Granny Flats & Secondary Dwellings Cost Guide & Council Planning Rules (2026)
Detached secondary dwellings, modular prefabricated granny flats, studio conversions, and dual-occupancy builds.
Material Pricing & Longevity Comparison
Supply and installation brackets for common residential specifications in Australia.
| Material Option | Installed Range (per m²) | Expected Lifespan | Description & Best Application |
|---|---|---|---|
| Modular Flatpack / Prefab (1 Bed, 30-40 sqm) | $1800 –$2400 | 30+ yrs | Factory-built steel chassis modular pods. Fast assembly on pier foundations. |
| Standard Turnkey Build (2 Bed, 60 sqm) | $2400 –$3200 | 50+ yrs | Complete slab-on-ground brick veneer or clad construction including bathroom/kitchen. |
| Architectural Custom Design (60 sqm) | $3200 –$4500 | 60+ yrs | High-end timber cladding, raked ceilings, double glazing, and premium finishes. |
State & Territory Exemption Thresholds
Select your state to view development approval exemption triggers under local planning schemes.
Secondary Residence: Minimum block size 500 sqm; Floor area 40-90 sqm
Complying Development (CDC): Max 60 sqm on lots >= 450 sqm with >= 12m frontage
Independent unit up to 50-80 sqm (depending on lot size and zone)
Self-assessable up to 70-80 sqm (depending on local planning scheme)
Ancillary Accommodation: Subordinated to primary dwelling; up to 60-70 sqm
Ancillary Dwelling: Floor area <= 60 sqm on residential lots
Building Permit only: Gross floor area <= 60 sqm on lots >= 300 sqm with no planning overlays
Ancillary Dwellings: Max 70 sqm on lots >= 350 sqm with no planning approval needed
Calculate by Local Government Area (LGA)
Select your council area for interactive dimension calculators and local certifier checklists.