Most home extensions need both, but at different moments and for completely different reasons.
Confusing the two is common, and it leads people to hire the wrong professional first or to forget one entirely until Building Control asks for something they do not have. If you are searching for an architect near me, it helps to know exactly where a structural engineer fits alongside them.
Here is the clear difference, and the point in your project where each one matters.
The One Line That Separates Them
An architect designs the space. A structural engineer makes sure it stands up.
The architect decides how the extension looks and works, where the rooms go, where the light comes from, how it meets the existing house. The structural engineer calculates the parts that carry weight, the beams, the foundations, the steel, so the building is safe and legal.
Design and structure. That is the whole distinction, and nearly everything else follows from it.
What Only an Architect Does
Some work belongs to the architect alone, and a structural engineer cannot replace it.
The architect surveys your home and works out what the planning rules allow on your plot. They design the scheme around how you live. They prepare and submit the planning application, and produce the drawings that show the whole design. The title architect is protected under the Architects Act 1997, so only someone registered with the Architects Registration Board can use it, and that register is public to check.
In short, if your question is about design, layout, planning permission or how the finished space will feel, that is architect territory.
What Only a Structural Engineer Does
Other work belongs to the structural engineer, and an architect will tell you to bring one in for it.
The engineer produces the structural calculations and drawings that prove your extension is safe. They size the steel beam that replaces a removed wall, design the foundations for the ground you are building on, and specify how new structure ties into the old. These calculations are what Building Control requires before it will sign off any structural work.
A chartered structural engineer carries letters such as MIStructE, CEng or MICE, and professional indemnity insurance sits behind their calculations. If your question involves load, support, beams or foundations, that is engineer territory.
When Do You Actually Need a Structural Engineer?
This is where people get caught out, so here are the moments that genuinely require one.
You need a structural engineer whenever the work affects something holding the building up, including when you:
- Remove a load bearing wall, including the rear wall you open up to extend
- Install a steel beam or RSJ
- Alter or cut into the roof structure for a loft conversion
- Remove a chimney breast and leave the stack above
- Dig new foundations, especially on clay or near trees
If none of those apply, for example a simple internal refit that touches nothing structural, you may not need one at all. But the moment a wall comes down or a beam goes in, the calculations are not optional, because Building Control will ask for them.
When an Architect Alone Is Enough
There are projects where you genuinely do not need to appoint a separate structural engineer, and it is fair to say so.
A small, non structural alteration, a cosmetic reconfiguration, or early stage feasibility and planning work can all proceed with just an architect or designer. The engineer is only essential once the design involves actually altering the structure, which for most real extensions it eventually does, but not always on day one.
So the honest answer to which one you need is: an architect first to design and get permission, and a structural engineer brought in during that design once it is clear the structure will change.
Why Having Both in One Team Helps
Here is the practical advantage most homeowners never consider until it bites them.
When the architect and the structural engineer work separately, the design goes out, the calculations come back, and any conflict between what was drawn and what is structurally sensible gets resolved late, often after planning. That is where delays and extra costs creep in.
When they sit in the same team, the engineer tests the beam spans and foundations while the layout is still being drawn, so the design is buildable from the start. Extension Architecture keeps structural engineering in house for exactly this reason, which is part of why a complex scheme like the Bromley new build, where a void connected the kitchen down to a basement level and the surrounding structure had to be designed around the missing floor, held together cleanly rather than stalling between two firms.
The Short Version Architect Near Me
You will almost certainly need both on a real extension, just not at the same moment. Bring in the structural engineer near me search once your design involves removing walls, adding beams or digging foundations, and let the architect lead the design and planning before that point. Hire the architect to decide what you build, and the structural engineer to make sure it stands, and the two together cover everything an extension needs.
