Most people start their renovation with the wrong question. They ask “do I need an architect or a structural engineer?” as if it’s an either/or decision like choosing between a plumber and an electrician. It isn’t. On any project with real structural implications, you’ll likely need both, just at different points in the process and for very different reasons.
Architect and structural engineer here’s the short version: an architect designs what your space looks like and how you’ll use it. A structural engineer works out whether the building will actually stay standing once you’ve made those changes. One deals in aesthetics and layout, the other in loads, forces, and materials. The confusion isn’t really about what they do it’s about when to bring each one in, and how much you actually need to spend to do it properly.
This article breaks that down properly, including the bits most guides skip: how these two professionals actually work together on a real project, what it costs when you add it all up, and specific guidance if you’re a landlord converting a property to an HMO, or an agent trying to work out why a sale just fell through.
What Does an Architect Actually Do?
An architect’s job starts long before anyone picks up a tape measure. They translate what you want more space, better light, a kitchen you can actually cook in into drawings that a planning department and a builder can both work from.
In the UK, “architect” is a legally protected title. Anyone using it must be registered with the Architects Registration Board (ARB). That matters more than it sounds like it should, because “architectural designer” and “architectural technologist” are different, unregulated titles. They can be perfectly good at what they do often at a lower cost but they haven’t gone through the same qualification route, and for anything complex or contentious with your local planning department, that distinction can matter.
A typical architect will produce:
- Concept designs and 3D visuals so you can actually picture the finished space
- Planning permission drawings and the application itself
- Building regulations drawings
- Ongoing project management, coordinating contractors and keeping things on budget
Here’s the part that trips people up: an architect can draw you a beautiful open-plan kitchen extension with a huge steel-free span, but they aren’t qualified to tell you whether your existing walls can actually take the new loads once that wall between the kitchen and dining room disappears. That’s not their job. That’s the next person’s job.
What Does a Structural Engineer Actually Do?
A structural engineer’s entire focus is one question: will this stand up safely? They run the calculations that tell you what size beam you need over that new opening, whether your foundations can handle an extra storey, and what happens to the load path once you’ve knocked through three internal walls to create one big living space.
Unlike “architect,” the title “structural engineer” isn’t legally protected in the UK. Anyone can call themselves one. What you actually want to check for is chartered status with the Institution of Structural Engineers (IStructE) or the Institution of Civil Engineers (ICE) . That’s the real marker of qualification, and it’s worth asking for it directly before you hire anyone.
A structural engineer typically delivers:
- Structural calculations for beams, foundations, and load-bearing changes
- Structural survey reports (useful if you’re worried about cracks, subsidence, or movement)
- Building regulations structural drawings
- Site inspections during construction to confirm the work matches the calculations
This is also the person whose sign-off actually matters to building control, and later, to a mortgage lender or buyer’s surveyor when you come to sell. An architect’s drawings look great in a portfolio. A structural engineer’s calculations are what stop a wall falling down and what get a completion certificate issued.
Architect vs Structural Engineer: The Key Differences at a Glance Architect and structural engineer
| Architect | Structural Engineer | |
| Main focus | Design, layout, aesthetics | Safety, loads, calculations |
| Legally protected title? | Yes (ARB-registered) | No (look for IStructE/ICE chartered status) |
| Typical fee structure | Hourly rate or % of build cost | Flat fee per project |
| Main deliverable | Drawings and planning applications | Calculations and structural sign-off |
| Who relies on their work | Planning department, you, the contractor | Building control, mortgage lenders, insurers |
On any project where the two roles overlap, they’re not competing for the same job; they’re sequential collaborators working from the same set of drawings, just solving different problems.
Do You Need an Architect, a Structural Engineer, or Both?
This is where most guides go vague. They’ll tell you “it depends on your project” and leave you to figure out the rest. Here’s the actual breakdown, by project type.
