Double-Storey Extension
Add bedrooms and bathrooms upstairs, while expanding below.
No obligation · Response within 24 hours
Benefits of a Double-Storey Extension.
A double-storey extension delivers twice the space for less than twice the cost. By building upward as well as outward, you can add a kitchen-diner downstairs with bedrooms or a home office above - maximising your plot without sacrificing garden space.
What's Included
Every double-storey extension project includes architect-led design and full technical documentation.
- Site survey and existing floor plans
- Ground and first floor layout design
- Planning application with design and access statement
- Structural engineer coordination for foundations and steelwork
- Full Building Regulations package
Why work with us?
- Architect-led from day one
- Fixed fees, no surprises
- Planning success rate over 95%
- Direct communication throughout
Why Choose a Double-Storey Extension?
A two-storey extension makes sense when:
- You need multiple rooms - A growing family often needs both living space and bedrooms
- Garden space is limited - Build up rather than spreading across your plot
- Budget efficiency matters - Shared foundations and roof mean the second storey costs around 50% more, not 100%
- Future-proofing - Adding an extra bedroom and bathroom can accommodate elderly parents or returning children
Planning Permission Considerations
Double-storey extensions almost always require planning permission. Key considerations include:
- 45-degree rule - Many councils use this to assess impact on neighbour light and outlook
- Overlooking - New first-floor windows should not directly overlook neighbouring gardens or windows
- Design quality - The extension should complement the existing house and streetscene
- Distance from boundaries - Two-storey elements typically need to be at least 2m from boundaries
We prepare a thorough planning application with supporting statements to address these concerns proactively.
Structural Requirements
Two-storey extensions need robust structural design:
- Foundations - Deeper and wider than single-storey, often requiring trial pits to assess ground conditions
- Steelwork - Opening up ground floor walls typically requires steel beams
- First floor - Engineered joists or steel frame to support the upper level
- Connection to existing - Tying the new structure into your existing house requires careful detailing
Common Questions
How much does a double-storey extension cost?
Build costs typically range from £1,800-£2,800 per square metre. A 40m² extension (20m² per floor) might cost £80,000-£110,000 depending on specification.
How long does a double-storey extension take?
Construction typically takes 16-24 weeks. Allow 8-12 weeks for design, planning application, and Building Regulations beforehand.
Can I extend to the side as well as the rear?
Yes, an L-shaped or wraparound two-storey extension is possible, though planning considerations increase. Side extensions visible from the street face more scrutiny.
Will I need to move out during construction?
Most families stay in their homes during a two-storey extension. There will be disruption, particularly when connecting the new structure to the existing house, but it is manageable.