Structural · 6 min read
Home extensions and renovations: what a structural engineer does
Renovations are harder than new builds because you inherit someone else's structure. Whether you are removing a wall, raising a Queenslander and building under, or adding a room at the back, here is what the engineering involves and what it costs in Brisbane.
Removing a wall or opening up a kitchen
The first question is whether the wall is load bearing. If it carries roof, ceiling or floor load, it needs a beam and posts sized for that load, plus a footing under each post and a temporary propping method during the work.
We can usually answer this from photos plus a short site inspection, then issue a beam and post design your builder and certifier can work from.
Raising and building under a Queenslander
Raising is common across Brisbane's older suburbs and it triggers a full structural review: new footings and steel or concrete posts, a braced lower level, floor diaphragm, tie-down for wind, and often new bearers where the existing timber has failed.
Termite and rot damage in old bearers and stumps is normal. We assess what is reusable and design what has to be replaced.
- New footing and post design for the raised structure
- Bracing and tie-down for the new lower storey
- Bearer, joist and floor frame strengthening
- Ground floor slab and drainage details
- Retaining and cut details where the ground slopes
Rear extensions, decks and alfresco areas
Extensions need their own footings designed for the site classification, plus a connection detail to the existing house that allows for differential movement. Tying a new stiff slab rigidly to an old flexible frame is a reliable way to create cracking.
Decks and alfresco roofs are quick jobs but still need certified post, bearer, footing and tie-down design.
Cost
Extension and structural modification design starts at $1,100. A single beam or wall removal is often less; raising and building under is quoted after an inspection.
Site inspections start at $400, and a full written assessment report adds $300.
Frequently asked questions
- Do I need an engineer to remove an internal wall?
- If the wall is load bearing, yes — you need a designed beam, posts and footings, and your certifier will ask for engineering. A non load bearing wall usually does not need design.
- How much does extension structural design cost in Brisbane?
- From $1,100 for a typical extension or structural modification, including drawings and RPEQ certification.
- Can you inspect before I commit to a design?
- Yes. A site inspection from $400 tells you what is structurally possible, and the fee is credited toward the design if you proceed.
Tell us what you want to change — extension design from $1,100.
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