You need one whenever the work changes how the house carries load, and that's a wider set of jobs than most people expect, and harder to tell from inside the room than it sounds.
The Short Version
You almost certainly need one if your renovation involves any of the following:
- removing or opening up an internal wall
- adding a storey, a room in the roof, or anything above an existing structure
- an extension with its own footings
- a new opening in an external wall wider than a standard door
- removing or relocating a supporting post or column
- underpinning, or building close to an existing footing
- a deck, balcony or carport attached to the house
You probably don't need one for a cosmetic renovation: kitchens and bathrooms where nothing structural moves, replacing linings, re-roofing with the same material weight, or non-structural partitions.
Why “Is This Wall Load-Bearing?” Is the Wrong First Question
It's the question everyone asks, and it's incomplete. A wall can carry no roof load at all and still be doing essential work as a bracing wall, resisting the horizontal forces that stop the house racking sideways in high wind. Removing a brace wall can be more consequential than removing a load-bearing one, and it's invisible from the room.
The other thing people miss is the load path. A beam that replaces a wall has to put its load somewhere. That somewhere is a post, then a footing, then the ground, and if the existing footing under that point was sized to carry a wall spreading load evenly, it may not be sized to carry a concentrated point load. The wall comes out beautifully, and eighteen months later a crack opens above the new opening because the footing under one end settled.
Older Adelaide Housing Has Its Own Issues
A lot of Adelaide's established suburbs are stone or double-brick cottages and bungalows on shallow footings, sitting on reactive clay. Three things follow from that.
First, the existing structure has usually already moved and settled into its own equilibrium. Changing the load distribution disturbs that. Second, shallow footings on reactive soil are sensitive to moisture changes, which is why a renovation that alters drainage, adds paving, or removes a large tree can cause movement that has nothing to do with the building work itself. Third, solid masonry walls don't behave like modern stud framing when you cut a hole in them, and they need propping that is designed rather than improvised.
When Approval Is Involved
Structural building work in South Australia is assessed under the Planning, Development and Infrastructure Act 2016. Most renovations that change the structure require development approval, and building rules consent will generally require engineering documentation for the structural elements. Your council or a private certifier will tell you exactly what's needed for your property.
Practically, this means the engineering isn't an optional extra you add if you feel cautious. It's usually part of the paperwork you need to get consent at all, so it's cheaper to organise it at the design stage than to discover it after you've priced the job.
When to Bring an Engineer In
Before you finalise the layout, not after. The most expensive version of this conversation is the one where a design has been drawn, quoted and approved by the client, and then the engineering reveals that the six-metre opening needs a column in the middle of it.
Bringing an engineer in during design costs a little and changes drawings on paper. Bringing one in after demolition costs a lot and changes drawings on site.
What We'd Need from You
To tell you whether your renovation needs structural design, we usually need the address, whatever plans exist (even a sketch), some photos of the area you want to change, and a description of what you're hoping to do. From that we can normally tell you within a day whether there's structural work involved and what it would take.
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.