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Why Choose a Two Storey Extension?
Better Value Per m²
Shared foundations and roof mean the upper floor costs far less than building separately
Double the Space
Add bedrooms, bathrooms and living areas in a single project without sacrificing garden
Adds Property Value
A well-designed two storey extension can add 15–20% to your home's market value
Future-Proof Design
Accommodate a growing family or create multi-generational living arrangements
Types of Two Storey Extension
Rear Two Storey
The most common configuration — extends the back of the house on both floors, typically adding a kitchen/dining area below and bedroom or bathroom above.
Side Two Storey
Built alongside the existing house, often above a garage or on a side plot. Ideal for wider plots and can significantly change the property's street presence.
Wrap-Around Two Storey
Combines side and rear extensions on both floors for maximum space. Perfect for corner plots or properties needing a complete transformation.
Over-the-Top Extension
Adding a second storey to an existing single-storey extension. Requires structural assessment of existing foundations and walls.
Planning Permission
Important: Two storey extensions almost always require full planning permission. They do not fall under Permitted Development rights in most cases.
Design & Structural Considerations
Structural Engineering
Steel beams, lintels and foundations must be designed by a structural engineer. New foundations are typically deeper than single-storey.
Building Regulations
Full building regulations approval required covering fire safety, thermal performance, structural stability, drainage and ventilation.
Foundation Design
Two storey extensions need deeper foundations — typically 1 metre minimum. Ground conditions and proximity to trees will influence depth.
Roof Integration
The new roof must tie in seamlessly with the existing structure. Ridge lines, pitch angles and materials all need careful design.
Fire Safety
Upper floors require fire-rated doors, smoke detection systems and adequate escape routes. Inner rooms may need additional measures.
Party Wall Matters
If building within 3 metres of a neighbour's property, you'll need to serve a Party Wall Notice under the Party Wall Act 1996.
Two Storey Extension Costs
A two storey extension typically costs between £1,800 – £2,800 per m² for construction, depending on specification, location and complexity. Design and planning fees are additional.
Small Two Storey (15–25 m²)
£35,000 – £70,000
Medium Two Storey (25–40 m²)
£55,000 – £110,000
Large Two Storey (40–60 m²)
£80,000 – £165,000
Wrap-Around (60+ m²)
£120,000+
Costs are indicative and based on 2024/25 market rates. Actual prices vary by specification, access and site conditions.
Our Design Process
Free Feasibility Call
We discuss your ideas, budget and what's achievable on your property
Site Survey & Design
Full measured survey followed by detailed architectural drawings
Planning Application
We prepare and submit your planning application with supporting documents
Building Regs Drawings
Technical construction drawings ready for building regulations approval and tendering
Explore our design packages or use our extension cost calculator to get an instant estimate.
Frequently Asked Questions
Two-storey extensions in Hampshire typically cost £60,000–£150,000 to build, depending on size and specification. Per square metre, they offer better value than single-storey because the roof and foundations serve two floors. Design packages start from £1,350+VAT.
Yes, most two-storey extensions require planning permission. Unlike single-storey extensions, two-storey builds rarely qualify under Permitted Development. Key considerations include distance from boundaries, impact on neighbours, and design compatibility with the existing property.
A two-storey extension typically takes 14–20 weeks to build once design and planning are complete. The design and planning phase takes 8–12 weeks. Complex designs with specialist finishes may take longer. We provide clear timelines from the initial consultation.
Yes. A two-storey extension costs approximately 50–60% more than single-storey but provides double the floor space. You save on foundations, roofing, and groundwork costs. This makes two-storey extensions the most cost-effective way to significantly increase your living space.
Yes, but there are restrictions. Two-storey extensions on semi-detached houses must maintain a minimum 2m gap from the boundary. You will likely need a Party Wall Agreement with your neighbour. We handle all design constraints and planning requirements.
