Permitted Development vs Planning Permission: The Definitive London Guide

Q: What is the 45-degree rule?

A rule of thumb used by planners. If your extension cuts a 45-degree line from the centre of your neighbour's nearest window, it might be refused.

Q: Can I build a balcony under Permitted Development?

No. Verandas, balconies, and raised platforms are specifically excluded from PD. You always need full planning.

Q: Do I need permission for a loft conversion?

Rear dormers are usually PD. Front dormers and Mansards always need full planning.

Q: What happens if I build without permission?

The council can issue an Enforcement Notice forcing demolition. Do not risk this.

Q: Can I change my windows without permission?

In a house: usually yes. In a flat: usually no.

Q: Does a garden room (office) need planning?

Rarely. If it is less than 2.5m tall and covers less than 50% of the garden, it is usually PD.

Q: What is the difference between Building Regs and Planning?

Planning is about appearance and amenity. Building Regs is about safety and insulation. You always need Building Regs.

Q: Can I appeal a refusal?

Yes, but it takes months. Often faster to redesign and resubmit.

Q: Why is my architect asking for a 'Pre-App'?

It gives you a temperature check from the council before strict timelines start.

By My Local London Builder Team | January 25, 2025

Grand London Grade II listed home with sensitive modern extension

Summary: In London, the difference between "Permitted Development" and "Full Planning Permission" is the difference between a project that starts in 8 weeks and a project that starts in 8 months. Or never. This guide dissects the rules, the risks, and the strategies. We explain how to navigate council bureaucracy, why you need a Certificate of Lawfulness, and how to avoid the heart-stopping moment of an enforcement notice.

Planning policy is dull. Until it stops you building your dream home. Then, it is the most interesting thing in the world.

For most London homeowners, the local council is a nebulous entity—a faceless bureaucracy that collects the bins. But when you decide to extend, the council becomes the gatekeeper. They hold the keys to your future. Understand their rules, and you can unlock incredible potential in your property.

The system is binary. You are either complying with "Permitted Development" (PD), or you are asking for "Planning Permission." These are two entirely different legal frameworks.

What is Permitted Development?

Permitted Development (PD) is a national grant of planning permission. It is a set of rights given by Parliament, not your local council. It allows you to undertake certain types of work without needing to make a full planning application.

Think of it as a pre-approved menu. If you order from the menu (e.g., "I want a 3-meter rear extension"), you get it. The council cannot say no, provided you follow the recipe exactly.

The Golden Rules of PD for Extensions:

Rear Extension Depth: For terraced houses, 3 meters. For detached, 4 meters.
Height: Single-storey extensions must not exceed 4 meters.
Materials: Must match existing.

The Trap: "I Don't Need Permission"

This is the most dangerous sentence in construction. Even if you are building under PD, you absolutely should apply for a formal confirmation. This is called a Certificate of Lawfulness. Without it, solicitors will block your future house sale.

What is Full Planning Permission?

Full Planning Permission is a request. You are showing the council your specific design and asking, "Please may I build this?" It is subjective. The planning officer decides if it looks "nice" and respects the area character.

When MUST you use Full Planning?

PD rights are powerful, but they are fragile. You HAVE to use full planning if:

1. You Live in a Flat

Flats have ZERO Permitted Development rights. Even if you own the garden flat, you cannot extend 1 inch without full planning permission.

2. Article 4 Directions

Some councils (especially in Conservation Areas) remove PD rights using an "Article 4 Direction." Even painting a front door might need permission.

The Strategy: PD Fallback

Here is a secret weapon: The PD Fallback Position. You apply for a better, larger extension. If the council refuses, you prove you could build a huge, ugly PD extension instead. They often approve the better design to avoid the ugly fallback. It is planning poker.

Conservation Areas: The London Factor

London is a patchwork of Conservation Areas. In these zones, design is king. Materials must be high quality (London stock brick, slate, timber). uPVC is banned. See our Side Return Guide for examples of sensitive design.

Prior Approval: The Middle Ground

For larger rear extensions (up to 6m for terraces), there is "Prior Approval." It is PD, but neighbours can object. If they do, the council assesses impact on amenity. This heavily incentivises being nice to neighbours—see our Party Wall Guide.

Courage in the Face of Council

Dealing with the council can feel like shouting into a void. Do not be intimidated. The planning system is logical, even if it feels chaotic. It runs on precedent.

Courage here means patience. It means hiring an architect who knows the specific planning officer in your borough. But with the right strategy, you will get the permission to build the home you need.

Frequently Asked Questions

1. How long does a planning application take?

Statutory time limit is 8 weeks. In reality, in busy London boroughs, it can take 10-12 weeks. PD Certificates of Lawfulness are also meant to take 8 weeks.

2. What is the 45-degree rule?

A rule of thumb used by planners. Draw a line at 45 degrees from the centre of your neighbour's nearest window. If your extension cuts that line, it might be refused for blocking light.

3. Can I build a balcony under Permitted Development?

No. Verandas, balconies, and raised platforms (above 300mm) are specifically excluded from PD. You always need full planning for a balcony.

4. Do I need permission for a loft conversion?

Often, no. Rear dormers are usually PD. However, Front dormers and Mansards always need full planning. See our Mansard vs Dormer Guide.

5. What happens if I build without permission?

The council can issue an Enforcement Notice. They can force you to knock it down. There is no time limit for enforcement against concealed breaches, but generally, if it's been there for 4 years, it becomes lawful.

6. Can I change my windows without permission?

In a house: usually yes, unless Listed or Article 4. In a flat: usually no, the windows belong to the freeholder and change the external appearance.

7. Does a garden room (office) need planning?

Rarely. If it is less than 2.5m tall (within 2m of boundary) and covers less than 50% of the garden, it is usually PD.

8. What is the difference between Building Regs and Planning?

Planning is about "What it looks like and occupier amenity." Building Regs is about "Is it safe and warm?" You always need Building Regs, even if you don't need Planning.

9. Can I appeal a refusal?

Yes. You can appeal to the Planning Inspectorate. It takes months (6-12 months). It is often faster to redesign and resubmit to the council.

10. Why is my architect asking for a "Pre-App"?

A Pre-Application meeting allows you to show the council sketches before submitting formally. It gives you a "temperature check." It involves a fee but can save time by highlighting objections early.