What Does a Structural Engineer Do?
A structural engineer calculates whether a building is strong enough to stand up safely under the loads placed on it. Where an architect decides what a building looks like and how it is laid out, a structural engineer works out whether the structure can carry the weight. Every beam, every floor, every foundation and every wall that carries load has to be designed to a standard that Building Control will accept, and that is what a structural engineer produces.
In residential work, most homeowners encounter a structural engineer when they want to remove a wall, convert a loft, build an extension or deal with cracking. You may never meet the engineer in person to most residential jobs are handled remotely to but the calculation pack they produce is the document that lets your builder do the work and Building Control approve it.
What a Structural Engineer Actually Does on a Residential Project
The work varies by project type, but the common thread is the same: an engineer takes the physical reality of your property, the loads acting on it and the change you want to make, and produces a mathematical proof that the proposed design is safe.
For a wall removal or RSJ beam
When you remove a load-bearing wall, something has to carry the floor, roof and wall loads that were previously held by the masonry. A structural engineer calculates the correct steel beam size for the span and load, specifies the padstones (the bearing blocks at each end of the beam), checks the masonry below can carry the new concentrated load, and produces the drawings your builder and Building Control need. Get the beam size wrong and the floor above will deflect and crack. Get the padstone wrong and the masonry below can fail. These are not guesses a builder can reliably make to they require calculation.
See our full guide: load bearing wall removal and wall removal cost guide.
For a loft conversion
Loft conversions need a structural floor strong enough to support people, furniture and the floor finish. The existing ceiling joists that span across the loft are almost never adequate for this. A structural engineer designs the new floor joist schedule, sizes any steel ridge beams or floor beams required, checks the existing roof structure for adequacy and produces all the drawings needed for Building Control approval.
See our guide: loft conversion structural engineer.
For a home extension
Extensions involve new foundations, new steelwork over the opening where the extension connects to the existing house, roof structure and lintel checks. The structural engineer designs all of these elements and produces a Building Control-ready pack covering the full structural scope of the extension.
See our guide: structural engineer for home extensions.
For a chimney breast removal
Removing a chimney breast is more complex than it looks. If the stack above is being retained, the load from that stack needs to transfer to somewhere else in the structure. A structural engineer designs the gallows brackets or steel beam arrangement to carry the remaining stack safely. See our guide: chimney breast removal structural calculations.
For cracks and structural inspections
When cracks appear in a property, a structural engineer visits the site, assesses the crack patterns and identifies the cause. Diagonal cracks, horizontal cracks and stepped cracks all mean different things, and distinguishing a cosmetic crack from a structural one requires professional judgement. A written report explains the cause, severity and recommended action. See our guide: structural engineer report.
When Do You Need a Structural Engineer?
The short answer is: whenever you are changing something structural. Building Control will require structural calculations for any of the following:
| Project | Why an Engineer Is Needed |
|---|---|
| Load bearing wall removal | Beam and padstone design required |
| Loft conversion (any type) | Floor structure and roof checks required |
| Home extension | Foundation, steelwork and roof design required |
| Chimney breast removal | Stack support design required |
| Bi-fold or large door opening | Goalpost steel frame required |
| Structural cracks or movement | Inspection and report required |
| New build or commercial build | Full structural design required |
| Garage conversion | Floor strengthening and lintel checks required |
The projects where you might not need a structural engineer are purely cosmetic works to decorating, flooring, kitchen fitting, bathroom fitting to where no structural element is being changed. As soon as a wall, floor, roof or foundation is being altered, an engineer is almost always required.
What a Structural Engineer Does Not Do
It is worth being clear about what falls outside a structural engineer's scope in residential work, because there is sometimes confusion between the different professionals involved in a project.
Planning permission
Structural engineers do not handle planning applications. Planning is the architect's or planning consultant's territory. A structural engineer is brought in once the layout is decided, to design the structure that makes the layout work safely. Many projects do not need planning permission at all to they fall under Permitted Development to but they still need structural calculations for Building Control.
Building Control submissions
A structural engineer produces the calculation pack that goes into a Building Control submission, but does not usually handle the submission itself. That is typically done by you, your architect or your builder. We produce packs formatted for Building Control and answer any technical queries inspectors raise. See our guide: structural calculations for Building Control.
Project management
A structural engineer is not a project manager. We design the structural elements, produce the drawings and answer technical questions. The builder manages the build programme and the sequencing of works on site.
