Truganina ground: basalt clay, slab design and why houses crack
Truganina lies on the volcanic basalt plains of Melbourne's west. Subsoils across these plains are commonly clays that shrink and swell as they dry and wet, which is why footing design and site drainage matter so much here.
What the ground is made of
Regional soil mapping describes the Werribee plains as basalt derived soils, often with heavy clay subsoils that crack deeply when dry. Basalt rock can sit close to the surface in places. The soil report for your own lot is the only reliable guide to what is under it.
Site classification
Under AS 2870 a geotechnical engineer classifies each lot by how much its ground is expected to move. The class sets the slab design. We never assume a class for a Truganina lot; it is on your soil report and engineering.
Why slabs are stiffened
On moving clay, slabs are designed with deep, closely spaced beams so the house rides the movement as a unit. That only works if beams, stems and reinforcement are built as drawn, which is what a slab inspection checks.
Water is the trigger
Uneven wetting is what makes clay move unevenly: a leaking downpipe, condensate dripping at one spot, a garden bed watered against the slab, or ground that falls towards the house. Keeping moisture even around the slab is the owner's part.
Reading cracks
Hairline cracks in plaster and minor brick cracks are common as a new house settles. Wider cracks, cracks at window corners and slab cracks beyond tolerance need measuring and sometimes an engineer.
More about Truganina
- Building a new home in Truganina: stages, sites and common faults
- Buying a house in Truganina: prices, housing age and what to check
- Truganina's growth: precinct plans, population and what is still coming
- Permits, councils and building disputes in Truganina
- Termite and timber pest risk in Truganina
- What our inspectors find in Truganina homes
- Truganina site conditions: water, wind and planning overlays
Written by our local inspection team from work carried out in Truganina. Licensed building practitioners, Building & Plumbing Commission registration CDB-U 53425.
