Along with rear extensions, loft and basement conversions are the most popular home renovations in the UK. In high-density areas, it’s not always possible for homeowners to create more space by building outwards, which is why the number of planning applications for expanding above and beneath a property has soared over the last few years.

The majority of plans for building or renovating a domestic basement or loft are going to affect at least one neighbouring property due to access, excavation or cutting into the party wall, meaning that the Party Wall etc. Act 1996 will apply. If this is the case, it is essential that the legislation is carefully followed to prevent significant delays and financial burdens on the Building Owner. You will need to serve the required Notice so that your neighbour can consent to the works. If they do not, a Party Wall Agreement will be required.

Required Notice

There are three areas covered by the Act that typically affect basement extensions and loft conversions. Depending on which section of the Act applies and the design of your alteration, you may need to serve more than one type of Notice on your Adjoining Owner(s), although they will be served at the same time.

Adjacent Excavation

This part typically applies to basement excavations. Section 6 of the Act states that if the proposed basement extension is within 3 metres of a shared or neighbouring structure and excavation intends to go below the foundation of that structure, then a Notice of Adjacent Excavation must be served. If you intend to excavate past a certain depth, this proximity extends to 6 metres.

Party Structure

If you live in a terraced or semi-detached property and your basement extension will require underpinning the party wall (or walls), you must serve a Party Structure Notice on your Adjoining Owner. This is also required if you intend to cut into a party wall to place supporting beams, for either a basement or loft project.

Line of Junction

Where your basement or loft design or will extend beyond the footprint of your main building to the property boundary line, you will need to serve a Line of Junction Notice, under section 1 of the Act. This is typically required where the basement is extended to the end of a rear garden or light wells are installed at the side of a building. It may also be required if you are extending the floor space of your loft area, although this is less common.

Basements: Special Foundations

To allow for a greater useable floor space in a basement extension, many designs will underpin the main property with foundations that have been reinforced with metal rods, also known as special foundations.

If your basement extension is a party wall matter, you will require explicit permission from your Adjoining Owner before you can use special foundations. It is therefore recommended that you discuss this with your neighbours early in the process, so that an alternative solution to special foundations can be used if necessary.

A 2013 County Court case, Chaturanchanda v Fairholme, demonstrated that certain engineering may negate the requirement for written permission in regards to a special foundation. However, the circumstances and basement design were very specific, so if you intend to rely on the outcome of this case then alert your surveyor and engineer as soon as possible.

Will I definitely need a basement or loft conversion party wall agreement?

In some circumstances, the condition of your existing basement or loft space may mean that your renovations won’t affect the neighbouring property. However, these scenarios are uncommon and it is recommended that you check your plans with a professional surveyor to confirm that this is the case.

Failing to serve Notice when required can result in an injunction being taken out against you, causing delays and additional costs to your project. You may also be liable for any damage to a neighbours’ property that may have been caused as a result of the construction. Without a schedule of condition and party wall agreement for the loft conversion or basement extension, it can be difficult to prove you were not at fault.

Why work with Squarepoint Chartered Surveyors?

Basement extensions are complex and require an expert team to help you ensure they are built safely and legally. The various ways in which building or converting a basement can affect your Adjoining Owners means that working with an experienced surveyor is essential.

Our team at Squarepoint works on party wall matters all across London and the South East and our founder and Managing Director, Scott Buchanan, has over 20 years’ experience in surveying all kinds of property. We are passionate about understanding buildings and would be happy to provide our attentive, customer-focused service to help any Building Owner or Adjoining Owner negotiate a basement extension project.

For more information or to discuss your case, call our team on 0207 651 0000 or send an email via our contact page.