What You Need To Know About Soil Types

What You Need To Know About Soil Types

A builder’s guide to soil types

Soil types are extremely important to consider when building a new home, as foundations need to be on stable and strong soils.

Some soils are able to support a large dwelling or a skyscraper, while others are barely able to support the weight of a human.

The earth under your home is the foundation for your building, it could have an impact for your home over its lifetime. Therefore, it is important to have the soil engineered and certified by professionals.

We chat to Stroud Homes Brisbane South Residential builder Peter Simpson to find out all you need to know about different soil types.


What are the different types of soil?

Generally, there are six different soil classifications, starting off at Class A and finishing with E.

  • A – Acceptable
  • S – Satisfactory
  • M – Moderately Reactive
  • H1  & H2 – Highly Reactive
  • E – Extreme
  • P – Problem site (usually as a result of trees on site)

Stroud Homes can build on any type of soil, but some types will result in a more complicated, and therefore more expensive, build.


How much is a soil test and how long does it take?

Having your soil tested with Stroud Homes Brisbane South Residential costs $462, and we do not make any money off these tests.

A soil test is required for the builder to give you a fixed priced quote, as they need to determine which slab type to quote you for.

Each block of land must have its own soil test completed as the reactivity of the soil can change from block to block. This could be a result of how estate developers have shaped their land. For instance, one block might be sitting on rock, where as the block next to it was levelled using fill, thus making it more or less reactive than its neighbouring blocks.

Once paid for, two to three bore holes are drilled on your site (usually 2m down) and soil samples are removed and taken to the laboratory for testing. This process will take seven to ten days.


What slab to use on what soil type?

The Structural Engineer plays an important role in making the final decision on what type and size of slab will be used based on the results of your soil test. Generally the more extreme the soil type, the thicker and stronger the slab and foundations must be:

  • Soil types of A, S, M, H1 & H2 – these have the typical specification of ‘nominal/standard waffle design’.
  • Soil types of E – the engineer usually recommends using a conventional stiffened raft slab with ground beams.
  • Site types of P – are looked at on a case-by-case basis as no two sites will be the same. They may determine a need to have concrete piers into the ground.

However, no matter what your soil test comes back as, Stroud Homes Brisbane South Residential can build your dream home on that block.


How much does the soil type affect the cost of my home?

Example: Why does a H1 class slab cost more than an M class slab and what are the differences between an M class and H class slab?

The additional cost for an H1 slab vs an M class slab and the differences are as follows:

  • N16 reinforcing steel in lieu of N12/N11 for the trench mesh and rib mesh.
  • SL92 sheet mesh in lieu of SL82 for the slab portion and 300mm pods in lieu of 225mm pods (these are more expensive, but more importantly take a lot more concrete).
  • More concrete in ribs, trenches and thicker slab. Highly probable that deeper and more piers are required.
  • Additional row of bricks required due to the brick rebate on H1 slabs vs M slabs.


Ask us!

The team at Stroud Homes Brisbane South Residential can organise a free site inspection prior to your purchase, give you advice on the area, and arrange soil testing to be carried out.

Once the classification report is received it will be used to plan building site preparation and provide site-specific information to assist in appropriate foundation design.

Peter  Simpson
Peter Simpson

Ask us about building your new home