Soil classes 1-7 and homogeneous areas: An essential guide for builders

Soil classes and homogeneous areas

The importance of soil classes and homogeneous areas

When building your own home, the condition of the soil is of crucial importance. A sound understanding of Soil classes and Homogeneous areas is therefore essential for prospective builders. These classifications provide important information on how the soil will behave during and after construction, which construction methods are suitable and what costs can be expected for soil cultivation.

A Soil expertise is the be-all and end-all before deciding on a plot of land. It provides a precise analysis of the soil and assigns it to a specific soil class. This classification has a direct impact on the planning and realisation of the construction project. But what exactly do these classifications mean?

Soil classes are essentially a categorisation of soil and rock material according to their composition and workability. From loose topsoil to hard rock, they distinguish between seven different categories. This categorisation helps to determine the costs and methods for the excavation and foundation of the building.

Homogeneous areas are a relatively new addition to the world of civil engineering. In a way, they replace the traditional soil classes by allowing a more differentiated view of soil and rock types. Each homogeneous area defines an area with similar characteristics, which allows for more precise planning and execution of construction work.

But why is all this so important? The correct assessment of the floor can not only save time and money, but also ensure the safety and longevity of the structure. Incorrect assessments can lead to serious problems, from additional costs to serious structural damage.

To minimise these risks, we offer you a deep insight into the world of soil classes and homogeneous areas in this guide. We explain what they mean, how they affect your construction project and how you can use them to your advantage. We also give you practical tips on how you can recognise and exploit potential savings by knowing these classifications.

This knowledge is not only useful for the planning and realisation of your construction project, but also for the long-term safety and stability of your dream home. So let us take a deep dive into the matter and ensure that your building project is on solid ground.

Understanding the basics

Definition and relevance of soil classes

Soil classes serve as a foundation for the planning and execution of construction projects. They classify soil and rock according to their physical properties and workability. This categorisation is crucial as it directly influences which construction techniques are used, which machines are deployed and which safety precautions need to be taken.

Classification in Germany is based on DIN 18300, which defines seven main categories of soil and rock types. These range from Soil class 1the topsoil, which is easy to cultivate, through to Soil class 7the rocky ground, which is difficult to work on. Each class has its own specific characteristics, which must be taken into account during planning in order to organise the construction project efficiently and safely.

Homogeneous areas explained

With the introduction of Homogeneous areas the soil classification has been further refined. Homogeneous areas group soil and rock types not only according to their physical properties, but also according to other factors such as chemical composition or contamination. This enables an even more precise assessment of the construction requirements and risks.

The classification into homogeneous areas is based on the actual properties of the soil and rock with regard to the planned construction work. This means that one and the same plot of land can be divided into different homogeneous areas, depending on which construction work is to be carried out in which area. This division helps to avoid unforeseen problems during construction and to increase the safety and cost-effectiveness of the project.

The definition and categorisation of homogeneous areas requires a detailed analysis of the soil by experienced experts. A well-conducted soil survey that identifies the various homogeneous areas is therefore essential for the successful planning and realisation of a construction project.

Floor classes 1-7 in detail

Soil class 1: Topsoil and its properties

Soil class 1also known as topsoil, represents the uppermost layer of the soil. This layer is rich in organic material and plays a crucial role in agriculture as it is extremely fertile. In construction, however, topsoil is less desirable as its composition is not considered stable enough for the foundations of buildings. Before construction work can begin, the topsoil must therefore usually be removed and stored separately or disposed of, which incurs additional costs.

It is important for builders to know that the excavation and disposal of topsoil is associated with costs. These costs vary depending on the region and the availability of landfill sites. Early planning and budgeting of these costs is crucial to avoid surprises in the construction process.

Soil class 2: The special features of flowing soil types

Soil class 2 includes water-saturated or flowing soil types such as mud and silt. These soils have a low load-bearing capacity and are unsuitable for direct construction. Structures in areas with such soil conditions require special foundation techniques such as pile foundations in order to create a stable base.

Choosing the right foundation method has a direct impact on construction costs and the long-term stability of the building. A detailed soil analysis helps to plan the necessary measures at an early stage and to calculate costs effectively.

Floor class 3: Easily removable floor and its advantages

Soil class 3 refers to easily removable soils such as sand and gravel. These types of soil offer good load-bearing capacity and are easier to work with, which can reduce construction costs. They also have high permeability, which is advantageous when planning drainage systems and rainwater infiltration.

For builders, this means that buildings can often be erected more cost-effectively and more quickly on soil class 3 ground. However, it is important to consider the tendency to erosion and subsidence and to take appropriate precautions.

