UK House Extension Planning Permission Guide
- Harper Latter Architects
- Aug 21
- 17 min read
Updated: Aug 22
So, you're planning a house extension. It's an exciting prospect, but before you get lost in mood boards and kitchen layouts, there's a big question you need to answer first: do you actually need planning permission?
For a lot of homeowners in the UK, the answer is a welcome "no." This is all thanks to something called Permitted Development Rights, a set of rules that allow certain types of extensions without you having to go through the whole planning application process.
Getting to Grips with Permitted Development Rights
Think of Permitted Development (PD) rights as a kind of national green light for specific home improvements. The government has essentially pre-approved certain works, making it much quicker and easier to get common, straightforward projects off the ground.
But—and this is a big but—these rights aren't a free-for-all. They come with a very strict set of rules and limitations. You can't just build whatever you fancy. The guidelines are incredibly specific, covering everything from the size and height of your extension to how close it sits to your garden fence.
When Can You Build Under Permitted Development?
Whether your project gets the nod under PD depends on the type of house you have (detached, semi, or terraced) and what kind of extension you’re planning. The good news is that for many single-storey rear extensions, the rules are pretty generous.
Here’s a quick rundown of some of the main conditions your project will need to meet:
Your extension can’t cover more than 50% of the land around the "original house" (that’s the house as it was first built or as it stood on 1 July 1948).
It can’t extend beyond the front of your house or a side wall that faces a road.
The materials you use on the outside must look similar to those on the rest of your house.
The eaves of the extension can’t be higher than the eaves of your existing house.
For a single-storey rear extension on a detached house, you can generally build out by up to eight metres. If your home is semi-detached or terraced, this is reduced to six metres. It's important to know that for these larger extensions (anything over four metres for detached, or three for others), you’ll need to go through the Neighbour Consultation Scheme.
The Critical Exceptions to the Rule
It's a classic mistake to just assume your property has PD rights. They don’t apply everywhere. Certain properties and locations have had these rights restricted or even removed entirely, meaning you'll almost certainly need full house extension planning permission.
Key Takeaway: Never assume you can build under Permitted Development. Always, always check with your local planning authority first. The rules can be surprisingly complex, especially if your home is in a designated area.
You need to be extra careful if your property is:
In a Conservation Area: The rules here are much tougher to protect the special architectural or historic character of the neighbourhood.
Within a National Park or an Area of Outstanding Natural Beauty (AONB): Just like with conservation areas, strict protections are in place to preserve the landscape.
A Listed Building: Any change to a listed building needs Listed Building Consent, which is completely separate from planning permission. PD rights simply do not apply here.
Under an Article 4 Direction: Sometimes, a local council will issue an 'Article 4 Direction' to remove specific PD rights in an area to protect its character.
This is where working with experienced professionals really pays off. An architect won’t just help you design a fantastic space; they’ll also figure out the right planning route from the very beginning. You can learn more about the benefits of working with house extension architects in our detailed guide.
Ultimately, figuring out whether you need to apply for planning permission is the first, most crucial step. If your project fits neatly inside the PD box and your property doesn't have any special designations, you can move forward with confidence. If not, your journey will start with a formal planning application—and we'll dive into what that involves next.
The Full Planning Application Process Step-By-Step
So, your extension ideas fall outside the safety net of Permitted Development. Don't worry, that just means you’ll need to submit a full planning application. While it sounds more formal and detailed, understanding the stages makes the whole thing feel far less intimidating. Think of it as a clear, structured path from your initial idea to getting that official green light.
Your first port of call should always be to consider pre-application advice from your local council. It's an invaluable service—though often chargeable—where you can chat through your initial plans with a planning officer. They can give you early feedback, flag potential issues, and point out local policies that might affect your design. A bit of upfront investment here can save you a mountain of time and money later on.
Gathering Your Essential Documents
A successful application is built on a foundation of clear, professional, and comprehensive documents. The council needs to know exactly what you're proposing, from its position on your property right down to the materials you plan to use. Vague or incomplete paperwork is one of the most common reasons for hitting a delay.
You'll almost certainly need to pull together a few key documents:
Architectural Drawings: These are the heart of your application. You'll need existing and proposed floor plans, elevations showing every side of the property, and detailed roof plans.
Site and Location Plans: These are the maps that put your project in context. A location plan shows the site within the wider neighbourhood, while a site plan (or block plan) details your property boundary and exactly where the new extension will sit.
Design and Access Statement: For many applications, this is a crucial piece of the puzzle. It’s a written report explaining the thinking behind your extension, how it fits into the local environment, and how it will be accessed. This is your chance to build a compelling case for your project.
This infographic lays out the foundational steps for getting your planning submission ready.
