Rear House Extensions in London: Costs, Planning and What to Expect in 2026

A rear house extension is the most popular type of house extension in London, creating additional ground floor living space by extending the back of your property. Whether you want a larger kitchen, an open-plan kitchen-diner or a family living area with garden views, a rear extension is one of the most effective ways to transform your home. LCCL Construction has delivered hundreds of rear extensions across London and Hertfordshire with prices starting from £40,000.

Rear House Extensions in London: Costs, Planning and What to Expect in 2026

What Is a Rear House Extension? Rear House Extensions in London Cost 2026

Rear house extensions in london cost 2026. A rear house extension extends the back wall of your property outward into the garden to create additional ground floor living space. It is the most common type of extension in London because most properties have rear gardens that can accommodate additional space without affecting the street frontage. Rear extensions range from modest 3-metre single storey additions to large 6 or 8 metre extensions that completely transform the ground floor layout. The most popular use is creating open-plan kitchen-dining-living areas that open onto the garden through bi-fold or sliding doors.

How Much Does a Rear Extension Cost in London?

A single storey rear extension in London typically costs £40,000 to £80,000 in 2026 depending on size, specification and location. A 3-metre rear extension on a standard terraced house costs approximately £40,000 to £55,000. A 6-metre extension on a semi-detached house costs £55,000 to £75,000. Larger 8-metre extensions on detached properties can cost £65,000 to £80,000 or more. These prices include all design, structural calculations, building regulations and construction when using a design and build company like LCCL Construction. Kitchen fitting, flooring and high-end finishes are additional costs that vary significantly based on specification.

Do I Need Planning Permission for a Rear Extension?

Many single storey rear extensions in London fall under permitted development rights and do not require planning permission. The size limits are 6 metres from the original rear wall on terraced and semi-detached houses, or 8 metres on detached houses, with a maximum eaves height of 3 metres and overall height of 4 metres. If your property is in a conservation area, is a listed building, or has already used its permitted development allowance through previous extensions, you will need planning permission. LCCL Construction recommends obtaining a Certificate of Lawfulness even when planning permission is not required, to provide legal certainty for future property sales.

How Long Does a Rear Extension Take to Build?

A single storey rear extension typically takes 10 to 16 weeks to build depending on size and complexity. A straightforward 3-metre extension can be completed in 10 to 12 weeks. Larger extensions with structural steel beams, underfloor heating and high-specification kitchens take 14 to 16 weeks. The full project timeline including design, planning, building regulations and party wall agreements adds 8 to 16 weeks before construction starts. The total from initial consultation to completion is typically 6 to 9 months. Using a design and build company like LCCL Construction eliminates gaps between stages.

Why Choose LCCL Construction for Your Rear Extension?

LCCL Construction won the LABC Awards Regional Winner 2024 for Best Residential Extension London. We have over 20 years of experience delivering rear extensions across London and Hertfordshire, more than 200 reviews rated 4.7 out of 5, and offer a complete design and build service from architectural design through to construction and finishing. We provide fixed-price quotes, stage-based payments, dedicated project management, and an optional 10-year LABC warranty. Call 020 8037 7332, email info@lcclconstruction.co.uk, or book a free consultation at lcclconstruction.co.uk/booking-calendar/free-consultation-call.