Rear Extension London 2026: Complete Guide to Costs, Planning and Design
- LCCL Construction
- May 14
- 3 min read
A rear extension is the most popular type of house extension in London and one of the highest-value home improvements available to London homeowners. By extending the back of the ground floor, a rear extension creates a larger kitchen, dining room, living room or open plan space — transforming how you use the ground floor of your home. LCCL Construction has delivered rear extensions across London and Hertfordshire for over 20 years as part of our complete design and build service.
How Much Does a Rear Extension Cost in London in 2026?
Rear extension costs in London range from £35,000 for a small single storey rear extension to £120,000 for a large double storey rear extension with premium finishes. The typical single storey rear extension in London costs between £45,000 and £75,000 for a full design and build service including architectural design, planning permission, building regulations, structural calculations, party wall agreements, construction, electrics, plumbing, plastering and decoration. Key factors affecting cost include the size of the extension, specification of glazing and roof, whether bifold or sliding doors are used, kitchen fit-out if included and location within London.
Rear Extension London: Planning Permission Rules in 2026
Most single storey rear extensions in London can be built under permitted development without planning permission, subject to size limits. Under standard permitted development a single storey rear extension can extend up to 3 metres beyond the original rear wall for a semi-detached or terraced house, or 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 double storey rear extensions, extensions in conservation areas, on listed buildings, flats and maisonettes.
Rear Extension Design Ideas for London Homes in 2026
The most popular rear extension design in London is the open plan kitchen, dining and living space with bifold or sliding doors opening fully onto the garden. Other popular designs include a flat roof rear extension with a large rooflight over the kitchen area for natural light, a rear extension with a glazed gable end wall, a lantern roof over the dining area and a rear extension with underfloor heating throughout. The key design principles for a successful rear extension are maximising natural light, creating a strong connection to the garden and ensuring the new space flows naturally from the existing house.
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 including design, planning permission or prior approval 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.
How Much Value Does a Rear Extension Add in London?
A well-executed rear extension in London typically adds 10 to 20 per cent to the value of a house. For a London terraced house worth £700,000 a rear extension costing £55,000 might add £70,000 to £140,000 to the value — a return of 127 to 254 per cent on the construction cost. The open plan kitchen diner created by a rear extension is consistently the most valued feature by buyers across London.
Frequently Asked Questions About Rear Extensions in London
How far can I extend at the rear without planning permission in London?
Under permitted development you can extend 3 metres (semi/terraced) or 4 metres (detached) without planning permission. Under the Larger Home Extension Scheme you can extend 6 metres (semi/terraced) or 8 metres (detached) with prior approval.
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 service. A double storey rear extension costs £85,000 to £120,000.
To get a free consultation and estimate for your rear extension call LCCL Construction on 020 8037 7332 or get an instant quote online.
