings (vertical and horizontal) at set intervals using total stations and laser equipment. The data is compared against a baseline reading taken before works begin to detect any movement and its trend.
When It's Needed in the UK
Basement monitoring is typically required when planning permission is sought for new basement excavations, large basement extensions, or deep underpinning, especially in London where many boroughs treat basements as high-risk:
- Planning stage — Most London local authorities require a Basement Impact Assessment (BIA) that includes a monitoring methodology for adjacent properties
- Before works start — At least one pre-construction survey is essential to establish baseline readings
- During major works — Weekly monitoring during excavation, underpinning, and concrete pours is common practice
- After major works — Often reduced to monthly visits until internal fit-out, then discontinued once movement stabilises
- Party Wall Act — Commonly advised or commissioned by a Party Wall Surveyor or Structural Engineer where party walls or shared structures are involved
Key Deliverables
| Deliverable | Content | | --- | --- | | Baseline survey report | Pre-construction condition and initial readings | | Monitoring plan/method statement | Target locations, frequencies, tolerance limits, escalation triggers | | Periodic monitoring reports | Raw readings (vertical/horizontal) per target, change-from-baseline values, cumulative movement, graphs and trend plots | | Summary analysis | Identification of any exceedances of agreed thresholds (e.g., Burland damage categories) and recommendations for remediation or work-stoppage if needed | | Final report | At completion, confirming overall movement outcomes and closure of the monitoring regime |
Typical Costs (London Residential2025)
| Service | Cost (ex VAT) | | --- | --- | | Setup/installation | £500–£1,000 | | Each subsequent visit/report | £200–£400 |
Costs vary by property size, monitoring frequency, and number of neighbouring properties.
Frequently Asked Questions
Q: Do I need basement monitoring for planning permission?
Most London local authorities require a Basement Impact Assessment (BIA) that includes monitoring methodology for adjacent properties. Requirements vary by borough — Kensington& Chelsea, Camden, and Westminster have particularly strict requirements.
Q: What are Burland damage categories?
Burland damage categories (0 to 5) classify the severity of building damage based on crack width and deflection-to-length ratios. They are used to set trigger levels for monitoring and define acceptable movement limits during construction.
Q: How long does monitoring continue?
Monitoring runs from before excavation through construction and into the post-construction period. Frequency typically reduces from daily during active excavation to weekly during construction, then monthly post-construction until movement stabilises.