15 Oct Do You Need Planning Permission for a home extension in Kent? A 2026 Guide
Do You Need Planning Permission for a home extension in Kent? A 2026 Guide
Short answer: often not, if your extension is small enough to be Permitted Development. But many Kent homes fall outside those rules because of restrictions including Conservation Area designations, Article 4 or Listed Building restrictions, or because the extension is simply too big. If your plans don’t fit, you’ll need a householder planning application (£548 in England from 1 April 2026). When in doubt, get a Certificate of Lawfulness or professional advice before you build.
By Graham Simpkin Planning, planning consultants and architects in Hartley, Kent, advising homeowners across Kent and London since 1986.
Quick answer: do I need planning permission for an extension?
In England, you can extend many houses without applying for planning permission, because householder Permitted Development Rights (PDR) allow certain works to be carried out without the need for consent. These rights come from the General Permitted Development Order and come with strict size, height and position limitations.
You are more likely to need planning permission if:
- Your extension exceeds the Permitted Development size limits;
- your home is a flat or maisonette (PDR for these types of homes doesn’t apply);
- Your property is in a Conservation Area, Area of Outstanding Natural Beauty (AONB), or is a Listed Building;
- An Article 4 Direction or a condition on an earlier permission has removed your rights;
- Your house was built or converted under certain other Permitted Development routes (change of use etc).
The only way to be certain is to check your property’s planning history and constraints, which is exactly what our initial planning advice service does.
What is Permitted Development for a home extension?
Permitted Development means you can build without a planning application, provided you stay within the rules. For houses (not flats) in England, the key limits for a single-storey rear extensions are:
- It cannot extend beyond the rear wall of the original house by more than 4 metres for a detached house, or 3 metres for any other house (semi-detached or terraced).
- It must be no more than 4 metres high, and no more than 3 metres high at the eaves if within 2 metres of a boundary.
- It must not sit forward of the principal elevation or front onto a highway.
- Materials must be similar in appearance to the existing house (unless it is a conservatory).
- No verandas, balconies or raised platforms.
For two-storey rear extensions, the limits are tighter. They cannot extend more than 3 metres beyond the rear wall of the original house and must be at least 7 metres from the rear boundary.
Side extensions under Permitted Development must be single-storey, no wider than half the width of the original house, and no more than 4 metres high.
The “original house” means the property as it stood on 1 July 1948, or as originally built if later. Earlier extensions count towards your limits, which catches many Kent homeowners out.
What about the larger home extension scheme?
A separate prior approval route lets some homeowners build single-storey rear extensions of up to 6 metres (semi-detached or terraced houses) or 8 metres (detached houses). You must notify your local planning authority, which then consults your neighbours. If a neighbour objects, the council assesses the impact on their amenity before deciding. It isn’t available on protected land, so check carefully before relying on it.
When Permitted Development doesn’t apply in Kent
Kent has more constrained land than many people expect. Common reasons for needing a full application include:
- Conservation Areas and AONBs. Kent contains the Kent Downs and High Weald AONBs and hundreds of Conservation Areas. Rear extensions of more than one storey are not Permitted Development on this land, and cladding and side extension rights are restricted.
- Listed Buildings. Permitted Development rights don’t extend to the building itself, and you will usually need Listed Building consent as well as planning permission.
- Article 4 Directions. Some councils remove Permitted Development rights in specific streets or areas to protect their character.
- Planning conditions. Many modern estates, and houses built under past permissions, have had Permitted Development rights removed by condition.
Our team has worked with 47 local planning authorities in the last financial year alone, so we know that how each council reads its policies can differ.
Planning Permission vs Lawful Development Certificate: which do you need?
If your extension is Permitted Development, you don’t need planning permission, but it’s still wise to get a Lawful Development Certificate (Proposed). It is a formal decision from your council confirming that your plans are lawful, and it can save you problems when you sell, remortgage or deal with a neighbour dispute.
Graham Simpkin Planning can review your proposal, advise whether permission is required, and submit a Certificate of Lawfulness application on your behalf.
How much does a planning application for an extension cost in 2026?
From 1 April 2026, the national householder planning application fee in England is £548 for alterations or extensions to a single dwelling house (not flats). A reduced fee of £272 applies to minor works within the boundary, such as gates, fences and walls.
These fees are set by government and paid to the council, separate from professional fees for drawings, a planning statement or specialist surveys. Some councils also charge an administration fee if an application is invalid on submission, so a properly prepared application matters.
How long does a householder application take?
Councils aim to determine householder applications within 8 weeks of validation. Timescales can stretch if the council needs further information or the case is contentious. Preparing a robust application, with accurate drawings, a clear design and access statement and a policy-led justification, is the best way to avoid delays.
What if your application is refused?
A refusal is not the end. You can appeal to the Planning Inspectorate against a refusal, or against a condition that makes your scheme unworkable. Many householder schemes are refused because of a specific, fixable issue, such as the impact on a neighbour’s light or the scale of the design. We can review the decision notice and advise whether to revise and resubmit or appeal.
Should you get pre-application advice?
For anything complex, such as Green Belt sites, Conservation Areas, Listed Buildings, large two-storey extensions or garden developments, pre-application advice lets you test the council’s view before committing to a full application. It is optional but can be the difference between smooth approval and an expensive refusal.
Frequently asked questions
Can I build a single-storey rear extension without planning permission in Kent?
Yes, in many cases. Under Permitted Development you can usually build up to 3 metres (or 4 metres on a detached house) beyond the original rear wall, subject to height, boundary and garden coverage limits. Protected land, Article 4 Directions and planning conditions can remove those rights, so check before you build.
How much does it cost to apply for planning permission for an extension?
The 2026 householder application fee in England is £548 for most extensions. Add the cost of architectural drawings, any required reports and professional fees.
Do I need planning permission for a two-storey extension?
Usually yes. Two-storey extensions have tight Permitted Development limits (3 metres depth, 7 metres from the rear boundary), and these rights do not apply on protected land such as Conservation Areas.
Do I need planning permission for an extension in the Green Belt?
Not always, because many Permitted Development rights still apply to houses in the Green Belt. If you do need permission, councils assess whether the extension is a disproportionate addition to the original building, so proportionality is key.
What is a Certificate of Lawfulness and do I need one?
It is an official council decision confirming that works are lawful, either proposed or already built. It isn’t compulsory for Permitted Development, but it gives you written proof for future buyers, lenders and solicitors.
Can I extend a house that has already been extended?
Possibly, but earlier extensions count towards your Permitted Development allowance, so a previous extension may use up some or all of your allowance. A planning history check will clarify what is left.
Who can help with a planning application for a house extension in Kent?
Graham Simpkin Planning is a multi-disciplinary consultancy, based in Hartley near Longfield, offering both architectural drawings and planning advocacy for householders across Kent and London.
Talk to a planning consultant before you build
Whether you’re planning a kitchen extension in Dartford, a side extension in Sevenoaks, a loft or garden room in Bexley, or a more ambitious project on a constrained site, getting early advice protects your budget and your timeline.
Graham Simpkin Planning has helped clients navigate the planning system for 40 years. We can check your site constraints and planning history, tell you whether you need permission, prepare your drawings and make your case to the council.
Request a free, no-obligation quote: complete our online enquiry form in about two minutes, call 01474 703705, or email office@gsplanning.uk.
This article is general guidance based on rules in force at the time of writing (October 2026) and is not a substitute for advice on your specific property. Permitted Development rules and fees change, so always check your site’s constraints before starting work.