The Home Builders Guide to Soil Types 2025

Article Overview

Soil Classification | Soil Class Types | Uncommon Soil Circumstances | Soil Test Kits

Guide to Soil Types

Soil type might not seem like the most obvious consideration when building a home. But the reality is, it’s crucial. The type of foundation you lay your house upon can have an impact on the stability and security of that house for decades to come. At Prime Building Projects we’re committed to the quality of our projects from concept to completion of the building process. We want the best for you each step of the way. That includes taking into consideration your soil and how it will affect the goal of building your dream home.

The Mornington Peninsula is a wonderful place to build a life. Our registered builders and tradies are locals who know the area intimately, including its soil, and can offer you their expert advice. We’ve already built comfortable and luxurious homes all over the Peninsula, and we have the skills to assess your soil situation and work with it.

There may be a number of questions on your mind. Why is my soil type important? What are the different categories of soil? Is my soil type the same as my next door neighbour’s? This blog post should clear up any confusion and bring you some answers.

Water and Reactive Soil

Having “reactive” soil doesn’t mean the soil is defective. Instead, it refers to the soil’s propensity to react to moisture changes in its environment. Reactive soil can expand, shrink, or shift depending on the amount of water present. This movement is a natural characteristic of all soils, as they have the potential to change volume based on their composition and surrounding moisture levels.

The degree of soil reactivity is a critical factor in construction. It determines how much movement is likely to occur and what measures are necessary to mitigate potential risks. Some soils, like sandy or rocky types, exhibit minimal reactivity and remain stable even with fluctuating moisture levels. Others, such as clay-rich soils, are highly reactive and can cause significant ground movement, requiring specialised engineering solutions to ensure structural stability.

When building on reactive soil, understanding its classification is key. For example, low-reactivity soils (Class A and S) might only need standard foundations, while highly reactive soils (Class H1, H2, and E) demand advanced techniques such as deep footings, moisture barriers, or soil stabilisation. Additionally, proactive site management, such as maintaining proper drainage systems and controlling vegetation, can help manage the effects of soil reactivity.

Importantly, soil profiles can vary even within a small geographic area. This means the soil on your property may behave differently from your neighbour’s, underscoring the need for site-specific soil testing. A thorough assessment provides the insights required to design foundations and structures that can withstand the challenges posed by reactive soils.

Soil Types Guide – Soil Classification

There are six categories of classification based on soil reactivity:

Understanding soil reactivity is essential for ensuring the stability and safety of construction projects.

Soil Class Types – Six Categories of Soil Reactivity

Here are the six categories of soil classification based on their reactivity:

SOIL TYPE 1: CLASS A – ACCEPTABLE (0-10mm Movement)

✔ Can You Build on Class A Soil? → ✅ Yes, with standard construction methods

Class A soils have very low reactivity, meaning they experience little to no movement due to moisture changes. These soils are mostly composed of sand and rock, making them highly stable and ideal for construction.

Building Implications:

✔ Suitable for all residential and commercial buildings.
✔ Standard foundation systems like slab-on-ground or strip footings are typically sufficient.
✔ Minimal reinforcement is required due to the soil’s low movement potential.

Precautions:

✔ Proper drainage is still necessary to prevent erosion.
✔ Not suitable for high water retention landscaping, as sandy soil drains quickly.

SOIL TYPE 2: CLASS S – SATISFACTORY (10-20mm Movement)

✔ Can You Build on Class S Soil? → ✅ Yes, with minor adjustments

Class S soils are mildly reactive, meaning they experience slight movement as moisture levels fluctuate. These soils are still considered stable, but minor precautions are needed to ensure foundation integrity.

Building Implications:

✔ Suitable for most standard homes, with reinforced foundations.
✔ Some moisture control measures (such as site drainage) may be required.

Precautions:

✔ Buildings must have proper drainage systems to avoid waterlogging.
✔ Avoid planting large trees too close to the structure, as roots can impact soil stability.

SOIL TYPE 3: CLASS M – MODERATE (20-40mm Movement)

✔ Can You Build on Class M Soil? → ✅ Yes, with reinforced foundations

Class M soils are moderately reactive, meaning they experience noticeable movement due to changes in moisture levels. Homes built on these soils require reinforced foundations and moisture management strategies.

Building Implications:

✔ Requires reinforced slab-on-ground foundations or waffle pod systems.
✔ Additional moisture barriers and site drainage solutions are recommended.

