Party Walls and Basements

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Posted by Mark Amodio | July 24th, 2018

Basement Excavations, what are they?

In this blog we will look briefly at what basement excavation it is and what you are required to do or indeed what your neighbours should do when they want to undertake a basement excavation.

Put simply, land and space in London particularly are at a premium. Most owners have already gone out with an extension, up with the loft leaving only the ground beneath the house un-extended and as a result basement excavation is becoming increasingly popular.

The Hopps Partnership have a wealth of experience in dealing with basement excavations in London having worked with some of the foremost contractors over the years.

The process is complicated and involves carefully excavating beneath the house in what are known as bays, usually 1 m long stretches which are then backfilled with concrete to create a box beneath the house piece by piece. If not undertaken properly this can lead to damage although most contractors will have a good deal of experience and if undertaken properly damage is not likely.

The Party Wall Process and Basements

Given that housing in London is usually within close proximity of each other, the Party Wall Act has never been more relevant than today. This process both allows the work to proceed was controlling the time and manner of the work. In this way a party wall surveyor has a good deal of power to ensure that the work is undertaken properly by obtaining all necessary and relevant information before works commence.

The process starts by serving a notice upon a neighbour where they wish to undertake basement excavations. This is necessary both warehouses join such is the case of a terraced or semi detached property and also when excavations are taking place within 3 m of a neighbour or 6 m if deeper foundations are proposed.

A neighbour then has the right to appoint a surveyor and from that point forward where surveyors are appointed they will use their best endeavours to review the package of information to ensure that there is no undue risk.

This process is, complicated and can be time-consuming and requires collation of the following information:

1. Obtaining all necessary architectural drawings.

2. Obtaining all necessary engineering drawings and accompanying calculations.

3. Obtaining information relating to the soil conditions including borehole information and trial hole information.

4. Obtaining all temporary works information. This is perhaps the most key piece of information as it relates to how the basement will be dug which is arguably the time where both the subject property and neighbouring properties are most at risk. It is key that temporary works such a support of excavated soil faces and the removal of spoil is carefully thought out to minimise risk.

Security for Expenses

This is a complex part of the Party Wall Act and a link to the relevant paragraphs can be found here:

In short where there is perceived risk, a neighbour also known as an Adjoining Owner may formally request security for expenses under section 12 of the act. Once requested this cannot be denied and this usually takes the form of a sum of money deposited by the person undertaking the building work also known as a building owner's Building Owner to be used in the event of the contractor stopping works in a critical phase for any reason.

The sum of money is often hotly disputed but can reach many tens of thousands and sometimes even into six-figure numbers. Therefore it is important that you appoint the right party wall surveyor to protect all parties interests.


If on completion of the works damage is noted to have occurred, this is where the Party Wall Act is very useful and a Party Wall Surveyor will normally inspect said damage and negotiate a reasonable cost for reinstatement. They can then serve formal paperwork which is legally binding on all parties which will ensure that the Building Owner settles sums in lieu of damage. In this way a professional surveyor will straddle both a legal and technical standpoint in identifying damage, ensuring due diligence in obtaining reasonable costs and preparing legal documentation. This will invariably be cheaper then appointing solicitors who will not have technical expertise in respect of defects and remedial action thereof.

Here at The Hopps Partnership we have surveyors with many years experience in dealing with these technical and legal issues and as a result have built up a wealth of knowledge to enable us to both negotiate on your behalf and ensure that fairness prevails.

Feel free to give us a call to discuss matters further.

The Hopps Partnership
Second Floor, 34 - 40 High Street
Wanstead, London E11 2RJ

The Hopps Partnership
70 Cowcross Street
London EC1M 6EJ

020 8502 6323

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The Hopps Partnership