Soil class 4: Medium-heavy soil - ideal for construction

Soil class 4 includes soils that are a mixture of sand, clay and silt. These soils provide an excellent base for most building projects as they have a good balance between bearing capacity and workability. They generally do not require extensive soil replacement, which saves time and money.

Builders who own a plot with soil class 4 can count themselves lucky, as they can expect relatively low additional costs for soil preparation. Nevertheless, precise analysis and planning is required to avoid potential problems such as water accumulation or subsidence.

Soil class 5: Difficult-to-remove soil and its challenges

Soil class 5 includes soils that are difficult to loosen and are characterised by high density and strength. These include, for example, stiff clay, firm loam and compacted gravel. These types of soil require specialised construction machinery for excavation and can increase construction costs, but also provide an excellent basis for the foundations of structures.

Builders should factor in the additional costs for excavation and any necessary soil improvement. Precise planning and soil testing is crucial to identify the best solutions for the foundation and avoid unnecessary costs.

Soil class 6: Light rocky soil - A solid basis for foundations

Soil class 6 refers to rock that is easier to work with, such as loosely bedded or friable rock. This type of soil provides an excellent basis for the construction of foundations as it has a high load-bearing capacity and stability. Working on light rock soil can still be challenging and require specialised equipment, but is generally less costly and time-consuming than heavy rock soil.

Thorough planning is essential for projects built on light rock soils in order to maximise the benefits of this stable foundation. This can significantly reduce the cost of the foundation and ensure the longevity of the structure.

Soil class 7: Heavy rocky soil - challenges and opportunities

Soil class 7 comprises heavy rock soil characterised by its strength and stability. However, dealing with heavy rock often requires the use of blasting techniques or specialised drilling equipment, which can increase the cost of excavation. Despite the higher initial investment, heavy rock soil provides an exceptionally solid foundation for structures, which is beneficial in the long term.

Builders should factor the additional costs of working on heavy rocky ground into their budget planning. At the same time, it is an opportunity to build on extremely stable ground that is less susceptible to subsidence and other ground movements.

Soil classes DIN 18300 - changes and innovations

The categorisation of floors according to the DIN 18300 was an essential component of the German Construction Contract Procedures (VOB) for decades. This classification, which primarily relates to the loading, loosening, conveying, compacting and installation of loose rock, assessed the recoverability of rock and other materials in earthworks. Soils were categorised into different classes according to their physical resistance.

However, a significant change took place with the new edition of VOB/C in 2015: The traditional soil classes were replaced by so-called Homogeneous areas replaced. This change now requires soil and rock to be categorised into different homogeneous areas according to their condition before earthworks begin. Specific properties and characteristics of the material are decisive for this categorisation.

A major innovation of the homogeneous areas is the consideration of soil chemistry. This innovation reflects the increasing importance of construction on former industrial sites, which are often characterised by contamination. The adjustment takes account of the fact that the construction industry is increasingly confronted with contaminated sites and requires a more detailed assessment of soil properties.

Homogeneous areas in construction - Soil classes new

Homogeneous areas define zones that consist of one or more layers of rock or soil and extend over a limited area. Allocation to a homogeneous zone is based on the properties that are relevant for processing by earthmoving equipment and is characterised by corresponding DIN standards regulated. A homogeneous area therefore summarises soil and rock areas that have similar processing characteristics.

There are no fixed designations for the classification of homogeneous areas in DIN, which makes the classification partially subjective and leaves it up to the expertise of the assessor. Frequently used designations are, for example, A1, A2, A3 or B1, B2, B3, but this can lead to confusion, as the allocation to certain construction works is not always clear. To simplify this assignment, it is recommended that the corresponding trade is named first and the areas are numbered consecutively. The homogeneous areas include

  • EA (earthworks): This area includes general earthworks, such as excavation and backfilling, and is probably the most common homogeneous area in construction projects.
  • BA (drilling work): Specialising in work that requires drilling, for example for foundations, wells or geothermal systems.
  • RA (pile driving, vibrating and pressing work): For civil engineering work where elements have to be inserted into the ground, such as piles or sheet piling.
  • NA (dredging work): Refers to work in water-bearing areas, for example when constructing canals or removing soil material from bodies of water.
  • UA (underground construction work): For tunnelling and other underground construction activities.
  • SA (diaphragm wall work), RVA (pipe jacking work), LA (landscaping work), DA (jet grouting work), and HBA (horizontal directional drilling): Specialise in very specific technical requirements and areas of application in the construction industry.

These innovations in the classification and assessment of the subsoil are of great importance for building owners and planners, as they enable more precise planning and calculation of construction projects.

