When carrying out building work near a boundary, especially if it involves excavation, the Party Wall etc. Act 1996 is critical in protecting both the Building Owner and the Adjoining Owner. In particular, Section 6 of the Act governs the requirements when excavation occurs close to a neighbouring property’s foundations. Here’s a breakdown of key issues related to excavations near party walls and what both parties need to be aware of.
What Triggers the Party Wall Act for Excavations?
The Party Wall Act isn’t just limited to shared walls—it also covers excavations near adjoining properties. Specifically, if an excavation is made within three metres or six metres of a neighbouring building, it triggers the need to serve notice under Section 6 of the Act. This can apply even if the excavation doesn’t involve the shared party wall itself. In simpler terms:
- Three-Metre Rule: Excavation within 3 metres of an existing structure can trigger the Act.
- Six-Metre Rule: Excavation within 6 metres is applicable when deeper foundations or certain types of works are involved.
The Act ensures that any excavation, whether for repairs, new construction, or even forming a basement, does not undermine the stability of the neighbouring property’s foundations.
Risks Associated with Excavations Near Neighbouring Foundations
The risks posed by excavations near a neighbour’s property depend on several factors:
- Depth of Foundations: The deeper the existing foundations of the neighbouring property, the less likely the excavation will disturb them. Modern buildings typically have deeper foundations compared to older properties (e.g., Victorian terraced houses), meaning the risks for older buildings are greater.
- Type of Soil: The type of subsoil plays a significant role in determining the risk. Sandy or unstable soils are more likely to shift during excavation, while solid clay or rock provides better stability.
- Proximity to Excavation: If the excavation is close to the neighbour’s foundation, it can disrupt the support to the adjacent wall or property, especially with machine-dug excavations or piled foundations.
- Types of Excavation:
- Hand-Dug Excavations: These are typically shallow and cause minimal risk.
- Machine-Dug Excavations: These are deeper and involve larger machinery, which can cause vibration that might affect nearby foundations.
- Piled Foundations: Piling involves removing soil and replacing it with concrete or steel and is one of the most likely causes of vibration and disruption to adjacent properties. The depth of the pile and the technique used can significantly impact the level of disturbance.
Understanding Different Types of Piling and Their Impact
Piling can be a useful solution in certain excavation scenarios, but it must be carefully selected based on the proximity of neighbouring foundations and the nature of the subsoil.
- Driven Piles:
- These piles are hammered into the ground, causing significant vibrations. This method can affect the structural stability of neighbouring foundations, especially in built-up areas.
- Augered Piles:
- These piles are drilled into the soil with a screw-like auger, which generates less vibration than driven piles. Augered piles are the preferred option for densely built-up areas as they minimize the risk of disturbance to adjacent properties.
- Steel Sheet Piles:
- These are driven into the ground with a mechanical hammer, much like driven piles. Due to the force used, they can cause vibrations that impact neighbouring structures. Careful planning and monitoring are essential when using this method.
Mitigating Risks and Ensuring Structural Integrity
Excavation near a neighbouring property’s foundations requires a risk assessment to ensure minimal disturbance and maintain structural stability:
- Risk Assessment: A qualified structural engineer should assess the risks associated with excavation, especially when piles are involved. This can help predict the likelihood of movement or damage to the neighbouring property.
- Temporary Supports: In deep excavations, using temporary supports, such as propping or strutting, can reduce movement and prevent subsidence or cracking in adjacent structures.
- Monitoring Systems: It’s often advisable to set up structural monitoring systems to measure any movement in the neighbouring property. This can include:
- Tell-tales: Small devices that track changes in the size of cracks.
- Steel Stud Pins: Placed in the wall to monitor any shift or movement.
- Targets: Used for larger-scale projects to detect shifts and ensure no damage occurs.
Party Wall Surveyors and Their Role
In any complex excavation near a party wall, Party Wall Surveyors play a crucial role in ensuring compliance with the Act. The surveyors will:
- Serve Notices: The Building Owner must inform the Adjoining Owner of their intentions and provide adequate time for them to respond.
- Inspect Plans and Proposals: Surveyors will review the detailed plans and assess the potential risks of the proposed works, including the type of foundations, depth of excavation, and construction methods.
- Agree on Solutions: The surveyor will help negotiate and agree on the best way to proceed with the work, including advising on mitigation strategies, such as limiting vibration or using less intrusive piling techniques.
- Monitor Progress: Surveyors may also be involved in monitoring the works to ensure that any potential risk of movement is mitigated and any issues are promptly addressed.
Dealing with Potential Structural Movement
If excavation leads to movement in the neighbouring property, such as cracks in walls or floors, it’s essential to understand the underlying causes and determine the best course of action. This movement is often due to a loss of support to the foundations of the adjoining property.
- Assessing the Cause: Structural engineers can evaluate the degree of movement and determine whether the excavation is indeed responsible. If so, the project may need to implement additional stabilisation measures, such as underpinning the adjacent foundations.
- Reinforcing the Foundations: In some cases, the foundation of the adjoining property may need to be reinforced (e.g., through underpinning) to restore support and prevent further movement.
The Role of Drainage and Building Materials
- Drainage: Older buildings, especially those built with traditional lime mortar, may be more forgiving of movement. However, modern buildings made with rigid cement mortar may crack or show signs of damage more quickly when subjected to ground movement. Drainage systems may help mitigate some of this by allowing for controlled moisture and movement around foundations.
- Building Materials: The age and quality of the masonry also affect how well a building tolerates movement. Buildings made of brick or stone with well-maintained mortar are more likely to resist minor movement, while poorly maintained buildings or those with weaker mortar may show cracks more easily.
Legal Considerations: Consents and Notices
Before commencing any work near a party wall or boundary, the Building Owner must ensure that all statutory consents are obtained. This includes:
- Building Control Approval: Ensuring the proposed works comply with local building regulations.
- Planning Permission: If required for the project.
- Listed Building Consent: If the property is a listed building, special permission is required.
- Party Wall Notices: Proper notice must be served to the Adjoining Owner as per the Party Wall etc. Act 1996 to give them the opportunity to consent or raise objections.
Conclusion: Protecting Both Parties During Excavation Works
The Party Wall Act 1996 provides a legal framework for ensuring that excavation work does not unduly affect the structural integrity of neighbouring properties. Through proper planning, risk assessments, and the use of qualified Party Wall Surveyors, both the Building Owner and the Adjoining Owner can minimize risks and avoid unnecessary disputes.
Engaging a structural engineer early on is crucial to assess the impact of any excavation, particularly with piled foundations or deep works, while maintaining open communication between the parties ensures that everyone’s interests are considered. Monitoring systems, careful excavation methods, and the right foundation techniques will reduce the likelihood of disruption or damage to neighbouring properties.