Planning a basement, deep foundation or major extension close to another property? You may need to serve a Party Wall notice even when the proposed excavation is several metres away from your neighbour’s building.
Many homeowners know about the Party Wall Act’s three-metre excavation rule. Fewer realise that the legislation also contains a separate test for excavations within six metres of a neighbouring building or structure.
The six-metre rule does not mean every excavation within six metres requires a Party Wall notice. It applies where the proposed excavation meets a specific depth test involving a 45-degree line drawn from the bottom of the neighbouring foundations.
Understanding this distinction is important because the distance between buildings is only one part of the assessment. The foundation depths, proposed excavation level and relative positions of the structures also matter.
For projects involving basements, deep foundations or substantial structural alterations, these details should be established before excavation begins.
What Is the Party Wall Act 6-Metre Rule?
The six-metre rule comes from Section 6(2) of the Party Wall etc. Act 1996, which applies in England and Wales.
It concerns proposed excavation or construction of foundations within six metres of an adjoining owner’s building or structure.
The statutory test applies where any part of the proposed excavation or foundation work intersects a plane drawn downwards at an angle of 45 degrees from the bottom of the adjoining owner’s foundations, taken from the relevant external wall or other relevant part of the structure.
In practical terms, the rule considers whether a relatively deep excavation could extend into the zone identified by that statutory geometric test.
The legislation does not automatically establish that an excavation is unsafe. Nor does passing or failing the test replace a structural engineering assessment.
It establishes whether the proposed work falls within a category requiring the statutory notice procedure.
How Does the 45-Degree Rule Work?
The 45-degree test compares the depth of the proposed excavation with the position and depth of the neighbouring foundations.
Imagine that a homeowner is planning a basement extension several metres from the neighbouring property.
The neighbouring building has relatively shallow foundations, while the proposed basement excavation will extend substantially deeper.
To assess whether Section 6(2) applies, the relevant foundation level and excavation geometry need to be established.
A 45-degree plane is projected downwards from the bottom of the neighbouring foundations in the manner prescribed by the Act.
If the proposed excavation or foundation work intersects that plane, the six-metre provision may apply.
The assessment should be based on reliable dimensions rather than a rough estimate from a site photograph.
For example, the following information may be necessary:
- The distance between the proposed excavation and the neighbouring structure.
- The level of the bottom of the adjoining foundations.
- The proposed excavation depth.
- The position and dimensions of the proposed foundations.
- Relevant site levels and changes in ground elevation.
The correct assessment depends on the actual geometry.
A simple assumption that an excavation is more than three metres away, and therefore exempt from Party Wall requirements, can be incorrect.
What Is the Difference Between the 3-Metre and 6-Metre Rules?
Section 6 contains two separate excavation tests.
The 3-metre rule
Under Section 6(1), notice is generally required where the building owner proposes to excavate within three metres of an adjoining owner’s building or structure and to a lower level than the bottom of its foundations.
The relevant questions are the distance and relative foundation depths.
The 6-metre rule
Under Section 6(2), the assessment extends to excavation or foundation work within six metres where the statutory 45-degree plane is intersected.
This is particularly relevant to deeper excavations.
|
Requirement |
3-metre rule |
6-metre rule |
|
Statutory provision |
Section 6(1) |
Section 6(2) |
|
Distance |
Within 3 metres |
Within 6 metres |
|
Main depth test |
Excavation below the bottom of adjoining foundations |
Intersection with the statutory 45-degree plane |
|
Common project examples |
Extension foundations near a neighbouring building |
Deep basements and substantial foundation excavations |
|
Normal notice period |
One month |
One month |
Both provisions should be checked where relevant.
The six-metre test is not simply an extension of the three-metre test. It has its own statutory requirements.
Does Every Basement Require a Party Wall Notice?
Not automatically.
A basement project may involve several types of work covered by the Act, including excavation near neighbouring structures, underpinning or alterations to existing party walls.
However, the need for notice depends on the particular design and site conditions.
