Structural engineer or building surveyor: who to instruct

If you need calculations, instruct a structural engineer. If you need a diagnosis, instruct a building surveyor. That single distinction answers most structural engineer or surveyor report questions, and it explains why the two professions are not interchangeable even though their work overlaps on an ordinary house extension.

An engineer works out whether a beam, a foundation or a wall will carry the load, and produces the figures that building control checks. A surveyor works out what is wrong with a building, why it is happening and what should be done about it, and produces the report that tells you whether to proceed at all.

What each discipline is trained to do

A chartered structural engineer is trained in analysis and design. Loads, spans, deflections, bearing capacities, lateral stability, temporary support during construction. The output is drawings and calculations, often with a design certificate.

A chartered building surveyor is trained in building pathology and construction technology. Why that wall is cracking, whether the damp is rising, penetrating or condensation, whether the roof structure has been altered, what the previous owner did to the chimney breast. The output is a report with findings, a cause and a recommendation, sometimes with a schedule of works.

Overlap exists at the edges. Many building surveyors are experienced in movement diagnosis and will tell you confidently whether a crack is historic settlement or active subsidence. Many engineers will comment on the condition of what they find. Neither strays far outside their training if they are good at the job.

Which report a council actually asks for

Councils ask for structural evidence at planning stage in a small number of situations, and knowing which one applies tells you who to appoint.

On a conversion, the governing question is whether the existing structure is capable of taking the conversion works without being substantially rebuilt. That is a structural judgement, and the report that answers it is a Structural Survey by a suitably qualified author. Councils expect an engineer's appraisal rather than a general condition report, and professional review of any draft before submission is strongly advised.

For a basement, the evidence set is wider. A Basement Impact Assessment deals with groundwater, ground movement and effects on neighbouring property, and in many London boroughs it is a validation requirement with its own local guidance. A Geotechnical Assessment covers the ground itself, and the competence of the firm carrying out the investigation matters as much as the design, which our note on ground investigation contractor competence covers.

Calculations and the building control route

Planning and building control are separate processes, and structural work belongs mainly to the second.

Planning permission is about land use, appearance, amenity and impact. Building control is about whether the building is safe, warm and accessible, under the Building Regulations. Structural adequacy is dealt with in Approved Document A, and the usual evidence is calculations from an engineer submitted with the building control application or during the works.

So the sequence on a typical extension is: architect or designer produces the scheme, planning permission is obtained where needed, then an engineer designs the structure and issues calculations, then building control inspects. Appointing the engineer before planning is settled often means paying for calculations on a design that then changes.

The exception is any scheme where the structure drives the design. Removing most of a rear wall for sliding doors, forming a large opening in a spine wall, building over or close to a drain, or underpinning. In those cases a short engineering appraisal before the planning drawings are finalised stops the design from promising something the structure cannot deliver.

Defect diagnosis and monitoring

This is where a building surveyor earns their fee, and where appointing an engineer first often wastes money.

A crack appears above a window. The question is not what beam is needed. The question is what caused the crack: seasonal clay shrinkage near a tree, a failed lintel, thermal movement, a leaking drain softening the ground, or historic movement that settled decades ago. A surveyor investigates and reaches a view, then recommends either repair, further investigation, or a period of monitoring.

Monitoring means fixing tell-tales or taking level readings at intervals, usually over a year so that seasonal movement shows. It is slow, unglamorous and more often the right answer than people expect, because repairing active movement without identifying the cause produces the same crack again.

If the diagnosis turns out to need structural intervention, the surveyor then briefs an engineer with a clear problem statement. That order of appointment costs less than the reverse.

Where you need both

Larger or older projects need the two disciplines together, with their roles written down so neither assumes the other has dealt with something.

A sensible division on a house project: the surveyor reports on condition, damp, timber and movement, and specifies repairs. The engineer designs new structure and any temporary support, and issues calculations. The designer coordinates. Someone has to hold the question of sequencing, because taking out a wall before the propping design exists is how accidents happen.

Where a neighbouring property is involved, a third regime appears. The Party Wall etc. Act 1996 applies to works to a shared wall, excavation near a neighbour's foundations and certain other works, and it runs on its own notices and timetable regardless of your planning permission. Party wall surveyors are often building surveyors, and the appointment under the Act is separate from any advice they give you as your own consultant.

Insurance, liability and what to check

Four questions before you appoint anyone.

1. Which institution are they chartered with, and can you verify the membership. Structural engineers are commonly chartered through the structural or civil engineering institutions, and building surveyors through the surveying institution.
2. What does their professional indemnity insurance cover, and at what level. Ask for the certificate, not a verbal assurance.
3. What exactly is in scope, written as a list. A condition report with no opening up is a different product from an investigation with trial holes.
4. Who signs the output. For calculations submitted to building control, the signature and the competence behind it are the point of the exercise.

Read the exclusions in a condition report. Most exclude anything concealed, which is reasonable, but it means that a report on a 1900s house without any opening up has not looked at the joist ends, the wall ties or the lintels.

If you need a qualified reviewer to check a draft before it is submitted, the professional directory is the route to sign-off by someone in the relevant discipline.

Briefing for an extension on an older house

For a typical two-storey Victorian or interwar house with a rear extension planned, a workable sequence:

1. Walk the house with a building surveyor if there is any visible crack, damp or sagging, before the design starts. A short report is enough.
2. Have the designer produce the scheme, with the survey findings informing it.
3. Obtain planning permission, or confirm the works are permitted development, before committing to structural design.
4. Appoint an engineer for the opening, the foundations and any temporary works, and give them the surveyor's report.
5. Serve party wall notices where the Act applies, allowing for the statutory periods.
6. Submit calculations to building control and keep the engineer available for site queries.

The one shortcut worth taking is combining the first and second steps where your designer already has a structural engineer they work with regularly. The one shortcut never worth taking is skipping the diagnosis on a house that is already moving.

Work out which documents the planning side needs before you commission any structural work. Enter your postcode on PlanScope to see which reports a house extension or conversion is likely to need.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.