Ground movement and damage assessment
A prediction of how much the ground will move during basement construction and the likely damage category for neighbouring buildings.
About this service
Digging a basement changes the ground around it. As soil is removed, the ground beside and beneath the excavation moves slightly inward and upward, and clay can continue to heave over time. Installing walls and underpinning adds its own movement. A ground movement and damage assessment predicts how much movement neighbouring buildings are likely to experience, and what that means in terms of visible damage to them.
Councils with detailed basement policies often require this assessment within a Basement Impact Assessment, and neighbours' party wall surveyors frequently ask for it when concerns are raised. The output is a predicted damage category for each neighbouring building, using a widely recognised scale that runs from negligible hairline cracks up to severe damage needing major repair. Most councils expect predictions at the low end of that scale.
We base predictions on the proposed construction method, the ground conditions and the form of the neighbouring buildings, then set out mitigation and monitoring to keep movement within the predicted range. Calculations go through our three-step quality control process with final sign-off by our Head of Engineering. Fees start from £1,500 + VAT, confirmed as a fixed fee in writing before work starts.
When you need it
- A Basement Impact Assessment requires a ground movement assessment
- Neighbours or their surveyors are concerned about damage
- The council has asked for damage category predictions
What's included
- Ground movement predictions
- Assessment of neighbouring buildings
- Damage category assessment to recognised guidance
- Mitigation and monitoring proposals
How it works
- Gather ground and design dataWe review site investigation results, the basement method statement and the proposed retaining wall and underpinning scheme, since movement depends heavily on how the basement is built.
- Predict ground movementWe estimate horizontal and vertical movement caused by wall installation, excavation and long-term clay heave, using recognised empirical methods and, where the site justifies it, numerical analysis.
- Assess neighbouring buildingsWe consider each neighbouring wall within the zone of influence and calculate strains from the predicted movement, taking account of building length, height and construction.
- Assign damage categoriesWe convert the calculated strains into damage categories, identify which neighbouring buildings are most sensitive, and check the results against the council's published acceptance criteria.
- Recommend mitigation and monitoringWe set out measures such as stiffer propping, shorter underpinning bays or a different wall type where needed, plus monitoring points and trigger levels for use during construction.
What you receive
What a damage category means for neighbours in practice
Damage categories describe how cracking looks and how easily it can be repaired, not structural safety in itself. The lowest categories cover hairline cracks dealt with during normal redecoration. Further up the scale, cracks become visible outside, doors and windows may stick, and repairs need a builder. Most London councils set an acceptable limit near the bottom of the scale, and the council will confirm its threshold for your project.
Predictions are only as reliable as their inputs. A neighbouring house already affected by subsidence or poor alterations may be more sensitive than the method assumes, which is why the assessment works alongside a schedule of condition and monitoring. Our guide to the Party Wall Act explains how these documents fit together, and our London Clay guide covers heave.
Frequently asked questions
What is a ground movement assessment for a basement?
It is an engineering prediction of how much the ground and neighbouring buildings will move when a basement is excavated and built. It considers the construction method, ground conditions and the form of adjoining buildings, and is usually required within a Basement Impact Assessment in London boroughs with basement policies.
What damage category is acceptable for a basement?
Many councils expect predicted damage to neighbouring buildings to stay within the lowest categories, meaning very slight cracking that can be repaired during normal decoration. The exact threshold differs between boroughs and is set out in their basement guidance. If predictions exceed it, the construction method usually needs to change.
Can a basement cause damage to my neighbour's house?
Some movement is unavoidable, but a well-designed and well-built basement should keep it to minor, repairable cracking. Damage usually comes from poor sequencing, inadequate propping or unexpected ground and water conditions. Assessment, monitoring and a party wall award reduce the risk and set out how any damage is put right.
How is ground movement monitored during basement construction?
Survey targets are fixed to neighbouring walls and read regularly, often with crack gauges across existing cracks. Readings are compared with trigger levels agreed in advance. At an amber level the team reviews the method, and at a red level work stops until the cause is understood and addressed.