Welcome to our comprehensive guide to house extension costs in 2023. At My, we understand the importance of accurate and detailed information when it comes to planning and budgeting for a house extension project. In this guide, we will provide you with in-depth insights into the factors that influence house extension costs, as well as valuable tips to help you make informed decisions. Let’s dive in!

1. Understanding House Extensions

A house extension is a popular solution for homeowners who need additional space without the hassle of moving. It involves expanding the existing structure of a house to create more living area, whether it’s adding extra rooms, extending existing rooms, or creating new functional spaces. Before embarking on a house extension project, it’s essential to consider various factors that can impact the overall cost.

Factors Affecting House Extension Costs

The cost of a house extension can vary significantly depending on several factors. By understanding these key elements, you can estimate the budget required for your project more accurately:

  1. Size and Complexity: The size and complexity of the extension will have a direct impact on the cost. Larger and more complex extensions generally require more materials, labour, and time to complete.
  2. Design and Specifications: The architectural design and specifications of the extension, such as the type of materials used and the level of customization required, will influence the overall cost.
  3. Foundation and Structural Work: If your extension involves significant structural changes or requires additional foundation work, it will contribute to the overall cost.
  4. Building Regulations and Permits: Compliance with building regulations and obtaining the necessary permits can add to the project costs.
  5. Location: The location of your property can affect the cost of materials, labor, and permits. Regional variations in prices should be considered when estimating the budget.
  6. Finishes and Fixtures: The choice of finishes, fixtures, and fittings will impact the overall cost. Higher-quality materials and finishes will generally result in higher expenses.
  7. Utilities and Services: Extending utilities such as plumbing, electrical wiring, and HVAC systems to the new space may require additional investment.
  8. Professional Fees: Hiring architects, engineers, and other professionals for design and project management will add to the overall cost.

House Extension Cost Breakdown

To provide you with a clearer picture, here’s a breakdown of the typical costs involved in a house extension project:

  1. Design and Planning: This includes architectural design fees, survey costs, and obtaining necessary permits. It generally accounts for around 10-15% of the total project cost.
  2. Construction and Materials: The actual construction work and materials form the bulk of the project cost, usually accounting for 70-80% of the total. This includes labor, building materials, structural work, and finishes.
  3. Utilities and Services: Extending utilities to the new space, such as plumbing, electrical, and HVAC systems, can account for around 5-10% of the total cost.
  4. Contingency: It’s advisable to set aside a contingency budget of around 5-10% to account for unforeseen expenses or design changes during the construction process.

2. Estimating House Extension Costs

While every house extension project is unique, it’s helpful to have a ballpark figure to start your budgeting process. Here are some rough estimates for different types of house extensions based on average costs:

  1. Single-Storey Extension: A single-storey extension typically costs between $1,500 and $3,000 per square meter, depending on the complexity of the design and finishes.
  2. Double-Storey Extension: A double-storey extension is generally more cost-effective compared to building two separate storeys. It can range from $2,000 to $4,000 per square meter, considering factors such as structural work and additional utilities.
  3. Loft Conversion: Converting an existing loft space into a livable area is an excellent option for adding space. The cost can vary between $1,200 and $2,500 per square meter, depending on the level of insulation, finishes, and structural modifications required.
  4. Basement Extension: Creating a basement extension involves significant excavation and structural work. Costs can range from $2,000 to $4,500 per square meter, considering factors such as site conditions and waterproofing requirements.

Remember that these are rough estimates, and it’s essential to consult with professionals to get accurate cost estimates tailored to your specific project.

3. Maximizing Your Budget

Now that you have an understanding of the factors influencing house extension costs, let’s explore some strategies to make the most of your budget:

1. Plan and Design Efficiently

Investing time and effort into well-thought-out planning and design can help optimize the use of space and minimize unnecessary costs. Consider consulting with an experienced architect or designer to ensure your extension meets your needs while remaining within budget.

2. Choose Materials Wisely

Opt for materials that strike a balance between quality and cost. Work with your contractor to explore affordable yet durable options that align with your aesthetic preferences.

3. Get Multiple Quotes

Obtain quotes from several reputable builders or contractors to compare prices and services. Be cautious of extremely low-cost estimates, as they may indicate a compromise in quality.

4. Consider Value Engineering

Collaborate with your design and construction team to identify cost-saving alternatives without compromising the overall functionality and aesthetics of your extension.

5. Stick to the Plan

While it’s tempting to make changes during the construction phase, they can add to the cost. Minimize variations once the project is underway to avoid unexpected expenses.

6. Regular Communication

Maintain open and regular communication with your builder or contractor to stay updated on the progress and address any concerns promptly. This helps ensure that the project stays on track and within budget.


In conclusion, planning a house extension requires careful consideration of various factors that influence costs. By understanding the key elements involved, estimating the budget, and implementing cost-saving strategies, you can embark on your house extension project with confidence. At My, we are dedicated to providing expert guidance and assistance throughout your journey. Contact us today to start turning your extension dreams into reality.


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