How Much Does a Two-Storey Extension Cost?
If you’re looking to create more space for your growing family or simply want to add long-term value to your home, a two-storey extension could be the perfect solution.
It’s one of the most cost-effective ways to double your living area-providing extra bedrooms, larger kitchens, or even a home office and bathroom combination-without the need to move.
At Garnet Construction, we’ve completed countless two-storey extensions across Hertfordshire, Essex, and North London, helping homeowners transform their properties with expert design and high-quality workmanship. One of the first questions we’re often asked is: “How much will it cost?”
Let’s break down the key factors that influence the cost of a two-storey extension and what you can expect to budget for your project.
Average Cost of a Two-Storey Extension
As a general rule, a two-storey extension will cost around 50–60% more than a single-storey extension of the same footprint. This is because the second floor adds extra structure, insulation, and finishes, but the foundations and roof work are already part of the main build.
In the UK, typical two-storey extension prices are:
Basic specification: £1,800 – £2,400 per m²
Mid-range finish: £2,400 – £3,000 per m²
High-end or bespoke finish: £3,000 – £3,500+ per m²
That means a 30m² two-storey extension could cost anywhere from £60,000 to £90,000+, depending on the level of finish, design complexity, and location.
What’s Included in the Quote?
A full two-storey extension project involves more than just building extra walls. Your budget typically includes:
- Foundations and structural work – digging foundations, pouring concrete, installing steel beams if needed.
- Brickwork and roofing – matching your home’s existing brick, tiles, and style for a seamless look.
- Windows and doors – bi-folds, French doors, or sash windows depending on design.
- Internal walls and insulation – ensuring the space is energy-efficient and soundproof.
- Plumbing and electrics – for kitchens, bathrooms, or utility spaces.
- Staircase installation – connecting the two floors safely and attractively.
- Plastering, decorating and flooring – ready for you to move straight in.
Factors That Affect the Cost of a Two-Storey Extension
Every property is different, and the final price depends on several key factors:
- Size and Design Complexity
A simple rectangular extension will cost less than a bespoke, architecturally detailed build with multiple rooms and finishes. - Use of the Space
Adding bathrooms or kitchens will increase costs due to plumbing, drainage, and specialist fittings. Bedrooms or living areas are generally cheaper to build. - Access and Location
If your home is in a tight plot, terrace, or has limited rear access, labour and delivery costs can rise. London and the South East also tend to have higher rates. - Material Choices
Brickwork to match your home, roof tiles, glazing, and finishes all affect your final budget. - Planning and Design Fees
You may need an architect, structural engineer, or planning permission depending on your local council and the scale of your extension. - Ground Conditions
Poor soil or drainage may require deeper foundations or specialist structural work.
Is a Two-Storey Extension Worth the Investment?
In most cases-yes. A high-quality two-storey extension not only gives you extra living space but can increase your property’s value by 15-25%, depending on your location and design. Compared to moving house (and paying stamp duty, legal fees, and estate agent commissions), it’s often the smarter financial choice.
- A two-storey extension can be used for:
- Additional bedrooms and bathrooms
- A larger kitchen-diner with family space
- A home office or guest suite upstairs
- Extended living space for multigenerational families
Why Choose Garnet Construction?
At Garnet Construction, we specialise in home extensions, loft conversions, and renovations across Hertfordshire, Essex, and North London. We’ll guide you through every stage-from initial design and planning permission to construction, finishes, and final handover.
Our experienced team ensures
- Clear, transparent quotes
- Professional project management
- Quality materials and craftsmanship
- Excellent communication from start to finish
Ready to Plan Your Two-Storey Extension?
If you’re thinking about extending your home, contact Garnet Construction today for a free consultation and quote. We’ll help you design the perfect extension to suit your lifestyle, your property, and your budget.
