You want more space at home. Knowing the rules on permitted development in Kent is the quickest way to plan it. The big question is simple: can you build it, or must you apply first?

Many extensions and loft conversions need no planning application. Get it wrong, though, and you risk enforcement, delays and cost. This guide covers both routes in plain English. You will learn the size limits, the local Kent rules that trip people up, and how to check your home.

Permitted Development vs Planning Permission: The Quick Answer

Two routes lead to a legal build in England. The first is permitted development. The second is planning permission.

Use permitted development for smaller, low-impact projects within set limits. Apply for planning permission when a project is larger or sits in a protected area.

What Is Permitted Development?

Permitted development is a national right that lets you carry out certain building work without a planning application. It covers many single-storey extensions, loft conversions, outbuildings and porches, as long as you stay within set limits. These rights are not a blank cheque, and conditions always apply.

These rules come from the General Permitted Development Order 2015. You can read the government’s technical guidance for householders for the full detail. You can also prove a project was lawful with a Lawful Development Certificate, covered below.

How Far Can I Extend Under Permitted Development?

How far you can extend depends on your house type. Detached homes get the most room. If you are planning a house extension, here are the standard single-storey rear limits for 2026.

1. Detached house: up to 4 metres deep.
2. Semi-detached or terraced house: up to 3 metres deep.
3. Larger home extension scheme, detached: up to 8 metres with prior approval.
4. Larger home extension scheme, semi or terraced: up to 6 metres with prior approval.
5. Maximum height: 4 metres overall.
6. Maximum eaves: 3 metres if within 2 metres of a boundary.

There are two more rules to remember. A side extension must be single storey and no wider than half your house. The 50 percent rule limits all extensions and outbuildings to half the land around your original home.

When Do You Need Planning Permission?

Some projects always need planning permission. The most common triggers are easy to spot.

• Your extension is bigger than the permitted limits.
• You live in a flat or maisonette, which get no householder rights.
• Your home is listed, which also needs listed building consent.
• You want to change how the building is used.
• Your property sits in a protected area, covered next.

The Kent Catch: Conservation Areas and the Kent Downs National Landscape

Here is where Kent homeowners get caught out. Protected areas reduce or remove permitted development rights. Works allowed in one street may need permission in another.

The Kent Downs National Landscape, once called an Area of Outstanding Natural Beauty, covers parts of Maidstone borough. Homes near the North Downs often sit inside it. Within this area, side extensions, cladding and larger projects can lose their automatic rights.

Conservation areas work the same way. Maidstone, Bearsted and nearby villages contain several of them. Article 4 directions go further, and can remove specific rights street by street.

Always check your own address before you plan. Search your property on your council’s planning map and on the government’s MAGIC map. Look for conservation area, National Landscape or Article 4 labels.

How Much Does Planning Permission Cost in 2026?

A full householder planning application is the main cost to plan for. According to the Planning Portal, it costs around £548 in England as of 2026. Permitted development needs no fee to build.

• Householder planning application: around £548 (confirm the current figure).
• Lawful Development Certificate: about half the planning fee, near £264.
• Larger home extension prior approval: lower and faster than full planning.
• Planning Portal service charge: added for online applications.

Fees rise every April through annual indexation, so always check the latest figure. A planning decision usually takes about 8 weeks. Prior approval is normally quicker.

Permitted Development Is Not the Same as Building Regulations

Planning and Building Regulations are two different things. Planning controls whether you can build. Building Regulations control how safely you build it.

Even fully permitted work can still need Building Regulations sign-off. These cover structure, fire safety, insulation and drainage. The Party Wall Act is separate again, and applies near a shared boundary.

What Happens If You Get It Wrong?

Building without the right permission can be expensive. Your council can demand changes or removal. You may also need a retrospective application, which costs more.

In our work across Maidstone, we see the same mistake often. Someone builds a side extension inside the Kent Downs National Landscape without permission. We have guided hundreds of Kent homeowners through this exact question.

Resale is where a bad assumption bites. A buyer’s solicitor may ask for proof your work was lawful. Without a Lawful Development Certificate, the sale can stall.

The Bottom Line for Kent Homeowners

Getting this right comes down to three steps. Know your house type, check your size limits, then check your local designations. In Kent, protected areas decide which route applies to you.

Before you build, get your project pre-qualified by BDC Construction. We confirm exactly which route fits your home before a single brick is laid. That upfront clarity saves you from costly planning mistakes.

Not sure whether your extension counts as permitted development? That is the first thing worth checking.