If you’re thinking about adding an extension to your home, one of the first questions you’ll have is: do I need planning permission? It’s one of the most common questions we get at Arkiplan, and the honest answer is — it depends. But don’t worry, this guide will walk you through exactly what you need to know.
What Is Planning Permission?
Planning permission is formal approval from your local council to carry out certain types of building work. In England and Wales, it’s governed by national planning policy, but individual councils have their own Local Development Plans which can affect what’s allowed in your area.
Not all building work needs it, though. That’s where Permitted Development (PD) rights come in — a set of rules that allow you to extend your home without applying for full planning permission, as long as you stay within defined limits.
When Do You NOT Need Planning Permission for an Extension?
Many homeowners are surprised to learn they can extend their home without applying for planning permission at all. Under Permitted Development rights, you can often build a single-storey rear extension without any formal application — if it meets certain criteria.
Single-Storey Rear Extension Rules
- Maximum depth of 3 metres for a semi-detached or terraced house
- Maximum depth of 4 metres for a detached house
- Maximum height of 4 metres (or no higher than the existing eaves)
- No more than half the area of land around the original house covered by extensions or outbuildings
- Materials should be similar in appearance to the existing house
Prior Approval — The Larger Home Extension Scheme
There’s also a route called Prior Approval (sometimes called the Larger Home Extension Scheme) that lets you build a bigger single-storey rear extension — up to 6 metres for terraced/semi-detached and up to 8 metres for detached homes. You still need to notify the council and give neighbours a chance to object, but it’s a much lighter-touch process than full planning permission.
At Arkiplan, we handle Prior Approval applications as part of our service — it’s quicker than you think. Find out how we can help you with your house extension drawings and application here.
When Do You Need Planning Permission for an Extension?
There are several situations where you will need to apply for full planning permission for your extension:
- Double-storey extensions — most two-storey extensions require planning permission, especially if they’re within 7 metres of the rear boundary
- Side extensions — adding width to the side of your home typically needs planning permission
- Your home is in a designated area — if you’re in a Conservation Area, National Park, Area of Outstanding Natural Beauty, or your home is Listed, Permitted Development rights are restricted or removed entirely
- Your PD rights have been removed — some councils remove PD rights via Article 4 Directions, particularly on newer estates or in sensitive areas
- The extension is on the front of the house — any extension forward of the principal elevation (the front) needs planning permission
- You’ve already used your PD allowance — if previous extensions have already used up the permitted limits, any further work will need permission
How Do You Know If Your Home Is in a Restricted Area?
The easiest way to check is to use the Planning Portal’s interactive guide, or simply ask your local council’s planning department. A quick call or email to them can save you a lot of time and stress.
Alternatively, when you work with Arkiplan, we check all of this for you as part of the design process. We’ll tell you from the outset whether your extension needs full planning permission, Prior Approval, or nothing at all — so there are no surprises.
What About a Loft Conversion?
Loft conversions are slightly different. Many fall under Permitted Development, particularly if they don’t alter the roofline dramatically. A standard dormer loft conversion to the rear of a terraced or semi-detached house often qualifies, as long as it doesn’t exceed 40 cubic metres (for terraced homes) or 50 cubic metres (for detached and semi-detached).
Hip-to-gable conversions and mansard roof alterations usually need planning permission. If you’re considering a loft conversion, our loft conversion drawing and application service covers both Permitted Development and full planning routes.
What Happens If You Build Without Planning Permission?
This is a question we hear a lot — usually from people who’ve bought a house with an extension built without permission, or who’ve heard of a neighbour who “got away with it”.
Building without the required planning permission is risky. Here’s why:
- The council can issue an Enforcement Notice, requiring you to demolish or alter the work
- It can complicate or block a house sale — solicitors will flag it and buyers (or their mortgage lenders) may pull out
- You may have difficulty getting buildings insurance to cover the extension
- Even if the council doesn’t act immediately, they can take enforcement action for up to 4 years (10 years for changes of use)
The bottom line: it’s not worth the risk. Getting the right permissions sorted upfront protects your investment and gives you peace of mind.
How Long Does Planning Permission Take?
A standard householder planning application should be decided within 8 weeks by law — though in reality, some councils take longer, especially if they’re dealing with a backlog.
Prior Approval decisions must be made within 42 days, which makes it a faster route for larger single-storey extensions.
At Arkiplan, we typically have your drawings and application ready to submit within 2–4 weeks of your design meeting. Compare that to the 3+ months it can take with a traditional architect practice. See how our process works here.
Do You Always Need Building Regulations Approval?
Planning permission and Building Regulations are two separate things — and it’s a really common source of confusion. Planning permission is about whether you can build. Building Regulations are about how it must be built to meet safety, structural, and energy efficiency standards.
Almost all extensions need Building Regulations approval, even if they don’t need planning permission. Your builder will need to work to an approved set of drawings, and a Building Control inspector will sign off the work at key stages and at completion.
Arkiplan handles both your planning drawings and your Building Regulations package in-house, so everything is coordinated and you’re not juggling multiple consultants.
Ready to Start Your Extension?
Whether you need full planning permission, Prior Approval, or you’re working within Permitted Development, Arkiplan handles the entire process for you — from initial design right through to approved drawings, planning submissions, and Building Regulations. Fixed price from the start, with no hidden costs.
We’ve completed thousands of projects across England and Wales. Let’s make yours the next one.