Structural Engineer vs Architect vs Builder
These three professionals are often confused by homeowners starting a renovation. Here is how they differ and when you need each one.
The architect
An architect designs the space: the layout, the aesthetics, the planning drawings and the general arrangement of rooms. Architects are essential for complex projects and planning applications. For simpler projects like a wall removal or a loft conversion, you may not need a separate architect at all to many homeowners go directly to a structural engineer with their own sketch plans.
The structural engineer
A structural engineer designs the strength: the beams, the foundations, the floor structures and the connections. Where the architect says "there will be an opening here," the structural engineer calculates what size steel beam goes in that opening and how it bears at each end. The two disciplines work together on larger projects.
The builder
The builder installs everything on site. They follow the structural engineer's drawings and calculations to order and fit the correct steel, pour the correct foundations and build the correct connections. A good builder will flag any discrepancy between the drawings and the site conditions, which the structural engineer then resolves.
What You Receive from a Structural Engineer
For a standard residential project, the structural engineer produces a PDF calculation pack. This is what you submit to Building Control and what your builder works from. It contains:
- Structural calculations: the mathematics proving the design is safe to Eurocode standards
- Structural drawings: dimensioned drawings showing beam positions, padstone locations, connection details and floor layouts
- Specification notes: material grades, fixing types and any specific construction requirements
- Padstone design: the bearing blocks under each beam end, sized for the masonry below
If Building Control raises queries about the design after submission, a good structural engineer responds directly as part of the service, at no extra charge. If the layout changes on site, the engineer reviews and updates the drawings.
How Much Does a Structural Engineer Cost?
Fees for residential structural engineering run from £245 for a single beam calculation to £1,500 for a full extension structural design. All our fees are fixed and confirmed in writing before work starts. There are no hourly rates.
- Single RSJ beam calculation: £245 to £450
- Load bearing wall removal (full pack): £300 to £600
- Loft conversion structural design: £395 to £1,200
- Home extension structural design: £600 to £1,500
- Structural inspection and report: £250 to £400
For a full breakdown of costs by project type, including what affects the fee and how to get the most from your engineer: full structural engineer cost guide.
How to Work with a Structural Engineer
The process is straightforward and most residential projects are handled entirely remotely. You do not usually need a site visit.
- Send your plans: a sketch, estate agent floor plans, architect's drawings or photos. Anything that shows the existing layout and what you want to change.
- Receive a fixed fee: we review the scope and confirm a fixed price in writing before starting. No surprises.
- Receive your pack: calculations and drawings delivered as a PDF, typically within 24 to 72 hours for simpler projects.
- Submit to Building Control: you or your builder submits the pack to your local Building Control authority or private approved inspector.
- Build: your builder installs the steel and other structural elements following the drawings. Any queries from the inspector or builder are answered as part of the service.
Frequently Asked Questions
Can I remove a wall without a structural engineer?
Not safely or legally if it is a load-bearing wall. Building Control will not approve the work without structural calculations. Even if a builder fits a beam without calculations and it does not fail immediately, you will face problems when you come to sell the property to solicitors and mortgage lenders will ask for the Building Control certificate, and without calculations that certificate cannot be issued.
Do structural engineers visit the property?
For most beam designs and loft conversion structural packs, no. We work from your drawings and photos, which keeps the cost down and the turnaround fast. For crack assessments and structural inspections we visit the site to assess the defect in person. Site visits are typically £250 to £400.
How long does a structural engineer take?
A single RSJ beam calculation is typically ready the next working day. A full loft conversion pack takes 3 to 5 working days. A home extension structural design takes 5 to 7 working days. Turnaround is confirmed in writing with the fixed-fee quote.
Do I need an architect as well as a structural engineer?
For planning applications and complex projects, yes. For a straightforward wall removal or loft conversion where the layout is already decided, many homeowners go directly to a structural engineer without an architect. We work from sketch plans and photographs and produce everything Building Control needs.
What is the difference between a structural engineer and a building surveyor?
A building surveyor assesses the overall condition of a property to finishes, services, damp, roof, drainage. A structural engineer focuses specifically on the load-bearing structure: beams, foundations, walls and floors. For a pre-purchase crack assessment or structural concern, you need a structural engineer. See our structural engineer report guide for more detail.
Get a Fixed-Fee Structural Engineering Quote
Tell us about your project and we will confirm a fixed fee the same day. Most residential jobs are ready within 24 to 72 hours. Call 07359 267907 or fill in the form opposite.