Many homeowners are unclear about the difference between an architect and a structural engineer, and exactly when they need a structural engineer rather than — or in addition to — an architect. Understanding this distinction helps you assemble the right professional team for your project and avoid gaps in the advice you receive.

This guide explains what structural engineers do, the qualifications to look for, when you need one, and how much their services typically cost for domestic projects in the UK.

What Is a Structural Engineer?

A structural engineer is a qualified professional who designs, analyses, and assesses the structural elements of buildings and other structures. Their work focuses on ensuring that structures are safe, stable, and capable of carrying the loads they will be subjected to — gravity loads (the weight of the building, its contents, and occupants), wind loads, snow loads, and in some cases seismic loads.

For domestic projects, a structural engineer’s work typically centres on:

• Designing steel beams and columns
• Designing foundations
• Assessing and specifying structural elements of extensions and loft conversions
• Investigating and remedying structural defects (cracking, subsidence, movement)
• Producing calculations that satisfy building control

Structural Engineer Qualifications

When appointing a structural engineer for domestic work, look for:

• MIStructE: Member of the Institution of Structural Engineers — the primary professional qualification for structural engineers in the UK. Requires passing the IStructE examination or equivalent recognised degree plus experience.
• CEng: Chartered Engineer — a broader engineering qualification relevant across disciplines. Structural engineers may hold CEng alongside MIStructE.
• BEng/MEng (Civil or Structural Engineering): Undergraduate degree as a starting point, but membership of IStructE or ICE is the mark of professional qualification.
• Professional indemnity insurance: All practising structural engineers should carry PI insurance. Ask for confirmation before appointing.

Architect vs Structural Engineer: What Is the Difference?

Architects and structural engineers are distinct professions with complementary roles:

Architect	Structural Engineer
Designs the form, function, and aesthetics of the building	Designs the structural elements that make the building safe
Prepares planning and building regulations drawings	Prepares structural calculations and drawings
Manages the planning application process	Manages the structural engineering aspects of building control
Regulates space layout and room sizes	Sizes beams, columns, foundations, and reinforcement
ARB registered (protected title in UK)	Typically IStructE member (title not legally protected)

For most domestic extension projects, you need both. The architect designs the extension; the structural engineer ensures it is safe. Crown Architecture & Structural Engineering provides both services as a combined package, which is more efficient and cost-effective than appointing separate consultants. Call 07443804841 for a fixed-fee quote.

When Do You Need a Structural Engineer for Domestic Work?

House Extensions

All house extensions require structural calculations from a structural engineer to satisfy building regulations (Part A — Structure). The engineer designs the foundations, any steelwork at openings in the rear wall, the first-floor structure (for two-storey extensions), and the roof structure. Building control will not approve the extension without stamped structural calculations.

Removing Load-Bearing Walls

Removing any load-bearing wall — to create an open-plan ground floor or to form a wider opening — requires a structural engineer to calculate the correct steel beam size. An undersized beam will deflect under load, causing visible cracking above the opening and potential structural failure over time.

Loft Conversions

Loft conversions require structural engineering for the new floor structure, any dormer structures, purlins and ridge reinforcement, and the stair opening trimmer beams. The existing ceiling joists (typically 50×100mm) are almost never adequate to carry habitable floor loads — the structural engineer specifies the required new floor structure.

Subsidence, Cracking, and Structural Defects

Where a house shows signs of structural distress — diagonal cracks, door frames out of square, floors that slope — a structural engineer’s survey identifies the cause and specifies remedial action. This is distinct from a standard surveyor’s report: a structural engineer provides the technical diagnosis and the engineering solution.

Underpinning and Ground Engineering

Where foundations are failing or inadequate (typically due to subsidence, tree root damage, or poor original construction), a structural engineer specifies the underpinning or ground improvement method and oversees the remedial works.

Basement Conversions

Basement excavations are among the most structurally complex domestic projects. The structural engineer designs the temporary and permanent retention systems, the waterproofing strategy, and the new concrete frame that forms the basement structure.

Structural Engineer Fees for Domestic Projects in 2025

Service	Typical Fee Range (2025)
Single steel beam calculation (simple wall removal)	£350–£700
Extension steelwork and foundation package	£800–£2,000
Loft conversion structural package	£800–£1,800
Two-storey extension full structural package	£1,500–£3,000
Subsidence investigation and remediation specification	£700–£2,500
Basement structural design	£3,000–£10,000+

Frequently Asked Questions

Can my builder do the structural calculations?

No. Structural calculations must be produced by a qualified structural engineer and are submitted to building control as part of the building regulations application. An experienced builder may have a general understanding of beam sizing, but this is not a substitute for engineering calculations. Using an undersized beam without calculations exposes you to liability if the structure fails.

Do I need a structural engineer for permitted development work?

Permitted development refers to the planning system — it means you do not need planning permission. However, building regulations still apply to PD work, and structural calculations are required for any structural elements. You always need a structural engineer for extensions and structural alterations, regardless of whether planning permission is required.

What is an IStructE engineer?

A Member of the Institution of Structural Engineers (MIStructE) is a professionally qualified structural engineer who has passed the IStructE examination — widely regarded as one of the most rigorous professional engineering examinations in the world. IStructE members are required to maintain continuing professional development and adhere to a code of conduct.

How long does it take to get structural calculations?

A site visit and structural calculations for a straightforward domestic project (single beam, extension foundations) typically takes 1–3 weeks from instruction. More complex projects (two-storey extension with multiple steel frames, basement) may take 3–6 weeks. Building control then takes a further 2–4 weeks to review and approve the calculations.

Do structural engineers carry out inspections during construction?

Some structural engineers offer on-site inspection services during construction — visiting to inspect steel beam installations, foundations, and other structural elements before they are covered. This is separate from building control inspections. For complex projects, structural engineer inspections provide an additional layer of quality assurance.

Work With Crown Architecture’s Structural Engineers

Crown Architecture & Structural Engineering includes qualified structural engineers as part of our integrated service. We provide architectural design and structural engineering for extensions, loft conversions, structural alterations, and building defect investigations across the UK.

Call 07443804841 or complete the enquiry form above to discuss your project.