Understanding Your Site Classification Report and Soil Test Results

By Matt Rohde | August 4, 2025

Aerial view of a construction site where foundations are being actively poured, showcasing the preparation and outlining of the building's footprint.

Building a new home is a significant investment, and understanding your site classification report and soil test results is a critical first step to ensure a strong foundation. At Yellowwood Building

Group, we guide Australian homeowners through this process to make informed decisions for their new home builds. Here’s what you need to know about these essential reports.

What is a Site Classification Report?

A site classification report, mandated under the National Construction Code (NCC) in Australia, assesses the soil and site conditions to determine the type of foundation required. It’s typically conducted by a geotechnical engineer and classifies your site from A to S based on soil reactivity and stability.

• Classes Explained:

  • Class A: Highly stable, minimal movement (e.g., rock or sand sites).

  • Class E: Extremely reactive sites with high clay content, prone to significant expansion or contraction.

  • Classes P, M, H, S: Vary from slightly reactive to highly reactive, depending on moisture changes.

• Why It Matters: The classification dictates foundation design, impacting costs and construction methods. For instance, a Class H site may require deeper footings or special slabs compared to a Class M site.

  
  

Decoding Soil Test Results

Soil tests accompany the site classification to provide detailed data on soil composition, bearing capacity, and moisture levels. These results help engineers design foundations that withstand local conditions.

• Key Elements:

  • Soil Type: Identifies whether your site has sand, clay, loam, or a mix, affecting stability.

  • Bearing Capacity: Measures how much weight the soil can support (e.g., 50–150 kPa for most residential sites).

  • Moisture Content: High moisture can lead to swelling clays, while dry conditions may cause shrinkage.

  • Contaminants: Checks for hazards like acid sulfate soils or fill material.

• Why It Matters: Accurate soil data prevents issues like cracking or uneven settling. For example, a site with high clay content may need moisture barriers.

  
  

How to Use These Reports

1. Consult Experts: Work with your builder and geotechnical engineer to interpret the data. Yellowwood Building Group collaborates with specialists to tailor solutions.

2. Plan Your Foundation: Match the design to the site class—e.g., reinforced slabs for Class E or pier-and-beam for Class S.

3. Consider Drainage: Poor drainage can worsen soil movement. Plan for 1–2% slope away from the house and install subsurface drains if needed.

4. Budget Accordingly: Reactive sites (e.g., Class H or E) may increase foundation costs by 20–40%, so factor this into your planning.

   
   

Common Challenges and Solutions

• Challenge: High reactivity (Class H or E) causing foundation movement.

  • Solution: Use waffle pod slabs or adjustable piers to accommodate soil shifts.

• Challenge: Poor drainage leading to water pooling.

  • Solution: Install 100mm agricultural pipes with gravel trenches to redirect water.

• Challenge: Unstable fill material.

  • Solution: Remove and replace with compacted, stable soil to a depth of at least 0.5 metres or implement deeper piering to a solid founding material.

    
    

Why Choose Yellowwood Building Group?

At Yellowwood Building Group, we turn complex site data into actionable insights. Our team ensures your home’s foundation is built to last, complying with Australian standards and leveraging the latest 2025 construction techniques. From initial soil testing to final design, we’re with you every step of the way.

Ready to build on solid ground? Contact Yellowwood Building Group today to understand your site classification and start your dream home project.

Matt Rohde - Yellowwood Building Group – Building Your Future, One Foundation at a Time.