How to Get Planning Permission for a Home Extension in Cornwall
By Forma Architecture | Architectural Design Studio, Cornwall
In this guide, we'll walk you through everything you need to know about getting planning permission for a home extension in Cornwall: what it involves, when you need it, how long it takes, and how to give your application the best possible chance of success.
Do You Always Need Planning Permission for a Home Extension in Cornwall?
Not always. Many home extensions in Cornwall fall under Permitted Development Rights (PDR) – a set of rules that allow certain types of work to go ahead without a formal planning application.
Under Permitted Development, you may be able to extend your home without planning permission if your extension:
• Extends no more than 4 metres beyond the rear wall of the original house (for a detached property) or 3 metres for a semi-detached or terraced house
• Is no higher than 4 metres at the ridge and no higher than the existing eaves
• Does not cover more than half the area of land around the original house
• Is not forward of the principal elevation (i.e. doesn't project beyond the front of the house)
• Is no higher than 4 metres at the ridge and no higher than the existing eaves
• Does not cover more than half the area of land around the original house
• Is not forward of the principal elevation (i.e. doesn't project beyond the front of the house)
However, Permitted Development Rights are subject to a number of exceptions and limitations – and in Cornwall especially, there are additional considerations.
Cornwall has a large number of properties in:
• Conservation Areas
• Areas of Outstanding Natural Beauty (AONB), including parts of the Cornwall AONB
• National Landscapes
• Listed Building designations
• Areas of Outstanding Natural Beauty (AONB), including parts of the Cornwall AONB
• National Landscapes
• Listed Building designations
If your property falls into any of these categories, your Permitted Development Rights may be restricted or removed entirely. In these cases, a full planning application will almost certainly be required.
If you're unsure whether your project qualifies for Permitted Development, the safest approach is to apply for a Lawful Development Certificate (LDC) – a formal confirmation from Cornwall Council that your project is lawful. This provides important legal protection when it comes to selling your home in the future.
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When Do You Definitely Need Planning Permission?
You will need to submit a full planning application to Cornwall Council if:
• Your extension exceeds the Permitted Development size limits
• Your property is Listed, in a Conservation Area, or within the AONB
• The extension would affect a shared boundary in a way that requires neighbour consent
• You want to change the use of part of your home (for example, converting a garage into a self-contained annex)
• Your property has had its Permitted Development Rights removed by a planning condition (common on newer-build estates)
• Your property is Listed, in a Conservation Area, or within the AONB
• The extension would affect a shared boundary in a way that requires neighbour consent
• You want to change the use of part of your home (for example, converting a garage into a self-contained annex)
• Your property has had its Permitted Development Rights removed by a planning condition (common on newer-build estates)
It's worth noting that Cornwall Council has specific local policies that go beyond the national planning framework. Understanding these nuances is one of the key reasons it pays to work with an architect or architectural designer who knows the local planning landscape well.
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What Does the Planning Application Process Look Like?
Here's a step-by-step overview of what to expect when applying for planning permission for a home extension in Cornwall.
Step 1: Pre-Application Advice (Optional but Recommended)
Before submitting a formal application, you can request pre-application advice from Cornwall Council's planning team. This is particularly useful for more complex or sensitive sites – such as Listed Buildings, properties in the AONB, or where you're unsure how the local planning policies apply.
Pre-application advice typically costs between £100 and £300 depending on the scale of the project. While it's not a guarantee of approval, it gives you valuable early insight into the likely issues and how to address them in your application.
Step 2: Concept Design and Planning Drawings
You'll need a full set of planning drawings to submit with your application. These typically include:
• A location plan (usually OS-based, showing the site in context)
• A site plan (showing the footprint of the proposed extension relative to the existing building and boundaries)
• Existing and proposed floor plans at 1:50 or 1:100 scale
• Existing and proposed elevations showing all affected sides of the property
• Existing and proposed sections where relevant
• A site plan (showing the footprint of the proposed extension relative to the existing building and boundaries)
• Existing and proposed floor plans at 1:50 or 1:100 scale
• Existing and proposed elevations showing all affected sides of the property
• Existing and proposed sections where relevant
Good architectural drawings do more than just fulfil the technical requirements – they tell the story of your project clearly and persuasively, making it easy for the planning officer to understand and support your proposal.
Step 3: Supporting Documents
Depending on the nature of your project, your application may also need to include:
• A Design and Access Statement – explaining the design rationale and how the extension relates to the existing building and its surroundings
• A Heritage Statement – required for Listed Buildings or applications in Conservation Areas
• A Biodiversity Net Gain assessment – increasingly required as part of Cornwall Council's approach to environmental policy
• Flood risk information – if your property is in or near a flood zone
• A Heritage Statement – required for Listed Buildings or applications in Conservation Areas
• A Biodiversity Net Gain assessment – increasingly required as part of Cornwall Council's approach to environmental policy
• Flood risk information – if your property is in or near a flood zone
Step 4: Submitting to Cornwall Council
Planning applications in Cornwall are submitted via the Planning Portal (planningportal.co.uk). The current application fee for a householder extension is £528 (as of 2026 – fees are subject to change) (Note: Planning Portal will also charge a service fee of around £90.)
