Planning Applications & Building Regs: UK Home Extension Guide

The Complete Guide to Planning Applications, Building Regulations, and Home

Extensions in the UK

Introduction

Planning a home extension or conversion can feel overwhelming, especially if you’ve never dealt with planning applications or building regulations before. This guide breaks everything down into clear, simple steps. Whether you’re planning a 6m rear extension, a loft conversion, or a garage conversion, you’ll learn the exact rules, processes, and expert tips to get it right.

Beginner’s Guide: How the UK Planning System Works

The UK planning system can seem confusing at first, but once you understand the basics, everything becomes easier to navigate. The process is designed to balance your right to improve your home with the council’s duty to protect local character, neighbours, and the environment. Think of it as a rulebook that keeps the area looking and functioning well.

2.1 What Local Planning Authorities Actually DoLocal Planning Authorities (LPAs) review planning applications, check designs against planning policies, and make sure proposals fit local character. They assess privacy, daylight, materials, and overall design. For a deeper introduction, see Planning & Building Regs (West London):https://www.sydesignstudio.co.uk/post/navigating-planning-permission-and-building-regulations-in-west-london-1

2.2 Difference Between Planning Permission & Building RegulationsPlanning permission focuses on appearance, impact, and suitability. Building Regulations ensure safety, structure, fire protection, drainage, and insulation. They are completely separate processes. Learn more in Planning & Building Regs (West London):https://www.sydesignstudio.co.uk/post/navigating-planning-permission-and-building-regulations-in-west-london-1

2.3 Role of Local Plans, Design Codes, and SPDsLocal Plans, design codes, and Supplementary Planning Documents guide design standards, materials, extensions, and neighbourhood character. They vary by borough, so always check your local council’s policies.

2.4 How Applications Are AssessedCouncils assess your proposal against national and local policies, neighbour impact, design quality, and street character before making a decision—usually within eight weeks.

Do I Need Planning Permission?

Before starting any project, it’s essential to know whether you need planning permission. Not every home improvement requires an application. Some works fall under Permitted Development (PD), meaning you can build without formal permission if you follow specific rules.

3.1 When Planning Permission IS RequiredYou need planning permission if your extension exceeds PD limits, affects a listed building, sits in a conservation area, or changes the building’s use. Two-storey extensions, side extensions on some homes, and large loft dormers often require approval.

3.2 Situations Where Permitted Development AppliesPD allows certain rear extensions, loft conversions, and garage conversions without needing a full application—as long as you follow extension permission rules and UK extension guidelines. Flats and maisonettes do not benefit from PD rights.

3.3 Common Homeowner MistakesPeople often assume small projects don’t need permission, forget height limits, or design extensions too close to boundaries. Others skip checking drains or build with materials that don’t match the house.

3.4 Quick Checks Before Designing Your Project• Check if your street is under an Article 4 restriction• Measure boundaries, heights, and roof slopes• Review your borough’s design code• Confirm sewer locations• Speak to a planning consultant or architectural designer early on

What Is a 6m Rear Extension?

A 6m rear extension is a single-storey extension projecting up to six metres from the rear wall of a terraced or semi-detached house. It creates a large open-plan space ideal for modern living.

4.1 Purpose & Typical UsesMost homeowners use a 6m extension for a kitchen-diner, family living area, or a mix of both.

4.2 Who Can Build a 6m ExtensionTerraced and semi-detached homes can build up to six metres under Prior Approval. Detached homes can go up to eight metres.

4.3 How It Fits Under PD & Prior ApprovalA 6m extension requires the Larger Home Extension Prior Approval process. It’s not full planning, but you must get council confirmation before construction.

Benefits of a 6m Rear Extension

A 6m extension creates the kind of living space many households dream of. It offers more room, better flow, and a brighter space that connects the home to the garden.

5.1 Increased Living SpaceYou gain a large, flexible area for cooking, dining, and entertaining.

5.2 Higher Property ValueA well-designed extension can significantly increase the value of your home.

5.3 Improved Layout & FunctionalityIt creates an open layout that suits modern living.

5.4 Ideal for Open-Plan Kitchen-DinersMany homeowners choose a large island kitchen with skylights and garden access.

5.5 Perfect for Growing FamiliesMore space means better comfort without having to move house.

Planning Permission Rules for 6m Extensions

Building a 6m extension requires following strict planning rules to meet home extension regulations and UK home extension standards.

6.1 Height RestrictionsMaximum height must not exceed 4 metres for flat or pitched roofs.

6.2 Material RequirementsMaterials should match or complement the existing house.

6.3 Boundary Distance RulesYou must consider side boundaries and avoid overbearing impacts.

6.4 Impact on Neighbouring Properties (Daylight/Overshadowing)Councils check for overshadowing, overlooking, and daylight loss.

