You may not need planning permission if your extension fits within permitted development rules, but you still need to check three things before you get too excited:

1. Whether your home has permitted development rights and whether the extension meets the limits and conditions (these vary by house type and location).

2. Whether your project needs “prior approval” (this often applies to larger single storey rear extensions and involves neighbour consultation).

3. Building regulations are separate from planning and most extensions still need building regulations approval.

If you are in a conservation area, on other designated land or the property is listed, it is much more likely that you will need formal permission and extra checks.

Why this feels confusing (you are not alone)

Most homeowners search for “do I need planning permission for an extension” because they are trying to answer one question:

Can I actually start this project without the council stopping it later?

The problem is that planning permission, permitted development, prior approval, building regulations and the Party Wall Act are different systems. You can be totally fine on one and still get caught out by another.

This guide is the practical, homeowner-friendly version.

Step 1: Work out if you are aiming for permitted development or planning permission

What is permitted development?

Permitted development rights let you extend your home without applying for planning permission as long as the work stays within specific limits and conditions.

This is where most people want to land, because it is usually simpler.

A quick reality check

Permitted development is not “do whatever you want”. The rules can change depending on things like:

• whether the house is detached, semi-detached or terraced

• whether you are on designated land (for example some conservation areas)

• whether the extension is to the rear or side

• whether it is single storey or more than one storey

If you are around Bromley or Romford, you will often find streets where conservation area rules or local constraints are a factor, so it is worth checking early rather than halfway through your design.

Step 2: Use the simple “which type of extension is it?” test

Planning Portal gives clear starting rules for common extension types. Here are the most useful homeowner takeaways.

Side extensions

Side extensions have tighter restrictions. Planning Portal notes conditions such as being single storey, height limits and not exceeding half the width of the original house and that on designated land all side extensions require householder planning permission.

Single storey rear extensions

Planning Portal summarises the usual depth limits for single storey rear extensions and explains that larger rear extensions can be possible under a prior approval process (neighbour consultation), with higher limits in certain cases.

Two storey extensions and anything “bigger”

Two storey extensions and more complex designs are much more likely to need a planning application, particularly in sensitive areas.

If your project is:

• more than a simple rear addition

• close to a boundary

• changing the look of the front of the house

• likely to affect neighbours’ light or privacy

assume you will need more checks and possibly formal permission.

Step 3: Understand “prior approval” before it surprises you

A lot of homeowners think permitted development means “no council involvement”. That is not always true.

Planning Portal explains that the prior approval process applies to larger single storey rear extensions. In practice this often involves a neighbour consultation scheme.

What this means in normal language:

• your neighbours may be notified

• there is a process to consider impacts

• getting this wrong can slow the project down later

This is why we always recommend talking to neighbours early, even if you believe your design is within the rules.

Step 4: Planning permission is not the same as building regulations

This is one of the biggest gaps in most online articles. They focus on permission, then stop.

Even if your extension is permitted development, building regulations can still apply.

GOV.UK explains when you need building regulations approval and how the process works.
Planning Portal also states that most extensions require building regulations approval, with only certain exemptions.

In the real world, building regulations is the part that ensures:

• the structure is safe

• insulation and ventilation are adequate

• the electrics and drainage are compliant

• the build gets signed off correctly

If you are planning an extension because of damp or condensation issues, remember that ventilation is often part of building regulations considerations too.

Step 5: Do not ignore the Party Wall Act if you share a wall or are digging near a neighbour

This catches people out in terraced and semi-detached homes all the time.

The government’s Party Wall etc. Act 1996 explanatory booklet sets out notice requirements and the basic framework for avoiding disputes, including that notice is required and gives an example of 14 days’ notice for rights of entry in certain situations.

If you are:

• working on or near a shared wall

• building up to a boundary

• excavating for foundations close to a neighbour

it is worth checking early whether the Act applies. Some councils also publish plain English summaries of what the Act covers.

The practical advice is simple: Have the neighbour conversation before drawings become a surprise.

A quick “neighbour conversation” script that actually works

Most disputes are not about the extension itself. They are about fear of disruption or uncertainty.

Try this:

• “We are exploring an extension and we want to do it properly.”

• “Before anything is final, we wanted to show you what we are thinking.”

• “We will keep you updated on timings, access and any noisy stages.”

• “If you have concerns about privacy or light, we would rather hear them now than later.”

It is not about getting permission from your neighbour. It is about removing surprises.

The homeowner’s extension checklist for 2026

Use this to keep your project moving without overwhelm.

Before design is final

• Confirm whether the property has permitted development rights and whether any restrictions apply.

• Decide whether you want to pursue permitted development, prior approval or full planning.

• Identify boundaries, drains and any obvious constraints.

• Start the neighbour chat early if you share walls or close boundaries.

Before work starts

• Confirm building regulations route and inspections.

• If relevant, check Party Wall Act steps.

• Make sure access, welfare and protection of existing areas are planned.

• Agree how you will manage disruption, waste, deliveries and security.

How Barry Turner and Son can help you move from “thinking about it” to “ready to start”

If you are in the early stages, what most homeowners need is clarity:

• what’s realistic for the property

• what permissions or approvals may apply

• how to sequence the work so it does not drag on

• how to keep it calm with neighbours and building control

We can help you plan the build properly, coordinate the right trades and deliver the extension with a clean, professional finish.

• Domestic services overview (includes extension-related work)

• Brickwork (useful for structural and extension-related masonry)

• Contact