As you can see, the flow from reviewing local rules to consulting an officer before preparing documents highlights a strategic, proactive approach. Get this right, and you'll dramatically improve the quality of your final application.
Navigating The Submission And Decision Timeline
Once your documents are ready, the application is usually submitted online via the Planning Portal, the standard national platform for England and Wales. After you hit submit, the council's first job is to validate your application, which is just a check to make sure you've provided all the necessary information correctly.
The clock officially starts ticking once it’s validated. For most minor applications like house extensions, a statutory determination period of eight weeks begins. During this time, the council kicks off a public consultation, which involves notifying your immediate neighbours and sometimes putting up a notice near your property.
This consultation period gives neighbours and other interested parties a chance to view your plans and submit comments. Crucially, they can only object on valid planning grounds, which are known as ‘material considerations’.
A planning officer will assess your application against local and national planning policies, taking into account all consultation responses. Their goal is to determine whether the proposal is acceptable in planning terms.
This means they’ll be focusing on specific impacts, such as:
The effect on neighbouring properties (e.g., loss of light or privacy).
The design, scale, and appearance of the extension.
Its impact on the character of the street scene.
Whether there are any highway safety or parking issues.
This process is pretty standard for most extensions. However, for more complex projects like digging out a new living space underground, you might want to explore our guide to navigating basement extension planning permission for more specialised advice.
Interestingly, while the number of applications is falling, the system seems to be getting more efficient. The Planning Portal Application Index reported that district-level authorities received 85,800 applications between January and March, an 11% drop from the previous year. Despite this, decision times have improved, with 90% of major applications processed within their 13-week target period.
By the end of the eight-week period, you'll receive a decision notice from the council, either granting or refusing permission for your house extension.
Budgeting For Your Planning Application Costs
Getting any extension project off the ground successfully hinges on a realistic budget. It’s easy to focus on the big-ticket items like building materials and labour, but the costs for your house extension planning permission application are a crucial piece of that initial financial puzzle.
Lots of homeowners only budget for the statutory fee paid to the council, but that's just one part of the picture. To avoid any unwelcome surprises down the line, you need to factor in the professional expertise required to assemble a robust, persuasive application. Thinking about this now gives you a clear financial roadmap from the very start.
The Statutory Application Fee
First up is the most straightforward cost: the fee you pay directly to your local planning authority when you submit your application. This is a fixed cost set by the government, though it does vary slightly across the UK.
In England, the standard fee for a householder application – which covers alterations or extensions to a single home – is currently £206. It’s a similar story in Wales, while Scotland and Northern Ireland have their own fee structures. While this fee is predictable, it’s really just the starting line.
Professional Fees: An Essential Investment
The bulk of your pre-construction budget will almost certainly go towards the professionals who design your extension and pull together the detailed documents for your submission. I know it's tempting, but cutting corners here is a false economy. A well-prepared application managed by an experienced professional massively boosts your chances of getting a first-time approval.
These are the key professional services you'll need to budget for:
Architect or Architectural Designer: This is your primary cost. Their job is to create all the detailed drawings – existing and proposed floor plans, elevations, and site plans. Fees can vary hugely, from £2,000 to £7,000+, depending on how complex your project is, the firm’s reputation, and how involved they are.
Planning Consultant: While your architect will often handle the planning submission, for a particularly complex or contentious project, you might bring in a specialist planning consultant. They offer strategic advice and are brilliant at navigating tricky local policies. Their fees typically range from £1,000 to £3,000.
Expert Tip: When you're getting quotes, always ask for a clear, itemised breakdown of services. Does the fee include managing the application and talking to the planning officer, or is it just for producing the drawings? Transparency is key to avoiding hidden costs later on.
Costs For Specialist Surveys And Reports
Depending on where your property is located and its specific features, your local council might ask for additional specialist reports to support your application. These are needed to address specific planning considerations and prove that your proposal won’t have a negative impact on the local environment.
Common reports you might need include:
Tree Survey (Arboricultural Report): If you have significant trees on your property (or a neighbour’s) that are close to the proposed work, you'll almost certainly need one of these. Expect to pay between £350 and £1,000.
Ecological Survey: This becomes a requirement if your project could disturb protected species, like bats. This can cost anywhere from £400 to £2,000+, depending on the scope of the survey.
Flood Risk Assessment: If your home is in an area identified as being at risk of flooding, this report is mandatory. Costs for this typically start from around £500.
Anticipating these potential requirements early on is crucial for accurate budgeting. A good architect will spot the need for reports like these during the initial design phase, making sure your financial planning for the house extension planning permission process is comprehensive and realistic from day one.
Common Reasons Planning Applications Are Refused
Navigating the planning process can feel like a minefield, but understanding why applications get rejected is half the battle. If you know where the common pitfalls lie, you can steer clear of them from the very start. Let's break down the most frequent reasons planning officers say "no," and more importantly, how you can avoid them.
