What Does a Structural Engineer Do?
Written by James Walker · Last reviewed 16 August 2026
James Walker has 2 degrees in construction (BSc (Hons) Building Surveying · MSc Environmental Design of Buildings) and an extensive background in issue resolution, resolving over £4 billion of consumer issues.
A structural engineer calculates the loads in a building and specifies what is needed to carry them, beam sizes, foundation design, and how a structure behaves when part of it is removed.
When you need one
Removing a load-bearing wall. Inserting a beam. Extensions and loft conversions. Underpinning. Anything where building control needs calculations rather than an assurance.
Their output is a set of drawings and calculations that building control assesses and the builder works to.
Who engages them
Usually you, not the builder. This surprises people and it is a common gap: the builder assumes the drawings will arrive, the architect assumes someone else is instructing the engineer, and nobody has.
Establish it explicitly before work starts, and confirm whether the fee sits inside anyone's quote.
Why it is worth the fee
An engineer specifies what is actually required. Without calculations, a builder either over-specifies, which costs you in steel and in the labour to lift it, or under-specifies, which is worse.
On anything structural, the fee is small relative to the cost of getting it wrong.
How it works
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