Homogeneous areas vs. soil classes

To illustrate the difference and the effects of the introduction of homogeneous areas compared to the traditional soil classes, the following table can be used as an example to show the changes in earthworks:

Soil/rockDIN 18300 (old) - Soil classes EarthworksDIN 18300 (new) - Homogeneous areas earthworks
Layer 1Soil class XHomogeneous area EA 1
Layer 2Soil class YHomogeneous area EA 2
Layer 3Soil class ZHomogeneous area EA 3

This table illustrates how the categorisation into homogeneous areas enables a more differentiated view of the various soil and rock types. Instead of a general categorisation, each layer is now assessed according to its specific properties and suitability for certain earthworks. This leads to more precise planning and execution of construction projects.

Slope angle table

Another important aspect in the planning of construction projects is the slope angle. The following table provides information on the slope angles that can be maintained for trenches with a maximum depth of 5 metres without mathematical verification, provided that there are no external disturbance influences (in accordance with DIN 4124):

Slope angleFloorExample
45°Cohesive or soft cohesiveTopsoil, sand, gravel
60°Stiff or semi-solid cohesiveLoam, marl, solid clay
80°Healthy, unbroken rockWithout weathering

These guide values help to take the necessary safety precautions into account when planning excavation work and support builders and planners in ensuring the stability of trenches and embankments.

Practical tips for builders

The importance of a soil survey

A soil survey is a crucial tool for any builder to understand the nature of the ground in detail. It not only provides a precise analysis of the soil and rock types on your property, but also identifies homogeneous areas and potential risks, such as contamination or the need for special construction techniques. Before planning a construction project, a soil survey is therefore essential to avoid surprises and additional costs. It helps to realistically plan the construction project, make the right construction decisions and ensure the long-term safety and stability of the building.

Recognising and exploiting potential savings

Knowledge of the soil properties and homogeneous areas enables builders to recognise potential savings. For example, a soil with good load-bearing capacity can reduce the need for costly foundation measures, while precise knowledge of the soil classes helps to avoid unnecessary expenditure on oversizing. By involving an experienced ground surveyor at an early stage, you can receive advice on cost-effective construction techniques that are specifically tailored to the conditions of your property. In addition, the choice of alternative construction methods or materials based on the results of the survey can lead to considerable cost savings.

Dealing with soil classes and homogeneous areas in practice

In practice, dealing with soil classes and homogeneous areas means working closely with your architect, civil engineer and soil surveyor. Make sure that your construction team is fully informed about the results of the soil survey and that they coordinate their planning accordingly. Communicate your budget constraints clearly and discuss possible risks and solutions.

It is also advisable to familiarise yourself with the basic concepts of soil classes and homogeneous areas in order to better participate in the decision-making process. This knowledge will allow you to understand the recommendations of your experts and make informed decisions that will positively impact the cost, construction time and quality of your project.

Frequently asked questions

How do I determine soil classes?

Through a detailed Soil expertiseThe use of a soil analysis and classification system, which analyses and classifies the soil, enables builders to choose the best method for foundations and construction techniques and to plan costs effectively.

For more detailed examinations and professional advice, visit Earth baronto obtain your customised building site survey.

What soil classes are there?

Seven soil classes cover the spectrum from topsoil with a high organic composition to hard rocky soil, each with specific processing requirements and implications for the construction industry.

What is the difference between soil classes and soil types?

Soil classes are based on processing properties for construction purposes, while Soil types describe the material composition of the soil, such as sand, clay or loam.

Which floor is load-bearing?

Soil classes 3 and 4.

In terms of load-bearing capacity for construction projects, soil classes 3 and 4 are highly suitable. These classes include easily removable soils such as sand and gravel (soil class 3) and medium removable soils, which are a mixture of sand, clay and silt (soil class 4). Both provide a solid base for most construction projects due to a good balance between bearing capacity and workability, making them a favoured choice for foundations.

How are the floors categorised?

Soil types, homogeneous areas and soil classes.

Soils are categorised according to various criteria. Soil types are differentiated according to grain size and composition. Homogeneous areas offer a more detailed view of the properties of the soil, particularly in the construction industry, and take into account both the physical and chemical properties. Finally, soil classes classify the soil according to its workability and solubility, which is crucial for the planning and execution of construction projects.

Which soil class is clay?

Clay usually belongs to the Soil class 4. This class is known for its good balance of load-bearing capacity and workability, which makes it particularly suitable for the construction of foundations and buildings.

However, a detailed soil survey is essential for an accurate categorisation and assessment of the soil conditions. Such a report, prepared by an experienced soil surveyor, can identify specific properties of the clay soil on your property and thus provide a reliable basis for planning your construction project. Request a Request a subsoil expertise

Is clay a stable soil?

Yes, clay is considered load-bearing due to its consistency and ability to store and release water. It can absorb subsidence well, which makes it a solid base for residential buildings.

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