Overlooking And Loss Of Privacy
This is a big one. One of the most sensitive issues for any planning officer is how your extension will affect your neighbours' privacy. A new window, balcony, or roof terrace that looks directly into their garden or main living areas is a huge red flag for the council.
Imagine a new two-storey side extension with a large bedroom window that gives a perfect view straight into the master bedroom next door. That’s a classic, textbook example of a design that’s doomed to fail. The principle of 'right to light' is also a major factor; your new structure can't just plunge your neighbour's home into permanent shadow.
To get around this, think strategically about where your windows are going. Could you use high-level windows that let light in without creating a direct line of sight? Or perhaps obscure glazing for sensitive areas like bathrooms? A professional Daylight and Sunlight Assessment can be a powerful tool here, proving that you’ve considered the impact and your design is respectful.
Out Of Character With The Area
Your extension doesn't need to be a carbon copy of your existing house, but it absolutely must respect the character and feel of the street. Planners will scrutinise the scale, design, and materials of your proposal to make sure it doesn’t stick out like a sore thumb.
Trying to build an ultra-modern, glass-and-steel box on a street of traditional Victorian terraces, for instance, is likely to meet fierce opposition. A planner's job is to protect the local character, so a design that feels totally alien is almost guaranteed to be rejected.
The trick is to propose a design that is either sympathetic to the existing architecture or offers a high-quality, complementary contrast. Using materials that are already common in the local area is a simple but incredibly effective way to show your design is thoughtful and well-considered.
Overdevelopment Of The Site
Every property has its limits. 'Overdevelopment' is the term planners use when a proposed extension is just too big for the plot. It leaves behind a tiny garden, makes the property feel cramped, and can appear overbearing to neighbours.
This often happens when homeowners get a bit carried away trying to maximise every last square inch of their land. An extension that covers almost the entire rear garden, for example, would be seen as poor design and a loss of valuable amenity space.
Key Insight: Planning isn't just about your property in isolation; it's about how it fits into the wider environment. A successful application demonstrates a balance between your needs and the needs of the community and local character.
To get this right, you need to be realistic. Make sure your extension is proportionate to the original house and the size of your plot. It should feel like a natural, seamless addition, not something that has been shoehorned in.
It’s worth noting just how many of these applications are processed. In one recent three-month period, district authorities in England decided on 60,200 householder development applications. That’s an 8% increase on the previous year and accounted for 58% of all planning decisions. You can explore more data on UK planning application statistics to really understand the landscape.
To help you get ahead, we’ve put together a quick-glance table of the most common reasons for refusal and what you can do about them.
Common Planning Refusal Reasons And How To Avoid Them
Being aware of these potential hurdles is the first step to a successful application. A well-prepared, thoughtful design that anticipates the planners' concerns stands a much better chance of sailing through the process.
What To Do If Your Application Is Refused
Getting a refusal notice is disappointing, but it's definitely not the end of the road. You essentially have two choices: appeal the decision or submit a revised application. The great thing is, the refusal notice will clearly lay out the reasons, giving you a perfect roadmap for what needs to be fixed.
In my experience, the most effective route is usually to work with your architect to tweak the design based on the planning officer's feedback and then resubmit. This is typically faster and less confrontational than lodging a formal appeal with the Planning Inspectorate, which can be a very long and uncertain process.
Planning Permission vs Building Regulations
When you start looking into a home extension, you'll quickly come across two terms that sound similar but are worlds apart: Planning Permission and Building Regulations. It’s a common mistake to think they’re the same thing, but getting this wrong can cause serious headaches down the line. Understanding their distinct roles is the first step to a smooth, legally sound project.
In the simplest terms, planning permission is all about the principle of your extension. It’s the council looking at the bigger picture and asking broad questions. Will it look right in the street? Will it overshadow your neighbours or block their light? Is it an appropriate use of the land? It deals with aesthetics, scale, and the overall effect on the local area.
Building Regulations, on the other hand, couldn’t be more different. They aren’t concerned with whether your extension is a good idea in principle, but with how it’s actually built. This is the technical stuff—the nuts and bolts that ensure your new structure is safe, structurally sound, energy-efficient, and accessible for everyone.
What Does Each Process Actually Cover?
Think of it this way: a planning officer cares about the visual impact, while a building control inspector is focused on the technical specification of your insulation or the fire safety of your escape routes. Planning permission decides if you can build; Building Regulations dictate how you must build it.
To make this crystal clear, here’s a breakdown of what each one focuses on:
This distinction is absolutely vital, because getting approval for one doesn’t mean you have approval for the other. This brings us to a point that trips up countless homeowners.
