There is a lot of confident, contradictory advice about whether you need an architect to extend your home. Some of it is sales talk, some of it is years out of date. So here are the common beliefs, set against what is actually true in 2026.
Myth: You Legally Need an Architect to Extend
Reality: you do not. There is no law in England and Wales requiring an architect for a house extension, of any size.
What the law actually requires is that the work complies with planning rules or permitted development, and with Building Regulations. That means someone competent has to produce the design, the drawings, the structural calculations and the approvals. It does not have to be an architect.
The title “architect” is protected and only ARB registered professionals can use it, but the work itself can legally be done by an architectural technologist, a building surveyor, a design and build firm, or an experienced designer. Hiring an architect for extension work is a choice about quality and risk, not a legal box to tick.
Myth: Every Extension Needs an Architect
Reality: plenty do not, and it is worth being honest about which.
A small, straightforward rear or side extension on an unconstrained house, well within permitted development, often does not justify a full architect’s service. An architectural technologist or a competent design and build team can produce the drawings and handle Building Regulations perfectly well, usually for less.
Where that logic breaks down is the moment the project stops being simple. A double storey extension, a loft that reworks the roof, a listed building, a conservation area, an awkward plot, or a whole house reconfiguration all carry design and planning risk that an architect is specifically trained to manage.
The honest test is not the size of the extension but the number of ways it can go wrong. Few risks, and you can keep it simple. Several, and you want someone whose job is to see them coming.
Myth: An Architect Is Just an Expensive Draughtsman
Reality: the drawings are the smallest part of what you are paying for.
An architect’s real value sits in the decisions made before and around the drawings. Getting the most usable space from a difficult footprint. Spotting that the existing rear wall needs underpinning before you have committed to a design. Shaping a scheme so it actually gets through planning rather than bouncing back.
A refused application costs months and a redesign fee. A poorly planned extension can add far less value than a well designed one for the same build cost. Those avoided mistakes are where the fee earns itself, not in the lines on the page.
There is also the question of how the finished space feels day to day. Light, flow, ceiling height, the connection to the garden, the things you cannot easily change later are exactly the things good design gets right at the start.
Myth: Architects Are Unaffordable
Reality: the cost is more flexible than people assume.
A full architectural service, from concept through to construction support, typically runs 8 to 15 per cent of build cost. But you do not have to buy the whole service. Many practices quote a fixed fee, and for a single storey extension, planning drawings alone commonly start from a few thousand pounds, with a planning plus Building Regulations package higher.
You can also commission just the early design and planning stages, then hand the detailed drawings to a builder or technologist. For a straightforward house extensions london project, that staged approach keeps the architect’s input where it matters most and controls the cost.
Set against the size of the overall budget, the design fee is usually a small share of the total, and the part most likely to protect the rest of it.
Myth: Any Architect Will Do
Reality: local and relevant experience changes the outcome more than reputation does.
An architect who regularly works in your borough knows its conservation areas, its Article 4 directions and how its planning officers assess schemes. One who does not will be learning your council on your project. For anything planning sensitive, that difference often decides whether you are approved first time.
It also helps when design and structure sit in the same team. Extension Architecture, a RIBA chartered and ARB registered practice across London and Surrey, keeps architects and structural engineers in house and offers a free initial feasibility check, so the planning position and the structural reality are understood before the design is fixed, rather than discovered mid build.
Myth: Hiring One Means Handing Over Control
Reality: a good architect gives you more control, not less, because you are making informed decisions earlier.
The fear is that an architect imposes their taste and runs up the cost. In practice the opposite tends to happen on a well run project. You see options, understand the trade-offs, and lock in the big decisions, budget, scale, layout, before anyone starts building, which is exactly when changes are cheap rather than expensive.
Where control genuinely slips is on projects with no clear design lead, where the builder makes design calls on site to suit the build rather than the brief. An architect, or an equally competent designer, is what keeps the finished result the one you actually chose.
The One Rule Worth Following
Spend on an architect in proportion to what can go wrong.
On a small, rights intact extension, not much can, and a technologist or design and build team covers it cheaply and well. On a double storey, a listed building, a conservation area or a reworked roof, the things that can go wrong are expensive and hard to undo, and that is precisely where an architect stops being a cost and starts being insurance.
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