You’ve pictured your dream extension—light-filled, functional, and designed to elevate your everyday living. But how close can you build to your neighbour’s boundary?

In most cases, you can build as close as 50mm from the boundary—about the width of a pencil—so long as your plans comply with permitted development rights or you’ve been granted planning permission. If you have a Party Wall Agreement, it may even be possible to build directly on or across the boundary. However, the true answer depends on various factors—your home’s location, size, and whether development restrictions apply.

As a trusted extension builder in Surrey and London, we at KT5 Construction Ltd have guided countless homeowners through this very issue—ensuring every project is compliant, neighbour-friendly, and built to the highest standards. Our people-first approach means we take the time to understand your goals while ensuring your project respects neighbours’ rights and legal boundaries. So, let’s unpack what “close” really means when building next to someone else’s property.

Understanding Your Property Boundaries

Your property’s boundaries are typically defined in your Title Plan, which you can obtain through the HM Land Registry. Boundaries may be marked by fences, hedges, or walls—but these aren’t always precise. That’s why one of our first steps at KT5 is helping homeowners confirm the legal boundary line before any work begins.

Knowing exactly where your land ends is essential, especially when you’re planning a side return, rear, or wraparound extension. Misjudging this can result in neighbour disputes or costly redesigns.

Permitted Development Rights: What You Can Do Without Permission

You may not need planning permission at all if your project qualifies under permitted development (PD) rights. These rules let you build extensions within specific height, width, and location limits, as long as they don’t significantly affect your neighbours.

Here’s a snapshot of PD limits:

• • Single-storey rear extension:

    • Up to 8m from the original rear wall (detached houses)

    • Up to 6m (semis/terraced homes)

  • Side return extension:

    • Must be single-storey, no more than 4m high

    • Cannot exceed half the width of the original house

  • Double-storey extensions:

    • Can project 3m from the rear wall

    • Must stay at least 7m away from the rear boundary

And most critically:
If you’re building within 2 metres of the boundary, the eaves (the bottom edge of the roof) must not exceed 3 metres in height, and the overall height must stay below 4 metres.

Why Homeowners Choose KT5 Construction? 

At KT5 Construction Ltd, we’re more than just builders—we’re your trusted extension partner in Surrey and London.

Homeowners choose us because we:

• • Know the local rules inside out – From planning permission to party wall agreements, we’ve got it covered.
  • Put people first – We listen, plan, and deliver with care, keeping your goals at the heart of every build.
  • Handle everything – Design, permissions, project management—we do it all, so you don’t have to.
  • Build to last – Our craftsmanship speaks for itself. No shortcuts, no surprises—just quality, through and through.

Let’s talk today—your dream space is closer than you think.

How Close Is Too Close?

This is where things get specific. You can build your extension:

• • Up to 50mm from the boundary without a Party Wall Agreement, as long as it meets PD rights or planning approvalEnhance Privacy_ Minimum…How close can you build…
  • Right up to or across the boundary line with a formal Party Wall Agreement
  • No closer than 7m to the rear boundary for multi-storey extensions under PD

Anything closer may breach building codes or upset your neighbours’ privacy and light rights. That’s why we always advise open communication—and sometimes even a cup of tea with the neighbour—before breaking ground.

The Importance of a Party Wall Agreement

A Party Wall Agreement, as per the Party Wall etc. Act 1996, is a legally binding arrangement between you and your neighbour when any building work could affect shared or adjoining structures. You’ll need to serve a Party Wall Notice at least two months before construction begins how close can you build….

Works that may trigger the Act include:

• • Building astride or directly against a boundary

  • Excavation within 3–6 metres of a neighbouring structure

  • Modifying shared walls, inserting steel beams, or adding foundations

At KT5 Construction, we manage this process for you—from issuing notices to appointing surveyors—ensuring your build is compliant and conflict-free.

Neighbour Relations: It Pays to Be Considerate

Extensions near a boundary affect more than just measurements. They influence privacy, light, and even property value.

To prevent complaints, planning authorities use tools like the 45-degree rule, which ensures your extension won’t unreasonably block your neighbour’s windows or garden views. Our in-house design team works closely with clients to create layouts that optimise space while preserving neighbourly respect.

We also recommend pre-construction discussions with neighbours about:

• • Temporary access through shared driveways

  • Construction noise and timescales

  • Shared fencing or trees near the boundary

A courteous approach often saves time—and relationships.

Design and Sustainability Considerations

When you’re building close to the boundary, design becomes even more crucial. Authorities may require you to match existing materials, and certain conservation zones restrict cladding or significant exterior changes.

Additionally, we always encourage sustainable choices, such as:

• • Eco-friendly insulation to reduce heating loss

  • Renewable energy sources like solar panels

  • Maximised natural light through skylights and glazed doors

Not only do these features align with emerging planning standards, but they also enhance your property’s long-term value.

Can Building Too Close Affect Property Value?

Absolutely—and it can go either way. A well-executed extension that respects regulations and aesthetics can significantly boost market value and improve daily living. However, a poorly designed or illegal build could reduce value and lead to enforcement notices.

That’s why KT5 ensures every extension project we handle enhances—not harms—your home’s value, function, and street appeal.

Final Thoughts: Build Smart, Build Respectfully

So, how close can you build an extension to your neighbour? Technically, as close as 50mm, but practically, it depends on local rules, your building type, and your relationship with those next door.

With KT5 Construction, you don’t need to worry about deciphering legal jargon or managing tricky negotiations. Our friendly, knowledgeable team takes care of everything—from boundary checks and Party Wall Agreements to thoughtful, high-quality design and construction.

Let’s Get Started

📞 Call KT5 Construction Ltd today for a free consultation and property assessment.
📧 Email us your initial plans—we’ll guide you on how close you can build, what permissions you need, and what to expect next.

At KT5 Construction, we don’t just build walls—we build trust.