What the Berkeley report actually describes
The soils are shallow and stony on the crests, under 50 cm, then deep red and brown krasnozems and red podzolic soils on the mid and lower slopes, reaching up to two metres. Then comes the sentence that tells you the most: those soils grade "into Yellow Podzolic Soils (Dy4.41) in areas of poor drainage". The report is telling you that drainage is poor often enough on this unit to have changed which soil formed there. Individually, its soils bk1 through bk4 all carry "Moderate shrink-swell potential", one is noted as locally sodic, and its landscape limitations include "Moderately to highly reactive soils" alongside "Seasonal waterlogging (localised)".
Two properties, then, arriving together: material that changes volume with moisture, and drainage that does not readily remove the moisture. They are not independent problems. Water is the trigger for the movement, so a base without an outlet does not merely pond, it feeds the mechanism that lifts the lawn.
The rest of Figtree is not a soft option
It would be convenient if the other 79.4 per cent of the suburb were simple. It is not. The Gwynneville share brings shallow mid and lower slope soils with a gw3 subsoil rated "Low permeability", and a summary limitations line describing "Reactive subsoils and impermeable, low wet bearing strength clay subsoils", which we always pair with the fact that the same report's reactivity section says the materials "vary from stable to slightly reactive". The escarpment share brings slope and colluvium whose reactivity section warns that movement "may be set off by poor drainage". The fill share brings unpredictability. The alluvial share brings a seasonal water table.
There is no combination of those where the answer is to skip the base and lay turf on graded soil. Our guide to reactive soils and impeded drainage under Figtree lawns works through each mechanism in turn, and explains why four of the five things that fix them are earthworks.
Getting a Figtree job specified properly
On this ground, the useful comparison between quotes is not the per square metre rate. It is what each quote says below the grass line. Look for an excavation depth in millimetres and a reason for it; a named base material rather than the word base; a compaction method and a number of passes; the words that describe where water leaves and where it goes; and an edge restraint detail. If two quotes differ by a third and only one of them names those five things, you are not looking at the same job.
Roughly 40 per cent of a residential job is materials, 30 per cent base preparation and 30 per cent labour, which is set out with the published tier pricing in our guide to what a Figtree lawn costs per square metre. The build sequence itself is on the Illawarra installation page, applied to Figtree ground.
Figtree: reactive ground, plainly answered
Is Figtree really the most reactive ground in the Illawarra?
One fifth of it is, and that fifth is the most reactive ground mapped anywhere in this set. The Berkeley unit covers 20.6 per cent of Figtree, and its Surface Movement Potential section is a single sentence: 'Highly reactive soils.' No other Illawarra unit's report uses that wording, and we do not extend it to any other unit. Its limitations line also names 'reactive subsoils' and 'Locally impeded drainage', and its landscape limitations include 'Seasonal waterlogging (localised)'.
What does highly reactive mean for a lawn, as opposed to a house?
Under a house it is a footings question and it is governed by AS 2870, which classifies building sites by soil reactivity. That standard has nothing to say to a turf installer, and anyone citing it at you in a landscaping quote is padding. Under a synthetic lawn the same soil behaviour shows up as a levels problem: the ground swells and shrinks unevenly with moisture, and a flexible sheet pinned at its edges reproduces every one of those movements as a dip or a ripple, permanently, because nothing is growing to mask it.
Why is there fill in Figtree too?
Disturbed Terrain covers 9.9 per cent of the suburb, which is a smaller share than Unanderra's 47.3 per cent but well above nothing. It is ground where 'The original soil has been removed, greatly disturbed or buried', and the report is explicit that its limitations depend on what the fill happens to be. There is no reactivity rating published for it on either Illawarra map sheet, so we do not give one.
Can a good product compensate for reactive soil?
No, and it is worth being blunt about it because this is where money gets wasted. Pile height, yarn shape, backing chemistry and infill decide how a lawn looks, feels, drains at the surface and holds up in ultraviolet light. Not one of them changes the volume of a clay subsoil or gives trapped water somewhere to go. Those are ground problems with ground solutions: excavation depth, base material, compaction and a drainage exit.
What about the nature strip in Figtree?
Wollongong City Council publishes nothing specific about synthetic turf on the verge. Its Verge Garden Guidelines were read in full and never use the words artificial or synthetic. They do say 'Do not install any structures or hard surfaces in your verge garden' and require a 1500mm-wide level pedestrian strip and 600mm of clearance from the kerb. Works on the verge generally need Council approval because it is public land. Ask first, and note that none of it applies inside your fence.
Does a warranty cover me if the lawn moves?
Usually not, and this is the strongest financial argument for spending on the base rather than the grass. Australian warranties typically run 8 to 15 years and generally cover ultraviolet degradation and fibre loss. Base failure is commonly excluded, along with pet damage and flood. On ground the government describes as highly reactive with locally impeded drainage, the layer most likely to fail first is the layer the warranty does not cover. Ask to see the exclusions in writing before you choose on warranty length.
The suburb the government calls highly reactive deserves a specified quote
Send the space, the area and what it will be used for. A single vetted local installer will look at the ground, then price it in writing. Free, without obligation, and with the base itemised rather than assumed.
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