How to Get Planning Permission for a House Extension
If you’re thinking about extending your home, one of the first questions you’re likely to ask is: do I need planning permission? And then, once you’ve worked that out: how do I actually get it?
It’s a question we’re often asked, and it’s completely understandable – the planning system can feel opaque and frankly, a little intimidating. So let’s walk through it together.
Do you actually need planning permission?
The good news is that a lot of home extensions don’t need a formal planning application at all. This is thanks to what’s called Permitted Development Rights (PD for short) – a set of pre-granted permissions from the government that allow certain types of building work to go ahead within defined limits.
But – and this is important – “you probably don’t need permission” is very different from “you can build whatever you like”. The PD rules are precise, and if you stray outside them without realising it, you risk enforcement action. In the worst case, that means being required to demolish what you’ve built at your own cost.
One thing to check before anything else: are your Permitted Development Rights still intact? They can be removed by the council via what’s called an Article 4 Direction, or may never have applied in the first place – for example, if you’re in a flat, in a newer property, or in a conservation area. This is always the very first thing we check.
The “original house” rule
One of the most common traps is the “original house” rule. Under PD, your allowances are calculated against the house as it was first built – or as it stood on 1st July 1948 – not as it stands today. So if there’s already an extension on the property (even if it was there when you bought it), it might impact your PD allowance. Always check the planning history of your property before assuming you have full PD rights available.
The simplified PD size limits
The main limits for common extension types are shown in the table below. These apply in England – the rules in Wales and Scotland might be different.
| Extension Type | Semi / Detached House | Terraced |
|---|---|---|
| Single storey rear extension (standard) | Up to 4m | Up to 3m |
| Single storey rear extension (larger home extension scheme – needs prior approval) | Up to 8m | Up to 6m |
| Two storey rear extension | Up to 3m | Up to 3m |
| Side extension | Up to half the width of the original house | Up to half the width of the original house |
| Loft conversion | Up to 50m3 additional roof volume | Up to 40m3 additional roof volume |
| Garage conversion | Usually permitted | Usually permitted |
Depths all apply from the original rear wall; and there are numerous detailed caveats.
Size alone isn’t the whole picture. There are other conditions to meet too – there are limitations on height, distance requirements from boundaries, the extension can’t project beyond the front of the house, upper-floor side windows must be obscure-glazed, materials should match the existing building, and extensions plus outbuildings together can’t cover more than 50% of the garden area. It’s a “pass everything” test, not a pick-and-mix. …and sometimes, the prescriptive limitations aren’t entirely clear when it comes to the specifics of a particular project.
Always get a Lawful Development Certificate
Even if your extension clearly falls within PD limits, we always recommend applying for a Lawful Development Certificate (LDC) from your local planning authority. It’s a formal, legal document confirming your extension is lawful – and it’s invaluable when you come to sell or re-mortgage. The PD technical rules can be surprisingly nuanced; getting this document gives you certainty now and protects you later.
When you’ll need full planning permission
If your extension falls outside the PD limits, or your PD rights are restricted, you’ll need to submit a Householder planning application. This is also always the case for:
* Any work to a listed building (which also requires separate Listed Building Consent)
* Extensions in conservation areas that affect the character of the area
* Larger two-storey or side extensions
* Wrap-around extensions
* Anything creating a separate dwelling or annexe
* Any property where PD rights have been removed
If you’re ever unsure, it’s always better to apply and have certainty than to assume and find out later that you were wrong. The cost of a planning application is a fraction of the cost of an enforcement notice.
Doing the groundwork before you apply
The homeowners we see coming through planning most successfully are those who prepare before they submit. A few weeks of groundwork can make a real difference to the outcome.
* Read your council’s design guidance
Every council publishes supplementary planning documents – design guides, residential design guides or similar – that set out what they expect from extensions in their area. These are the standard case officers measure applications against…. although they are suppose to consider every application on it’s own individual merit. Download the guides, read them, and let them shape the design. Your architect should be doing this as a matter of course.
* Use the planning portal to do your research
Your local council’s planning portal lets you search previous applications in your street and neighbourhood. Looking at what’s been approved – and what’s been refused, and why – is super useful intelligence. The reasons for refusal on declined applications are especially worth reading. This research costs nothing and can save a lot of time.
* Book pre-application advice from the council
Most councils offer a paid pre-application consultation – a formal response from a planning officer before you submit. This typically costs £200 – £500+ depending on the council and the scale of the project. It’s not a guarantee of approval, and the officer who gives the advice may not be the one who determines the application – but it can tell you what the problems are likely to be, and it demonstrates good faith to whoever does decide it.
* Talk to your neighbours early
We say this to every client. Neighbour objections don’t automatically block a planning application – planning decisions are made on planning grounds, not as a popularity vote – but an objection from next door adds friction and takes time to address. A friendly conversation early, showing your neighbour what you’re planning and genuinely listening to any concerns, often means those concerns get resolved in the design before you’re committed to anything.
* Check your boundaries
Understand exactly where your property boundaries are. Extensions built right on or over a boundary trigger the Party Wall Act – a separate legal process from planning – and boundary disputes mid-build are expensive and stressful. Know what you own before we start designing.
