Do I need planning permission for an extension in Kent?

Most single-storey rear extensions under 6m (detached) or 4m (semi or terraced) fall within permitted development and need no application. You'll need full planning permission if you exceed those limits, your property is listed or in a conservation area, you want to extend the front of the house, or earlier extensions have used up permitted development rights.

Do I need planning permission for a garden room in a Kent conservation area?

Yes. Conservation areas remove most permitted development rights for outbuildings. This affects much of Tunbridge Wells, central Sevenoaks, Tonbridge Old High Street, West Malling, Maidstone town centre, and any property within an Area of Outstanding Natural Beauty (which covers much of the High Weald and Kent Downs).

What size garden room can I build without planning permission?

Up to 50 percent of the land around your house (excluding the house itself), single-storey, eaves under 2.5m, total ridge under 4m if pitched roof or 3m if flat. The building cannot include a verandah, balcony, or raised platform. Conservation areas, listed buildings, and AONBs override these allowances.

How long does Kent planning permission take?

8 weeks statutory for householder applications. Tonbridge & Malling, Sevenoaks, and Tunbridge Wells councils typically meet that target. Maidstone and Ashford have run longer in 2025 and 2026. Pre-application advice at £150 to £400 is cheaper than a refused application.

What's the cost of planning permission for an extension in Kent?

£258 for a householder application (national fee, 2026). Architect drawings add £1,500 to £4,000 depending on complexity. A structural engineer's input adds £600 to £1,500. Refused applications can be resubmitted free within 12 months on the same site.

Do I Need Planning Permission? Kent Homeowner's Guide 2026

"Do I need planning permission?" is the single most common question homeowners ask us. The answer is often more nuanced than a simple yes or no — it depends on what you are building, where your property is, and what has been done to it previously. This guide provides clear, practical guidance for Kent homeowners in 2026, covering the most common projects and the specific considerations for Kent's local planning authorities.

Planning Permission vs Permitted Development

Planning permission is formal consent from your local council to carry out development. You submit an application with plans and supporting documents, pay a fee, and wait for a decision (typically 8 weeks). The council assesses your proposal against planning policies and considers impacts on neighbours, the streetscene, and the wider environment.

Permitted development rights allow certain types of work without needing to apply for planning permission. These rights are granted by the government (through the General Permitted Development Order) and allow homeowners to make reasonable alterations and extensions within specified limits. However, permitted development is not a free-for-all — there are strict size, height, and positioning rules.

Building Regulations are separate from planning permission. Almost all building work must comply with Building Regulations, which cover structural safety, fire protection, energy efficiency, ventilation, and accessibility. You need Building Regulations approval even for work that does not require planning permission.

What You Can Build Under Permitted Development

Rear Extensions

Single-storey rear extensions:

Detached houses: up to 6 metres beyond the original rear wall (or 8 metres under prior approval for larger home extensions)
Semi-detached and terraced houses: up to 4 metres (or 6 metres under prior approval)
Maximum eaves height: 3 metres
Maximum overall height: 4 metres (within 2 metres of a boundary, maximum height is 3 metres)

Two-storey rear extensions:

Maximum depth: 3 metres beyond the original rear wall
Minimum 7 metres from the rear boundary
Maximum eaves height matching existing house
No closer than 2 metres to any boundary at eaves level

Side Extensions

Maximum height: 4 metres
Maximum width: no more than half the width of the original house
Must be single-storey
Must not be on a side elevation fronting a highway

Loft Conversions

Maximum additional volume: 40 cubic metres (terraced houses), 50 cubic metres (semi-detached and detached)
Dormers must not exceed the highest point of the existing roof
Side-facing windows must be obscure-glazed and non-opening below 1.7 metres
Materials must be similar in appearance to existing
No verandas, balconies, or raised platforms

Outbuildings (Including Garden Rooms)

Maximum 50% of garden area covered by outbuildings
Maximum eaves height: 2.5 metres
Maximum overall height: 4 metres (pitched roof), 3 metres (flat roof), 2.5 metres if within 2 metres of a boundary
Not forward of the principal elevation
Single-storey only
Not used as self-contained living accommodation

Other Permitted Development

Porches: Up to 3 sqm floor area, 3 metres high, more than 2 metres from a highway
Fences and walls: Up to 2 metres (1 metre adjacent to a highway)
Solar panels: On roof slopes not facing a highway (in conservation areas, additional restrictions)
Internal alterations: Generally do not require planning permission (but Building Regulations may apply for structural changes)

When You Definitely Need Planning Permission

Certain projects always require formal planning consent:

New dwellings: Any new house, flat, or self-contained unit (including annexes with separate cooking, sleeping, and bathroom facilities)
Extensions exceeding permitted development limits: Anything larger than the dimensions above
Front extensions: Building forward of the principal elevation
Change of use: Converting a house to flats, a commercial premises, or an HMO
Work to listed buildings: Listed Building Consent is required for any alteration (internal or external) that affects the building's character
Demolition in conservation areas: Requires conservation area consent
Properties with removed permitted development rights: Some properties (particularly newer estates, flats, and those in designated areas) have had permitted development rights removed by planning conditions

Kent-Specific Planning Considerations

Kent has multiple local planning authorities, each with their own Local Plan and policies. Here are the specifics for the main authorities in our area:

