Building a Prefab Extension Within 1 Metre of a Boundary in the UK: What You Need to Know

If you’re a homeowner in the UK considering a prefab extension, especially one that’s located within 1 metre of your property boundary, there are some important building control and planning rules to understand. These guidelines help ensure your extension is safe, legal, and doesn’t negatively impact your neighbours. In this article, I will cover all you need to know to build confidently within close proximity to your property line.

What Are the Rules for Building Close to a Boundary?

Extensions built within 1 metre of a boundary must meet several requirements governed by Building Regulations, Planning Permission, and potentially the Party Wall Act. Here’s what’s involved:

Key Building Control Requirements

1. Fire Safety (Approved Document B)

Any wall of your extension built within 1 metre of a boundary must be made of fire-resistant materials. This usually means:

• Minimum 60-minute fire resistance
• No windows or openings permitted in walls within 1m unless fire-rated
• Use of non-combustible finishes (e.g., steel or brick cladding)

2. Structural Support and Foundations

Extensions near a boundary may require deeper or specially designed foundations to prevent structural issues, especially if there are trees, drains or neighbouring buildings nearby.

3. Thermal Efficiency and Ventilation

• Walls must meet Part L energy efficiency standards.
• Adequate ventilation is required under Part F of the Building Regulations.

4. Drainage and Water Management

• Check if your extension affects drainage or existing water systems.
• You may need a Build Over Agreement from the water authority if building near a sewer.

What Are the Rules for Building Close to a Boundary?

In the UK, if an extensions is built within 1 metre of a boundary, it must meet several requirements governed by Building Regulations, Planning Permission, and potentially the Party Wall Act. Here’s what’s involved:

Key Building Control Requirements

1. Fire Safety (Approved Document B)

Any wall of your extension built within 1 metre of a boundary must be made of fire-resistant materials. This usually means:

• Minimum 60-minute fire resistance
• No windows or openings permitted in walls within 1m unless fire-rated
• Use of non-combustible finishes (e.g., steel or brick cladding)

2. Structural Support and Foundations

Extensions near a boundary may require deeper or specially designed foundations to prevent structural issues, especially if there are trees, drains or neighbouring buildings nearby.

3. Thermal Efficiency and Ventilation

• Walls must meet Part L energy efficiency standards.
• Adequate ventilation is required under Part F of the Building Regulations.

4. Drainage and Water Management

• Check if your extension affects drainage or existing water systems.
• You may need a Build Over Agreement from the water authority if building near a sewer.

Download our FREE PDF guide:

Do You Need Planning Permission?

You may not need planning permission if your extension falls under Permitted Development Rights. However, if you are within 1m of a boundary, extra conditions apply:

• Height restrictions: Eaves can’t exceed 3m; overall height can’t exceed 4m for single-storey.
• Rear extension: Must not extend more than 3m from the original wall (or 6m under prior approval).
• Side extension: Must not exceed half the width of the original house.

If these are exceeded, or your property is listed, in a conservation area, or a flat, then you will likely need full planning permission.

Party Wall Agreements

Under the Party Wall Act 1996, if your extension involves:

• Building on the boundary line
• Excavating within 3-6 metres of a neighbour’s structure
• Altering a shared wall

You must serve a Party Wall Notice and obtain written agreement from affected neighbours. This process must begin at least two months before work starts.

Working with a Prefab Extension Near Boundaries

A prefab extension —like the Vergolus Modular System—are designed to be space-efficient and meet UK Building Regulations. Our system is:

• Pre-approved for Building Control
• Fire-compliant with options like real brick cladding
• Perfect for terraced homes or restricted access sites

With a prefab extension, installation times are significantly faster, and disruption is minimised.

FAQs About Building A Prefab Extension Near Boundaries in the UK

1. Can I build right up to my boundary?

Yes, but it must comply with fire safety rules and may need planning permission and a party wall agreement.

2. What if my neighbour objects?

Their consent is needed if the Party Wall Act applies. Planning objections are assessed by the local authority.

3. Do prefab extensions follow the same rules?

Yes, prefab or modular extensions must comply with all Building Regulations and planning rules.

4. Can I put windows in a wall close to the boundary?

Not usually. Walls within 1 metre must be fire-rated and typically can’t include windows.

5. How close can foundations be to the boundary?

There’s no minimum distance, but foundations must not compromise neighbouring structures.

6. Who is responsible for drainage near boundaries?

You are, unless connecting to public sewers, which requires consent from the water authority.

7. Will a boundary extension affect my neighbours’ light?

Possibly. The 45-degree rule and right to light laws may apply and affect approval.

8. Is a Party Wall Notice legally required?

Yes, if building on or near the boundary or excavating close to a neighbour’s structure.

9. How long does approval take?

Planning can take 8 weeks or more. Party Wall processes must begin 2 months before work starts.

10. What happens if I build too close without consent?

You could face enforcement action, be forced to remove the structure, or face legal disputes.

Download Your Free Guide

Want a simple checklist to help you plan your boundary extension properly? Click here to download our FREE PDF guide This downloadable version includes:

• Compliance checklist
• Planning steps
• Foundation tips
• Fire safety wall options

Building A Prefab Extension Within A Metre Boundary

Building a prefab extension within 1 metre of a boundary in the UK can be perfectly legal—if you follow the correct steps. Whether you are building a rear kitchen extension, a new workspace, or a garden room, understanding your legal obligations upfront helps prevent costly errors and neighbour disputes. However, there are law experts that specialise in boundary disputes, whom we have no affiliation with. At Vergolus, we specialise in modular extensions that comply with all relevant UK building standards, including fire safety and energy efficiency. Contact our team today for a free site consultation and let’s design something bespoke for your space.