So, Are House Extensions Expensive
If you’re considering adding more space to your home, you may be asking yourself: are house extensions expensive? The short answer is—they can be, but the cost depends on various factors including size, location, materials, and complexity.
In this blog, I’ll break down what affects extension costs, what to expect in terms of pricing, and how to make sure your investment delivers both space and long-term value.
What Determines the Cost of a House Extension?
1. Size and Layout
The larger the extension, the higher the cost. Costs are usually calculated per square metre, with added complexity for multi-storey or wraparound designs. Simpler layouts with fewer internal walls are generally more affordable.
2. Type of Extension
- Single-storey extensions: Typically more affordable
- Double-storey extensions: More costly due to additional structural and planning requirements
- Loft or garage conversions: Often more cost-effective as they use existing structures
3. Materials Used
Premium finishes, bespoke fittings, and high-performance glazing will increase the budget. Opting for standard materials can help keep costs down without compromising quality.
4. Site Conditions
If your home is on a slope or has drainage issues, groundwork will be more intensive—and therefore more expensive. Limited access for machinery can also raise labour costs.
5. Planning and Structural Work
Complex structural alterations, such as steel beam installation or underpinning, can add significantly to the overall cost. You may also need planning permission, depending on the size and location of the extension. For help navigating this, we offer full planning support.
Average Cost of a House Extension in the UK
While prices can vary, here’s a general estimate:
- Single-storey extension: £1,200 – £2,500 per m²
- Double-storey extension: £1,800 – £3,000 per m²
- Loft conversion: £20,000 – £70,000 depending on structure and finish
Always allow a 10–15% contingency for unexpected changes or additional work that might arise once the project starts.
Other Expenses to Consider
1. Planning Applications
Not all extensions require planning permission—some fall under permitted development rights. However, where full approval is needed, you’ll need to account for application fees, surveys, and architectural drawings.
2. Building Regulations Approval
Even if your extension doesn’t require planning permission, it must still comply with UK building regulations. This may include insulation standards, fire safety, and structural integrity.
3. Utility Upgrades
If your extension includes a kitchen or bathroom, consider the costs for plumbing, electrical work, heating, and ventilation.
4. Interior Finishes
Paint, flooring, lighting, and fitted furniture can add a significant amount to your final bill. It’s important to include these in your budget from the start.
Ways to Keep Costs Under Control
- Keep the design simple: Fewer corners, walls, and roof changes reduce construction time and material waste
- Choose standard materials: These are more readily available and cost-effective
- Work with local builders: Minimises travel costs and supports better communication. You can view our construction services to see how we support projects across Kent
- Use experienced contractors: Reduces the chance of delays, errors, and costly corrections
Is an Extension Worth the Cost?
Despite the expense, an extension can be a wise investment if it meets your needs and improves your property’s value. A well-executed project could increase the value of your home by up to 20%.
That said, always compare the cost of extending with the cost of moving. Factor in stamp duty, legal fees, estate agent charges, and the inconvenience of relocating.
How We Can Help
We’ve delivered house extensions across Kent that balance cost, design, and function. Whether you need a kitchen extension, new bedroom, or open-plan living area, we provide:
- Honest budgeting advice
- Clear construction timelines
- Skilled delivery from start to finish
We also offer complete extension services and ongoing aftercare to ensure the build stays in top condition.
Contact us here to discuss your ideas and receive a tailored quote based on your needs.