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How close can you build your extension to your neighbours' boundary?

If you share a boundary with your neighbour, you might need a Party Wall Agreement. Here's everything you need to know.

3 min read

© Matt Gamble

When it comes to building a house extension, it’s vital to establish whether you share a Party Wall with your neighbours. Depending on the nature of your extension and the proximity of your existing property to the next door, it could have an impact on whether or not your proposed works can go ahead. In order to give your plans the best chance of going ahead, it’s important to know what constitutes a boundary, how it may influence your extension ideas and whether you need to secure a Party Wall Agreement.

What is a boundary?

A boundary isn’t necessarily a solid structure like a wall or a fence but it represents the point that separates one property from another.

How close to your neighbour’s boundary can you build your extension?

You can build your extension up to 50mm from your neighbours’ boundary as long as you have either Permitted Development Rights or have Planning Permission. This could be a suitable option if you aren’t able to secure a Party Wall Agreement.

Alternatively, if you are able to come to an understanding with your neighbour and secure a Party Wall Agreement, you’ll be able to build on the boundary line. This is our recommended approach if you’re hoping to extend your home to the maximum size possible.

Securing a Party Wall Agreement

Do you need a Party Wall Agreement?

What is a Party Wall Agreement?

For the uninitiated, a Party Wall Agreement is a sort of contract between yourself and your neighbour that outlines an understanding between you regarding any building work that could impact a shared wall, boundary or outbuilding.

When should you need one?

You may need a Party Wall agreement if you share a boundary wall with a neighbouring property or properties and the work is likely to affect them. If you’re lucky, you may receive written consent from your neighbour to say that they’re happy for the building work to go ahead. You should let them know two months ahead of the proposed start date. However, agreement is not guaranteed and it can prove to be a contentious issue.

What happens if your neighbour refuses your build?

Once you request compliance, your neighbours will have 14 days to respond to your request for whether they agree or disagree to it. Following this, they’ll be sent another letter requesting a response and allocated another 10 days to reply.

Failure to respond or refusal at this point could lead to you needing to have a surveyor to request a Party Wall Agreement. Your neighbour can request the opinion of a second professional ove the one that you’ve selected for the task. As the responsibility for the legal bills falls is yours, you’re obliged to provide this for them.

In addition to cordially agreeing to cover their legal costs and securing them a second surveyor, our most significant advice is to be nice to your neighbours from the very beginning. The more transparent you are about your plans from day one, the more understanding your neighbours are likely to be.

Learn more about the next steps for how to serve a Party Wall Notice.

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What is a Party Wall agreement?

A Party Wall Agreement is an understanding between two neighbouring properties that outlines a set of agreed terms and conditions that allow building work to be carried out.

Do I need a Party Wall Agreement?

You may require a Party Wall Agreement if your proposed extension plans are large enough that they would come within 50mm of your neighbour’s boundary. If this is the case, you can seek a written agreement that may allow you to proceed without a Party Wall Agreement. If you don’t secure consent or receive refusal of the works, the next step is to serve a Party Wall Notice.

What is a boundary?

A boundary is the line that joins two neighbouring houses. It’s not necessarily a literal line, fence, structure or wall.

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