The short answer
An architect designs the building — layout, space, light, proportion, how it looks and functions, and the drawings for planning. A structural engineer designs the structure — they calculate and specify the beams, foundations and load paths that make the building stand up safely, and produce the structural calculations Building Control requires. They're different professions with different training: "architect" is an ARB-protected title, while a structural engineer is typically a member of a body such as the Institution of Structural Engineers (IStructE). They're not really rivals — on most extensions, lofts and new builds you need both, with the architect shaping the space and the engineer making the structure work. Only on a purely structural job (like a steel beam) might you need just the engineer.
These two roles are frequently confused, but they cover completely different parts of a building project. Understanding what each does makes it obvious why most projects need both.
Architect vs engineer
- Architect designsSpace, layout, appearance
- Engineer designsStructure, beams, foundations
- Architect bodyARB / RIBA
- Engineer bodyIStructE / ICE
- Most projects needBoth
What an architect does
An architect's job is the design and shape of the building as a place to live or work. That covers:
- Concept and layout — how rooms relate, how you move through the space, where the light comes from, and the proportions that make a space feel right.
- Appearance — the elevations, materials and how the building sits in its setting.
- Planning drawings — the existing and proposed plans and elevations for a planning application, and often the case for approval.
- Running the project — many architects manage the job through the RIBA Plan of Work, from brief to handover.
"Architect" is a protected title: only ARB-registered professionals can use it, and most are RIBA chartered. What an architect typically does not do is the detailed structural calculations — that's the engineer's territory.
What a structural engineer does
A structural engineer's job is to make sure the building stands up and stays up. Their work is mathematical and load-focused:
- Sizing beams and lintels — working out the steel or timber needed to span an opening.
- Designing foundations — what's needed to carry the building's loads safely into the ground.
- Load paths and stability — checking how forces travel through the structure and how alterations affect it.
- Structural calculations — the documented proof Building Control requires for any structural change.
Structural engineers are typically chartered or qualified members of bodies such as the Institution of Structural Engineers (IStructE) or the Institution of Civil Engineers (ICE). On a home project, you'll usually meet them whenever there's a beam, a removed wall, an extension foundation, or a new build frame.
| Aspect | Architect | Structural engineer |
|---|---|---|
| Designs | Space, layout, appearance | Structure, loads, foundations |
| Key output | Drawings for planning/design | Structural calculations |
| Professional body | ARB / RIBA | IStructE / ICE |
| Protected title | Yes (architect) | Engineer title not protected |
| When needed | Design-led projects | Any structural change |
Indicative comparison for guidance only. Sources: RIBA and IStructE guidance.
How they work together
Because they handle different things, the two roles usually run in sequence and feed the same approvals. A typical pattern:
- The architect develops the design and produces the drawings for planning permission.
- Once the scheme is agreed, the structural engineer designs and calculates the beams, foundations and load paths for it.
- Both contribute to the Building Regulations submission — the architect's drawings plus the engineer's calculations — and Building Control checks and inspects the work.
Some architects bring an engineer into the team for you, which keeps coordination tidy. The honest bottom line: it's rarely architect versus engineer. They cover different halves of the same project, and most extensions, lofts and new builds need both. The only time you'd use just one is a purely structural job — a beam or a removed wall with no design questions — where an engineer alone may be enough, or a purely cosmetic redesign with no structural work, where you may only need the architect or a designer.
Frequently asked questions
Do I need both an architect and a structural engineer?
For most extensions, loft conversions and new builds, yes — the architect designs the space and the engineer designs the structure. Purely structural jobs (like a steel beam) may need only an engineer; purely cosmetic redesigns may need only an architect or designer.
Can an architect do structural calculations?
Generally no. Architects design the space and detailing, but the structural calculations for beams, foundations and load paths come from a structural engineer. Some architects work with an engineer as part of their service so the calculations are covered.
Is a structural engineer a protected title like architect?
The title "architect" is legally protected by the ARB, but "engineer" is not protected in the same way. However, structural engineers are usually chartered or qualified members of recognised bodies such as IStructE or ICE, which you can check.
Sources & further reading
- IStructE — when do I need a structural engineer
- RIBA — working with an architect
- ARB — what architects do
Figures on this page are typical UK ranges drawn from published sources and depend on your specific project. They are guidance, not a quotation.