A basement excavation may fall within Section 6 because of its depth and proximity to another building.
If the work also involves cutting into or underpinning an existing party wall, Section 2 may apply.
This means a single project can involve more than one category of notifiable work.
For example, a terraced-house basement may require consideration of:
- Excavation close to neighbouring foundations.
- Underpinning or structural work affecting shared walls.
- Temporary support during construction.
- Retaining-wall design.
- The sequence of excavation and foundation works.
The statutory notices and engineering design need to be coordinated.
A Party Wall Award does not replace the structural design, temporary-works assessment or Building Regulations requirements.
Can a House Extension Trigger the 6-Metre Rule?
Yes, although not every house extension involves sufficiently deep excavation.
A conventional rear extension may involve relatively shallow foundations and fall under the three-metre test where applicable.
However, some extensions require deeper foundations because of site conditions, structural loads or other design considerations.
An extension on a sloping site, for example, may have substantially different excavation levels from the neighbouring building.
A lower-ground-floor extension may also involve deeper excavation than a conventional ground-floor addition.
Where the proposed work is within six metres of a neighbouring structure, the relevant foundation levels and excavation depths should be checked.
The type of extension alone does not determine whether the rule applies.
Why Are Neighbouring Foundation Depths Important?
The six-metre assessment cannot be completed accurately without adequate information about the relevant foundation levels.
Older London properties may have different foundation arrangements from modern buildings.
Even adjoining properties of a similar age may have undergone different alterations.
One property may have been extended or underpinned while another retains its original foundations.
The surveyor and structural engineer should therefore avoid assuming that neighbouring foundations are identical.
Where reliable records are unavailable, further investigation may be appropriate.
This could include reviewing existing drawings, examining available construction records or arranging carefully controlled investigation where necessary.
The scope of any investigation should be determined by competent professionals.
A Party Wall surveyor may identify the information required for the statutory process, while a structural engineer or geotechnical specialist addresses the relevant technical assessment.
What Drawings Are Required for a Section 6 Notice?
Section 6 has specific notice requirements.
A notice for qualifying excavation must be accompanied by plans and sections showing the proposed work.
These should identify the site and depth of the excavation and, where applicable, the proposed building or structure.
For practical review, the design package may also need to explain the relationship between the excavation and the adjoining foundations.
Depending on the project, relevant information may include:
- Existing and proposed site plans.
- Foundation layouts.
- Excavation sections and levels.
- Structural drawings and calculations.
- Retaining-wall details.
- Temporary support proposals.
- Relevant construction sequencing information.
Not every document listed above is a universal statutory attachment requirement. The additional information needed depends on the project and the issues being considered.
AC Design Solution’s Party Wall Surveyor service includes reviewing architectural drawings, foundation depths, excavation details and structural information before advising on the notices required.
Where further technical information is needed, the practice’s structural engineering team can assist with the relevant design work.
How Much Notice Must You Give Before Excavating?
For work falling within Section 6, the normal statutory notice period is one month.
The building owner should serve the required notice before beginning the relevant excavation.
The adjoining owner may consent in writing.
Where the statutory procedure results in a dispute, surveyors can be appointed under Section 10 to resolve matters arising under the Act.
For Section 6 notices, a failure to respond within 14 days generally results in a deemed dispute.
The appointed surveyor or surveyors can then address the relevant matters through a Party Wall Award.
An earlier start may be possible where the necessary written agreement has been obtained.
However, the building owner should not assume that a contractor can begin notifiable excavation merely because a notice has been sent.
The applicable notice period and any outstanding statutory dispute procedure must be properly addressed.
For additional guidance, see AC Design Solution’s Party Wall Notice service.
What Happens If Your Neighbour Objects?
An adjoining owner may be concerned about excavation close to their foundations, particularly where the proposed work involves a basement or substantial retaining structure.
Their concerns may relate to ground movement, cracking, temporary stability or the potential for damage.
The Party Wall process provides a statutory mechanism for resolving disputes about work covered by the Act.