What goes into a planning application
A householder planning application for an extension typically includes: a completed application form, a site location plan, a block plan, existing and proposed drawings (floor plans, all elevations, a section if relevant), and often a Design and Access Statement. We prepare all of these for our clients as part of our planning service.
Once submitted via the Planning Portal and validated by the council (usually within a week or so of submission), a 21-day neighbour consultation begins. Your application is publicly visible on the planning register, and anyone can submit comments. Internal council departments – highways, heritage, ecology – are also consulted depending on what the project involves.
A planning officer then reviews everything and assesses the application against local and national policy. For most householder applications, they can make the decision themselves under delegated powers – it doesn’t need to go to committee. The statutory target for a decision is eight weeks, though in practice many councils take longer. We build programme contingency in from the start so our clients aren’t caught out by this.
Many councils no longer allow changes to the submitted information, so submit the best package possible. A comprehensive submission pack will also help in case you have to resort to appeal a refused application – as the appeal process has changed recently too.
What officers are actually looking at
The things that come up most often in the assessment of a householder extension are:
* Scale and bulk – is the extension proportionate to the house and the plot? The original building should remain the dominant element.
* Design and appearance – does it relate to the host building in terms of proportion, rhythm and materials?
* Impact on neighbours’ amenity – particularly daylight and sunlight, outlook and privacy. This is the area that generates the most objections.
* Trees and hedges – protected trees (under a Tree Preservation Order or within a conservation area) must be considered from the very start of the design process.
* Heritage – in conservation areas and near listed buildings, the impact on character and appearance is given significant weight.
Planning conditions
Most approvals come with conditions attached – for example, a requirement to submit material samples before work begins, or to agree the exact details of rooflights with the council. Some conditions need to be formally discharged before work can start. We handle this for our clients and make sure nothing gets missed.
Planning permission and Building Regulations are two different things
Planning permission answers the question, “Can you build this here?” Building Regulations answers the question, “Is it safe, structurally sound, and energy efficient?”. You need both. They’re completely separate processes, administered by different people. We always make sure our clients understand this, to avoid surprises later.
Design that helps get planning approved
Good design doesn’t just make your home better to live in – it makes your application easier to approve. A few things to keep in mind:
* Design in context, not in isolation: Study your street. Understand the scale, rhythm and materials that define it. An extension that sits comfortably within its setting is almost always easier to approve than one that tries to impose a different aesthetic entirely. That doesn’t mean you can’t have a contemporary design. A well-reasoned contemporary design can and does get approved in traditional settings – it just needs to be well considered.
* Address neighbours’ privacy from the start: If we know a window might create a line of sight into a neighbour’s garden, we design around it from the beginning – whether by relocating it, reducing its size or specifying obscure glazing. Dealing with this proactively signals good faith and usually defuses objections before they’re made.
* The Design and Access Statement: A well-written statement explains the design rationale, demonstrates how the proposal responds to local character, and addresses potential concerns before they’re raised. It helps the planning officer understand – and defend – the decision. It’s worth investing in.
* Know the 45-degree rule: Many councils apply this when assessing whether an extension causes an unacceptable loss of daylight to a neighbouring window. Drawn from the nearest affected window (sometimes the boundary junction) at 45 degrees, the extension shouldn’t cross this line. We check this early in the design process so we’re designing to maximise your space while staying inside what’s defensible.
What does it cost, and how long does it take?
The current planning application fee for a householder extension in England is £528, payable to the local authority. This is subject to annual inflation-linked increases each April. A Lawful Development Certificate currently costs £264. The “free go” on resubmissions – which previously let you resubmit once for free within 12 months – was abolished in December 2023, so a resubmission now attracts the full fee.
Some councils no longer allow applications to be submitted directly to them, which means we have to use an online service to submit, which attracts an unavoidable service fee.
On timescales: the statutory target for a householder application is eight weeks, but many councils are running longer than this.
If the application is refused
Refusal isn’t the end of the road. The first thing to do is read the Decision Notice carefully – the reasons for refusal tell you exactly what the concern is. If the issues are design-related rather than fundamental, a resubmission with targeted amendments often succeeds where the original application didn’t. We’d suggest going with pre-application advice before resubmitting on anything where the issues feel substantive.
If you genuinely believe the refusal is wrong – that it runs contrary to national or local planning policy – you can appeal to the Planning Inspectorate, an independent government body. Appeals are free to submit but take time: a written representations appeal (the most common route for householder decisions) typically takes six to nine months from submission to decision.
Do you need an architect?
For very small, clearly straightforward Permitted Development projects, some homeowners do approach the process themselves. But for anything requiring a Householder planning application, we’d always recommend working with someone who knows the system – not just to produce the drawings, but to think strategically about the design, perhaps engage with the council’s pre-application service, write a compelling Design and Access Statement, and manage the process through to approval.
The other thing a good architect brings is design quality – and that matters beyond just getting permission. An extension that’s been designed well, that flows naturally from your existing home and genuinely improves how you live in it, is worth infinitely more than one that just cleared the planning bar.
Look for RIBA registration, local experience, and – most importantly – someone whose work you actually like and whose communication style feels right for you. This is a stressful process at times, and having someone calm, clear and genuinely on your side makes a real difference.