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Cost of Single-Story Extension: How to Avoid Hidden Costs and Unexpected Expenses

Updated: Mar 20

Red brick house with single-story extension


Inspired by this single-story extension? Let Rick help you create your dream project.

So, you're considering breathing new life into your home with a single-story extension. It's an exciting prospect, but the initial question that often pops up is: what’s the cost of a single story extension?

Before we delve into the nitty-gritty of costs, let's address some crucial things you need to know about single-story extensions. If you need help with your extension project, book a consultation with one of our Architecture Gurus or talk with one of our Structural Engineering Gurus today.

Understanding The Cost of Single-Story Extensions

Single-story extensions are a popular choice for homeowners seeking to expand their living space without adding an extra floor. They offer several advantages, including:

  • Increased living space: This is the most obvious benefit, allowing you to create additional rooms such as a kitchen extension, dining room, playroom, or even a home office.

  • Enhanced property value: Studies suggest that well-designed single-story extensions can add value to your property, making it a worthwhile investment.

  • Improved functionality: You can redesign your existing layout to improve flow and functionality, making your home more suited to your needs.

  • Cost-effective compared to double-story extensions: Generally, single-story extensions require less structural work and materials, making them a more budget-friendly option compared to adding another floor.

However, it's important to remember that single-story extensions aren't a one-size-fits-all solution. They come in various shapes and sizes, with different materials and design features, all of which significantly impact the final cost.

Back garden of a house with single-story extension


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Exploring the Cost Spectrum

Now, onto the big question: what does a single-story extension cost? Unfortunately, there's no simple answer, as the cost can vary greatly depending on several factors:

  • Size: This is the most significant factor. The larger the extension, the higher the cost of materials, labour, and potentially foundation work.

  • Location: Building costs tend to be higher in densely populated areas compared to rural locations.

  • Materials: The type of materials used for the roof, walls, windows, doors, and finishes will significantly impact the overall cost. Opting for high-end materials like slate roofs or solid wood windows will naturally push the price upwards.

  • Complexity: A simple, rectangular extension with minimal structural alterations will be much more affordable than one with intricate designs, multiple levels, or large bi-folding doors.

  • Building regulations: Depending on the size and complexity of your extension, you may need to adhere to specific building regulations, which might incur additional costs for surveys, plans, and inspections.

Here's a rough estimate to give you a starting point:

  • Small extension (15-20 square metres): This could range from £15,000 to £30,000.

  • Medium extension (25-35 square metres): Expect to pay between £35,000 and £55,000.

  • Large extension (40+ square metres): This could cost anywhere from £55,000 to £100,000 or even more.

Remember, these are just estimates, and the actual cost can deviate significantly depending on the factors mentioned above.

Read our article here and learn how online architectural services can be the best solution for you.

Opt for Online Platforms

While the process might seem daunting, online platforms like HiiGuru can be your key to a smoother and more transparent experience. HiiGuru connects homeowners directly with vetted experts like architects, builders, and other professionals, eliminating the need for extensive searching and long contracts. 

Here's how online platforms like HiiGuru can help:

  • Simplified project management: The platform acts as a central hub for communication and collaboration between you, the professionals you choose, and the platform itself. This streamlines communication keeps everyone on the same page, and facilitates a more efficient project flow.

  • Transparent pricing: Many platforms offer clear and upfront pricing structures, allowing you to compare quotes and make informed decisions without hidden fees or surprises.

  • Flexibility: You have the freedom to choose individual professionals based on their expertise, experience, and budget, rather than being tied to a single package deal.

  • No contract limitations: Unlike traditional contracting methods, these platforms often don't bind you to long-term contracts. This allows you to maintain control and adjust your project scope or team if necessary.

Modern single-story extension facing back garden


Do you want to know what's the best solution for you? Schedule a call with Zilvinas today.

Who to Work With

Building a single-story extension is a complex undertaking, and choosing the right professionals is crucial for a successful project. Here's who you should consider contacting:

  • Architect: An architect can help you design the extension, ensuring it seamlessly integrates with your existing home and adheres to building regulations.

  • Structural engineer: If your extension involves alterations to the existing structure, a structural engineer will be required to ensure the design is safe and sound.

  • Builder: A reputable builder with experience in single-story extensions will handle the actual construction work.

It's crucial to obtain quotes from several architects, builders, and any other relevant professionals before making a final decision. Ensure you understand the scope of their services, their fee structure, and whether they offer warranties on their work.

Permissions and Regulations

Before you embark on the building process, it's essential to determine whether you need planning permission for your single-story extension. Generally, smaller extensions may fall under permitted development rights, allowing you to build without formal permission.

However, it's crucial to check with your local planning authority to be on the safe side. They can advise you on any specific regulations and whether you need to apply for planning permission. Additionally, building regulations might still apply, even if planning permission isn't required. These regulations ensure the extension meets specific safety and performance standards.

Consult your chosen architect or builder, as they can guide you through the necessary permissions and regulations for your specific project.

Brick house with modern single-story extension


Additional Considerations: Budgeting and Financing

Building a single-story extension is a significant investment, and it's essential to have a realistic budget in place. Here are some additional points to consider:

  • Factor in unexpected costs: Allocate a contingency fund in your budget to account for unforeseen expenses that may arise during construction.

  • Explore financing options: Consider various financing options such as remortgages, home equity loans, or personal loans to cover the project cost.

  • Seek professional financial advice: Consulting a financial advisor can help you determine the best financing option based on your financial situation and long-term goals.

Our Final Thoughts

Building a single-story extension can be a rewarding experience, adding valuable space and functionality to your home. By understanding the factors influencing costs, choosing the right professionals, and navigating the permitting process, you can embark on this journey with confidence. Additionally, exploring online platforms like HiiGuru can help streamline the process, providing a more transparent and collaborative experience. Remember, thorough planning, realistic budgeting, and seeking professional advice when needed will be key to ensuring a successful and fulfilling single-story extension project.

Do you need the help of an architect? Book one of our Architecture Gurus for a 30-minute video call. Transforming your home into a space you love shouldn't be a daunting task. With HiiGuru you can save time, avoid costly mistakes and bring your goals to life with experts by your side.


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