As a design and build company, one of the most common questions we’re asked is, “How much will my extension cost?” The answer depends on several key factors, and while a general guide can be helpful, a detailed quote is only possible once the design, materials, and scope of the project are known.
Key Factors That Affect Extension Costs
The cost of a house extension depends on the following:
- Number of storeys
- Size and layout
- Quality of materials and finish
- Type of rooms included (e.g. kitchen or bathroom)
- Amount of glazing
- Build route and your level of involvement
Other Potential Costs to Consider
In addition to the build itself, you may also need to factor in:
- Architectural design
- Structural engineer input
- Surveys
- Planning permission (if required)
- Lawful Development Certificate
- Building Regulations applications
- Fitting out the space
- Party Wall Agreements (if applicable)
- Insurance
Quality Levels
Build costs are influenced by the level of quality you choose:
- Standard quality: Basic finishes, contract kitchen, radiator heating, interlocking roof tiles, and stud partitions.
- Good quality: Higher-grade materials such as clay tiles, better facing bricks, block partitions, quality joinery, and underfloor heating.
- Excellent quality: Premium finishes including hardwood joinery, bespoke kitchens, top-tier bricks and tiles, and high-spec sanitaryware.
Higher quality finishes can add a significant uplift to your budget, especially when opting for bespoke or luxury elements.
VAT on House Extensions
Most extension work is subject to standard VAT. However, reduced rates may apply in certain situations, such as:
- Converting a single dwelling into multiple units
- Work on buildings unoccupied for at least two years
To benefit from these rates, the work must be carried out by a VAT-registered contractor.
Will an Extension Add Value?
An extension can add significant value to your home, especially if it enhances liveable space or adds desirable features such as an open-plan kitchen or additional bedroom. If this is your long-term home, the benefit is not just financial — it also avoids the stress and cost of moving.
If you’re planning to sell, speak with local estate agents to understand property values in your area and ensure the extension is likely to deliver a return on investment.
Interested in a home extension?
Contact us to book a free consultation and find out how we can help you transform your space.