House Extension Design Guide 2025 - 1.0 Introduction and How to Use the Guide

Oct 24, 2026

House Extension Design Guide 2025 sets out design, planning, and compliance guidance for improving home extensions and residential development while protecting surrounding residential amenity. The document explains how to use the guide, who it is for, and key applications through a structured approach. It introduces strategies for defining needs, setting urgency and priorities, and aligning design interventions with built form principles. It also outlines statutory process elements such as planning permission, health and safety, and decision-maker checklists, supported by national guidance and referenced contacts.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages72

Reading Time3 h 1 min

AccessFree to download

1.0 Introduction and How to Use the Guide

1.1 Introduction to Guide

1.2 Who should use this guide?

1.3 Application of the Guide

1.4 Glossary

2.0 Strategies for Improving Your Home

2.1 Defining your Needs

2.2 Urgency, Importance and Priority

2.3 Meeting Needs through Design

2.4 Extensions and alterations

2.5 Managing visible interventions

3.0 Built Form Principles

3.1 General Considerations Relating to All Extensions

3.2 Front Extensions

3.3 Side Extensions

3.4 Rear Extensions

3.5 Roof Alterations

3.6 Garden Rooms

3.7 Other Alterations

4.0 Design Optimisation

4.1 Design Optimisation

4.2 Accessibility Strategies: Lifetime Adaptable Homes

4.3 Sustainable Drainage

5.0 Statutory Process

5.1 Statutory Guidance

5.2 Planning Permission

5.3 Health and Safety

5.4 Compliance, Regulations and Standards

5.5 Combined Checklist for Decision Makers

6.0 National Guidance

6.1 National Guidance

6.2 Architectural Conservation Areas and Protected Structures

House Extension Design Guide 2025 1.0 INTRODUCTION AND HOW TO USE THE GUIDE 1.1 Introduction to Guide 6 1.2 Who should use this guide? 7 1.3 Application of the Guide 7 1.4 Glossary 8 2.0 STRATEGIES FOR IMPROVING YOUR HOME 2.1 Defining your Needs 12 2.1.1 Developing a brief 12 2.2 Urgency, Importance and Priority 12 2.2.1 Urgency 12 2.2.2 Importance 12 2.2.3 Priority 12 2.3 Meeting Needs through Design 13 2.3.1 Engaging with experts to advise on design 13 2.3.2 Development Precedentsand Context Considerations 14 2.3.3 Accessibility, adaptability and flexibility 15 2.3.4 Size Guidelines (space requirements) 15 2.4 Extensions and alterations 16 2.4.1 General Principles 16 2.4.2 Invisible interventions and improvements 16 2.4.3 Visible interventions and improvements 17 2.4.4 Interventions to Protected Structures and buildings in Architectural Conservation Areas 18 2.5 Managing visible interventions 18 2.5.1 General Principles 18 2.5.2 Considerations for new extensions 19 2.5.3 Additional considerations 19 2.5.4 Privacy, Overlooking and Perceived Overlooking 20 3.0 BUILT FORM PRINCIPLES 3.1 General Considerations Relating to All Extensions 24 3.1.1 Introduction 24 3.1.2 Residential Extensions 24 3.1.3 SDCC Housing Types 25 3.1.4 House Types v Garden Types 26 3.1.5 Main Considerations 26 3.1.6 Elements of Good Extension Design 27 3.1.7 Built Form Principle (BFP) 1 – All Extensions and Alternations to Houses 29 3.2 Front Extensions 30 3.2.1 General Considerations relating to all front extensions 30 3.2.2 Built Form Principle (BFP) 2 – Front Extensions 31 3.3 Side Extensions 32 3.3.1 General Considerations relating to all side extensions 32 3.3.2 Built Form Principle (BFP) 3 – Side Extensions 34 3.4 Rear Extensions 35 3.4.1 General Considerations relating to all rear extensions 35 3.4.2 Built Form Principle (BFP) 4 – Rear Extensions 37 3.5 Roof Alterations 38 3.5.1 General Considerations relating to roof alterations 38 3.5.2 Built Form Principle (BFP) 5 – Roof Alterations and Extensions 38 3.6 Garden Rooms 40 3.6.1 General Considerations relating to structures within curtilage 40 3.6.2 Built Form Principle (BFP) 6 – Detached Garden Rooms and Sheds 40 3.7 Other Alterations 41 3.7.1 General Considerations relating to other alterations 41 3.7.2 Built Form Principle (BFP) 7 – Other Alterations 42 3.8 Future Considerationsand Amendments 43 4.0 DESIGN OPTIMISATION 4.1 Design Optimisation 46 4.1.1 Energetic efficiency 46 4.1.2 Materials 47 4.1.3 Insulation 47 4.1.4 Thermal Bridging 48 4.1.5 Airtight Construction 48 4.1.6 Orientation 49 4.1.7 Ventilation 50 4.1.8 High Performance Glazing and Doors 50 4.1.9 Compact Design 50 4.1.10 Renewable Energy Resources 50 4.1.11 Building Energy Rating (BER) Certificates 51 4.2 Accessibility Strategies: Lifetime Adaptable Homes 52 4.2.1 Universal Access Guidance 52 4.2.2 Existing Documentation 52 4.2.3 Application to House Extensions 52 4.2.4 Improving Accessibility 53 4.3 Sustainable Drainage 54 4.3.1 Application to this guide 54 4.3.2 Important Considerations for Implementation 55 5.0 STATUTORY PROCESS 5.1 Statutory Guidance 58 5.2 Planning Permission 58 5.2.1 General principles 58 5.2.2 Exempted Development 58 5.2.3 Planning Application Process 58 5.2.4 From Submission to Grant Planning Application Stages 59 5.2.5 After Planning Permission 59 5.2.6 Preparing for construction 59 5.3 Health and Safety 60 5.4 Compliance, Regulations and Standards 62 5.5 Combined Checklist for Decision Makers 64 5.5.1 BFP 1 – All Extensions and Alternations to Houses 64 5.5.2 BFP 2 – Front Extensions 64 5.5.3 BFP 3 – Side Extensions 64 5.5.4 BFP 4 – Rear Extensions 64 5.5.5 BFP 5 – Roof Extensions or Alterations 65 5.5.6 BFP 6 – Detached Garden Rooms and Sheds 65 5.5.7 BFP 7 – Other Alterations 65 6.0 NATIONAL

FAQs

What statutory topics are addressed regarding planning and compliance?

The guide provides a statutory process section covering planning permission, exempted development, application stages, health and safety, and compliance with regulations and standards, including a decision-maker checklist.

Oct 24, 2026

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