When you need a structural engineer (and how to hire one)

What a structural engineer does

Structural engineers assess and design the parts of a building that carry load — footings, beams, slabs, walls and framing. For homeowners, the work usually falls into two camps. The first is inspecting a problem: cracking, sagging floors, subsidence or a leaning retaining wall, resulting in a written report or letter. The second is certifying a change: sizing a beam to remove a load-bearing wall, or designing the structure for an extension or second storey.

Their output comes with certification your builder and certifier depend on — you generally can't remove a load-bearing wall or add a storey without an engineer's design. They're distinct from a building consultant doing a pre-purchase inspection; an engineer's role is to calculate and certify that structure will perform, not to give a general condition report.

How the fees work

Engineers charge either an hourly rate or, more commonly for residential work, a fixed fee for a defined job — which makes quotes easy to compare. An inspection and report sits at the low end, a beam or wall-removal design in the middle, and full structural drawings for an extension or new home higher again. The calculator on this page carries the current indicative bands.

The extras are where quotes diverge. If a geotechnical (soil) report is needed, that's a separate cost. Missing original plans mean the engineer must measure and model your existing structure first, adding hours. Sloping sites, reactive soils, heritage buildings and urgent turnarounds all add time or a priority fee. Ask what the fixed fee includes — particularly whether responding to council or certifier queries after lodgement is covered.

Registration and choosing well

Structural engineering is regulated, and most states now require registration for engineers doing structural work — RPEQ in Queensland, and equivalent registration schemes rolling out elsewhere. Check the engineer is registered where required and ask for the number; it's the clearest signal you're dealing with a qualified professional rather than someone working beyond their competence.

The practical differences are responsiveness and clarity. A good engineer turns reports and designs around promptly, explains their findings in plain language your builder can act on, and flags what else the job needs — a soil test, say — rather than leaving you to discover it. Crucially, engage them before removing anything that might be load-bearing; retrofitting a fix costs far more than designing it correctly the first time.

Mistakes to avoid

Structural engineering regrets are expensive because they involve the bones of the house. The classic is pulling out a wall or starting work before the engineer is involved, then paying much more to make safe what should have been designed from the start.

• Removing something that might be load-bearing before an engineer has assessed it
• Not checking the engineer's registration where your state requires it
• Assuming a soil report is included when it's usually a separate cost
• Overlooking that missing original plans add time to model the existing structure
• Not confirming whether post-lodgement council queries are inside the fixed fee
• Choosing on price alone when a slow turnaround can stall your whole project