Home Extension London: Costs, Planning and Design 2026 Complete Guide

Building a home extension in London is one of the best investments you can make as a homeowner. Adding space to your existing property — whether a new kitchen, an extra bedroom, a larger living area or a combined open plan ground floor — avoids the cost and disruption of moving while adding significant value and transforming how you live. LCCL Construction has delivered hundreds of home extensions across London and Hertfordshire for over 20 years as part of our complete design and build service.

LCCL Construction — award-winning home extension builders across London and Hertfordshire

How Much Does a Home Extension Cost in London in 2026?

A home extension in London costs between £35,000 and £160,000 in 2026 for a full design and build service depending on the type and size.

A single storey rear extension costs £35,000 to £75,000. A side return extension costs £35,000 to £75,000. A wraparound extension costs £60,000 to £110,000.

A double storey extension costs £85,000 to £160,000.

All costs include architectural design, planning permission, building regulations, structural calculations, construction and finishing.

See our full house extension cost guide.

What Is the Best Type of Home Extension for a London Property?

The best type of home extension depends on your property, your budget and what you want to achieve. For a Victorian terraced house with a side alley the wraparound extension is usually the best option — creating a large open plan ground floor by combining the rear extension with the side return. For a semi-detached or detached property a rear extension or double storey rear extension creates the most space. For maximum budget efficiency a single storey rear extension is the most cost-effective way to add a new room.

Do I Need Planning Permission for a Home Extension in London?

Most single storey rear home extensions in London do not need planning permission under permitted development. Under the Larger Home Extension Scheme you can extend up to 6 metres for a terraced or semi-detached house and 8 metres for a detached house. All double storey extensions require planning permission. Properties in conservation areas always require planning permission regardless of size. See our full guide to house extension planning permission.

Home Extension Design Ideas for London Homes

The most popular home extension design in London is a fully open plan kitchen, dining and living space with bifold or sliding doors opening onto the garden and a rooflight bringing natural light into the new space. A glass lantern roof over the side return section is one of the most impactful and sought-after features in London home extensions. Underfloor heating, large format tiles or engineered oak flooring and a kitchen island complete the typical specification.

How Much Value Does a Home Extension Add in London?

A home extension in London typically adds 10 to 20 per cent to the value of the property. A wraparound extension costing £80,000 generates a return of 140 to 200 per cent in most London locations. In premium areas the return is even stronger. See our guide on how much value an extension adds in London.

Frequently Asked Questions About Home Extensions in London

How much does a home extension cost in London in 2026?

Between £35,000 and £160,000 depending on type and size. A single storey rear extension costs £35,000 to £75,000. A wraparound costs £60,000 to £110,000.

How long does a home extension take in London?

A single storey home extension typically takes 10 to 14 weeks on site. The full project timeline from consultation to completion is 5 to 8 months.

To get a free consultation call LCCL Construction on 020 8037 7332 or get an instant quote online.