Do you need an architect for an extension?

“Architect” is a protected title. Only someone registered with the Architects Registration Board may use it, and getting there takes seven years. That is worth knowing mainly because it explains the price difference between an architect and the other people who can draw your extension — several of whom are entirely capable of doing it.

You do not always need an architect. You do always need drawings, and you very often need a structural engineer, which is a different job again.

Who does what

Architect. Registered, insured, trained in design as well as technical delivery. Best value where the design problem is genuinely difficult — an awkward site, a complicated brief, a listed building, a project where how the space feels is the whole point. They can also administer the contract and inspect the works, which is a distinct service worth paying for on larger jobs.

Architectural technologist or technician. Trained in the technical side of building design. Entirely capable of producing planning and building regulations drawings for a domestic extension, and typically less expensive than an architect. For a straightforward rear extension this is often the sensible choice.

Design-and-build through a builder. Some builders produce or arrange the drawings as part of the package. Fewer parties, one point of responsibility, and usually cheaper. The trade-off is that you get a design optimised by the person who is also building it, which is fine when the design is simple and less good when it needs someone advocating purely for you.

Structural engineer. Not an alternative to any of the above — an addition. They calculate the beams, the foundations and the load paths, and they are required wherever load-bearing structure is removed or spanned. Building control will want their calculations. Almost every extension that opens into the house needs one.

When an architect earns their fee

• The site is difficult. Awkward level changes, a tight urban plot, a strange existing layout, difficult orientation.
• You are in a conservation area, the National Park or the High Weald, or the building is listed. Here the design is being judged against a character test, and someone who knows how to make a case in that language materially improves your odds. Horsham District has 39 conservation areas, so this is not a rare situation locally.
• The brief is open. “We need more space and better light, work out how” is a design question. “Build a 4m rear extension” is not.
• You want somebody on your side during construction. Contract administration — checking the work, certifying payments, dealing with variations — is a real service, and on a large project it pays for itself.
• The project is large. On a whole-house remodel the design fee is a small percentage and a bad layout is permanent.

When you probably do not need one

• A straightforward single storey rear extension within permitted development
• A garage conversion
• A kitchen refit in the existing footprint
• Anything where the shape is essentially decided and what you need is accurate drawings that will satisfy planning and building control

In these cases a technologist, or a builder who arranges drawings, will get you there for less.

What you actually need to end up with

Whoever produces them, a project needs:

Planning drawings — location plan, block plan, existing and proposed floor plans and elevations, to scale. What the council decides on.

Building regulations drawings — the technical set. Construction details, insulation specification, drainage, ventilation, fire safety. What the work is actually built from.

Structural calculations — from the engineer.

The first two are different documents for different purposes and people sometimes assume the first set covers the second. It does not. Check what you are getting quoted for.

The false economy

The cheapest route is to skip formal drawings and let the builder work it out on site. On a very simple job with a builder you trust, that can be fine.

The risk is that you have no independent record of what was agreed. When there is a disagreement about what was supposed to be built, drawings are the answer. Without them it is your memory against theirs, and it is also very hard to get three comparable quotes — because each builder is pricing their own interpretation.

If you are getting more than one quote, drawings are what make the comparison possible. That alone usually justifies them.

How the fees generally work

Architects and technologists typically charge either a percentage of construction cost or a fixed fee for a defined stage. For a domestic extension a fixed fee for “drawings to planning” and another for “drawings to building regs” is common and easier to control.

Get in writing which stages are included, how many revisions, whether they will submit the applications, and whether they will deal with the council’s queries during determination. That last one matters — an application with an unanswered officer query gets refused.

What to do next

If you are unsure which route your project needs, the deciding questions are whether the design is genuinely open and whether you are in a designation that makes the design a judgement call.

Tell us what you are thinking and we will tell you honestly whether you need an architect for it — including when the answer is yes.