Every building approval for a second home needs a handful of reports from people the certifier trusts, and a flagged block needs more. The ones every job has: a structural engineer for the footings and tie-down, about $2,650; a soil test to classify the site, about $900; and an energy rating, about $650 if the maker has not already supplied one. The ones the block decides: a surveyor to fix the boundaries and set the home out, $2,400 to $3,850; a bushfire assessor where the land is bushfire prone, about $1,000; a flood engineer where it is flood mapped, $1,300 to $6,600; a geotechnical engineer on a steep block, $2,000 to $4,600; a hydraulic engineer for building near a sewer, $2,100 to $5,300. All inc GST, including a builder's cost to book and manage each one. A good installer runs all of them, so the owner deals with one builder, not seven.
Who each one is, and what the rule behind them says
| Consultant | What they produce | The rule | Guide price, inc GST |
|---|---|---|---|
| Structural engineer | Footing and tie-down design, the site inspection, and a Form 15 certifying the design for the certifier | A Registered Professional Engineer of Queensland under the Professional Engineers Act 2002. The certifier accepts the Form 15 under the Building Regulation 2021 | About $2,650 |
| Soil tester | Bore logs and a site classification | AS 2870, residential slabs and footings: class A, S, M, H1, H2, E or P | About $900 |
| Energy assessor | The NatHERS star rating and the energy report | QDC MP 4.1 Sustainable buildings. Since 14 August 2026 a detached home of 50 m² or less needs 5 stars, a raised-floor home 6, any other new home 7. Many makers supply the rating with the home | About $650, only if the maker has not supplied it |
| Surveyor | Identification or set-out survey: where the boundaries are, where the home goes | The siting rules measure setbacks from the boundary, and the certifier needs them located | $2,400 to $3,850, indicative |
| Bushfire assessor | The Bushfire Attack Level report | AS 3959, applied where council has designated the land bushfire prone under the Building Regulation 2021 | About $1,000, when mapped |
| Flood engineer | The flood report and the floor level | QDC MP 3.5: the habitable floor at the defined flood level plus freeboard | $1,300 to $6,600, indicative, when mapped |
| Geotechnical engineer | Slope stability | Asked for by the certifier or the engineer on a steep block | $2,000 to $4,600, indicative |
| Hydraulic engineer | Build-over-sewer design | Asked for by the water authority when the home sits over or near a sewer or stormwater line | $2,100 to $5,300, indicative |
| Building certifier | The approval itself, the inspections, the final certificate | Licensed by the QBCC | About $700 to $2,400 ex GST |
Prices marked indicative are market ranges; the others come from invoices on 2026 South East Queensland installs. A quote fixes them for the block.
Which ones a maker already covers
A home built in a factory arrives with most of its own paperwork: the plans, the frame engineering, often the energy rating and the compliance statements for the plumbing and electrical. What the maker cannot supply is anything about the block: the soil, the footings, the survey, the BAL, the flood level. Those are the installer's, or the owner's, to get. A home bought online or from overseas often arrives with none of it, and bought a modular home? lists what a certifier will ask for then.
Why they come first
The soil test prices the piers. The BAL changes the deck and the windows. The flood level lifts the floor. The survey decides whether the home fits inside the setbacks at all. Each costs little next to the thing it decides, which is why they belong before a deposit, not after the crane is booked.
See it for your block
- Install cost calculator, who's on your approval
- Check your block for bushfire and flood mapping
- Granny flat rules in Queensland: energy, BAL, flood, wind
Questions people ask next
Which reports does a granny flat building approval need?
Every job: a structural engineer's footing and tie-down design, a soil test, and an energy rating. Depending on the block: a survey, a bushfire attack level report, a flood report, a geotechnical report on a steep site, and a hydraulic design near a sewer.
What energy rating does a granny flat need in Queensland?
Under QDC MP 4.1, from 14 August 2026 a detached home of 50 m² or less needs 5 stars, a home with at least half its floor over open space 6 stars, and any other new home 7 stars. The energy assessor runs the rating and the certifier checks it.
Who can sign the engineering on a granny flat?
A Registered Professional Engineer of Queensland. The engineer certifies the footing and tie-down design on a Form 15 for the certifier and inspects the work being certified.
- Board of Professional Engineers of Queensland (RPEQ registration under the Professional Engineers Act 2002), read October 2026
- Building Regulation 2021 (competent persons, Form 15 design certificates), read October 2026
- Standards Australia, AS 2870 residential slabs and footings, read October 2026
- QDC MP 4.1 Sustainable buildings, version from 14 August 2026, read October 2026
- Queensland Government, building in bushfire prone areas (AS 3959), read 16 October 2026
- QDC MP 3.5, construction of buildings in flood hazard areas, read October 2026
- QBCC, find a licensed contractor or certifier, read October 2026
- Consultant prices behind the install cost calculator (South East Queensland invoices and market ranges, 2026), read 16 October 2026