Soil testing for new homes: don’t build until you read this!
The most crucial and fundamental of steps when looking to build a new home is knowing and understanding the ground in which your home will be built on. This understanding comes in the form of a Site Classification Report and is paramount in ensuring that your home is designed and built to stand the test of time. This standard process will be coordinated by your builder once you have chosen a design and are ready to proceed. But, by being even more prepared – testing the soil even before you sign your land contract – you could potentially save yourself thousands of dollars and a lot of heartache if your chosen block has unexpected challenges hidden below the surface.
In the early stages of designing your home and once the position of the dwelling is finalised, a qualified Soil Tester will be commissioned by your builder to visit your block of land to carry out a site investigation. This involves drilling down into the ground at certain points across your land under where your house slab is to be positioned with hydraulic or hand-driven augers and recording the type and composition of the soils at different depths below the surface.
Note that the accuracy of the investigation is extremely important and this is why it’s ideal to have this carried out once the positioning of your home has been established, so the field results directly correlate to the soils underneath the proposed construction.
A Site Classification Report (also referred to as a Soil Test Report) contains all the findings of the site investigation and will provide all the necessary details for your builder and engineer to determine the best design for the slab and foundation of your home. Those necessary details will include, but are not limited to, the following information:-
- Soil Reactivity and Moisture Levels – Soil reactivity refers to how much the soil on your block of land is likely to move whether by expanding, contracting, shifting or settling as a result of moisture changes in the soil.
- Soil Composition and Fill Depth – This will explain how much and what type of fill has been used to level the land, and how strong the bearing capacity is of the soil.
- Soil Classification – The reactivity, moisture levels, capacity and substrate materials are all broken down into categories for easy understanding:-
- Class A: Stable, non-reactive. Most sand and rock sites. Little or no ground movement likely as a result of moisture changes.
- Class S: Slightly reactive clay sites. May experience slight ground movement as a result of moisture changes.
- Class M: Moderately reactive clay or silt sites. May experience moderate ground movement as a result of moisture changes.
- Class H: Highly reactive clay sites. May experience a high amount of ground movement as a result of moisture changes.
- Class E: Extremely reactive sites. May experience extreme amounts of ground movement as a result of moisture changes.
- Class P: Problem sites. The ability of the soil to evenly bear a load is very poor. Sites may be classified as ‘Class P’ as a result of uncontrolled fill, rock, mine subsidence, landslip, collapse activity or coastal erosion or some other issue associated with the soil. Ground movement as a result of moisture changes may be very severe or within one of the classifications above.
- Wind Classification – A good report will even identify the wind rating required by the truss manufacturers to design your truss layout, bracing and tie-down for your home.
Why is this important and how is this information used?
Remember: No two blocks of land are the same and your block may very well be different to your neighbours.
With no way of knowing what has happened during the subdivision and civil works or the reactivity levels of the soil itself, to not have a Soil Test Report completed to help identify the potential for unforeseen circumstances is a risk that could severely affect the overall design of your home, and especially the cost of building your home.
To eliminate the possibility of detrimental situations occurring, the Engineer will review the findings identified in the Soil test Report to understand the density, materials and possible expansion or settlement levels of the soil in order to design the most suitable footings and slab solution for your home. The Builder will use the report, as well as the slab design provided by the Engineer to verify the requirements of the site works and calculate the cost to construct the slab and foundations of the new home.
Even if you have not decided on a house design for your land it is always prudent to make the land purchase contract subject to a satisfactory soil test and report. An engineer can carry out a preliminary soil test and report on any land and a builder can then assess the report and give a prospective purchaser feedback on the findings of the report and if this will affect the house slab requirements and give rise to additional costs. This way you have an avenue to terminate the contract if the soil report discovers some adverse soils which may cause issues and costs for your new home. This won’t negate the need to have a full investigation and report completed once the siting of your home is confirmed, but may assist in your consideration to purchase the land.
At Ownit Homes, we believe that building a beautiful and enduring home starts from the ground up. If you would like further information on our building process, feel free to contact us or visit any of our Building Consultants.