6.5 Design & Character ConsiderationsYour extension must respect local design codes and the surrounding streetscape.

The Larger Home Extension: Prior Approval Process Explained

Prior Approval is a streamlined version of planning permission but still requires council approval.

7.1 What Is Prior Approval?It allows rear extensions of 6m (terraced/semi-detached) and 8m (detached).

7.2 Eligibility CriteriaYour property must be a house—not a flat—and must not be in a restricted area.

7.3 The 56-Day Decision ProcessThe council has 56 days to respond, approve, or refuse.

7.4 The Neighbour Consultation SchemeNeighbours are notified and allowed to comment.

7.5 Documents You Must Submit• Existing & proposed drawings• Site plan• Neighbour consultation form• Prior Approval application

7.6 What Happens If the Council Says NoYou can redesign or appeal the decision.

Permitted Development: Extensions & Conversions Under PD

PD rights allow certain extensions without full planning permission.

8.1 PD Rules for Rear ExtensionsFollow size limits, height rules, and material requirements.

8.2 PD Rules for Loft ConversionsThis includes dormers up to 40–50m³ volume.For more guidance, see Loft Planning Rules:https://www.sydesignstudio.co.uk/post/do-i-need-planning-permission-for-a-loft-conversion-in-london

8.3 PD Rules for Garage ConversionsSee detailed guidance here: Garage Conversion Guidehttps://www.sydesignstudio.co.uk/garage-conversions-hounslow-west-london

8.4 Limitations: Conservation Areas, Flats, Article 4These locations often have PD removed.

8.5 When You Must Apply for Planning Permission InsteadWhen your design exceeds PD limits or changes the roof shape significantly.

Why Planning Applications Get Refused & How to Avoid It

Most refusals happen because homeowners don’t follow planning rules for extensions or fail to meet UK extension guidelines.

9.1 Overbearing or Out-of-Character DesignExtensions that look too bulky or modern for the area are often refused.See a related example: House-to-Flats Guidehttps://www.sydesignstudio.co.uk/post/how-to-split-a-house-into-two-flats-planning-and-legal-steps-explained

9.2 Impact on NeighboursLoss of daylight, privacy issues, or overshadowing triggers refusals.

9.3 Poor-Quality DrawingsInaccurate drawings cause delays and rejections.

9.4 Not Following Local PoliciesDifferent boroughs enforce different standards—ignoring these is a common mistake.

9.5 Lack of Supporting DocumentsMissing planning statements or heritage notes often lead to automatic refusal.

How to Prepare the PERFECT Planning Application Package

A strong planning package increases your chance of success.

10.1 Required DrawingsInclude existing and proposed plans, elevations, sections, and site plans.

10.2 Design & Access StatementsExplain your design choices clearly.

10.3 Technical ReportsDrainage, fire strategies, and parking studies may be required.

10.4 Planning Justification Against Local PolicyShow how your design meets local requirements.

10.5 How Architects Negotiate with Planning OfficersGood architects discuss concerns early to avoid refusal.

Building Regulations for a 6m Rear Extension

Building Regulations ensure safety, structure, and energy performance. Learn more in Building Regs Drawings:https://www.sydesignstudio.co.uk/post/the-importance-of-building-regulation-drawings-1

11.1 Structural Integrity (Part A)Your extension must have proper beams, foundations, and load transfer.

11.2 Fire Safety (Part B)This includes protected routes and fire-resistant materials.

11.3 Thermal Insulation (Part L)Ensures energy efficiency and prevents heat loss.

11.4 Drainage & Waste (Part H)Proper drainage and new connections are required.

11.5 Ventilation Requirements (Part F)Fresh air must circulate properly.

Building Regulations for Loft & Garage Conversions

Many households extend and convert lofts at the same time. For planning, see Loft Planning Rules above.

12.1 Fire Escape RoutesLofts need protected escape paths and fire doors.

12.2 Floor Strength & Load-Bearing ChecksStructural upgrades are often required.

12.3 Insulation UpgradesRoof, walls, and floors must meet thermal standards.

12.4 Head Height & Stair RegulationsMinimum headroom is 2m.

12.5 Soundproofing & Party Wall RequirementsLoft floors and walls must meet sound regulations.

Structural Calculations & Engineering Considerations

Every extension relies on safe structural design.

