Rear Extension London 2026: Costs, Planning and Design Complete Guide
- LCCL Construction
- 2 days ago
- 3 min read
A rear extension is the most common and popular type of house extension in London — adding a new kitchen, dining room, living space or open plan area to the back of the ground floor. For millions of London homeowners a rear extension is the most practical and financially rewarding home improvement available. 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?
A single storey rear extension in London costs between £35,000 and £75,000 in 2026 for a full design and build service. The typical rear extension creating a new kitchen diner costs £45,000 to £65,000. A double storey rear extension costs £85,000 to £145,000. Key cost factors include the size, specification of glazing, whether bifold or sliding doors are used and the location within London. See our full house extension cost guide.
Do I Need Planning Permission for a Rear Extension in London?
Most single storey rear extensions in London can be built under permitted development without planning permission. Under standard permitted development a rear extension can extend up to 3 metres beyond the original rear wall for a terraced or semi-detached house, or 4 metres for a detached house. Under the Larger Home Extension Scheme these limits increase to 6 metres and 8 metres respectively. Properties in conservation areas always require planning permission. See our full guide to house extension planning permission in London.
Rear Extension Design Ideas for London Homes
The most popular rear extension design in London is a fully open plan kitchen, dining and living space with bifold or sliding doors opening fully onto the garden. A flat roof with a large rooflight over the kitchen brings natural light deep into the new space. Underfloor heating and large format tiles or engineered oak flooring complete the finish. The glass rear wall or glazed lantern roof are increasingly popular features that transform the quality of natural light in the new space.
How Much Value Does a Rear Extension Add in London?
A rear extension typically adds 10 to 15 per cent to the value of a London property. For a house worth £700,000 this means £70,000 to £105,000 added value from an extension costing £50,000 to £65,000 — a return of 120 to 180 per cent. Premium London locations generate even stronger returns. See our full guide on how much value an extension adds in London.
How Long Does a Rear Extension Take in London?
A single storey rear extension in London typically takes 10 to 14 weeks on site. The full project timeline from initial consultation including design, planning and building regulations is 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.
Frequently Asked Questions About Rear Extensions in London
How much does a rear extension cost in London?
Between £35,000 and £75,000 for a single storey rear extension with full design and build service. A double storey rear extension costs £85,000 to £145,000.
How far can I extend at the rear without planning permission?
3 metres for terraced or semi-detached, 4 metres for detached under standard permitted development. Up to 6 and 8 metres under the Larger Home Extension Scheme.
To get a free consultation call LCCL Construction on 020 8037 7332 or get an instant quote online.
