Conservation Area Extension Guide London 2025
Planning to extend in a conservation area? Understand the restricted development rights, stricter planning requirements, and design guidelines that apply to your project.
Key Takeaways
- Conservation areas have NO permitted development for side extensions or loft conversions
- Rear extensions are smaller (3m terraced/semi, 4m detached) and require planning permission
- Materials and design must preserve the character of the conservation area
- Check if you're in a conservation area (Free)
What Are Conservation Areas?
Conservation areas are designated parts of a town or city with special architectural or historic interest. They're protected by law to preserve their character and appearance. London has over 600 conservation areas, covering approximately 25% of the capital. Learn more about conservation areas from Historic England.
Living in a conservation area means stricter controls on what you can build and change. The goal is to protect the unique character of these historic neighborhoods while allowing sympathetic modern development.
How to Check If You're in a Conservation Area
Before planning any extension work, you need to confirm whether your property is in a conservation area:
- 1Visit your local borough council's planning portal and search their conservation area map
- 2Search the planning portal for your address to see planning history and designations
- 3Use our free PD checker which automatically identifies conservation area designations
- 4Request a conservation area appraisal document from your borough (free)
Important: If any part of your property boundary touches a conservation area, the stricter conservation area rules apply to your entire property. Check boundary lines carefully.
Restricted Permitted Development Rights
Conservation areas have significantly reduced permitted development (PD) rights compared to standard residential properties. This means more changes require planning permission.
What You CANNOT Do Under Permitted Development
- NO side extensions at all (even small side returns require planning permission)
- NO loft conversions or roof extensions (no dormers or roof alterations on rear or side slopes)
- NO cladding of external walls
- NO satellite dishes or antennas on chimneys or front/side elevations facing a highway
- Reduced size limits for rear extensions (see below)
Reduced Rear Extension Limits
In conservation areas, single-storey rear extensions under PD are limited to:
Detached House
- Maximum 4m from rear wall (vs 8m normally)
- Maximum 4m height
- Maximum 3m to eaves
Terraced/Semi-Detached
- Maximum 3m from rear wall (vs 6m normally)
- Maximum 4m height
- Maximum 3m to eaves
Reality check: Most London extensions exceed these limits, meaning planning permission is required in practice.
Planning Permission Requirements
Since most extensions in conservation areas require planning permission, understanding the process is crucial:
| Aspect | Standard Property | Conservation Area |
|---|---|---|
| Timeline | 8-12 weeks | 12-16 weeks (longer consultation) |
| Application fee | £258-462 | £258-462 (same) |
| Design requirements | Standard policy compliance | Must preserve/enhance character |
| Materials scrutiny | Moderate | Very high (must match) |
| Officer consultation | Planning officer | Planning + Heritage officer |
The key difference is the heritage officer consultation. They assess whether your proposal preserves or enhances the character of the conservation area. Their recommendation heavily influences the planning decision. More information about planning permission is available on GOV.UK.
Materials and Design Guidelines
Conservation areas require careful attention to materials, detailing, and design. The goal is sympathetic development that respects the historic character.
Key Design Principles
- Materials must match existing: Use the same brickwork, roofing, and window styles as the original house
- Proportions matter: Window and door sizes should relate to existing openings
- Subservient design: Extensions should be clearly secondary to the original building
- Preserve historic features: Retain original chimneys, cornices, and architectural details
- Context is key: Look at neighboring properties and follow the streetscape pattern
Common Material Requirements
Often Required
- Matching brick (same color/texture)
- Traditional timber windows
- Slate or clay tile roofing
- Traditional render finishes
Often Refused
- UPVC windows and doors
- Modern cladding systems
- Concrete roof tiles
- Bright or mismatched colors
Borough-Specific Rules and Article 4 Directions
Each London borough has its own conservation area policies and guidelines. Some boroughs also layer Article 4 directionson top of conservation areas, removing even more permitted development rights.
Common Article 4 Restrictions in Conservation Areas
- Require planning permission for all rear extensions (even 3m/4m ones)
- Require permission for window replacements (even like-for-like)
- Require permission for painting external brickwork or stonework
- Require permission for front boundary walls and gates
Always check your specific borough: Conservation area policies vary significantly. Download your borough's conservation area appraisal and design guidelines before starting design work.
Heritage Officer Consultations
Your planning application will be reviewed by both a planning officer and a heritage/conservation officer. The heritage officer's opinion carries significant weight.
