Building your own home is an exciting journey! Having the chance to design all the little features you’ve been dreaming of is a lot of fun. It’s easy to get lost in that process though, and most people aren’t particularly worried about things like soil classification. It might seem like a minor detail, but your builder will need soil testing results before work can even begin. In this article, we’ll be exploring more about the role of testing and soil classification in the new home build process.
The Role of Soil Classification in Building
Soil classification and ground features play a major role in building projects. In your hunt for the perfect block, it’s easy to focus on things like orientation and slope, but the quality of the soil isn’t always so apparent. Before you get too excited by a property, it’s worth having the soil tested. A professional tester can take samples from a block to develop a soil classification that will inform your new home’s slab, footing and engineering requirements.
What Are the Soil Classifications?
Because soil plays such an important role in the building process, soil classifications are laid out in AS2870 by the Australian Government. Soil is typically classified based on how reactive it is. Soils that are prone to movement (such as after it rains) are considered more reactive and they may need additional preparation work before building. According to AS2870, the soil classifications are as follows:
| Site Classification | Surface Movement | Description |
|---|---|---|
| A | – | Sandy or rocky sites that show almost no movement due to changes in moisture. |
| S | 0mm to 20mm | Mildly reactive clay sites that show slight fluctuations due to moisture. |
| M | 20mm to 40mm | Moderately reactive clay sites that show middling amounts of ground movement. |
| H1 | 40mm to 60mm | Highly reactive clay sites that are prone to lots of movement. |
| H2 | 60mm to 75mm | Highly reactive clay sites that demonstrate lots of movement. |
| E | 75mm or more | Extremely reactive sites. |
| P | – | Problematic sites, usually composed of soft sand, silt or filled material. P grade sites often have abnormal water conditions. |
What Are the Soil Classifications?
Because soil plays such an important role in the building process, soil classifications are laid out in AS2870 by the Australian Government. Soil is typically classified based on how reactive it is. Soils that are prone to movement (such as after it rains) are considered more reactive and they may need additional preparation work before building. According to AS2870, the soil classifications are as follows:
Testing and Classification of Soil
Classification of soil is a compulsory part of the construction process in Queensland. During a soil test, a geotechnical engineer will visit the site and use a hollow drill to take cylindrical samples from the ground. These samples show the soil composition and what’s happening underground, and they allow the geotechnical engineer to develop a soil report for your builder. When preparing land for a new home build, it’s important to take soil samples from all over the block. Soil classifications can vary from one part of your land to another, so taking a single sample won’t provide the information builders need.
Other Soil Classification Factors
Geotechnical engineers determine soil classification based on how reactive the ground is. While that plays an important role in how the foundations of your home are designed, builders will also test other factors:
- Erosion. Highly reactive soils tend to absorb lots of water, which often leads to erosion. Soil erosion causes major shifts that may crack your foundations, so your builder will need to take extra precautions to prevent erosion.
- Load Bearing Capacity. The ground beneath your foundations needs to be capable of bearing the weight of your home. It’s possible for soils to have low reactivity but also low bearing capacity. If that’s the case, the soil will need additional compaction treatments to make it suitable for building.
- Seasonal Shrinkage. Prolonged rainy or dry seasons also need to be accounted for when designing foundations. Excessively wet soil can swell and damage footings, while very dry soils can shrink away from the slab and compromise its support. In areas that are prone to seasonal shrinkage and swelling, engineers often use additional drainage to reduce the impact of changing soil conditions.
Getting Ready to Build Your Own Home? Contact McCarthy Homes for Inspiration!
The process of a knock down rebuild or building a custom home can be highly involved. With thousands of little details like soil classifications and engineering to worry about, it’s important to work with reputable Hampton style builders. If you’re ready to build but need someone to take the hard work out of the process, start a conversation with McCarthy Homes! McCarthy Homes is a bespoke house builder working throughout the Brisbane region. We specialise in designing incredible properties that deliver all the stunning lifestyle features our clients need. When you build with us you’ll have access to leading designers and trades who can take care of the little details like soil testing and classification. Contact us today if you’d like to find out more about building with McCarthy Homes!
