Nobody enjoys the answer “it depends”, so this is an attempt to explain what it depends on, which is at least something you can price against.
Why Structural Fees Aren't a Fixed Price List
Two houses of identical size can need very different amounts of engineering. The variables that actually move the fee are the site, the complexity, and how much of the work has already been done before we're involved.
What Drives the Number
Site Classification
A Class A site and a Class H2 site need different footing systems, different detailing and different amounts of design work. A Class P site, meaning uncontrolled fill, soft ground or slope instability, cannot use the standard tables at all and has to be specifically engineered, which is a meaningfully larger job.
Slope and Levels
A flat block is straightforward. A sloping block usually brings split-level footings, retaining, and the interaction between the two: three problems where a flat site has one.
Structural Complexity
Long spans, cantilevers, raked ceilings, large glazed openings, upper-level structure over open plan living, and anything with an irregular roof form all take more design and more documentation than a conventional layout does.
Scope
Footing design alone is a smaller piece of work than a full structural package with framing, beams, retaining and certification. Booking the whole sequence at once is usually cheaper than booking each piece separately, because the site information carries across instead of being re-established.
What You Already Hold
If you already have a current soil report and a survey, that's work we don't repeat and don't charge for. If you don't, they're part of the scope.
Documentation Standard
Documentation for building consent and documentation a builder can construct from without ringing you are not always the same thing. We aim to produce the second one, which takes longer to draw and saves money on site.
Timeframe
Standard turnaround is priced normally. Genuine expedited work reorders other people's jobs, and is priced accordingly.
What Tends to Cost More Than People Expect
- Retaining walls with surcharge. A driveway or structure above a wall changes it from a garden wall into a designed structure.
- Working around existing structure. Renovations need the existing building assessed before anything new can be designed, and that assessment is real work.
- Class P sites, often not discovered until the soil report arrives, which is why we'd rather that report came early.
- Redesign after a change. Moving a wall on the architectural plan after the structure is drawn means redoing the structure.
What Tends to Cost Less Than People Expect
Coming back to us for a later stage at the same address. We already hold the survey, the classification and the earlier design, so the second engagement starts from what we know rather than from scratch.
Also: asking early. A fifteen-minute conversation at the design stage is free and routinely saves a redesign.
How We Quote
A written fee for a defined scope, before any work starts. Not an hourly estimate that drifts. If the scope changes, because the soil report comes back Class P, or the design changes, we tell you what that means before we do the extra work, not afterwards on the invoice.
The Comparison That Matters
Structural engineering is a small fraction of a build budget. The things it prevents are not a small fraction of anything: a footing redesign after excavation, a failed retaining wall, a beam that deflects and cracks the ceiling, a consent application knocked back for insufficient documentation.
This article is general information about structural engineering practice in South Australia. It isn't advice for a specific site, and it doesn't replace confirming requirements with your local council or a registered building certifier. Requirements vary between council areas and change over time.