Extension drawings: what you need, and who should draw them
Nearly six in ten of the people who come to us have no drawings yet. It is the point where an extension stops being an idea, and the point where the job titles get confusing.
You need two sets, not one
This is the thing nobody explains up front. A planning application and a building control submission want different drawings, and a quote for “drawings” might mean either.
Planning drawings show what the extension looks like and where it sits: a location plan, a site plan, and existing and proposed elevations and floor plans at a stated scale. They're about form, position and appearance. They contain almost no technical information, and they are not enough to build from.
Building regulations drawings — construction or technical drawings — show how it's actually built. Foundation depths, wall build-ups, insulation values, ventilation, drainage, structural members. This is the set a builder prices accurately from and Building Control approves against.
If you only buy the first set, you'll be back for the second, and a builder pricing off planning drawings alone is guessing. Some of the gap between quotes on the same job is just that: different people guessing differently.
Who can do it
Architect is a protected title in the UK. Only someone registered with the Architects Registration Board may use it, which is checkable in about thirty seconds on the ARB register. Architects are trained in design as well as technical delivery, and for anything where the look of the thing matters — a wraparound reworking the whole ground floor, a contemporary rear on a period house — that training shows.
Architectural technologist is not protected, but the professional body is CIAT and its members carry MCIAT or FCIAT. Technologists specialise in the technical side: detailing, construction, compliance. For a straightforward rear extension where you already know roughly what you want, a good technologist produces a better technical package than a mediocre architect and usually charges less.
Architectural designer or draughtsman is an unregulated description. That doesn't make them bad — plenty are very experienced ex-technologists — but the title tells you nothing, so ask what they're a member of and look at three jobs like yours.
A design-and-build contractor bundles drawings into the build contract. Convenient, and the drawings tend to be built exactly as drawn because the same firm is doing both. The trade-off is that you're committing to a builder before you've got anything to put out to competitive tender.
And the structural engineer
Separate from all of the above. Anything that removes a load-bearing wall or spans an opening needs beam calculations, and neither an architect nor a technologist will normally produce those themselves — they'll send it to a structural engineer. Building Control wants the calculations, and your builder wants to know what steel to order.
Budget for it as its own line rather than assuming it's inside the drawing fee. Ask explicitly. It's one of the most common gaps between what people think they've bought and what they've actually bought.
What to ask before you appoint anyone
Which of the two drawing sets is in the fee, and what does the other one cost. Whether structural calculations are included or excluded. Whether they'll handle the planning submission and answer the council's questions, or hand you the files and wish you luck. Whether they've done this on your type of property — a Victorian terrace with a side return is a different problem from a 1970s detached.
On fees: BestBuilders publishes the architect and design cost ranges, and rather than duplicate them here we'd point you at their architect cost page. It's a sister site. What matters on this page is that you know which of the four you're hiring, and which set of drawings you're getting for the money.
Frequently asked
Where this comes from
Title protection for architects is in the Architects Act 1997, administered by the Architects Registration Board. CIAT publishes its membership grades. Application drawing requirements are set out by the Planning Portal and by your local authority's validation checklist, which varies slightly between councils — always read yours before submitting.
Get quotes from extension builders near you
Tell us what you are planning and we will match you with builders who cover your area. Free, no obligation, and you decide whether to go ahead.
Get free quotes