Basement Monitoring Survey for Homeowners
If your neighbour is building a basement extension, you may receive a Party Wall notice informing you that monitoring will be installed on your property. This guide explains what basement monitoring is, why it is required, what it costs, and what your rights and obligations are as a homeowner.
What Is Basement Monitoring?
Basement monitoring (also called structural movement monitoring) is the systematic measurement of structural movement in your property during your neighbour's basement excavation works. It detects potentially damaging movement early, protecting your home from structural damage.
| Aspect | Details | | --- | --- | | What it is | Installation of reflective targets and markers on your property (front, rear, and flank walls) measured regularly with electronic distance measuring instruments | | Accuracy | ±1mm | | What is measured | Settlement, subsidence, heave, or deflection of supporting structures | | Frequency | Typically weekly visits — baseline reading before work starts, then during works and for a period after completion |
Why Is Basement Monitoring Needed?
| Reason | Why It Matters | | --- | --- | | Early detection | Catches movement caused by excavation before it becomes serious structural damage | | Risk mitigation | Prevents damage to your property during complex excavation works | | Legal requirement | Required for works under Section 6 of the Party Wall etc. Act 1996 (adjacent excavation) | | Causes determination | Distinguishes between pre-existing conditions, scatter effects, and actual foundation movement |
Party Wall Act Requirements
When Does It Apply?
The Party Wall etc. Act 1996 is triggered when your neighbour excavates:
- Within 3m of your property and goes below your foundations, or
- Within 6m where the excavation intersects a 45° line from the bottom of your foundations
Notice Periods
| Notice Type | Notice Period | What It Covers | | --- | --- | --- | | Section 3 (Party Structure) | 2 months | Work to a shared wall | | Sections 1 and 6 (Adjacent Excavation) | 1 month | Excavation near or below your foundations |
Is Monitoring Legally Required?
The Party Wall Act does not explicitly require monitoring, but engineers and surveyors routinely include it in Party Wall Awards for basement works. The Schedule of Condition — which documents the pre-works condition of your property — is often included in Awards at a cost of £350–£585 plus VAT.
Your Rights Under the Party Wall Act
| Your Right | Details | | --- | --- | | Be notified | You must receive written notice at least 1 month before adjacent excavation begins | | Have your own surveyor | The Building Owner pays your surveyor's reasonable fees | | Receive monitoring reports | You are entitled to copies of all monitoring reports | | Be notified of trigger breaches | You must be informed immediately if trigger levels are reached | | Dispute resolution | If you disagree with the monitoring regime, the two surveyors appoint a third surveyor |
Trigger Levels
| Parameter | Typical Value | | --- | --- | | Standard trigger (residential) | 1–3mm movement | | Accuracy | ±1mm | | What happens at trigger | Work stops immediately on site until the engineer and contractor agree action to prevent further movement | | Who sets triggers | Project engineer agrees reasonable trigger level with both parties |
Trigger levels are set before works begin and must be agreed and documented in the Party Wall Award.
2025 Costs
| Cost Component | Typical Price (ex VAT) | | --- | --- | | Installation and base reading | £800 (one-off) | | Weekly monitoring visit | £300 per visit | | Total for typical project | £2,000–£5,000+ depending on duration |
Who pays: The Building Owner (your neighbour doing the works) pays all reasonable monitoring costs under the Party Wall Act. You pay nothing for the monitoring itself.
What Happens If Movement Is Detected?
| Scenario | Action | | --- | --- | | Green (0–3mm) | Monitoring continues as planned — construction proceeds normally | | Amber (3–7mm) | Monitoring frequency increases — your surveyor reviews data | | Red (over trigger) | All construction works stop immediately — structural engineer investigates — works cannot resume until safe |
If movement is detected, your surveyor will advise on the appropriate course of action and whether any remedial works are needed to your property.
How Long Does Monitoring Last?
| Phase | Duration | | --- | --- | | Pre-works baseline | 2–4 weeks before works begin | | During excavation | Weekly visits throughout | | During construction | Weekly to fortnightly | | Post-completion | Monthly for 3–12 months |
Monitoring continues until your structural engineer confirms movement has stabilised and poses no risk to your property.
Schedule of Condition
Before monitoring begins, a Schedule of Condition documents your property's current state:
| Item | Details | | --- | --- | | Photographs | High-resolution images of all existing defects | | Crack records | Width, length, orientation, and type | | Floor levels | Existing differences in floor levels | | Structural notes | Observations on current structural condition |
This document is critical — it establishes what was pre-existing vs. what occurred during construction. If damage occurs, the Schedule of Condition provides the evidence needed to make a claim under the Party Wall Award.
What You Will Receive
| Document | When | | --- | --- | | Schedule of Condition | Before works begin | | Monitoring reports | Weekly or fortnightly throughout works | | Alert notifications | Immediately if amber or red trigger is reached | | Final report | After practical completion confirming stability |
Frequently Asked Questions
Q: Can I refuse to have monitoring targets installed on my property?
Your neighbour has a right to install monitoring targets on your property under the Party Wall Act — provided they serve proper notice. You cannot unreasonably refuse, but you can have your own surveyor present during installation.
Q: Who pays for my surveyor?
The Building Owner (your neighbour) pays your surveyor's reasonable fees. This is a legal right under the Party Wall Act.
Q: What happens if movement exceeds the trigger level?
All construction works stop immediately. Your structural engineer and the project engineer investigate and agree remedial action. Works cannot resume until it is confirmed safe.
Q: How accurate is basement monitoring?
Modern electronic monitoring achieves ±1mm accuracy. This is significantly more sensitive than the level at which cosmetic cracking begins, providing early warning before damage becomes visible.
Q: Will monitoring affect my property?
Monitoring targets are small reflective discs glued to your walls — approximately 40mm in diameter. They are non-invasive and leave minimal residue when removed.
Q: What if I am not the adjoining owner?
If you are the Building Owner (doing the works), you are responsible for funding monitoring on adjoining properties. If you are unsure which role applies, consult a Party Wall surveyor.
Q: Can I claim compensation if my property is damaged?
Yes — if damage occurs as a result of the works, you can make a claim under the Party Wall Award. The Schedule of Condition establishes the pre-works condition, making it clear what damage was caused by the works vs. pre-existing.