Once submitted, Cornwall Council has a target of 8 weeks to make a decision on a standard householder application. More complex applications – such as those involving Listed Buildings or Environmental Impact Assessments – can take longer.
Step 5: The Decision
The planning officer will assess your application against Cornwall Council's local planning policies (set out in the Cornwall Local Plan) as well as national planning policy. They will typically consult with neighbours and other stakeholders, and may request additional information or amendments before making a decision.
Possible outcomes include:
• Approval – with or without conditions
• Refusal – with reasons given; you have the right to appeal
• Approval with conditions – for example, requiring certain materials to be agreed before work starts
• Refusal – with reasons given; you have the right to appeal
• Approval with conditions – for example, requiring certain materials to be agreed before work starts
Common Reasons Planning Applications Are Refused in Cornwall
Understanding why applications get refused is the first step to avoiding those pitfalls. Common reasons include:
• Overdevelopment – the extension is considered too large or bulky relative to the existing property or the character of the area
• Impact on neighbouring amenity – loss of light, overlooking, or overbearing effect on adjacent properties
• Harm to the character of a Conservation Area or Listed Building – extensions in sensitive locations must be designed with particular care to preserve or enhance the historic character
• Design quality – poorly considered or generic designs that don't respond to the local vernacular or the character of the host building
• Departure from local policy – Cornwall Council has specific policies on things like flat roofs, materials, and the relationship between extensions and the streetscene
• Impact on neighbouring amenity – loss of light, overlooking, or overbearing effect on adjacent properties
• Harm to the character of a Conservation Area or Listed Building – extensions in sensitive locations must be designed with particular care to preserve or enhance the historic character
• Design quality – poorly considered or generic designs that don't respond to the local vernacular or the character of the host building
• Departure from local policy – Cornwall Council has specific policies on things like flat roofs, materials, and the relationship between extensions and the streetscene
Working with an experienced architectural designer from the outset significantly reduces the risk of refusal. Good design and a well-prepared application – one that anticipates the planning officer's concerns and addresses them proactively – makes a real difference to the outcome.
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How Long Does the Whole Process Take?
It's worth being realistic about timescales. Here's a rough guide from initial enquiry to being ready to build:
• Stage 1: Initial consultation and brief – 1-2 weeks
• Stage 2A: Concept design and planning drawings – 4-8 weeks
• Stage 2B: Pre-application advice (if required) – 4-6 weeks
• Stage 3: Planning application decision – 8-13 weeks
• Total (from start to approval) – 3-6 months
• Stage 2A: Concept design and planning drawings – 4-8 weeks
• Stage 2B: Pre-application advice (if required) – 4-6 weeks
• Stage 3: Planning application decision – 8-13 weeks
• Total (from start to approval) – 3-6 months
This can vary significantly depending on the complexity of your project, the workload at Cornwall Council, and whether any revisions are needed during the process.
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How Much Does Planning Permission Cost in Cornwall?
There are two main costs to budget for:
1. The planning application fee – currently £528 for a standard householder extension application (payable to Cornwall Council).
2. Architectural fees for the design work and drawings needed to support your application. Fees vary depending on the scale and complexity of the project, but for a typical home extension you should expect to budget in the region of £1,500–£4,000 for planning-stage services.
It's worth viewing this as an investment. A well-designed extension – one that gets approved first time and adds real value to your home – more than pays for itself.
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Tips for a Successful Planning Application in Cornwall
Based on our experience working with Cornwall Council, here are our top tips for getting your application approved:
1. Engage an architect or architectural designer early. Good design and good advice at the outset makes everything easier – and significantly improves your chances of a smooth application.
2. Research your local constraints before you start. Is your property Listed? In a Conservation Area? In the AONB? Knowing this upfront shapes the entire design approach.
3. Talk to your neighbours. Notifying neighbours before you submit – and, where possible, addressing any concerns they have – reduces the risk of objections that could delay or derail your application.
4. Consider the character of your home and its setting. Extensions that respond sensitively to the existing building – in terms of scale, materials, and detailing – are far more likely to be approved than generic bolt-on additions.
5. Don't underestimate the value of a well-written Design and Access Statement. This document gives you the opportunity to explain your thinking to the planning officer and demonstrate that you've considered the planning policies. It's not just a box-ticking exercise – it can make a real difference.
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How Forma Architecture Can Help
At Forma Architecture, we guide clients through every stage of the planning process – from initial feasibility and concept design through to preparing and submitting a complete planning application to Cornwall Council.
We understand the local planning policies, we know what Cornwall Council's planning officers are looking for, and we produce drawings and supporting documents of the highest quality.
Whether you're planning a modest single-storey extension or a more ambitious transformation of your home, we'd love to have a conversation about what's possible.
Forma Architecture is an architectural design studio based in Cornwall. We offer a full range of services from concept design through to planning permission and construction drawings, for residential and commercial projects across the UK and internationally.
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