Excavation and Neighbouring Properties: What the Party Wall etc. Act 1996 Requires

Planning an extension? If so, your project likely involves the excavation of new foundations, or even substantial landscaping works. Why is this relevant? Surely you only need to worry about serving notice for works to the shared party wall between you and your neighbour - it is called the Party Wall etc. Act 1996? This is a common and costly misconception.

The Party Wall etc. Act 1996 (the Act) exists not just for works to party walls shared with adjoining properties, but also to regulate major construction work when undertaken near a structure on your neighbours land. Why? Excavations can and have, affect the stability of nearby foundations and the structures upon them. Therefore, if your proposed works involve excavation - even entirely on your own land - you must understand the rules set out in Section 6 of the Act.

Failing to follow these requirements means bypassing the legal framework designed to protect you, and the Adjoining Owner. It also leaves you vulnerable to expensive common law actions like trespass or nuisance.

The Legal Triggers: When You Must Serve a Notice

If you are proposing excavation works, you must assess whether your plans trigger one of two critical statutory distance and depth thresholds, regardless of where the legal boundary lies. The requirement to serve a formal Notice of Adjacent Excavation and Construction (at least one month before starting work,) is triggered when your plans meet either the "Three-Metre Rule" or the "Six-Metre/45-Degree Rule."

1.     The Three-Metre Rule (Section 6(1)) - This rule is straightforward. You must serve notice if:

• You plan to excavate or build within three metres horizontally of any part of your neighbour’s building or structure; and,

• Any part of your excavation or new foundation will extend to a lower level than the bottom of their existing foundations.

If your excavation is within three metres, but stops short of going deeper than your neighbour’s foundations, this rule is not triggered and you do not need to serve notice.

2.  The Six-Metre/45-Degree Rule (Section 6(2)) - This rule is invoked when the work is further away but still potentially impactful. You must serve notice if:

• You plan to excavate or build within six metres horizontally of any part of your neighbour’s building or structure; and,

• Your excavation or new foundation intersects (or ‘meets’) an imaginary plane drawn downwards at a 45-degree angle that begins at the lowest level of their foundations.

The key takeaway here is that if your excavations are likely to be deep, the area of risk extends significantly outwards.

It is important to realise that in the UK, most of the housing built before the late 1970’s will have foundations that are likely to be shallower than those proposed for your new extension. The effect of clay soils in much of the country has meant modern foundations need to be at least 1 metre in depth, and even deeper near trees.

What does this mean for your extension? If your home is either a terraced or semi-detached property, an excavation notice will almost certainly need to be served if you plan to build a new rear extension. This could also apply to more than one of your neighbours. The best advice we can give is to let a qualified party wall surveyor take a look at your proposals well in advance, so you know either way.

Getting professional advice for excavation works is also highly recommended due to the notice requirements. When serving an excavation notice, it must be accompanied by certain plans and sections, clearly showing the site and depth of the proposed excavation. This is essential to ensure that your neighbour (the Adjoining Owner) has sufficient information to understand the potential impact of the work on their property. This is almost always missed by Building Owner’s serving their own notices, rendering the notices invalid.

Navigating the Statutory Process

Once a valid notice is served, the Adjoining Owner has 14 days to respond with either consent or dissent.

If no consent is sent to the notice from the Adjoining Owner, a dispute is deemed to have arisen, automatically triggering the legal framework under Section 10 of the Act. This then means surveyor(s) need to be appointed to formally resolve the matter via a legally binding Award. Of course, the Adjoining Owner may respond & directly dissent to the notice and appoint a surveyor within that time.

Special Foundations

Both owners must also be aware of the restrictions concerning 'special foundations'—those using an assemblage of beams or rods, typically reinforced concrete, to distribute load. The Act grants the Adjoining Owner an absolute right to veto the placement of special foundations on their land, for example, under a party wall. Once steel is placed in a concrete foundation altering it – by say cutting it back later on – can create structural issues for the foundation as a whole. Therefore, most Adjoining Owner’s are unwilling to allow special foundations on their land, as it could restrict works they may wish to carry out in the future.

Why This is Not Just Bureaucracy: Protecting Yourself

The Act exists to enable necessary construction while imposing clear safeguards for both owners. As the Building Owner looking to carry out the works and following the procedure by serving a valid notice, you benefit from the statutory protection the Act provides.

1. Schedule of Condition: If you serve notice, the Adjoining Owner will likely request that a photographic record of their property is taken in the vicinity of the works, before the works commence. If they don’t, you can always request this takes place. Why is this so important? The written schedule and its accompanying photographs will enable you to protect yourself from any spurious claims for damage that may, or may not occur.

2. Avoiding Injunctions and Unlimited Liability: If you fail to serve a valid notice, the Act is not invoked - the well-known principle is "No Notice, No Act". Your activity immediately reverts to common law, where liability for unauthorised, unlawful works (like digging near a foundation) is determined by the civil courts. This exposes you to potential injunctions halting your project immediately, as well as claims for damages based on trespass or nuisance.

By understanding the rules set out in Section 6, you ensure that your work is authorised from the outset and you maintain as reasonable relationship with your neighbour as you can. Importantly, early engagement with a party wall surveyor can help you avoid some of the pitfalls.

Charterhouse Surveying are experts in matters related to the Party Wall etc. Act 1996 and we are happy to give you free advice about your project. Feel free to contact us by clicking here.