Permitted Development or Planning Permission: Which Route is Right for Your Extension?

Key Takeaway

Understanding the key differences between Permitted Development rights and full Planning Permission can save you time, money and frustration. Here's what every homeowner needs to know before starting their extension project.

Understanding Your Planning Options

Before breaking ground on any extension project, every homeowner faces the same fundamental question: do I need to apply for Planning Permission, or can my project proceed under Permitted Development rights? Getting this decision right from the start can save you weeks of delays and hundreds of pounds in unnecessary fees.

At Hampshire Build, we assess planning routes for every project we undertake. This guide explains the practical differences between these two pathways and helps you understand which is likely to apply to your situation.

Permitted Development Rights Explained

Permitted Development (PD) is a set of national planning rules that allow certain types of building work to proceed without requiring a formal planning application. These rights are granted automatically to most residential properties, enabling homeowners to make specific alterations and extensions within defined limits.

Common extension projects that typically fall within PD rights include:

• Single-storey rear extensions: Up to 4 metres for detached houses (3 metres for semi-detached or terraced)
• Loft conversions: Adding up to 40 cubic metres of space (50 cubic metres for detached houses)
• Side extensions: Single storey with maximum height of 4 metres and width no more than half the original house
• Outbuildings: Garden rooms and home offices within specific size limits

However, even if your project falls within these size limits, PD rights come with numerous conditions relating to materials, height, proximity to boundaries, and more. We always recommend obtaining a Lawful Development Certificate to confirm your project qualifies.

When Full Planning Permission is Required

Planning Permission involves submitting a formal application to your local council, who will assess your proposals against planning policies and consult neighbours before making a decision. This process typically takes 8-12 weeks and involves a fee (currently £528 for householder applications as of April 2025).

You will need Planning Permission if:

• Your extension exceeds Permitted Development size limits
• You want to build a two-storey side extension (two-storey rear extensions may qualify under PD if no more than 3m deep and 7m+ from the rear boundary)
• Your property is in a Conservation Area, AONB, or National Park
• An Article 4 Direction has removed PD rights in your area
• You live in a flat or maisonette (which have no PD rights)
• Your property is listed or in a listed building's curtilage
• Previous extensions have used up your PD allowance

Comparing Timelines and Costs

The practical differences between these routes are significant:

Permitted Development Route

• Timeline: Lawful Development Certificate takes 8 weeks (or skip this and proceed at your own risk)
• Council fee: £264 for a Certificate of Lawful Development (as of April 2025)
• Design fees: Drawings still required for Building Regulations
• Neighbour consultation: Not required (though prior notification may apply for larger rear extensions)

Planning Permission Route

• Timeline: 8 weeks for decision (13 weeks if complex)
• Council fee: £528 for householder applications (as of April 2025)
• Design fees: Detailed drawings, design statements and application forms
• Neighbour consultation: Council notifies neighbours who can comment

While PD appears faster and cheaper on paper, the prior approval process for larger extensions can take 42 days plus preparation time. In practice, a straightforward Planning Application often progresses just as quickly.

Common Pitfalls to Avoid

Over hundreds of extension projects, we've seen homeowners make costly mistakes when navigating these routes:

• Assuming PD applies without checking: Many properties have had PD rights removed or restricted. Always verify with your local planning authority.
• Ignoring cumulative limits: Previous extensions, including those by former owners, count against your PD allowance.
• Forgetting Building Regulations: Both routes still require Building Regulations approval. PD only covers planning - it doesn't exempt you from structural and safety standards.
• Skipping the Certificate: Proceeding without a Lawful Development Certificate means no official confirmation your build is legal. This can cause major problems when selling.
• Boundary disputes: PD has strict rules about proximity to boundaries. Getting measurements wrong can invalidate your rights.

Conservation Areas and Special Designations

If your property sits within a Conservation Area, Area of Outstanding Natural Beauty (AONB), or similar designation, your Permitted Development rights are significantly reduced. Many councils in Hampshire, Surrey and across South England have Conservation Areas covering historic town centres and villages.

In these areas, you typically cannot:

• Add cladding to external walls
• Build side extensions under PD
• Extend beyond the rear wall line visible from a public highway

Our area-specific guides for Winchester, Salisbury, Southampton and other locations detail the particular restrictions that may affect your property.

Making the Right Choice for Your Project

The best route depends entirely on your specific property and ambitions. Here's our general guidance:

Permitted Development works well when:

• Your extension is clearly within size limits
• Your property has no special designations
• You want to avoid neighbour consultation
• Time is your priority over design flexibility

Planning Permission is often better when:

• You want design freedom beyond PD constraints
• Your project is on the boundary of PD limits (applying provides certainty)
• You're considering future extensions (preserving PD allowance for later)
• You want formal approval on record for resale value

How Hampshire Build Can Help

During your complimentary consultation, we assess which planning route suits your project. Our fixed-fee packages include all necessary drawings and application management, whether you're pursuing a Lawful Development Certificate or full Planning Permission.

With a 98% planning approval success rate across Hampshire, Surrey, Dorset and beyond, we understand what local authorities expect to see. More importantly, we help you avoid the costly mistakes that can derail extension projects before they begin.

Book your complimentary consultation to discuss your extension plans and get expert guidance on the right planning route for your property.

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