Data Sources

Every cost figure in our calculator is derived from publicly available data. Here are our primary sources.

Builder pricing data

We analysed published pricing from these Australian granny flat builders:

  • Superior Granny Flats (VIC/QLD) — 10 designs with exact sqm and prices, itemised cost breakdowns
  • Granny Flat Solutions (NSW) — 7 design categories with price ranges
  • Master Granny Flats (NSW) — Floor plans with price ranges by bedroom count
  • Backyard Grannys (NSW) — 6 designs with published prices
  • Bungalow Granny Flats (NSW) — 8 custom designs with realistic cost ranges
  • Granny Flat Builders Sydney — Price guides with cost breakdowns
  • Premier Homes VIC — Range pricing for prefab models
  • Todd Devine Homes (VIC) — 7 exact models with prices
  • SKL Granny Flats Melbourne — Detailed component-level cost breakdown

State government sources

  • NSW: Environmental Planning and Assessment Act 1979, SEPP (Housing) 2021, BASIX requirements
  • VIC: Victorian Building Authority, Planning and Environment Act 1987, Small Second Dwellings provisions (Dec 2023)
  • QLD: Dwelling House Code, Planning Act 2016, council infrastructure charges
  • WA: Planning and Development Act 2005, April 2024 granny flat reforms
  • SA: Planning, Development and Infrastructure Act 2016, 2023-2024 ancillary dwelling reforms
  • TAS: Building Act 2016, Land Use Planning and Approvals Act 1993, SPP Amendment 01-2026

How we maintain accuracy

  • Builder pricing is refreshed quarterly from published websites
  • State regulations are updated when legislative changes are gazetted
  • Connection cost benchmarks use the most recent published builder packages
  • All cost adjustments are documented in our methodology

Last updated: April 2026. If you notice outdated information, please let us know.