What This Requirement Covers
Structural movement occurs in all buildings to some degree, but excessive or uneven movement can cause cracking, distortion, and structural instability. Subsidence (downward movement due to loss of ground support) and heave (upward movement due to swelling ground) are common in the UK, particularly on shrinkable clay soils.
Key Requirements
Types of Movement
- Subsidence: The ground beneath the foundation shrinks or compresses, causing the building to sink. Common causes: clay shrinkage in dry weather, tree root water extraction, leaking drains washing away soil
- Heave: The ground swells upward, typically after trees are removed from clay soils. The clay rehydrates and expands over months or years
- Settlement: The gradual compression of soil under the weight of a new building. Normal and usually stops within a few years of construction
- Thermal movement: Expansion and contraction of building materials with temperature changes; accommodated by movement joints
- Moisture movement: Expansion and contraction of materials (particularly clay bricks and timber) with changes in moisture content
Identifying Structural Movement
- Cracking: The most visible sign; the pattern, width, and location of cracks indicate the type and severity of movement
- Crack monitoring: Telltales (simple crack monitors) or digital monitoring can track whether movement is ongoing, seasonal, or historic
- Level surveys: Precise measurements of floor levels and wall positions to quantify any distortion
- Subsidence cracks: Typically wider at the top than the bottom, diagonal, and concentrated at weak points (around windows and doors)
- Heave cracks: Typically wider at the bottom than the top
Remediation
- Underpinning: Extending the foundation to a deeper, more stable stratum. Methods include mass concrete underpinning, mini-piling, and resin injection
- Tree management: Pruning or removing trees that are causing clay shrinkage; or managing newly planted trees near buildings
- Drain repair: Fixing leaking drains that are washing away soil beneath foundations
- Monitoring: Many cases of cracking are seasonal and do not require structural intervention; monitoring establishes the pattern before committing to expensive remedial work
Practical Compliance Tips
- If you notice new cracking in walls, monitor it for 12 months before committing to remedial work; seasonal movement may stabilise
- Install telltale crack monitors on significant cracks and record readings monthly
- Check the proximity of trees to the building; on clay soils, tree roots within the mature height distance of the building can cause subsidence
- If subsidence is suspected, notify your buildings insurer promptly; most policies cover subsidence
- Do not carry out underpinning without a structural engineer's assessment and Building Regulations approval
- When purchasing a property with visible cracking, commission a structural engineer's report before exchange
- Keep records of any structural repairs, underpinning, or tree management for future property sales