Basement Monitoring Survey Checklist
A comprehensive basement monitoring survey checklist ensures you capture all required documentation, set appropriate trigger levels, and deliver the right reports throughout your basement construction project. Use this checklist when commissioning, managing, or reviewing a basement monitoring survey.
1. Pre-Works Baseline Checklist
The most critical phase of any basement monitoring programme — a thorough pre-works baseline establishes the starting condition of all adjoining properties before construction begins.
| Item | What to Include | | --- | --- | | Schedule of Condition | Detailed record of adjoining properties within 3–6m (double for basement and underpinning projects) | | Photographic Documentation | High-resolution photos of all existing defects: cracks, damp, settlement, movement, and distortions | | Crack Measurements | Width, length, orientation, type (horizontal, vertical, diagonal) with written descriptions | | Reference Drawings | Annotated plans identifying inspection locations, elevations, and monitoring points | | Structural Assessment | Notes on structure, materials, drainage, foundation types, and environmental conditions | | Baseline Readings | Ground and structural readings recorded before any works commence | | Duration | Ideally 2–4 weeks of baseline data to capture diurnal and seasonal variations |
Important: A thorough Schedule of Condition is your legal record if a dispute arises later. Document everything — no matter how minor it appears.
2. Monitoring Schedule
| Phase | Frequency | Duration | | --- | --- | --- | | Baseline | 3 days per week minimum | At least 4 weeks prior to works | | During Excavation | Daily to weekly | Entire excavation period | | During Construction | Weekly to fortnightly | Throughout structural works | | Post-Completion | Monthly | 3–12 months depending on severity | | Trigger-Based | Increased frequency | When amber trigger reached |
Intervals depend on ground conditions, soil type (e.g., London Clay), and risk assessment.
Typical Visit Schedule for London Basements
| Stage | Frequency | Reason | | --- | --- | --- | | Initial breaking ground | Weekly | Highest risk of unexpected movement | | Deep excavation | Weekly or fortnightly | Ground stress redistribution | | Waterproofing installation | Fortnightly | Structural changes during tanking | | Superstructure build | Monthly | Lower risk as structure becomes stable | | Post-completion | Monthly | Confirm movement has stabilised |
3. Trigger Levels (Traffic Light Protocol)
| Trigger Level | Movement Range | Action Required | | --- | --- | --- | | Green | 0–7mm (within design) | Construction continues with routine reporting | | Amber | 7–12mm (warning) | Design review, increased monitoring frequency, contingency implementation | | Red | Over 12mm (limit exceeded) | Stop all works immediately for remedial action and emergency stabilisation |
For small residential projects, typical movement triggers are 1–3mm with weekly physical monitoring. Vibration trigger criteria: 2mm/s PPV for commercial buildings and 1mm/s PPV for residential properties.
Setting Project-Specific Triggers
| Factor | Consideration | | --- | --- | | Building age | Older Victorian properties have tighter thresholds | | Foundation depth | Deeper excavations allow tighter triggers | | Soil conditions | London Clay requires careful trigger setting | | Listed status | Heritage buildings require reduced triggers | | Previous movement | Existing cracking lowers acceptable thresholds |
4. Party Wall Requirements
| Requirement | Detail | | --- | --- | | Does it apply? | Yes — basement conversions almost always trigger the Party Wall etc. Act 1996 | | Section 6 (Adjacent Excavation) | Applies when excavating within 3m of neighbouring buildings or within 6m if below a 45° line from their foundation bottom | | Notice Period | Section 3: 2 months; Sections 1 and 6: 1 month | | Monitoring Obligation | Building Owner funds monitoring for adjoining properties | | Award Documentation | Monitoring regime must be specified in the Party Wall Award |
5. Equipment Checklist
| Equipment | Purpose | Accuracy | | --- | --- | --- | | Reflective targets | Glued to building faces for total station measurement | ±1mm | | Robotic total stations | Automated measurement of target positions | ±0.001" | | Crack gauges and tell-tales | Monitoring existing cracks for movement | ±0.1mm | | Tilt sensors and data loggers | Real-time monitoring for automated systems | ±0.001° | | Vibration monitors (seismographs) | Peak particle velocity measurement | ±0.1mm/s | | Level and staff | Precise level monitoring | ±0.5mm per km | | 3D laser scanners | Comprehensive deformation monitoring | ±2mm |
6. Deliverables Checklist
| Deliverable | When | Description | | --- | --- | --- | | Schedule of Condition | Pre-works | Photographs and written condition of adjoining properties | | Baseline report | Pre-works | Initial readings before any construction activity | | Monitoring visit reports | Each visit | Movement and vibration readings with trend data | | Alert notifications | As triggered | Immediate contact when amber or red triggers approached | | Trend analysis | Monthly | Data analysis distinguishing seasonal from construction movement | | Final monitoring report | Post-completion | Confirming movement has stabilised with recommendations | | Legal documentation | As required | Reports suitable for dispute resolution |
7. What to Look For in a Monitoring Report
| Item | What to Check | | --- | --- | | Date and time of visit | Confirm consistent scheduling | | Target positions | XYZ coordinates with change from baseline | | Graphical presentation | Plot of movement over time | | Crack gauge readings | Width change in mm | | Vibration levels | PPV in mm/s with trigger comparison | | Photographs | Current condition of monitored defects | | Engineer comments | Assessment of trend and recommended actions |
8. Common Mistakes to Avoid
| Mistake | Why It Matters | Prevention | | --- | --- | --- | | Insufficient baseline period | No reference for what was pre-existing | Record baseline for minimum 4 weeks | | Too few monitoring points | Gaps in coverage miss critical movement | Place points on all elevation faces | | Ignoring seasonal movement | Thermal expansion confused with structural movement | Account for diurnal and seasonal patterns | | No agreed trigger levels | Dispute when works should stop | Agree triggers before construction | | Delayed reporting | Problems identified too late | Reports within 2 working days | | Missing historical defects | Undocumented pre-existing damage | Full photographic survey of all adjoining properties |
Frequently Asked Questions
Q: How long before works should monitoring begin?
Baseline monitoring should ideally run for 2–4 weeks before any works commence. This captures seasonal and thermal variations so that construction-related movement can be distinguished from normal background movement.
Q: What are typical vibration trigger levels for residential properties?
Typical trigger: 1mm/s PPV (peak particle velocity) for residential properties. Commercial: 2mm/s PPV. These are the levels at which cosmetic cracking may begin.
Q: Who sets the trigger levels for my project?
Trigger levels are set by your structural engineer or party wall surveyor before works begin. They must be agreed and documented in the Party Wall Award.
Q: What happens if movement approaches the amber trigger?
When amber is reached, monitoring frequency increases, your structural engineer reviews the data, and contingency measures are implemented. Construction may continue but at a reduced pace or with additional precautions.
Q: What happens if movement exceeds the red trigger?
All works must stop immediately. Your structural engineer investigates and prescribes remedial actions. Works cannot resume until the engineer confirms it is safe.
Q: How long does monitoring continue after completion?
Post-completion monitoring typically runs for 3–12 months depending on project severity and ground conditions. Monthly visits continue until movement has stabilised.
Q: Do I need monitoring if there are no adjoining properties?
Yes — internal monitoring of your own structure is still recommended to track settlement, deflection, and crack development during basement construction.