Precautions:

✔ Regular monitoring of moisture levels is needed to prevent cracking and shifting.
✔ Not suitable for lightweight structures without proper footing systems.

SOIL TYPE 4: CLASS H1 – HIGHLY REACTIVE (40-60mm Movement)

✔ Can You Build on Class H1 Soil? → ✅ Yes, but requires engineered solutions

Class H1 soils are highly reactive, experiencing significant expansion and contraction with moisture changes. Homes built on these soils must use specialised engineering solutions to prevent foundation damage.

Building Implications:

✔ Suitable for homes with professionally engineered foundations, such as pier-and-beam systems or heavily reinforced slabs.
✔ Deep footings and stabilised soil preparation are required.

Precautions:

✔ Moisture control is critical—water pooling near the foundation can cause major structural issues.
✔ Unreinforced or shallow foundations are not recommended, as they can crack or shift.

SOIL TYPE 5: CLASS H2 – HIGHLY REACTIVE (60-75mm Movement)

✔ Can You Build on Class H2 Soil? → ✅ Yes, but requires advanced engineering

Class H2 soils are even more reactive than H1, meaning they undergo extreme movement when moisture levels fluctuate. Significant foundation reinforcements and soil stabilisation techniques are required.

Building Implications:

✔ Requires deep footings, pier foundations, or pile foundations.
✔ Must incorporate advanced moisture management systems to stabilise soil conditions.

Precautions:

✔ Homes without proper drainage and soil management systems are at high risk of structural failure.
✔ Engineering input is mandatory—building without professional design increases the likelihood of foundation problems.

SOIL TYPE 6: CLASS E – EXTREMELY REACTIVE (75mm+ Movement)

✔ Can You Build on Class E Soil? → ✅ Yes, but only with highly specialised foundations

Class E soils are extremely reactive, meaning they undergo significant ground movement. These sites require rigorous site analysis, advanced engineering solutions, and ongoing monitoring to ensure structural integrity.

Building Implications:

✔ Only suitable for homes with heavily engineered foundations, such as deep piers, piled raft systems, or post-tensioned slabs.
✔ Requires continuous site maintenance and soil moisture control.

Precautions:

✔ Standard slab or strip footing systems are not recommended, as they cannot withstand extreme ground movement.
✔ Long-term monitoring is required to maintain foundation stability.

CLASS P – PROBLEM SITES

✔ Can You Build on Class P Soil? → ✅ Yes, but extreme precautions are necessary

Class P soil is considered a problem site, meaning the load-bearing capacity of the soil is severely poor. These sites often experience abnormal moisture conditions, extreme soil movement, or unstable ground composition.

Common Causes of Class P Soil:

✔ Soft or loose soils that lack sufficient firmness for standard construction.
✔ Collapsing or eroding soils, which shift unpredictably under pressure.
✔ High water table levels, causing constant soil expansion and contraction.
✔ Environmental factors such as leaking plumbing, nearby excavation, or prolonged wet weather.

Building Implications:

✔ Requires extensive geotechnical assessments to determine load-bearing capacity.
✔ Specialised engineering solutions such as soil stabilisation, deep piering, or reinforced foundations are necessary.
✔ Proper drainage systems and ongoing monitoring must be implemented to maintain structural integrity.

Precautions:

✔ Standard slab-on-ground foundations are not recommended—they are at high risk of failure.
✔ Building without prior soil testing and engineering input increases the likelihood of foundation damage.

Take Aways on Soil Reactivity & Construction

✔ Before building, always conduct a professional soil test (geotechnical report) to identify the soil classification.
✔ Work with qualified engineers to design appropriate foundations based on soil reactivity.
✔ Implement drainage, moisture management, and reinforcement strategies to prevent structural issues.

At Prime Building Projects, we specialise in constructing durable homes on all types of soil, ensuring safe, long-lasting foundations for every project.

📞 Planning to build? Contact Prime Building Projects today for expert advice on soil classification and foundation solutions!

Soil Classification Chart

Credit to QBCC – Guide to Preventing Structural Damage

No matter the soil type, it’s necessary to build the proper foundation for it. For categories H1, H2, E, or P, an engineer will have to assess the property and determine how to construct a house on it without the risk of damage from soil movement.

The profile of the soil can change from property to property, as can the circumstances that affect it (more on that below). This variability underscores the importance of having your own soil tested rather than relying on neighbours’ observations or assumptions about nearby soil conditions. Site-specific testing provides the detailed data necessary for safe and durable construction.