Crucial Insight: Even if your extension falls under Permitted Development and doesn't need planning permission, it will almost certainly still require Building Regulations approval. This is non-negotiable for nearly all structural work.
Submitting For Building Regulations Approval
Once you know that Building Regulations are a separate, mandatory step, you have two main routes for getting approval. You can go through either your local authority’s building control department or an approved private inspector.
Full Plans Application: This is the path we almost always recommend. You submit a complete set of detailed architectural and structural drawings before any work starts. A building control officer will check these plans for compliance. Once they give you the green light, you can build with confidence, knowing your design is up to standard.
Building Notice: This is a quicker, simpler option for very straightforward jobs. You just notify the council that you're starting work, without submitting detailed plans first. An inspector then visits the site at key stages to check the work as it progresses. The risk here is obvious—if they find something non-compliant, you’ll have to undo it at your own cost.
The vast majority of house extension planning permission projects are relatively small, but they make up the backbone of residential development in the UK. Recent government figures show that out of 9,200 residential development decisions in a single quarter, 7,000 were granted permission. Single-unit projects, like a typical house extension, accounted for 39% of all projects, which shows just how many people are doing what you’re planning to do. You can find more of these planning application statistics on the GOV.UK website.
Whether you’re adding a small kitchen diner or something more ambitious, getting your head around these two approval systems is fundamental. Our experience in managing refurbishments and extensions has shown us that a clear, organised process is the key to success. Getting both right ensures your finished space isn't just beautiful and functional, but also safe, legal, and built to last.
Your House Extension Planning Questions Answered
Even when you have a good handle on the main process, navigating the world of house extension planning permission throws up plenty of specific questions. It's completely normal to have those niggling concerns that need a clear, direct answer before you can move forward with confidence.
We get asked these questions all the time, so we've gathered the most common ones here. Think of this as your quick-reference guide to the finer points of planning, designed to demystify the process and put your mind at ease.
How Long Does Planning Permission Last Once Granted?
This is a fantastic question and one that's crucial for scheduling your project. Once that decision notice lands on your doormat, the clock officially starts ticking.
Typically, standard planning permission is valid for three years from the date it’s granted. You must begin the development within this timeframe, otherwise, the permission expires and you'll have to go through the entire application process all over again.
So, what counts as "beginning" the development? It’s often more than just putting a spade in the ground. To be safe, you need to make a 'meaningful start', which usually involves substantive work like digging the foundations. It's always a good idea to check with your local planning authority to see exactly what they consider sufficient to secure your permission for the long term.
Can My Neighbours Object To My Planning Application?
In short, yes. Your neighbours will be formally consulted as part of the process, and they have every right to comment on your application. The key thing to remember, however, is that their objections must be based on valid planning grounds, which are known as 'material considerations'.
Personal grievances or worries about a potential drop in their property value simply don't count and will be disregarded by the planning officer.
Valid material considerations are things like:
Loss of privacy or light: Does your proposed extension significantly overshadow their home or garden, or allow direct views into their main rooms?
Parking and traffic issues: Will the development create unsafe access or put unreasonable pressure on local parking?
Design and character: Is the design so out of keeping with the local area that it harms the character of the street?
A well-thought-out application, developed with a professional architect, will anticipate and address these potential issues from the very beginning. This massively reduces the chance of any valid objections gaining traction.
What Happens If I Build An Extension Without Permission?
Building without the necessary planning permission is a serious breach of planning control. Frankly, it’s a risk that is never worth taking. Your local council has the power to issue an enforcement notice, which can demand that you alter or even completely demolish the unauthorised extension.
Imagine the cost and stress of having to tear down your newly built extension. While it's sometimes possible to apply for retrospective planning permission after the work is done, there is absolutely no guarantee it will be granted. If it's refused, you are legally obliged to remove the structure at your own expense. The message is simple: always, always get the right permissions in place before a single brick is laid.
Will I Need A Party Wall Agreement For My Extension?
This is a really common point of confusion. A Party Wall Agreement is a completely separate legal requirement from planning permission, governed by the Party Wall etc. Act 1996. It’s designed to prevent and resolve disputes between neighbours when building work involves a shared wall or boundary.
You will almost certainly need one if your extension plans involve:
Building on the boundary line that you share with a neighbour.
Excavating for new foundations within three metres of a neighbour's property.
Cutting into a shared 'party wall'.
You are legally required to serve a formal notice on any affected neighbours. If they give their consent in writing, you can proceed. If they dissent or don't respond, you'll need to appoint surveyors to draw up a Party Wall Award—a legal document that sets out exactly how the work should be carried out safely and fairly.
At Harper Latter Architects, we guide our clients through every stage of their project, from navigating complex planning rules to overseeing the final build. If you're planning an extension in South West London, contact us to see how we can bring your vision to life.