The Significance of Soil Examination in Home Construction
Building a new home is a major undertaking. As floorplans grow and block sizes shrink, builders are placing increasing importance on solid engineering and stable footings.
Soil testing is one of the most significant factors when building a new home. The soil you build on can have a major impact on the stability of a building, and improper construction can lead to critical failures.
In most Australian jurisdictions, soil tests are a requirement for obtaining building approval. In this article our expert house builders in Brisbane we will explore why this is the case and discuss the significance of soil examination and classification.
Why Soil Type Matters in Home Construction
The soil on your property can dramatically affect the long-term stability of anything you build. Different types of soil react differently under the footing of a building. They also have varying reactions to moisture, temperature and shifts in the ground.
Soils that are very reactive to these factors can be problematic for construction projects. They may be prone to erosion, poor drainage or excessive movement. This can cause the foundations of a building to crack or collapse, and repairing those issues is often incredibly costly.
In modern construction, we test soils to verify the long-term stability and safety of your property. If we don’t, issues with the soil that affect the foundation could lead to critical failures and serious injury.
How Soil Types are Classified
In Australia, soil classifications are laid out in AS2870-2011 – “Residential slabs and footings – Construction.” The Australian Standards set out a number of guidelines for designing footings based on the soil classification. These footing designs take into account three major factors:
Under AS2870, soil receives a letter grade – A, S, M, H, E, P. A and S class are suitable for normal slab construction. Soils with a higher reactivity (H to P) need to be evaluated by an engineer, and they may require compaction or earthworks during site preparation.
The residential footing code provides more detail on these soil classifications:
|A – Acceptable||Little ground movement due to moisture changes (sand and rock)||0mm|
|S – Satisfactory||Slightly reactive, slight movement with moisture change (clay)||0-20mm|
|M – Moderately Reactive||Moderate site movement due to moisture change||20-40mm|
|H – Highly Reactive||Highly reactive to moisture change (clay)||40-60mm|
|E – Extremely Reactive||Extreme reactivity due to moisture change (clay)||60-75mm|
|P – Problem||Soft soils, silt, loose sand and soft clay – sites that may collapse, soils that are likely to erode, sites with abnormal moisture conditions||N/A|
Factors Affecting Soil Classification
The letter grade recorded in your soil report is obtained by taking several samples from across the property. Samples are assessed in a lab to determine their composition, bearing capacity and other factors, such as:
When Should Soil Testing Be Conducted?
Soil tests are usually carried out before construction commences. Engineers may also order soil testing during construction to check changes in the surface, modify build plans or to verify that construction has been completed properly.
In an ideal scenario, home buyers should conduct soil testing during the purchase phase. If a buyer intends to build on a property, paying for a soil test will verify that the block is suitable, which can save significant expense during construction.
There’s no need to specifically avoid properties with reactive soils – in some cases, those issues can be addressed with simple engineering changes. However, having this information up front can help budget for additional earthworks and footings expenses, rather than incurring those costs unexpectedly.