Why do I need a Soil Test before Building?
There’s more to a soil test than meets the eye. Soil testing is an integral stage of your home build. It’s important to understand that the composition of your soil may affect structural details relating to your home’s foundation, which can significantly impact on the cost of your build.
So, let’s go back to basics and work from the ground up (excuse the pun!).
Foundations are Important
The foundation of your home is of all importance. The foundation must be perfect for the home to last, both structurally and aesthetically. The characteristics of the soil on your home site could dramatically influence structural details such as the strength and depth of the foundation required for your home to be supported sufficiently. Compromising or slackening off on the foundations can have serious repercussions down the track: surface cracking, water-tightness, pest control problems, general usage and comfort issues such as doors jamming etc. are all problems that will likely present themselves. In the worst-case scenario, a home with a dodgy foundation will become structurally unsafe.
Soil is a glorious mixture of minerals, organic matter, gases, liquids and living organisms. The varying ratios of these ingredients is what determines the soil type – thick, sticky orange clay; hard, rocky soil; dry, sandy soil or wet, muddy soil that literally moves in waves underfoot! Believe us when we say we’ve worked with a huge array of soil types and understand what’s involved in building on various sites!
Anyone visiting your site could give a basic appraisal of the soil (e.g. color, whether it’s wet or dry underfoot, whether it has cracks in it or is sandy) but it takes a professional to give a detailed analysis that can be used to determine the type of footings your home will require.
Who Conducts the Soil Test?
Soil tests are performed by a qualified Geotechnical Engineer, who is a person with qualifications in both geology and engineering. The geotechnical engineer visits the site and uses specialized equipment to bore holes in various positions, then he/she takes away the soil samples and tests them.
The soil is tested for several different things which essentially determine the soil’s capacity to support the weight of your home. Some of the factors the geotechnical engineer will assess include:
- Amount of sideways movement within the soil
- Bearing capacity (the amount of weight the soil can support, and how much it sinks)
- Moisture content
- How well the soil stays together (i.e. is yours a dry sandy soil that doesn’t stay together at all, a hard, sticky clay or something in between?)
- Presence of rock (does the soil contain a lot of large or small rocks, or is there sheet rock beneath the home site?)
- Mining – is it an old mining site?
- Underground water flows – is there a substratum of water beneath the site?
- Previously filled site – how long ago was the site filled? What was used to fill the site?
The soil is then classified into one of the following categories:
- A – non-reactive or stable soil
- S – slight movement
- M – moderate movement
- H – highly reactive (clay sites)
- E – extreme movement
- P – problematic soil (e.g.: filled sites, landslip danger, mining etc.)
The engineer drafts a report in which the different features of the soil are given in measurements (e.g.: the sideways movement of the soil is measured in “y’s” and the bearing capacity is measured in “kpa”). This report is then used by a structural engineer to design the relevant footings for your home.
Soil Report and Structural Design
The soil report contains vital information needed to design the right type of foundations for your new home. A structural engineer uses the report to determine the stability and bearing capacity of the soil, then specifies the depth and width of the footings required to support the home. Extra precautions may need to be taken if your soil is found to be sandy and unstable or damp and swampy.
In Victoria, the soil test is required before the local authorities will grant a building permit.
Who Arranges my Soil Test?
At Hensley Park Homes, we organize your soil test for you. Our admin staff arrange for a geotechnical engineer to visit your site and take soil samples, then we handle all the paperwork and technical details so that you can sit back, relax and enjoy your home building experience!
Your soil test is a valuable and necessary part of the construction process. It provides essential information that will affect the foundations of your house, and ultimately the aesthetics and comfort of your home. For more information on your soil test, phone us on 1800 01 05 09.