If you’re planning a small extension, such as a modest rear or side addition to your home, you may be wondering whether you actually need an architect. The short answer is no, there is no legal requirement to hire an architect for an extension project. However, that doesn’t necessarily mean it’s the best approach. A well-designed extension can add significant value to your home, and a design professional can help you make the most of your budget while avoiding costly mistakes.
Extension pictured above by Corinne, interior designer in Thanet. See her profile on Design for Me and shortlist her for your project.
What Can an Architect Offer for a Small Extension?
Even for a relatively simple project, an architect can provide valuable expertise in:
Optimising space and layout – ensuring your extension flows well with your existing home and maximises natural light.
Navigating planning rules – while some small extensions fall under permitted development, others require planning permission. An architect can advise on this.
Building Regulations compliance – making sure your extension meets structural and safety requirements.
Detailed design drawings – essential for obtaining accurate builder quotes and avoiding disputes during construction.
How Much Does an Architect Cost for an Extension?
We surveyed our community of architects across the UK to answer this question, basing it on one of the most common projects on Design for Me – a 10m² kitchen extension.
The responses showed that an architect’s fees for a ‘typical’ small extension would be:
✅ £3,000 – £4,500 in most of the UK
✅ £5,500 – £8,250 in London and the South East
This represents around 10-15% of the total construction cost.
Can You Reduce the Architect’s Fee?
For a small and relatively simple project, you might not need full architectural services (which include concept design, tendering, site inspections, and contract administration). Many architects split their fees into stages, typically:
Outline design (including planning, if needed) – 35%
Detailed design for tender – 35%
Construction phase support – 30%
If your project is straightforward, you could hire an architect for the initial design phase only and then pass the detailed drawings to your builder or an architectural technologist for execution.
Can I Go Straight to a Builder?
Some homeowners work directly with a builder, especially for simple extensions. While this can work, builders need detailed design drawings to price and construct the extension accurately. Without these, you might face unexpected costs or design compromises.
Alternatively, you can consider design and build companies, which handle both the design and construction aspects in-house. If you go down this route, be sure to check their design credentials before committing.
Other Design Professionals to Consider
Instead of hiring an architect, you might consider other home design professionals instead, depending on the work involved:
Architectural Technologists – specialists in the technical aspects of design who can create full planning and construction drawings.
Interior Architectural Designers – ideal if your extension is focused on interior reconfiguration rather than major structural changes.
Builders with In-House Designers – some builders provide design services, though the quality varies.
Do I Need a Structural Engineer?
If your extension involves:
✅ Removing load-bearing walls
✅ Altering the roof structure
✅ Making structural changes
✅ Underpinning foundations
…then you will need a structural engineer in addition to a design professional. They will ensure the structure is safe and compliant with Building Regulations.
Finding the Right Design Professional
Before appointing an architect or other designer, check:
✔ Qualifications – Architects must be ARB-registered, while Chartered Architectural Technologists (MCIAT) hold professional accreditation.
✔ Insurance – Ensure they have Professional Indemnity Insurance to cover potential errors.
✔ Experience – Ask to see examples of similar extension projects.
✔ Client Reviews – References from past clients can provide insight into their reliability.
Final Thoughts
While an architect isn’t legally required for a small extension, their expertise can be invaluable in ensuring a well-designed, well-executed project. If your budget is tight, alternative design professionals or builder-led design services could be an option. The key is to have a clear design plan, accurate drawings, and the right professionals involved to avoid costly mistakes.
Need Help Finding the Right Design Professional?
Design for Me can match you with architects, technologists, and designers who specialise in small extensions—helping you find the perfect fit for your project.
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