Rear House Extension London 2026: Complete Guide to Costs, Planning and Design
- LCCL Construction
- 4 days ago
- 3 min read
A rear house extension is the most popular type of home extension in London. Whether you are looking to create an open plan kitchen diner, a larger living space or an additional reception room, a rear extension offers the best value for money of any extension type. LCCL Construction has been delivering rear house extensions across London and Hertfordshire for over 20 years.
How Much Does a Rear House Extension Cost in London in 2026?
Rear house extension costs in London range from £35,000 for a small single storey extension to £120,000 for a large double storey rear extension with high specification finishes. The typical single storey rear extension in London costs between £45,000 and £75,000 for a full design and build including architectural design, planning permission, building regulations, structural engineering, party wall agreements, construction, electrics, plumbing, plastering and decoration.
Key factors affecting rear extension cost in London: size of the extension, ground conditions and foundation requirements, specification of glazing and roof type, whether a flat roof or pitched roof is used, structural steelwork requirements, kitchen or bathroom fit-out and location in London.
Do I Need Planning Permission for a Rear Extension in London?
Most single storey rear extensions in London fall under permitted development rights and do not require planning permission, provided they meet specific size limits. Under permitted development, a single storey rear extension can extend up to 3 metres beyond the original rear wall of a semi-detached or terraced house, or up to 4 metres for a detached house. Under the Larger Home Extension Scheme (prior approval), these limits increase to 6 metres for semi-detached and terraced houses and 8 metres for detached houses.
Planning permission is always required for rear extensions on properties in conservation areas, listed buildings, flats and maisonettes. LCCL Construction checks all planning requirements as part of our free initial consultation.
Rear House Extension Design Ideas for London Homes
The most popular rear extension design in London is the open plan kitchen diner extension. This involves extending the rear of the ground floor to create a large open plan space combining kitchen, dining and living areas, typically with bifold or sliding doors opening onto the garden. Other popular rear extension designs include the kitchen extension with a lantern roof or rooflight for natural light, the single storey rear extension with a glazed gable end and the L-shaped wraparound extension.
How Long Does a Rear Extension Take in London?
A single storey rear extension in London typically takes 10 to 14 weeks on site from start to completion. The full project timeline from initial consultation to completion including design, planning and building regulations is usually 5 to 8 months. A double storey rear extension takes 14 to 18 weeks on site with a full project timeline of 7 to 10 months.
What Is Included in a Rear Extension by LCCL Construction?
LCCL Construction provides a complete design and build service for rear house extensions covering: architectural measured survey, architectural design and drawings, planning permission application, building regulations application, structural engineer calculations, party wall agreements, construction of foundations, structure, roof, glazing, electrics, plumbing, plastering, decoration and project management. One company, one estimate, one point of contact.
Frequently Asked Questions About Rear House Extensions in London
How much does a rear extension cost in London?
A single storey rear extension typically costs £45,000 to £75,000 for a full design and build in London in 2026. Costs vary depending on size, specification and location.
Do I need planning permission for a rear extension in London?
Most single storey rear extensions up to 3 metres (semi/terraced) or 4 metres (detached) fall under permitted development and do not require planning permission. Extensions in conservation areas always require planning permission.
How long does a rear extension take in London?
A single storey rear extension takes 10 to 14 weeks on site. The full project from consultation to completion typically takes 5 to 8 months.
To get a free consultation and detailed estimate for your rear extension, call LCCL Construction on 020 8037 7332 or get an instant quote online.
