The short answer
It depends on the job. An architect (or architectural technologist) designs how a building looks and works — the layout, the drawings, the planning application — while a structural engineer proves it will stand up and sizes the beams, foundations and steel. For a simple load-bearing wall removal or single beam you usually only need an engineer. For a full extension, loft conversion or remodel you typically need both: the architect to design and gain approvals, the engineer to do the structural calculations Building Control requires under Part A. They are complementary, not interchangeable — the architect decides what you want, the engineer makes sure it won't fall down.
Homeowners often appoint the wrong one first, or pay for both when one would do. The split is actually simple once you see what each is responsible for. Here is the dividing line.
Who you need
- Remove one wall / fit a beamEngineer only
- Cracks / subsidence checkEngineer only
- ExtensionBoth, usually
- Loft conversionEngineer; often both
- New build / major remodelBoth
What each one actually does
The two roles overlap in people's minds but barely overlap in practice:
- Architect / architectural designer: works out the layout and appearance, produces the drawings, handles the planning application and the wider Building Regulations design (insulation, fire escape, accessibility). They are the designer of the space.
- Structural engineer: takes that design — or your builder's sketch — and proves it stands up. They size the beams, steels, foundations and lintels, produce structural calculations, and provide the detail Building Control needs to sign off the structure under Part A.
Put simply: the architect decides what gets built and how it looks; the engineer decides how big the steel has to be so it doesn't sag or collapse. On many jobs the architect appoints the engineer for you, so you deal with one party, but you are still paying for two distinct skills.
When you only need an engineer
Plenty of common jobs need no architect at all. If you are removing a single load-bearing wall, fitting one steel beam, removing a chimney breast, or you have cracks or movement you want assessed, a structural engineer alone can do the work. They will assess the structure, produce the calculations, and give Building Control what it needs — there is no design or planning piece for an architect to add.
For these jobs you might engage the engineer directly, or your builder may already work with one. Engineer fees for a single-element job (one wall, one beam) are commonly in the region of £300–£700 for the calculations, with a site visit and report costing more. Bringing an architect into a job this size usually just adds cost without adding value.
When you need both
Once a project involves changing the shape or footprint of the building — an extension, a loft conversion with a dormer, a knock-through-plus-extension remodel, or a new build — you generally need both professionals. The architect handles the design, the planning application and the look; the engineer handles the structure. The two coordinate so the steels the engineer specifies fit the spaces the architect has drawn.
The usual order is: architect first (to settle the design and get planning), then engineer (to make the agreed design stand up and provide the Building Regs structural calcs). On a wall-only or beam-only job, you skip straight to the engineer.
| Project | Architect | Engineer |
|---|---|---|
| Remove a load-bearing wall | Not usually | Yes |
| Chimney breast removal | No | Yes |
| Single-storey extension | Usually | Yes |
| Loft conversion (dormer) | Often | Yes |
| Crack / subsidence assessment | No | Yes |
| New build house | Yes | Yes |
Indicative guide to who you need for common UK projects. Sources: RIBA and IStructE guidance for homeowners.
Cost, sequence and avoiding wasted fees
The most common money mistake is appointing an architect for a job that only needed an engineer, or paying for full architectural drawings before the structure has been checked — only to have the engineer say a beam won't fit and the design has to change. For projects that need both, agree at the start who is coordinating: on many extensions the architect leads and sub-appoints the engineer, which keeps the structural calculations aligned with the drawings and avoids you managing two separate parties. For a simple structural alteration, go straight to a chartered structural engineer (look for IStructE or ICE membership) and keep it lean. The rule of thumb: match the professional to the question — design questions to the architect, 'will it stand up' questions to the engineer — and you won't overpay for either.
There's also a third role people sometimes confuse with these two: the architectural technologist or building surveyor who can produce Building Regs drawings and handle a straightforward extension's approvals without a full architect's design fee. For a modest, conventional extension where you don't need bespoke design flair, a technologist plus a structural engineer can be a leaner combination than a full architectural practice plus engineer. What none of these substitutes for is the engineer: whoever draws the plans, the structure still has to be calculated and proven by a chartered structural engineer before Building Control will pass it. So the practical hierarchy is — decide how much design input you actually need (full architect, technologist, or just a builder's sketch), then add the structural engineer on top, because that part is fixed regardless of which design route you take. Matching the design tier to the ambition of the project, while keeping the engineer constant, is how homeowners avoid both over-paying for design they don't need and under-providing for the structure they do. One last practical tip: when you appoint either professional, check their accreditation rather than relying on the job title alone. For the structure, look for membership of the Institution of Structural Engineers (IStructE) or the Institution of Civil Engineers (ICE), which signals a chartered engineer whose calculations Building Control will accept; for design, an architect registered with the ARB (and often RIBA) or a qualified architectural technologist. Matching the right accredited person to the right question — and getting them talking to each other early — is what keeps a project both well-designed and provably safe, without paying twice for overlapping work.
Frequently asked questions
Is a structural engineer cheaper than an architect?
For a single structural job — like removing a wall or fitting a beam — an engineer alone is usually the cheaper and correct route, often £300–£700 for calculations. For a full extension or remodel you generally need both, so it's not a like-for-like comparison; they do different jobs.
Can a structural engineer do architect's drawings?
Some engineers and engineering practices offer design and Building Regs drawings, but a structural engineer's core job is calculations and proving the structure stands up, not architectural design, planning applications or aesthetics. For layout and planning you generally want an architect or architectural technologist.
Who do I appoint first, the architect or the engineer?
For projects that change the building's shape, the architect usually comes first to settle the design and secure planning permission, then the engineer makes that design stand up. For a wall removal or single beam with no design element, go straight to the structural engineer.
Sources & further reading
- RIBA — find an architect and what they do
- Institution of Structural Engineers — find an engineer
- HomeOwners Alliance — architect vs structural engineer
Figures on this page are typical UK ranges drawn from published sources and depend on your specific project. They are guidance, not a quotation.