The appointed surveyor or surveyors can review the relevant information and determine matters within their jurisdiction.
An Award may address:
- The work authorised under the Act.
- Relevant drawings and construction information.
- How and when the work may be carried out.
- Necessary protective measures.
- Access arrangements where statutory rights apply.
- Procedures relating to damage.
- Responsibility for reasonable costs.
A Schedule of Condition is commonly prepared to record relevant existing conditions before the work begins.
Although the Act does not expressly require a Schedule of Condition in every case, it can provide an important reference if damage is alleged later.
The adjoining owner cannot use the Party Wall process simply to veto lawful development, but their statutory rights must be respected.
Why Deep Excavation Requires Structural Coordination
A Party Wall notice identifies the relevant statutory work. It does not demonstrate that the proposed excavation can be undertaken safely.
Deep excavation can affect the stability of the ground and surrounding structures.
The structural design may need to address retaining walls, foundation support, temporary propping and the construction sequence.
For example, excavation beside an existing building may require a carefully designed temporary support system.
The final basement or foundation structure may also need to resist lateral ground pressures and other relevant loads.
These matters should be assessed by appropriately competent designers and contractors.
The Health and Safety Executive’s excavation guidance explains the importance of preventing excavation collapse and protecting nearby structures.
The Party Wall surveyor and structural engineer have different responsibilities, but their work may need to be closely coordinated.
AC Design Solution provides structural drawings and calculations alongside Party Wall surveying, helping the statutory process respond to the actual construction proposal.
How the 6-Metre Rule Relates to AC Design Solution’s Project Experience
AC Design Solution’s published 16 Vivian Road project demonstrates the importance of coordinating Party Wall matters with foundation, boundary and structural design.
The residential scheme involved a lower-ground-floor extension, mansard alterations, steelwork and retaining structures.
Notices were served under Sections 1, 2 and 6 of the Act.
During the Party Wall review, the proposed boundary-wall arrangement was examined in greater detail.
The drawings were revised so that the new flank and retaining walls remained wholly on the building owner’s land, avoiding unnecessary interference with the adjoining property’s steps and paving.
The case demonstrates how reviewing the construction details can lead to a more appropriate design.
The published project information does not establish that the Section 6(2) six-metre test was specifically triggered. It should therefore be treated as an example of coordinated Party Wall and structural design, not as proof of a six-metre-rule case.
That distinction is important when using project experience to explain statutory requirements.
Does Planning Permission Remove the Need for a Section 6 Notice?
No.
Planning permission and the Party Wall procedure are separate.
A local planning authority may approve a proposed basement or extension without determining whether the excavation requires a Party Wall notice.
Building Regulations approval is also separate.
A project can therefore have planning permission and an appropriate Building Regulations design while still requiring compliance with Section 6.
The Party Wall procedure should be considered during technical design and construction planning, not left until excavation is about to begin.
Who Pays for the Party Wall Surveyor?
The building owner normally bears the reasonable Party Wall costs where the proposed work is undertaken solely for their benefit.
However, the Act provides for different cost arrangements depending on the circumstances.
Where surveyors are appointed, they can determine responsibility for reasonable costs within their statutory jurisdiction.
The number of adjoining owners, complexity of the excavation and technical information required can influence the overall fees.
AC Design Solution explains its appointment options and starting prices on its Party Wall Surveyor Fees page.
Get the Excavation and Party Wall Requirements Checked Early
The Party Wall Act’s six-metre rule is often misunderstood.
It does not apply simply because an excavation is within six metres of another building. The statutory 45-degree test, foundation levels and proposed excavation geometry must be considered.
For homeowners planning basements, deep foundations or substantial extensions, early technical review can help identify the correct notices and reduce avoidable construction delays.
AC Design Solution provides Party Wall surveying services across London, supported by in-house architectural and structural engineering expertise.
If your project involves deep excavation near a neighbouring property, contact AC Design Solution with the proposed drawings and foundation information for an initial review.
