Enclosing on the neighbours’ extension wall

House prices in London have experienced significant increases in the past two decades, this has created a surge in homeowners and developers carrying out works such as a loft conversion and rear extension. People have seen how adding more square foot to a property can increase its appeal, living space and value.


Before commencing any building work you ensure you discharge your legal obligations in respect to the Party Wall Act of 1996, if you intend to do any of the following:

- Excavate within 3 or 6 metres of an adjoining building or structure, this is dependent on the depth of the works.

- Work on existing Party Walls or structures

- If you intend to construct a new wall or structure at or astride the boundary line with the adjoining property.

This Act provides a framework for neighbours who share a boundary usually in terraced homes to carry out building work. This also provides a resolution if any disputes occurs, this Act protects the interests of the Adjoining Owner whilst giving the Building Owner the right to complete the project and other rights such as access not normally granted under common law.

Building on a neighbour’s extended external wall casomeone couldn't be contentious but mutually beneficial to both owners. it is usually worth having a discussion with your neighbour in the first instance of your proposed rear extension to gauge their support for the proposed works.

When you in close up on the neighbours flank wall the Party Wall Act applies a compensation value to the proportion of the wall which you are in closing at a 50% rate, as you both now share the wall.

You will require the help of a Party Wall specialist who will draw up the Agreement within the Party Wall Award which is legally binding, a Party Wall Surveyor in London can also Act on the neighbour’s part as an agreed Surveyor.

There are many benefits of building on neighbours extension wall such as:

- By building on the neighbour’s extended external wall, the Building Owner will benefit from a slightly larger extension. Whilst this may not seem like a big space 300mm can make all the difference on a rear extension.

- By building on the neighbours extended external wall you would be saving proportionate construction costs as the costs are only at 50% of the enclosure.

- When two neighbours carry out works in conjunction with one another they can agree to build one single party war between the two rear extensions and agree the cost at 50% to ensure both benefit from the cost savings and increased internal space. A Party Wall Surveyor in London will ensure the costs are transparent, calculated
impartially and legally documented.


- Enclosing on the existing flank wall with no Party Wall agreement Is illegal and as such will make you liable for compensation in legal costs. In the worst case scenario a court order to rebuild the flank wall as an individual wall. therefore it is really important to obtain the advice of a Party Wall Specialists.

Are you or your neighbour looking to build on an extended external wall? Do you need assistance with Party Wall Surveying? We at Seven One Associates are here to help.

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