What Heritage Officers Look For
- Whether the proposal preserves or enhances the character of the conservation area
- Impact on the streetscape and neighboring historic buildings
- Quality and appropriateness of materials
- Retention of historic features and architectural details
- Precedents set by similar approved schemes in the area
Working With Heritage Officers
Many boroughs offer pre-application advice where you can meet with officers before submitting. This costs £100-300 but can save thousands in design revisions and resubmissions.
Common Approval and Rejection Reasons
Why Applications Get Approved
- High-quality materials that match or complement the existing building
- Design that respects the proportions and scale of the original building
- Limited visibility from public viewpoints (street, parks)
- Evidence of similar approved schemes in the conservation area
- Professional design with detailed heritage statement
Common Rejection Reasons
- Inappropriate modern materials (UPVC, aluminum, concrete)
- Excessive size that dominates the original building
- Loss of historic features (original windows, chimneys, brickwork)
- Visible from street/public areas with negative impact on streetscape
- Design out of character with the conservation area's special qualities
Cost Implications
Building in a conservation area typically costs 10-25% more than similar work outside conservation areas. These costs come from several sources:
Additional Design Costs
- Architect fees: £5,000-15,000+ (higher due to heritage expertise needed)
- Heritage statement: £500-2,000 (explaining how design preserves character)
- Pre-application advice: £100-300 (highly recommended)
- Design revisions: £1,000-3,000 (if heritage officer requests changes)
Higher Material Costs
- Traditional timber windows: 2-3x cost of UPVC
- Matching heritage bricks: £80-150/m² vs £40-60/m² standard
- Slate roofing: £100-180/m² vs £50-80/m² for concrete tiles
- Specialist lime mortar and traditional building techniques
Typical Extension Cost Comparison
Standard Property
£2,000-3,000/m²
Conservation Area
£2,500-3,500/m²
For a typical 20m² rear extension, expect to budget an extra £5,000-15,000 for conservation area requirements.
Timeline Expectations
Conservation area projects take longer due to additional review requirements:
- 1Design phase: 6-10 weeks (vs 4-6 weeks standard) - extra time for heritage considerations
- 2Pre-application: 4-6 weeks (optional but recommended) - meet with planning/heritage officers
- 3Planning application: 12-16 weeks (vs 8-12 weeks standard) - longer due to heritage consultation
- 4Building regulations: 6-8 weeks (standard timeline)
- 5Construction: Same as standard (but material sourcing may add time)
Total timeline from start to construction: 6-10 months (vs 4-6 months outside conservation areas).
Check Your Conservation Area Status
Our Free PD Checker identifies conservation area restrictions and provides:
- Instant conservation area designation check
- Article 4 direction status for your property
- Exact permitted development rights remaining
- Borough-specific policy guidance
Frequently Asked Questions
Can I use modern materials if they look traditional?
It depends on the borough. Some accept high-quality replicas (like timber-effect aluminum), but many conservation areas require genuine traditional materials. Check with your heritage officer during pre-application advice.
What if my neighbor built a similar extension?
Precedents matter. If similar schemes have been approved in your conservation area, reference them in your application. However, each application is judged on its own merits - what worked next door isn't a guarantee for your property.
Can I appeal if my application is refused?
Yes, you have 6 months to appeal. However, conservation area appeals have lower success rates (around 30%) compared to standard planning appeals. Consider revising your design based on the refusal reasons instead.
Do I need planning permission to replace windows?
In many conservation areas, yes - especially if there's an Article 4 direction. Even like-for-like replacements may require permission if the windows face a highway. Always check before ordering replacement windows.
Will living in a conservation area affect my property value?
Generally, conservation area properties have 5-10% higher values than similar non-designated properties. However, building restrictions can limit future development potential, which some buyers factor into their offer.
Can conservation area designation be removed?
Rarely. Councils must review conservation areas every 5 years, but de-designation is extremely uncommon. More often, boundaries are adjusted or additional areas are designated. Consider conservation status as permanent when purchasing property.
Summary
Building in a conservation area requires careful planning, higher-quality materials, and sympathetic design. While restrictions are stricter and costs are higher, many homeowners successfully extend their conservation area properties every year.
The key is working with experienced architects who understand conservation requirements, engaging with heritage officers early through pre-application advice, and budgeting appropriately for the higher material and professional costs.
Before starting design work, confirm your conservation area status and understand the specific policies that apply to your borough. This will save time and money in the long run.