Architect only projects with no load-bearing changes:
- Cosmetic renovations (new kitchen, new bathroom, redecorating)
- Internal reconfiguration that doesn’t touch load-bearing walls
- Interior-led projects where the layout stays the same but the finish changes
Structural engineer only targeted structural jobs that don’t need a full design overhaul:
- Removing a single load-bearing wall
- Chimney breast removal
- Underpinning or foundation repair
- Investigating cracks or movement in a wall
- Assessing whether your roof can take the extra weight of solar panels
Architect and structural engineer required anything that changes the shape, size, or structural layout of the building:
- Rear or side extensions
- Loft conversions
- New builds
- Basement digs
- HMO conversions
- Any project needing full planning permission alongside structural changes
Skipping the right professional here isn’t a shortcut, it’s a delayed cost. Take a loft conversion: plenty of people hire an architect to draw up the dormer and the new staircase, get planning permission sorted, and then discover at building control stage that the existing floor joists can’t take the new load without a structural engineer’s calculations and a steel beam they hadn’t budgeted for. Now you’re paying for the engineer anyway, plus the delay, plus possibly redesigning the staircase position because the beam needs to sit somewhere specific.
The same logic applies in reverse. Say you just want a load-bearing wall removed to open up your kitchen a structural engineer alone can usually handle this, working out the beam size and getting building regulations approval. Bringing in an architect on top would just add cost for a design decision that isn’t really in question.
How Architects and Structural Engineers Work Together (The Part No One Explains)
This is the piece that’s genuinely missing from most guides on this topic, and it’s usually the thing people most want to understand.
Here’s roughly how it plays out on a typical rear extension:
- You brief the architect. They come up with a concept design where the walls go, how big the opening to the garden is, where the roof line sits.
- The architect submits for planning permission (if needed) based on that concept.
- Once planning is approved (or if it’s permitted development), the structural engineer gets involved. They review the architect’s drawings and work out what’s actually needed to make it stand up: beam sizes, foundation depths, whether the existing structure can take the new loads.
- Sometimes the engineer’s requirements force a redesign. This is the bit nobody warns you about. That beautiful full-width glass opening the architect drew might need a steel beam that’s deeper than expected, eating into your ceiling height, or needing extra support columns the original design didn’t account for. The drawings go back to the architect, get revised, and come back to the engineer for a final check.
- Both sets of drawings architectural and structural go to building control together as part of the building regulations application.
- During construction, the structural engineer does site visits to confirm the work matches the calculations, particularly at key stages like when foundations are dug or steel beams go in.
A real example: a client wants a rear extension with a huge glazed opening and no visible support columns. The architect draws it up. The structural engineer comes back and says a support column is unavoidable given the span but it can go in a corner where it becomes part of the kitchen island layout instead of standing in the middle of the room. That back-and-forth is the actual working relationship, and it’s exactly why using an architect and structural engineer who already work together regularly (or a firm offering both services) tends to save time and arguments.
Costs: What to Budget for an Architect and Structural Engineer
Fees vary by location and project complexity, but here’s a realistic UK range for each, plus what a couple of common projects cost when you add it all up.
Architect fees:
- Hourly rate: roughly £50–£100 per hour
- Percentage of build cost: typically 5–12%, depending on the level of service (concept only vs. full project management)
Structural engineer fees:
- Basic residential project: around £1,000
- More complex residential project: up to £5,000 or more
Worked examples:
Single-storey rear extension: Architect (concept design, planning drawings, building regs drawings) around £2,000–£4,000, plus a structural engineer for calculations and building control sign-off around £1,000–£1,500. Total professional fees before builders: roughly £3,000–£5,500.
Loft conversion with dormer: Architect drawings and planning support around £1,500–£3,000, structural engineer for floor strengthening and stair calculations around £1,200–£2,000. Total: roughly £2,700–£5,000.
HMO conversion (mid-sized terrace, adding rooms and en-suites): Architect for layout and HMO-compliant room sizing around £2,500–£4,500, structural engineer for load-bearing changes and fire safety-related structural work around £1,500–£3,000. Total: roughly £4,000–£7,500, before licensing fees.
One thing worth knowing: firms that offer both architectural and structural engineering services under one roof can sometimes bring the combined cost down and cut out a chunk of the back-and-forth delay described above, since the design and the calculations are happening in the same office rather than being emailed between two separate practices.
For Landlords and HMO Operators: What You Need to Know
If you’re converting a property into an HMO, you’ll almost always need a structural engineer, and usually an architect too this isn’t optional territory the way it might be for a straightforward homeowner extension.
