Lambeth Extension Rules 2026: Planning, Costs & Policy Guide
Complete guide to extending your home in Lambeth. Planning rules, basement SPD, conservation area requirements, design guidance, and typical costs.
Quick Answer
Lambeth has 44 conservation areas and a strict Basement SPD requiring structural assessments. Costs run £1,950-2,800/m² (add 9-13% in conservation areas). Planning takes 8-16 weeks depending on complexity.
£1,950-2,800
Cost per m²
8-16 weeks
Planning time
44
Conservation areas
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Free Property CheckPlanning Permission in Lambeth
Lambeth has 44 conservation areas covering areas like Brixton, Clapham, Streatham Hill, Herne Hill, and Tulse Hill. The Lambeth Design Guide SPD provides detailed guidance on extensions, alterations, and basements.
Before planning any extension, check your property against permitted development rights and use our free checker tool to see what planning constraints apply.
Permitted Development Rights
Standard permitted development rules apply in most of Lambeth, with restrictions in conservation areas:
| Extension Type | Max Without Permission | Lambeth Notes |
|---|---|---|
| Single-storey rear (detached) | 6m deep, 4m high | Limited in conservation areas |
| Single-storey rear (semi/terrace) | 3m deep, 4m high | Check for Article 4 directions |
| Side extension | Half width of house | Usually needs permission in Lambeth |
| Two-storey rear | 3m deep max | Almost always requires permission |
| Basement | N/A | Always requires planning permission |
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Lambeth Basement Policy
Lambeth's Basement SPD (Part 5 of the Design Guide) sets out strict requirements for basement developments to protect neighbors and the local environment.
Key Requirements
- Structural Impact Assessment: Independent verification required for all basement excavations
- Flood Risk Assessment: Mandatory due to Lambeth's flood zones
- Construction Management Plan: Details on access, noise, vibration, working hours
- Garden retention: Significant outdoor space must be preserved
- Tree protection: Detailed arboricultural reports for nearby trees
Basement projects in Lambeth cost £115,000-230,000 for typical 40m² excavations. See our basement extension guide for complete costs and timelines.
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| Extension Type | Cost per m² | Typical Total |
|---|---|---|
| Single-storey rear (20m²) | £1,950-2,500 | £39,000-50,000 |
| Side return (12m²) | £2,450-3,300 | £29,400-39,600 |
| Two-storey rear (40m²) | £2,150-2,800 | £86,000-112,000 |
| Loft conversion (30m²) | £1,750-2,400 | £52,500-72,000 |
| Basement (40m²) | £2,850-3,850 | £114,000-154,000 |
Conservation area premium: Add 9-13% for matching materials and heritage details
Additional Costs
- Architect fees: £3,800-10,500 (10-13% of build cost)
- Structural engineer: £1,400-3,200
- Planning application: £206 (householder) or £462 (full planning)
- Party wall: £1,500-3,000 per neighbor
- Building Control: £750-1,900
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Frequently Asked Questions
Do I need planning permission for an extension in Lambeth?
It depends on size and location. Single-storey rear extensions up to 6m (detached) or 3m (terraced/semi) may qualify for permitted development. However, Lambeth has 44 conservation areas including Brixton, Clapham, Streatham Hill, and Herne Hill. These areas have additional restrictions. All basement excavations require planning permission under Lambeth's Basement SPD.
What is Lambeth's basement policy?
Lambeth's Basement SPD (Part 5 of the Design Guide) requires planning permission for all basement developments. Key requirements include structural impact assessments, flood risk assessments, construction management plans, and protection of trees. The policy restricts basement depth, requires garden retention, and mandates sustainable drainage systems.
How much does an extension cost in Lambeth?
Extension costs in Lambeth: £1,950-2,500/m² for single-storey rear extensions, £2,150-2,800/m² for two-storey extensions, £2,450-3,300/m² for side returns, and £2,850-3,850/m² for basements. Conservation areas add 9-13% for heritage materials. Total costs range from £39k for small single-storey to £190k+ for basements.
How long does planning permission take in Lambeth?
Standard planning applications take 8 weeks in Lambeth. Conservation area applications may take 10-14 weeks. Basement applications typically take 12-16 weeks due to additional technical assessments. Pre-application advice is available and strongly recommended for complex projects or conservation area properties.
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