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What is the difference between H1 and H2 slab classification?

H1 indicates a high reactivity soil, requiring a stronger slab design. H2 indicates very high reactivity — more reinforcement and engineering is required. Both sit above the standard M class.

How do I find out my soil classification?

A geotechnical engineer performs a soil test on your land and produces a site classification report. This is usually required before your building permit is issued.

Does an H2 classification cost more?

Yes. An H2 slab requires more steel reinforcement, deeper footings and a more complex engineer design. Expect $5,000–$15,000 more than an H1 slab.

Can I get finance if my land is H2 classified?

Yes. H2 classified land is very common in Queensland and Victoria. Lenders generally treat it the same as M or H1 — the classification affects building costs, not lend-ability.

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Home›Build Knowledge Hub›Building Process›Slabs & Siteworks›H1 vs H2 Slab Classification

Slabs & Siteworks

H1 vs H2 Slab Classification

What the H1 and H2 soil classifications mean for your slab, your build cost, and what your builder must include.

4 min·Compare My Build — Independent Resource· Updated June 2025

Introduction

Australia uses a site classification system (AS 2870) to categorise how reactive the soil is beneath a new home. The classification determines the type of slab required and directly affects your build cost. H1 and H2 are the two "high reactivity" classifications — both require more engineering than the standard M class site.

Key Differences

Feature	H1 Class	H2 Class
Soil reactivity	High	Very High
AS 2870 movement	40–60mm	60–75mm
Typical slab	Reinforced raft slab	Heavy raft or piered slab
Cost vs M class	+$5,000 – $12,000	+$10,000 – $20,000+
Common in	Many QLD and NSW sites	Expansive clay soils, some SEQ
Requires engineer	Yes — specific design	Yes — more complex design

Pros and Cons

Pros

+ Both classifications result in a properly engineered, structurally sound slab
+ Modern H1/H2 slabs perform well when designed and built correctly
+ Knowing your classification upfront avoids budget surprises
+ Engineers design site-specific solutions for H1/H2 conditions

Cons

− H1 and H2 slabs cost significantly more than M class
− Many builder base prices assume M class — H1/H2 incurs extras
− Delays possible if geotechnical report is not ordered early
− H2 sites may require additional drainage or moisture management

Cost Comparison

M class slab (waffle pod)$8,000 – $14,000

H1 class slab (raft)$13,000 – $22,000

H2 class slab (raft/piered)$18,000 – $35,000+

Site classification report (geotech)$500 – $1,500

Always get a geotechnical report before signing a building contract. Slab costs can vary by $10,000+ depending on classification.

Common Builder Inclusions

›Most volume builder base prices are based on M class (flat, reactive) sites
›H1 or H2 site upgrades are almost always charged as site costs on top of the base price
›Some builders include an H1 slab allowance but not H2 — always check the contract
›Site classification reports are usually the buyer's responsibility to arrange

Watch Out

Never sign a building contract without first knowing your soil classification. If the report comes back H1 or H2 after signing, you'll be required to pay additional site costs that weren't in your original quote.