The structural engineer’s involvement typically covers fire safety and means of escape (particularly if you’re adding partition walls to create extra bedrooms), and load-bearing calculations if you’re adding en-suites, converting a loft, or reconfiguring the layout to increase room count. The architect’s role is usually about layout compliance making sure room sizes meet HMO licensing minimums and that the overall design satisfies your local authority’s specific HMO standards, which vary by council.
Watch out for Article 4 directions, too. Many areas with high HMO density have Article 4 restrictions that remove permitted development rights, meaning changes that would otherwise be automatic now need full planning permission. Your architect should flag this early, but it’s worth asking the question yourself before you commit to a purchase or a conversion plan.
The insurance angle is one landlords often miss: structural work that hasn’t been properly signed off by building control (with the structural engineer’s calculations on file) can invalidate your landlord insurance policy entirely. It also becomes a real problem if you ever try to remortgage or sell the property lenders and their surveyors will ask for building regulations completion certificates, and “we did the work ourselves and it seems fine” doesn’t satisfy anyone with money on the line.
For Real Estate Agents and Sellers: Why This Matters at the Point of Sale
If you’re an agent, you’ve probably seen this before: a sale gets to the final stages, the buyer’s mortgage valuation flags a past extension or loft conversion, and suddenly there’s no paperwork proving it was done properly. Deal stalls, sometimes collapses entirely.
The fix is straightforward but often skipped: before listing a property with any history of extension, conversion, or structural alteration, gather the architect’s drawings and, critically, the structural engineer’s calculations and building control completion certificate. If that paperwork genuinely doesn’t exist, indemnity insurance can sometimes bridge the gap but it only covers the risk of enforcement action, not the underlying question of whether the work is actually safe, and many lenders won’t accept it as a substitute for proper documentation on anything structurally significant.
For agents advising sellers, the practical advice is simple: ask about any past structural work at the valuation stage, not after an offer’s been accepted. It’s a much easier conversation to have early.
Who’s Liable If Something Goes Wrong?
Roughly speaking, an architect is liable for design and planning failures if the layout doesn’t comply with regulations or the design itself is flawed. A structural engineer is liable for calculation and safety failures if a beam is undersized or a foundation isn’t adequate for the load. In practice there’s overlap, especially on projects where design decisions and structural requirements are tightly linked, which is exactly why clear contracts matter.
Before hiring either professional, ask to see their professional indemnity (PI) insurance. It’s a completely reasonable question, and any properly qualified architect or engineer will have it and won’t be bothered by being asked.
Frequently Asked Questions
Can a structural engineer do an architect’s job? Not really. They can produce basic layout drawings for planning purposes on simple projects, but they aren’t trained in the design, space-planning, and aesthetic side of an architect’s role, and can’t submit planning applications requiring architectural expertise on complex schemes.
Do I need planning permission if I only hire a structural engineer? Possibly, depending on the work. Structural changes like removing a load-bearing wall usually need building regulations approval (which a structural engineer handles) but not necessarily planning permission, unless it affects the building’s external appearance or falls under an Article 4 direction.
What happens if my architect and structural engineer disagree? It’s normal and usually resolves through revised drawings the engineer flags a structural constraint, the architect adjusts the design around it. Problems only arise when the two aren’t communicating directly, which is another reason to use professionals who already work together.
Can one person or firm do architect and structural engineer jobs?
Yes some firms offer combined architectural and structural engineering services, which can streamline the process and reduce cost. Individual dual-qualified professionals are rarer but do exist.
Do I need a structural engineer to remove a wall in an HMO? Yes, virtually always, especially if it’s load-bearing or affects fire safety/means of escape, which HMO regulations are particularly strict about.
How do I check if my structural engineer is actually qualified? Ask if they’re chartered with IStructE or ICE, and check the institution’s public register directly rather than just taking their word for it.
Will I need a structural engineer’s report to sell my house? If you’ve had any structural work done extension, loft conversion, wall removal yes, buyers’ lenders will typically want to see the structural calculations and building control completion certificate as part of the conveyancing process.
Getting Started
The real question isn’t “architect and structural engineer” it’s “what does my project actually involve?” Start there, and the right professional (or pair of professionals) becomes obvious. If your project touches the shape, size, or structural layout of the building, budget for both from the outset rather than discovering the second one halfway through building control.
If you’re not sure which category your project falls into, that’s exactly the kind of question worth a quick conversation before you commit to drawings or a builder.