Double Storey Extensions in London: Add Space on Two Floors

A double storey extension adds space on both the ground floor and first floor of your property, making it the most cost-effective way to add significant living space to your London home. By sharing foundations, walls and a roof between two floors, you get roughly double the space of a single storey extension for approximately 50% to 60% more cost. LCCL Construction delivers double storey extensions across London and Hertfordshire with prices typically ranging from £84,000 inc. VAT (£70,000 + VAT) to £150,000 and more.

Double Storey Extensions in London

What Is a Double Storey Extensions in London?

A double storey extensions in london, also known as a two storey extension, adds new space on both the ground floor and first floor of your property simultaneously. A typical double storey extension might create an open-plan kitchen-diner on the ground floor and a bedroom with en-suite bathroom on the first floor. This type of extension is ideal for growing families who need both more living space downstairs and additional bedrooms upstairs. It is the most space-efficient extension type because both floors share the same foundations, external walls and roof structure.

How Much Does a Double Storey Extension Cost?

A double storey extension in London typically costs £90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT) and more in 2026 depending on size, specification and complexity. A modest double storey rear extension adding approximately 20 square metres per floor costs £42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT). A larger double storey extension with high-end finishes, en-suite bathroom and fitted kitchen costs £114,000 – £156,000 inc. VAT (£95,000 – £130,000 + VAT). Complex projects involving structural alterations to the existing property or premium finishes can exceed £150,000. The cost per square metre of a double storey extension is significantly lower than building two single storey extensions separately, making it excellent value.

Planning Permission for Double Storey Extensions

Double storey extensions almost always require planning permission in London. Unlike single storey extensions which can often be built under permitted development rights, two storey extensions have more restrictive rules. The extension must not extend beyond the rear wall of the original house by more than 3 metres, must not be closer than 7 metres to the rear boundary, and must not be higher than the existing eaves. Materials should match the existing property. In practice, many double storey extensions exceed these limits and require a full planning application. LCCL Construction handles all planning applications and has extensive experience securing approvals across London boroughs.

What Can You Create with a Double Storey Extension?

The ground floor of a double storey extension is commonly used for a larger kitchen, open-plan kitchen-diner, family living room, home office, or utility and storage space. The first floor typically accommodates an additional bedroom with en-suite bathroom, a master bedroom suite, a home office, or a children's playroom or study. Some homeowners use the first floor to create a larger family bathroom. The most popular configuration is an open-plan kitchen-diner-living area on the ground floor with a master bedroom and en-suite above, which creates the biggest impact on both daily living and property value.

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Can it be done under permitted development?

A single-storey rear extension of 3 m on a terrace or semi (4 m on a detached house), a side-return infill and a side extension up to half the original width are permitted development on a house outside a conservation area or Article 4 street — no planning application, just a Lawful Development Certificate, which we apply for on every one. Fixed-price permitted development extensions start from £42,000 inc. VAT (£35,000 + VAT) at economy specification, design and build inclusive, and the 6 m / 8 m larger home extension goes through a 42-day prior approval notification rather than a full application. See our permitted development projects page for every product with its from-price and the checks we run before we confirm a project qualifies. Not sure whether your project needs a planning application? Check if you need planning permission

LCCL Construction offers a complete design and build service for double storey extensions across London and Hertfordshire. From initial consultation and architectural design through planning permission, building regulations, structural calculations and all construction work, we handle everything. We won the LABC Awards Regional Winner 2024 for Best Residential Extension London, have over 200 reviews rated 4.7 out of 5, and offer an optional 10-year LABC structural warranty. Call 020 8037 7332, email info@lcclconstruction.co.uk, or book a free consultation at lcclconstruction.co.uk/booking-calendar/free-consultation-call.