Granny Flat Slab Adelaide — Engineer Spec, Costs & Council Approval

Intro — Secondary dwelling approvals have doubled in Adelaide metro since 2022. The slab is the most technically complex part.

What makes a granny flat slab different from a shed slab?

• Habitable structure: AS 2870 soil classification required
• NCC Section H requirements for habitable floors
• Engineer-designed — not standard formwork

The soil classification step (AS 2870 — A/M/H1/H2 classes across Adelaide)

Cost guide 2026

• Class M slab (30 m²): $4,500–$7,500
• Class H1 slab (30 m²): $5,500–$9,000
• Class H2 slab (30 m²): $7,000–$11,000
• (Includes excavation, engineer's design fee, concrete, inspection)

Council approval steps — Development SA lodgement, 30-day typical timeline

Case study preview — Elizabeth, AS 2870 Class H2, 150 mm edge beams, 3-day preparation + 1-day pour (links to Case Study 5 when published)

Our role — we pour from the engineer's certified drawings; we do not design (important trust/liability note)

CTA — Free on-site assessment; we can recommend structural engineers

Internal links: /concrete-slabs-adelaide, /services/concrete-slabs/elizabeth, /blogs/concrete-slab-cost-adelaide, /about-us