A growing family often feels like a tree that has outgrown its pot. Rooms become tight, storage disappears, and daily life starts to feel crowded. Many homeowners in the UK face this problem. Instead of moving to a new house, many people choose to build a double storey extension. It adds space both upstairs and downstairs, like stacking two boxes instead of one.
Still, the first question most people ask is simple: how much does a double storey extension cost? The price can change based on size, location, and materials. Some projects are simple and cost less, while others are larger and cost more. In this guide, you will learn the cost of a double storey extension in the UK and what affects the final price.
What Is a Double Storey Extension?
A double storey extension is a home addition built on two levels. It adds space to both the ground floor and the first floor. For example, a family may add a larger kitchen downstairs and a bedroom upstairs.
Think of it like building a small house attached to your home. The lower floor becomes a new living space, while the upper floor houses the sleeping area. Because the roof and foundation are shared between two floors, the cost per square metre can be lower than building two single extensions.
Average Double Storey Extension Cost in the UK
Many homeowners ask, how much does a double storey extension cost in the UK?
In most cases, the double storey extension cost ranges between £1,800 and £3,000 per square metre. This means the final price depends on the size of the project.
Here are some rough examples:
- Small extension (30 m² total space): £55,000 – £75,000
• Medium extension (40–50 m²): £75,000 – £120,000
• Large extension (60 m² or more): £120,000 – £180,000
So, the cost of a double storey extension UK project often sits between £70,000 and £150,000 for an average home. In London and the South East, prices can climb higher.
Many builders also talk about the double storey extension cost per m2. This is helpful because it works like a measuring tape for your budget. Once you know the price per square metre, you can estimate the full project.
Double Storey Extension Cost Per m2
The double storey extension cost per m2 in the UK normally falls between:
- £1,800 per m² for basic builds
• £2,200 – £2,500 per m² for standard quality
• £2,800 – £3,000+ per m² for high-end designs
For example, if your extension is 40 m² in total floor space and the build price is £2,200 per m², the project may cost around £88,000.
In this way, the cost works like filling a container with water. The bigger the container, the more water it needs.
Double Storey Side Extension Cost
A double storey side extension is one of the most popular choices in UK homes. This type of extension uses the empty space beside a house.
The double storey side extension cost often ranges between £60,000 and £120,000, depending on size. If the structure is simple and connects easily to the existing home, the price may stay on the lower side.
However, if walls need heavy changes or the foundation must be deep, the cost may rise. Each house is different, like two trees growing in the same garden but taking different shapes.
Using a Double Storey Extension Cost Calculator
Many homeowners search online for a double storey extension cost calculator. These tools help people estimate their budget before speaking with a builder.
A typical calculator asks for:
- Extension size in square metres
• Location in the UK
• Build quality level
• Type of extension (rear or side)
After entering these details, the tool gives a rough estimate of the cost of a double storey extension. It works like a compass on a journey. It will not give the exact price, but it points you in the right direction.
Factors That Affect the Cost
The double-storey extension cost can change for many reasons. Some homes are simple to extend, while others need more work.
Location
Building costs in London and the South East are usually higher. Labour and materials often cost more in these areas.
Size of the Extension
A larger extension increases the total price. Yet the cost per square metre may fall slightly as the project grows.
Design and Materials
Basic brick and tile designs cost less. Glass walls, large doors, and luxury finishes increase the cost.
Planning and Structural Work
If steel beams, deep foundations, or major structural changes are needed, the price may rise.
Access to the Site
If builders struggle to bring materials into the garden, labour time increases. This can push the cost higher.
Extra Costs to Plan For
The cost of a double storey extension is not only about bricks and walls. Several extra costs appear during a project.
Architect drawings
Usually £1,500 – £3,000.
Planning permission or building regulations
Often £500 – £1,000, depending on the council.
Structural engineer fees
Around £500 – £1,500.
Interior finishing
Kitchens, bathrooms, flooring, and lighting may add thousands more.
These costs are like small streams joining a river. One by one, they add to the final price.
Is a Double Storey Extension Worth the Cost?
For many families, the answer is yes. A double storey extension cost may feel large at first, but the added space can change daily life.
Instead of cramped rooms, families gain breathing space. Children can have their own bedrooms. A kitchen can grow large enough for family meals.
Also, extensions often increase property value. In many areas of the UK, a well-built extension can raise the home’s price by 10–20 percent. In this way, the project can feel like planting a seed that grows into a stronger home.
FAQs
Is £50,000 enough for a house extension in the UK?
In some cases, £50,000 can be enough for a small and simple house extension. However, most double storey extensions cost more than this amount. The final price depends on the size, design, materials, and location of the project.
Is it cheaper to extend a house or build up?
Building up is often slightly cheaper because it uses the same foundation and ground space. However, it may require stronger structural support for the existing house. The best option depends on the design of the property and local planning rules.
What is the 50% rule for house extensions in the UK?
The 50% rule means that extensions and other additions should not cover more than half of the land around the original house. This rule helps keep outdoor spaces like gardens and driveways. It is part of the permitted development guidelines in the UK.
What type of extension adds the most value to a home?
Extensions that create useful living space often add the most value. For example, adding a larger kitchen, extra bedroom, or open-plan living area can increase a home’s appeal. A well-designed double storey extension can raise property value significantly.
What can reduce the value of a house after an extension?
Poor design, low-quality construction, or losing too much garden space can reduce property value. Extensions that block natural light or do not match the style of the house may also affect buyer interest. Careful planning helps avoid these problems.
Final Thoughts
A double storey extension is one of the most effective ways to add space to a UK home. It builds upward and outward at the same time, like adding two layers to a cake.
The average double storey extension cost in the UK ranges from £70,000 to £150,000 for most homes. The final price depends on size, design, and location.
Before starting a project, it helps to check the double storey extension cost per m2, use a double storey extension cost calculator, and speak with builders for quotes. With the right plan, the new space can turn a crowded house into a home that feels open, calm, and ready for the future.
