Double Storey Extension Cost London 2026: Complete Price Guide by Size and Type
- LCCL Construction
- 13 hours ago
- 3 min read
A double storey extension — sometimes called a two storey extension — adds space on both ground and first floors, delivering the largest floor area of any extension type. It is ideal for families needing more bedrooms as well as expanded ground floor living space, and typically delivers the highest total value uplift of any extension. This guide gives you accurate 2026 double storey extension costs so you can budget realistically before starting your project. LCCL Construction has delivered dozens of double storey extensions across London and Hertfordshire.
How Much Does a Double Storey Extension Cost in London in 2026?
A double storey extension in London costs between £75,000 and £165,000 in 2026 for a full design and build service. The average project cost is £105,000 to £135,000 depending on size, specification and location. This includes architectural design, planning permission, building regulations, structural calculations, party wall agreements and all construction works from foundations to finished plaster.
Double Storey Extension Cost by Size in London
Small double storey (24 sqm total across both floors): £75,000 to £98,000.
Standard double storey (32 sqm total): £98,000 to £125,000.
Large double storey (44 sqm total): £125,000 to £165,000.
Premium specification with bifold doors, high-end finishes, en-suite bathrooms and Central London locations can exceed £185,000.
Double Storey Rear vs Double Storey Side: Cost Comparison
Double storey rear extension: £75,000 to £165,000. Adds ground floor living space and one or two extra bedrooms upstairs. Double storey side extension: £70,000 to £145,000. Ideal for semi-detached houses with room to build outward on the side. Wraparound double storey: £125,000 to £220,000. Combines both directions for maximum space — typically used on larger detached or semi-detached properties.
What Affects Double Storey Extension Cost in London?
The main factors are: total floor area across both storeys, complexity of structural steelwork required, number of bedrooms and bathrooms added on the first floor, whether an en-suite bathroom is included, complexity of roof tie-in with existing roof, specification of windows and doors, planning permission complexity, party wall agreement complexity and location within London. Central London postcodes cost 15-25 per cent more than outer London.
What Is Included in a Double Storey Extension Cost?
LCCL Construction double storey extension costs include: measured building survey, architectural design, planning permission application, building regulations, structural engineer calculations, party wall notices and agreements, groundworks and enhanced foundations to support two storeys, all structural steelwork, superstructure across both floors, new pitched roof with matching tiles, matching brickwork or render externally, windows and doors including any bifolds or sliding doors, first fix electrics and plumbing throughout, insulation, plastering, second fix, bathroom or en-suite installation labour and full decoration.
Do Double Storey Extensions Need Planning Permission?
Most double storey extensions require full planning permission because they typically exceed permitted development limits — a two storey rear extension can only fall within PD if it extends 3 metres or less from the original rear wall and sits at least 7 metres from the rear boundary. In London most sites do not meet those conditions. LCCL Construction handles all planning applications.
How Much Value Does a Double Storey Extension Add?
A double storey extension in London typically adds 175 to 300 per cent of the construction cost in property value. A £110,000 double storey rear extension typically adds £190,000 to £330,000 in outer London and £250,000 to £450,000+ in premium locations. Adding a second bedroom and bathroom is particularly valuable in London as it can uplift the property class — for example turning a three-bedroom family home into a five-bedroom home.
Frequently Asked Questions About Double Storey Extension Cost
How much does a double storey extension cost in London?
From £75,000 for a small double storey to £165,000 for a large double storey with premium specification.
How long does a double storey extension take?
Typically 18 to 24 weeks on site once construction starts. Add 12 to 20 weeks upfront for design, planning permission and building regulations.
Is a double storey cheaper per square metre than single storey?
Yes — a double storey adds twice the floor area for only around 60 per cent more cost than a single storey, because foundations, roof and steelwork are shared. See our full double storey extension guide and full home extension cost guide.
To get a free detailed estimate call LCCL Construction on 020 8037 7332 or get an instant quote online.
