A well-designed extension can completely transform how you use your home.
But if you’re considering spending £100,000 or more on an extension, there are some important things to understand before you commit to the design, appoint a builder or start ordering materials.
The cost of an extension can vary significantly depending on the size and complexity of the project, your existing property, specification, location and the level of finish you choose.
So rather than asking simply, “How much does an extension cost?”, it’s worth asking:
“What am I actually getting for my budget, and how can I make sure I spend it wisely?”
Here are some of the things we’d recommend considering.
1. Start with your budget, not your dream kitchen
It’s very easy to start designing your dream extension before thinking about what you realistically want to spend.
You might start with a large open-plan kitchen, huge areas of glazing, a new utility room, a downstairs WC, bespoke cabinetry and a beautiful garden connection.
There’s nothing wrong with having ambitious ideas.
But it’s much easier to design around a realistic budget from the beginning than to discover halfway through the process that your preferred design is significantly more expensive than expected.
Having a budget doesn’t mean compromising on good design.
It means making informed decisions about where your money will have the greatest impact.
2. The size of the extension isn’t the only thing that affects the price
Two extensions with the same floor area can have very different construction costs.
Why?
Because there is much more to an extension than its footprint.
The cost can be affected by things such as:
- The existing structure of your house
- Foundation requirements
- Structural steels
- Drainage
- Roof design
- The number and size of windows and doors
- Bi-fold or sliding doors
- Kitchen specification
- Bathroom specification
- Flooring
- Heating
- Lighting
- Internal finishes
- External works
- Access to the property
- The complexity of the design
This is why simple price-per-square-metre calculations should be treated as a starting point rather than a final project budget.
3. Don’t spend your entire budget on the building work
One mistake we often see homeowners make is thinking about their construction budget as the entire project budget.
There can be professional fees and other costs to consider alongside the construction itself.
Depending on your project, this could include:
- Architectural design
- Planning applications
- Structural engineering
- Building Regulations
- Building Control fees
- Surveys
- Drainage or sewer agreements
- Party Wall matters
- Kitchen and bathroom fittings
- Landscaping
- Decorating
- Contingency
The exact requirements will depend on your project, but it’s important to understand these costs early.