Tonbridge & Malling Borough Council

Conservation areas: Tonbridge town centre, several villages including Hadlow, West Malling, and Borough Green
Key policies: Strong emphasis on respecting the character of the High Weald and maintaining village identities
Local quirks: Relatively strict on front dormers and visible roof alterations; sympathetic to rear extensions that are not visible from the street
Pre-application advice: £250 for householder proposals — we strongly recommend this service

Sevenoaks District Council

AONB coverage: Much of the district falls within the Kent Downs Area of Outstanding Natural Beauty or the High Weald AONB
Green Belt: Extensive Green Belt coverage restricts new development and limits extensions to approximately 50% of the original dwelling volume
Conservation areas: Sevenoaks town, Westerham, Otford, Eynsford, and many others
Local quirks: One of the most restrictive planning authorities in Kent. Green Belt and AONB policies significantly limit what can be built. Professional advice is essential.

Tunbridge Wells Borough Council

AONB coverage: Much of the borough falls within the High Weald AONB
Conservation areas: Tunbridge Wells town centre, Pembury, Goudhurst, Cranbrook, and numerous rural villages
Key policies: Design quality is taken seriously. The council has a dedicated conservation team and expects high-quality materials and design.
Local quirks: Extensions in rural areas must demonstrate sensitivity to the High Weald landscape. Contemporary design is accepted where it is of genuinely high quality.

Maidstone Borough Council

Mix of urban and rural: Maidstone town has more flexibility; rural areas face AONB and landscape constraints
Conservation areas: Maidstone town centre, Headcorn, Lenham, and others
Key policies: The adopted Local Plan supports growth in Maidstone town while protecting the surrounding countryside
Local quirks: Generally more pragmatic than Sevenoaks or Tunbridge Wells for standard domestic extensions in urban areas

AONB and Green Belt: Special Restrictions

Two designations particularly affect Kent homeowners:

Areas of Outstanding Natural Beauty (AONB)

The Kent Downs and High Weald AONBs cover large parts of the county. Within AONBs:

Permitted development rights for outbuildings are reduced (maximum 10 sqm on land to the side of the property)
Planning applications receive heightened scrutiny regarding landscape impact
Materials and design must demonstrate sensitivity to the landscape
New development is generally more restricted, particularly in open countryside

Green Belt

Significant parts of Kent (particularly Sevenoaks district and northern Kent) fall within the Metropolitan Green Belt. Green Belt policy:

Presumes against new buildings unless they fall within specific exceptions
Limits extensions to a "reasonable" proportion of the original dwelling (typically 30–50% depending on the council)
Replacement dwellings should not be "materially larger" than the original
Outbuildings must be genuinely ancillary to the dwelling

These restrictions do not prevent all development, but they significantly influence what can be approved. Professional planning advice is strongly recommended for Green Belt projects.

The Pre-Application Process

We recommend pre-application consultation for any project where planning permission is needed or where you are uncertain about permitted development rights. The process:

Submit a pre-application form to your local council with a brief description and sketch plans
Pay the fee (typically £150–£400 for householder proposals in Kent)
Receive a written response from a planning officer (within 4–6 weeks) indicating whether your proposal is likely to be supported, and what changes might improve its chances
Refine your design based on this feedback before submitting a formal application

Pre-application advice is not binding — the council can still refuse a formal application even if pre-app feedback was positive — but it significantly reduces the risk of refusal and wasted fees.

Planning Permission vs Building Regulations: Key Differences

Many homeowners confuse these two separate processes:

	Planning Permission	Building Regulations
What it covers	How development affects appearance, neighbours, and the environment	How the building is constructed (safety, energy, accessibility)
When required	Only for certain types of development	Almost all building work
Who decides	Local planning authority	Building Control (council or approved inspector)
Process	Application, public consultation, decision	Plans submission or building notice, inspections, completion certificate
Timeline	8–12 weeks for a decision	Ongoing inspections during construction
Fee	£258 per dwelling (householder), variable for others	£1,000–£3,000 depending on project

You may need both, either, or just one for your project. Your builder should advise which approvals are required.

Common Mistakes Homeowners Make

1. Assuming permitted development applies without checking: Permitted development rights can be removed by planning conditions, Article 4 directions, or if your property is a flat. Always verify before building.

2. Ignoring the Lawful Development Certificate: For projects under permitted development, we recommend obtaining a Lawful Development Certificate (£129 fee). This provides formal confirmation that your project is lawful — invaluable when selling your property.

3. Starting work before approval: Building without the required permissions is a planning breach. The council can issue enforcement notices requiring demolition of unauthorised work. The cost and stress of this far exceeds the cost of a planning application.

4. Forgetting about Building Regulations: Even if planning permission is not required, Building Regulations almost certainly are. Work without a completion certificate causes problems when selling your property.

5. Not considering neighbours early: Discussing plans with neighbours before submission avoids objections that can delay or prevent approval. Most neighbour objections arise from surprise, not genuine planning issues.

Need guidance on planning for your Kent project? Carey Brothers & Sons navigate the planning process for clients across Kent every week. We handle pre-application consultations, formal applications, Building Regulations submissions, and all liaison with council officers. Contact us for a free consultation — we will advise you clearly on what approvals your project needs and manage the process from start to finish.