What does an architect do in an extension build?

You do not have to use an architect to design your house extension. Some homeowners have a distinct idea of what they would like to build, and can self-manage their extension.

Other property owners might employ an architect for a relatively simple project, such as installing a new bathroom.

An architect doesn’t just draw up plans; they can help you fine-tune your design if you aren’t sure what you want. Your architect can also be the essential link between you and your builder, and explain the plan and negotiate the work on your behalf.

Architects carry out several functions, which can be essential if you have not overseen a home extension build before, including:

  • Designing – materials, layout, structure.
  • Advising – which design choices meet your aspirations, whether you need planning permission.
  • Budgeting – creating plans that align with your budget and explaining the timeframes for each stage of the work.
  • Directing – managing the progress of the project and helping you understand what services will be useful.

How much does an architect cost?

It is very tricky to give a ballpark figure since the cost of your architect will vary significantly depending on how involved you wish for them to be in the project and the nature and size of your extension.

An architect can cost around 15% of your total build as a general indication. For an extension, you can secure an architect on a fixed fee or an hourly rate. Most extensions will cost around £500 – £1,000 in professional design fees.


What are the advantages of working with an architect for my house extension?

An architect can help manage your extension from start to finish. Their responsibility is making sure that your extension meets your aspirations, and is delivered on time and budget.

One of the main benefits of using an architect is that they understand the market, and what materials will be best suited.

Advantages to using an architect for your home extension include:

  • Receiving professional advice about building regulations, planning permission and whether or not you need a structural engineer.
  • Having a bespoke design drawn up to deliver your requirements for your home extension.
  • Seeing the finer detail such as enhancing natural light, ensuring a good flow between spaces, and making the external appearance harmonious with your existing property.
  • Helping you find the right builder, project managing your home extension for you, and controlling the budget.
  • Negotiating on your behalf and representing the project when dealing with planning inspectors, building control visits and your contractors.
  • Identifying finer details that can reduce your budget, such as planning utility wiring and pipework.

How do I choose a good architect?

There are many different types of architect, and more substantial building firms will offer in-house design services as part of a project package.

If you are looking for an architect, then you can check whether they are fully registered with the Architects Registration Board or another professional body.

Should you have a very tight budget, or think you need input from an architect and not be able to extend your costs to their fees, you could consider using a junior architect or another design professional.

Frequently Asked Questions

Are there any downsides to using an architect for a house extension?

The main reason some homeowners avoid using an architect is the cost. While it is true that these can be up to 15% of the build budget, an architect can also save you a lot of time and money by providing tailored professional advice.

It is crucial to establish your working parameters with your architect before work begins. Their job is to manage your project and make sure everything is finished perfectly for you. If you prefer to have a hands-on approach and project manage the smaller details yourself, it is worth discussing this with your architect to ensure you don’t end up stepping on each other’s toes!

Remember that your house extension is yours and that your architect works for you. Some architects can be quite set on a specific concept or material, so you need to remain in control and not defer decisions to your architect unless you feel comfortable doing so.

How is a design professional different from an architect?

A design professional means anybody qualified to assist with drawing up plans and designs for your house extension. This encompasses many professionals, some architects and some slightly different.

  • An architect is a professional who is registered with the Architects Registration Board and is fully qualified.
  • An Architectural Student is a junior architect, usually still studying for their qualifications. Using a student can be an excellent way of reducing costs for a small, simple project. However, remember that they are not yet qualified and should not be hired to assist with complicated builds. You should also take care to make sure they hold appropriate professional indemnity insurance should anything go wrong.
  • Overseas Architects – it is relatively common to come across a design professional that is a fully qualified architect but gained their accreditations in another country. Anybody not registered with the ARB cannot call themselves an architect, regardless of their experience.

While an architect can seem expensive, they provide value for money when it comes to planning and building your house extension.

Full architectural services extend well beyond drawing up the plans, and mean that you have a professional representing your project from start to finish.

How do I explain to my architect what I want?

Usually, you start with an initial meeting. Bring with you any photos, ideas or inspiration you have, or if the meeting is at your home take a look around and explain what you have in mind.

You don’t need to draw up plans immediately, so this is an opportunity to have a chat about your ideas and discuss the feasibility and options available.

Take the time to listen to your architect’s suggestions, even if they are a little different from your ideas. They will have planned and overseen many projects, and are a gold mine of information about ways to cut costs, complete a build faster, and negotiate the world of planning permission smoothly.

Mike Alexander
Hey there, I'm Mike - writer and part time home improvement expert at Refurbb. Since owning and refurbishing my own property in 2018, I've since been developing rental properties, writing about my home improvement endeavours, sharing what I've learned and connecting readers to reputable tradespeople in the UK.

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