Trial pits are commonly used before building work begins to establish the depth, size and construction of existing foundations.
They can be extremely useful when designing an extension close to a neighbouring property, but homeowners often ask an important question:
Do you need a Party Wall Notice just to dig a trial pit?
The answer depends on exactly where the trial pit is located, how deep it is and what it is intended to investigate.
What is a trial pit?
A trial pit is a small area of excavation used to expose part of an existing foundation.
It may help an architect, structural engineer or surveyor establish:
- foundation depth;
- foundation width;
- foundation type;
- ground conditions;
- changes between different parts of a building; or
- the relationship between existing and proposed foundations.
This information can be particularly valuable when considering whether Section 6 of the Party Wall etc. Act 1996 applies.
Does the Party Wall Act automatically apply?
Not necessarily.
A modest investigative excavation wholly within your own land does not automatically require a Party Wall Notice simply because it is called a trial pit.
However, the location and depth still matter.
A trial pit excavated immediately adjacent to a neighbouring structure or party wall should be approached carefully.
Do not undermine neighbouring foundations
The purpose of a trial pit is to obtain information, not to destabilise the building.
Excavation should therefore be controlled and appropriately positioned.
It may be sensible to obtain advice from a structural engineer where foundations are particularly shallow, unusual or difficult to access.
Trial pits can help establish whether Section 6 applies
One of the practical difficulties with Party Wall excavation notices is that the neighbouring foundation depth is often unknown.
A trial pit on your own side may help establish comparable foundation construction.
This can make the Party Wall assessment much more accurate.
Our Section 6 Party Wall Notice guide explains why foundation depth matters.
What if access to the neighbour’s property is required?
Do not assume that you can excavate on your neighbour’s land simply because the information would be useful.
Access rights under the Party Wall Act apply only in particular circumstances.
Our guide to Party Wall Access Rights explains the distinction.
Simple Survey can advise before investigation
If you are planning an extension but do not know the depth of the existing or neighbouring foundations, Simple Survey can review the proposals and advise on the Party Wall implications.
Contact Simple Survey before excavation begins and we can help you establish the correct approach.