Reactive Soil Explained: H1, H2 and E Classifications
H1, H2 and E aren’t just letters on a soil report — each represents a genuinely different level of ground movement your foundation needs to be designed to handle.
The Reactive Classification Scale
Under AS 2870, reactive classifications form a progression — from Class S (slightly reactive) and M (moderately reactive) through to H1, H2 and finally E, representing increasing levels of expected seasonal ground movement due to soil moisture change. Each step up this scale generally demands more robust foundation design.
Class H1: Highly Reactive
Class H1 sites have highly reactive soil, exhibiting meaningful seasonal expansion and contraction. This classification is common across parts of Melbourne’s clay-affected suburbs and typically drives toward a waffle slab or similarly designed foundation system capable of accommodating this level of movement.
Class H2: Very Highly Reactive
Class H2 represents an even greater degree of expected ground movement than H1 — common across significant parts of Melbourne’s western and northern basaltic clay growth corridors. Foundation design for H2 sites needs to account for correspondingly greater movement tolerance in the structural system.
Class E: Extremely Reactive
Class E is the most severe reactive classification under AS 2870, representing extreme expected ground movement. Sites with this classification require particularly robust, carefully engineered foundation solutions, since the movement being designed for is more significant than any of the preceding classes.
How These Classifications Drive Design
Across H1, H2 and E, the general foundation response is similar in kind (typically a waffle slab or, for more extreme cases, additional measures like deeper footings) but different in degree — the specific slab design, rib depth and reinforcement all scale to genuinely match the expected movement for your site’s actual classification, not a generic “reactive soil” assumption.
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Frequently Asked Questions
What's the difference between H1, H2 and E classifications?
They represent increasing levels of expected seasonal ground movement due to soil moisture change, with E being the most extreme, each requiring correspondingly more robust foundation design.
Does H1 need the same foundation as H2?
Both typically point toward a waffle slab or similar system, but the specific design (rib depth, reinforcement) differs to match the different levels of expected movement.
How do I know if my site is H1, H2 or E?
A site-specific geotechnical soil report determines your exact classification — this shouldn’t be assumed from general area knowledge.
Is Class E the worst possible classification?
Among the reactive classifications, yes, it represents the most extreme expected movement — Class P (problem sites) identifies different complicating factors rather than reactivity level alone.
Can a highly reactive site still be built on safely?
Yes — the vast majority of Melbourne’s reactive clay areas, including H1, H2 and E sites, are built on successfully every year using correctly engineered foundation systems.
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