People often assume these are alternatives, and on a project of any size they are not - they are two different jobs that happen to both involve drawings. The confusion costs money mostly through sequencing: bringing in the second one after the first has fixed something that cannot now be changed.
What each one does
An architect designs the building: what it looks like, how the spaces work, how light and circulation and materials come together, and how it sits in its context. On a domestic project they also usually drive the planning application, because planning is largely about appearance and impact.
A structural engineer makes it stand up: what carries what, how big the members need to be, how loads reach the ground, and what the calculations say. On a domestic project the engineer's output is usually what satisfies Building Regulations.
One more distinction worth knowing: 'architect' is a legally protected title in the UK, and only someone registered with the Architects Registration Board may use it. 'Engineer' is not protected, which is why asking about professional institution membership matters more on our side of the fence.
Which do you need?
| Project | Architect | Structural engineer |
|---|---|---|
| Removing a load-bearing wall | No | Yes - this is the whole job |
| Removing a chimney breast | No | Yes |
| Straightforward rear extension | Optional - a designer or the builder may suffice | Yes |
| Complex or highly visible extension | Worth it | Yes |
| Loft conversion | Usually not | Yes |
| New build house | Yes | Yes |
| Listed building or conservation area work | Yes, and early | Yes |
| Something has cracked or moved | No | Yes - and this is a survey, not a design job |
| Building Control has asked for calculations | No | Yes |
The overlap, and where it goes wrong
The two disciplines meet at one predictable point: when the architectural design assumes something structural that does not work. A five-metre opening with no visible support, a cantilever that has to land somewhere, a wall removed on two floors, a glazed corner with nothing above it - all of these are achievable, and all of them are cheaper to achieve if the engineer sees them while the layout is still movable.
The expensive version is the sequence where planning permission is granted, drawings are finalised, a builder is booked, and only then does anybody ask what is holding the roof up. Redesigning at that point means going back through approvals, and that is where months disappear.
The order to do things in
- Decide what you want, roughly
- Architect or designer takes it far enough to know the layout and the spans
- Engineer sanity-checks the structural implications while the layout can still move - this conversation is short and pays for itself
- Planning permission, if it is needed
- Full structural design and calculations
- Building Regulations submission - a separate system from planning, determined within five weeks or eight by written agreement
- Build, with both available for the questions that arise
- Completion certificate
Do you always need an architect?
No, and it is worth saying plainly. A great many domestic projects go from a designer, a technician or the builder's own drawings straight to an engineer, and come out perfectly well. Where an architect genuinely earns their fee is where the design problem is hard - a difficult site, a listed building, an awkward planning position, or a project where how it feels to live in matters as much as how big it is.
The engineer, on the other hand, is needed whenever the structure changes, which on most building work is always. That is not us talking our own book - it is that Building Control asks for calculations, and calculations have to come from someone.
Frequently asked questions
Do I need both an architect and a structural engineer?
On a new build or a complex project, yes. On a straightforward extension or a wall removal, often just an engineer - plenty of projects run from a designer's or the builder's drawings straight to structural design. The engineer is the one you cannot skip when the structure changes, because Building Control wants calculations.
Which one do I go to first?
Usually the designer or architect, to establish what you actually want. But bring the engineer in while the layout is still movable rather than after the drawings are frozen - a short conversation at that stage regularly saves a redesign.
Can an architect do the structural calculations?
Some are qualified to do simple ones, but structural design for Building Control is normally an engineer's work and most architects would say the same. It is a question worth asking directly rather than assuming either way.
Can a structural engineer design my extension?
We can design the structure, and for simple projects that plus the builder's or a technician's drawings is often the whole package. What we do not do is the architectural design - the spatial and aesthetic side - and we would rather say so than pretend otherwise.
Is 'engineer' a protected title?
No. 'Architect' is protected in the UK and only ARB-registered people may use it, but anyone can call themselves an engineer. That is why it is worth asking which professional institution someone belongs to, at what grade, and whether they carry professional indemnity insurance for the work.