Double Storey Extensions
Two floors of new space. One build programme.
Double storey extensions across London. Additional bedrooms, bathrooms and living space over two floors, with full planning, structural engineering and construction management by RCB.
Double storey extension contractors in London.
A double storey extension is the most cost-effective way to add substantial living space to your home. By building over two floors, you gain significantly more space per pound spent compared to two separate single-storey builds — shared foundations, shared roof structure, and one mobilisation.
These projects require more rigorous planning and structural engineering than single-storey extensions. Planning permission is almost always required, structural calculations must account for increased loads, and the design must respect overlooking, massing, and the character of the existing building.
RCB manages the full process — planning strategy, architectural design, structural engineering, Building Regulations, construction and handover. One principal contractor accountable for every element of your two-storey build.
What's included
A double storey extension can add 20-25% to your property value — significantly more cost-effective per square metre than single-storey
How It Works
The RCB process for this service.
Feasibility & Planning
We assess your property for a double storey extension, review planning constraints, overlooking issues and massing, and develop a planning strategy.
Design & Engineering
Full architectural drawings for both floors, structural engineering for increased loads, planning application submission and Building Regulations preparation.
Estimate & Contract
A comprehensive itemised estimate covering foundations, structure, first floor, roof, external envelope, internal fit-out on both levels and all finishes.
Build & Complete
Full construction management — groundworks, structural frame, first floor, roof, external works, internal fit-out on both floors and Building Control completion.
Planning & Regulations
Double storey extensions almost always require full planning permission — they rarely fall within Permitted Development rights due to height and proximity rules. Your local planning authority will assess the proposal against the Local Plan, including considerations around overlooking, loss of light, massing, and design compatibility. Building Regulations approval is mandatory and structural calculations are essential. Party wall matters apply where the extension is near a boundary. RCB coordinates all planning, structural and regulatory submissions.
FAQs
Common questions.
Do I need planning permission for a double storey extension?
Yes, in almost all cases. Double storey extensions rarely fall within Permitted Development rights. A full planning application is required, and approval depends on factors including size, height, proximity to boundaries, overlooking, and your local authority planning policies. RCB will assess the planning position and advise on the best strategy.
How much does a double storey extension cost in London?
Double storey extensions in London typically start from £65,000 and can reach £150,000+ depending on size, specification and complexity. However, on a cost-per-square-metre basis, they are significantly more economical than building two separate single-storey extensions. RCB provides a fully itemised estimate once the design and scope are agreed.
How long does a double storey extension take?
A typical double storey extension takes 16–28 weeks on site, depending on size and specification. Pre-construction — design, planning application, structural engineering and Building Regulations — typically adds 12–24 weeks. Planning application determination alone takes 8 weeks as standard.
Can I live in my house during a double storey extension?
In most cases, yes — though there will be periods of significant disruption, particularly during structural works, roof connection and first-floor construction. We recommend planning for temporary use of alternative living space during the most intensive phases if your household circumstances allow.
Will a double storey extension add value to my property?
A well-designed and properly built double storey extension typically adds 20–25% to your property value. The key is quality of design, proper planning approval, Building Control sign-off and professional construction. Poorly executed extensions can actually reduce value — which is why choosing an experienced principal contractor matters.
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