Key Takeaways

• Soil classification provides a clear understanding of potential ground movement risks.
• Proper soil testing and engineering strategies can mitigate risks associated with reactive soils.
• Builders must adapt construction techniques based on the specific soil class to ensure safety and durability.

Whether you’re planning a knockdown rebuild or a renovation, knowing your site’s soil classification can save time, costs, and potential structural issues in the future.

Understanding Primary Soil Types

Soil types are classified based on their physical and chemical properties, including texture, composition, and drainage capacity.

Here are the primary soil types and their characteristics:

1. Sandy Soil

Sandy soil is composed of large particles that allow water to drain quickly. It feels gritty to the touch and has poor nutrient retention due to its inability to hold onto organic matter and water. While it’s easy to work with and warms up quickly in spring, sandy soil requires frequent watering and fertilisation for plant growth.

Building Implications:

• Ideal for stable foundation construction with minimal ground movement.
• Suitable for slab-on-ground homes and lightweight structures.

Unsuitable for:

• Projects needing high water retention or heavy landscaping features.

2. Clay Soil

Clay soil has very fine particles that pack tightly together, making it dense and heavy. It retains water well but drains poorly, often becoming waterlogged. Clay soil is highly reactive and prone to expansion and contraction with moisture changes.

Building Implications:

• Requires deep foundations or reinforced slabs to counteract movement.
• Moisture barriers and advanced drainage systems are essential.

Unsuitable for:

• Homes with shallow or un-reinforced foundations.

 

3. Loamy Soil

Loamy soil is a balanced mixture of sand, silt, clay and organic matter. It is considered the ideal soil type for gardening due to its excellent drainage, high fertility, and ability to retain moisture.

Building Implications:

• Suitable for most residential construction projects with standard foundations.
• Minimal additional engineering required unless clay content is high.

Unsuitable for:

• Homes built without adequate drainage in areas with high clay proportions.

Resources:

• What is loam?

 

4. Silty Soil

Silty soil is composed of fine particles that are smooth and slippery to the touch. It retains water better than sandy soil but has poor drainage.

Building Implications:

• May require soil stabilisation and reinforced foundations to prevent erosion.
• Suitable for projects with proper water management systems in place.

Unsuitable for:

• Foundations prone to compaction without reinforcement.

Resources:

• Silty Soil by National Geographic

5. Peaty Soil

Peaty soil is rich in organic matter and has a dark, spongy texture. It retains water well and is highly acidic, making it less suitable for certain plants without pH adjustment. Peat soil is unsuitable for construction projects due to its low bearing capacity and poor stability, which can result in settlement issues and structural damage.

Building Implications:

• Requires extensive soil stabilisation and drainage to support construction.
• Suitable for lightweight structures with engineered foundations.

Unsuitable for:

• Heavy structures without significant site preparation.

Resources:

• What is Peaty Soil?

 

6. Rocky Soil

Rocky soil contains a significant amount of stones and boulders, making it difficult to cultivate. It drains quickly and is often found in hilly or mountainous regions.

Building Implications:

• Suitable for sturdy structures with anchoring systems to secure foundations.
• Rocky sites can pose additional challenges for installing septic tanks, pipes, and cables. Trenches for these utilities often need to be dug into the ground, which can be difficult on rocky terrain.
• Additional excavation and preparation may be required.

Unsuitable for:

• Projects requiring deep planting or landscaping without significant soil amendment.

 

7. Chalky Soil

Chalky soil is alkaline and often contains visible white stones. It has excellent drainage but lacks nutrients, requiring regular fertilisation for gardening.

Building Implications:

• Suitable for homes with proper foundation systems and water management.
• May require soil treatment for certain landscaping projects.

Unsuitable for:

• Projects requiring nutrient-rich soil without amendments.

Key Takeaways

• Soil classification provides a clear understanding of potential ground movement risks.
• Proper soil testing and engineering strategies can mitigate risks associated with reactive soils.
• Builders must adapt construction techniques based on the specific soil class to ensure safety and durability.

Whether you’re planning a new build or a renovation, knowing your site’s soil classification can save time, costs, and potential structural issues in the future.