13.1 RSJs & Steel Beam DesignEngineers design beams to carry roof and floor loads.

13.2 Load-Bearing Wall RemovalsOpening walls requires steel supports.

13.3 Foundation Depth & Soil ConditionsSoil type affects foundation specification.

13.4 Padstones & Column LoadsColumns transfer heavy loads to the foundation.

13.5 When You Need a Chartered Structural EngineerAny major structural work requires one.

Hidden Structural Issues Homeowners Never Expect

Many projects uncover surprises.

14.1 Shallow Neighbour FoundationsCan affect extension wall placement.

14.2 Thames Water SewersBuilding over or near them requires approval.

14.3 Shared DrainsShared pipes require special permissions.

14.4 Chimney Breast Load PathsRemoving chimneys affects support.

14.5 Weak or Rotten JoistsOften found in older homes.

 

Design Options for a 6m Rear Extension

Great design can transform your home.

15.1 Modern vs Traditional DesignsSmooth render, brick, or cladding—your choice.

15.2 Bifold, Sliding or French DoorsLarge openings connect home and garden.

15.3 Rooflights & LanternsSkylights brighten the space.

15.4 Island Kitchens & Utility RoomsPopular layouts for families.

15.5 Integrating Landscaping & GardensBlend indoor and outdoor living.

Costs of Building a 6m Rear Extension in 2025

Costs vary by location, design, and materials.

16.1 Construction Cost Breakdown Expect £1,800–£2,200 per m².

16.2 Architectural Fees Planning + building regs + support typically £2,500–£4,000.

16.3 Structural Engineering Fees£600–£1,200 depending on complexity.

16.4 Party Wall Costs Around £900–£1,500 per neighbour.

16.5 Council Fees Planning fees + building control fees.

16.6 Hidden Costs Homeowners Forget Drain diversions, steels, glazing upgrades, and finishes.

Timeline for a 6m Rear Extension

17.1 Planning Timeline8 weeks for Prior Approval.

17.2 Building Regulations Timeline2–4 weeks.

17.3 Structural Design Timeline1–2 weeks.

17.4 Construction Timeline8–14 weeks.

17.5 Snagging & Completion1–2 weeks.

Tips to Avoid Planning or Building Issues

18.1 Do a Pre-Application Get early council feedback.

18.2 Start Structural Design Early Avoid delays later.

18.3 Speak to Neighbours Before Submission It reduces objections.

18.4 Check Drains Before Designing Avoid costly redesigns.

18.5 Use an Approved Inspector Faster and often clearer than the council.

Planning Enforcement: What Triggers It & How to Avoid It

19.1 Building Without Permission Triggers investigations and notices.

19.2 Breaching Approved Drawings Stick to approved plans.

19.3 Overlooking Boundary Heights Common enforcement issue.

19.4 How to Apply for a Lawful Development Certificate Useful for proving PD works are legal.

19.5 How to Fix Enforcement Issues Submit a retrospective application or modify the build.

Borough-by-Borough Planning Rules in West London

20.1 Hounslow Focus on character and neighbour impact.

20.2 Ealing Strict on design and proportions.

20.3 Richmond Very strict due to conservation areas.

20.4 Hillingdon Clear SPD guidance.

20.5 Brent Mixed but practical policies.

20.6 Why Policies Differ by Borough Each borough has unique history, character, and constraints.

Why Work With a Professional Architectural Designer

21.1 Accuracy & Compliance Avoid mistakes in drawings.

21.2 Faster Council Approvals Experienced designers know what councils expect.

21.3 Better Design Quality Create beautiful, functional spaces.

21.4 Coordination With Structural Engineers Ensures safety and smooth progress.

21.5 Avoiding Expensive Mistakes Prevents costly errors and delays.

Get Local Help With Building Regulations & Structural Design

22.1 What a Full Building Regs Package Includes Detailed plans, notes, and construction details.

22.2 Structural Calculations & Details Essential for steel beams, foundations, and walls.

22.3 Support During Construction Helps builders follow the design correctly.

22.4 Why Local Knowledge Matters Local experts understand borough policies.

Frequently Asked Questions

Can I build a 6m extension without permission?

-Not without Prior Approval.

How long does planning take?

-Around 8 weeks.

 Do I need building regulations for a small extension?

-Yes, unless it’s very minor work.

How much does a structural engineer cost?

-£600–£1,200.

What is a party wall agreement?

-A legal notice for shared boundaries.

Will a 6m extension add value?

-Usually yes.

How close can I build to my neighbour's boundary?

-Often right up to it—subject to fire rules.

 What is Prior Approval?

-A streamlined planning process.

What if the council refuses my application?

-You can redesign or appeal.

How do I choose the right architect?

-Look for experience, local knowledge, and clear communication.