If you have read a Party Wall Award before, you may have seen wording along the lines of:
“Foundations are to be excavated and concreted (or otherwise filled) within 12 hours. If not, the excavation must be suitably supported.”
Building owners sometimes see this and think it is excessive. Adjoining owners sometimes see it and think it is essential. The truth is that this type of requirement is usually included for one reason: to reduce the risk of ground movement and instability, particularly where excavation is close to a neighbour’s property.
This article explains what the “12 hour fill” concept is, why it appears in Awards, where it fits within the Party Wall etc. Act 1996, and how it benefits both building owners and adjoining owners when managed properly.
1) The Party Wall etc. Act 1996 in plain terms
The Party Wall etc. Act 1996 applies in England and Wales. It provides a legal framework for certain works that may affect:
- a party wall (shared wall between neighbouring properties),
- a party structure (for example, shared walls or floors between flats),
- certain boundary wall situations, and
- excavations near neighbouring buildings where foundations could be affected.
The Act is designed to facilitate notifiable works by making the process orderly: clear notice, a clear neighbour response route, and—where required—a formal Award to conclude party wall matters properly.
2) Where “foundations” sit within the Act
Foundation excavation most commonly falls under Section 6 of the Act (adjacent excavation). Section 6 is concerned with excavations close enough to neighbouring buildings that depth and proximity may be relevant to the neighbour’s foundations.
However, foundation works are often part of projects that also involve:
- Section 1 (building a new wall at the boundary/line of junction), and/or
- Section 2 (works to an existing party wall/party structure), with notice served under Section 3.
The practical point is this: foundations and excavation often appear alongside other notifiable works. That is why you may see excavation-related controls discussed within an Award even where the overall project includes more than excavation alone.
3) The Party Wall process: Notice → Response → (if needed) Award
To understand why “12 hour fill” clauses appear, it helps to place them in the normal process.
Stage 1: Notice
The building owner serves the relevant notice(s):
- For excavation: a Section 6 notice, typically at least 1 month before works start.
- If other notifiable works exist: Section 1 and/or Section 3 notices (Section 2 works often require 2 months’ notice).
Stage 2: Response (14 days)
The adjoining owner can:
- consent in writing, or
- dissent, or
- not respond, which is generally treated as a dispute for procedural purposes.
Stage 3: Award where required (commonly Section 10)
If there is no written consent, surveyors may be required under the Act’s dispute procedures (commonly under Section 10) and an Award may be produced. This is where practical safeguards—such as excavation control measures—are commonly set out.
The purpose of these safeguards is not to create inconvenience. It is to reduce avoidable risk in a controlled and documented way.
4) What “12 hour fill” actually means
The principle is straightforward:
- If a foundation trench is excavated, it should not be left open longer than necessary.
- The longer an excavation is left open, the greater the potential for:
- ground softening (particularly in wet conditions),
- instability of trench edges,
- collapse of the excavation sides,
- localised movement of surrounding ground.
A “12 hour fill” clause is therefore intended to encourage good site discipline:
- dig the section you intend to pour,
- complete the pour promptly,
- avoid leaving long runs of open trench unsupported.
If it is not practical to pour within the stated period (for example due to unexpected ground conditions, weather, or programme disruption), the usual alternative requirement is:
support or shore the excavation properly until it can be safely filled.
5) Why this clause is often included in Party Wall Awards
In domestic projects, foundations are commonly dug close to boundaries and close to neighbouring structures. The adjoining owner cannot see below ground and cannot easily judge risk. A clear, written safeguard within an Award provides reassurance.
Surveyors often include this type of clause because it is:
- easy to understand,
- easy to follow,
- and directly linked to risk reduction.
It is also worth stating clearly: it is not a universal statutory rule that “all foundations must be filled within 12 hours”. Rather, it is a common Award condition used as a practical control measure.
A good Award condition should be:
- proportionate to the works,
- realistic for a competent contractor to implement,
- and clear enough that it does not become a source of argument.
6) “This applies to all works under the Act”: what that really means
The “12 hour fill” concept is most relevant to excavation and foundation works, particularly those associated with Section 6 (and often Section 1 where new boundary walls require foundations).
However, it may appear in Awards covering broader projects under the Act because:
- the Award is often the document that sets out the working rules for the notifiable elements, and
- excavation rules are a key risk-control component where the project includes foundation works.
In other words: you may see it in Awards that cover multiple notifiable elements, not because it governs every type of party wall work equally, but because the Award is capturing the excavation aspect within the overall party wall framework.
7) Benefits for building owners: peace of mind and fewer problems on site
Building owners sometimes view “12 hour fill” clauses as restrictive. In practice, it often helps building owners by:
- reducing the likelihood of trench collapse or safety incidents,
- reducing the likelihood of disputes arising from avoidable site practices,
- improving site discipline and programme control,
- helping prevent the sort of issues that cause neighbour alarm and formal complaints.
It is also a practical shield: if the building owner is later challenged on whether excavation was handled responsibly, a clear Award condition—and evidence that it was followed—supports the building owner’s position.
8) Benefits for adjoining owners: reduced risk of movement and clearer reassurance
Adjoining owners often worry about ground movement, even if the project is competently designed. A clearly stated excavation management clause helps because it:
- reduces the time open excavation is left unsupported,
- reduces uncertainty about how works will be managed,
- provides a written standard against which site practice can be measured.
The adjoining owner does not need to be a construction expert. They simply need to know that:
- the excavation will not be left open unnecessarily, and
- if it must remain open, it will be supported properly.
That is reassurance in plain English.
9) The key practical point: a good clause must be realistic, not theatrical
At Simple Survey, we believe safeguards should be real-world and deliverable. A clause that is impossible to comply with is not protection; it is an argument waiting to happen.
A well-managed approach is:
- plan the excavation sequence in workable lengths,
- ensure concrete supply and labour are coordinated,
- avoid long open trenches,
- and support trenches properly where delay is unavoidable.
This is good construction practice. The party wall framework simply makes it explicit and accountable.
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If your project involves foundations near a neighbour, or you have received an Award containing “12 hour fill” requirements and want to understand what it means in practice, contact Simple Survey. We explain party wall requirements clearly, keep Awards proportionate and workable, and focus on practical risk reduction that protects both sides. We are built around low-cost fixed-fee pricing and aim to be the UK’s cheapest party wall surveyors, without compromising professional standards.
Get in touch with Simple Survey and let us keep your party wall foundations approach safe, clear, and professionally controlled.