Resources:

• Understanding Chalk Soils

 

Unusual Soil Circumstances

Even with the right foundations in place for your soil type, certain circumstances can cause damage to the footings of your house. This occurs when these circumstances have an unusual impact on the amount of moisture in the soil and include:

Even with the right foundations in place for your soil type, certain circumstances can cause damage to the footings of your house. These occur when external factors have an unusual impact on the amount of moisture in the soil. Such circumstances include:

1. Extended Wet or Dry Periods

During prolonged wet periods, especially in the absence of proper drainage, water can pool and saturate the soil around your footing systems. This increased moisture can weaken the soil structure, causing uneven settling or even shifting of foundations. Conversely, extended dry periods can cause the ground to contract and pull away from the footings. This shrinkage not only reduces the soil’s support capacity but can also create gaps and voids beneath the foundation, leading to structural instability. Maintaining proper drainage systems and moisture control measures is vital to counteract these extreme conditions.

2. Water Leaks

Leaking storm water drains or pipes, town water or sewerage pipes beneath the house can create persistent wet spots in the soil. These concentrated moisture zones compromise the structural integrity of the soil and can lead to differential movement or sinking. Over time, the ongoing presence of leaks may result in significant damage to the property’s foundation and surrounding structures. To prevent this, homeowners should remain vigilant and address any leaking pipes as soon as they are identified. Regular inspections of plumbing systems can help detect and resolve issues before they escalate.

3. Air Conditioning and Hot Water Systems

These common household systems can inadvertently contribute to soil reactivity problems through their outflow pipes. If the discharged water from these systems is not directed into the storm water system, it can create “hot spots” where the soil becomes excessively wet. In reactive soils, these wet areas can trigger expansion and cause the ground to rise unevenly, leading to cracks in walls and floors. Installing proper drainage for outflow pipes and ensuring water is directed away from the foundation are essential preventative measures.

4. Nearby Construction Activities

Construction activities near your property can alter the natural drainage patterns or disrupt the soil’s stability. Heavy machinery, excavation, or changes to the surrounding landscape can lead to increased moisture accumulation or unexpected soil movement. It’s important to monitor nearby projects and work with professionals to mitigate any potential impact on your property.

5. Tree Roots and Vegetation

The presence of large trees near a property can significantly impact soil moisture levels. Tree roots draw moisture from the soil, leading to dehydration and shrinkage in reactive soils. On the other hand, removing large trees can cause the soil to rehydrate and expand. To manage these effects, ensure trees are planted at a safe distance from the foundation, and consult an arborist for advice on managing root systems.

These unusual circumstances underscore the importance of proactive site management and regular maintenance to protect your foundation from the effects of fluctuating soil moisture. A combination of vigilance, proper drainage, and timely repairs can prevent costly damage and ensure the long-term stability of your property.

Soil Tests – Test Kit Color Chart

Here at Prime Building Projects our team can inspect your site and organise a soil test on the property. Soil tests cost around $500 and take around a fortnight to complete.

Whether you’ve already purchased your land or are still in the decision-making phase, we’ll offer you our expert advice as you make your choice. Once we know what kind of soil we’re working with, we can take the necessary steps to construct your dream home on it.

What is a Soil Test Kit?

A soil test kit is a tool or collection of tools designed to help determine the characteristics of soil, such as its pH level, nutrient content, and overall composition. These kits are commonly used by gardeners, landscapers, farmers, and builders to assess soil quality for specific purposes, like plant growth or construction suitability.

Key Features of a Soil Test Kit:

1. pH Testing: Measures the acidity or alkalinity of the soil, which is crucial for determining soil health and its suitability for different plants or building materials.
2. Nutrient Analysis: Tests for essential nutrients like nitrogen (N), phosphorus (P), and potassium (K), as well as micronutrients such as iron or magnesium.
3. Texture Assessment: Some advanced kits can help identify the soil’s physical texture, such as sandy, clayey, or loamy.
4. Moisture Content: Provides information on how much water the soil retains, which can impact plant health or structural stability.
5. Chemical Testing: Identifies the presence of harmful substances like salts or heavy metals that could affect soil performance.

Types of Soil Test Kits:

• Basic Home Kits: Include color-coded strips, capsules, or drops for simple pH and nutrient testing.
• Digital Testers: Provide precise readings using electronic sensors for pH, moisture, and sometimes even light intensity.
• Laboratory Kits: Collect samples for detailed analysis by professional laboratories, often used for construction or agricultural projects.

Benefits of Soil Test Kits:

• Gardening: Helps gardeners understand soil conditions for optimal plant growth.
• Agriculture: Ensures that crops receive adequate nutrients while preventing over-fertilisation.
• Construction: Assists builders in determining soil stability and reactivity, ensuring proper foundation design.
• Environmental Assessment: Identifies pollutants or nutrient deficiencies in the soil.

Read More: New Home Builders Mornington Peninsula | Knockdown Rebuilds