As a homeowner, it’s essential to understand the importance of a solid foundation for your house. Over time, the soil conditions and external factors can impact the stability of your home’s foundation. When the original foundation is no longer strong enough to support the house, underpinning becomes necessary. In this comprehensive guide, we will explore the concept of house pinning, its importance, and when it is required.

What is House Pinning?

House pinning, also known as underpinning, refers to the process of reinforcing the existing foundation of a building or structure. It is a technique used to strengthen the foundation and ensure its stability. Underpinning can involve various methods such as introducing an expanding filler, extending the foundation, or reinforcing the existing foundation. The goal is to distribute the load over a greater surface area and provide additional support to the structure.

When is House Pinning Required?

There are several situations where house pinning becomes necessary. Let’s explore some common scenarios where underpinning is required:

Weak Foundation

One of the primary reasons for house pinning is a weak foundation. Over time, the soil conditions may change due to various factors such as subsidence, moisture changes, or the presence of large trees near the property. These changes can compromise the integrity of the foundation, leading to structural issues. If your house shows signs of foundation problems, such as cracks in walls or uneven floors, underpinning may be necessary to strengthen the foundation.

Soil Type and Site Classification

The type of soil on which your house is built plays a crucial role in the stability of the foundation. Reactive soils, which are prone to significant structural changes, can cause foundation problems. Soil classification, according to Australian Standard AS 2870/2011, helps determine the soil’s potential to support a structure. If your house is built on reactive soil, underpinning may be necessary to stabilise the foundation.

Changes in Property Usage

If you plan to make significant changes to your property, such as adding an upper floor extension or renovating extensively, underpinning may be required. These changes can increase the load on the foundation, and underpinning ensures that the existing foundation can support the additional weight.

Construction Nearby

If new construction is taking place near your property, it may involve excavation of the soil supporting your existing foundation. This excavation can weaken the foundation and compromise its stability. Underpinning can help reinforce the foundation and protect it from the potential impact of nearby construction.

Natural Disasters

Natural disasters like earthquakes, floods, or droughts can cause the structure to move or become unstable. If your house has been affected by such disasters, underpinning may be necessary to restore stability and prevent further damage.

Age of the Property

As houses age, the materials used for the foundation, such as concrete and steel, may deteriorate. This can weaken the foundation over time, leading to structural issues. Underpinning can provide a permanent solution by strengthening the foundation and extending the lifespan of the building.

Methods of House Pinning

Several methods can be used for house pinning, depending on the specific requirements and conditions of the property. Let’s explore some common methods of underpinning:

Mass Concrete Method

The mass concrete method is one of the traditional approaches to underpinning. It involves digging pits around the existing foundation and filling them with concrete to create an additional underlayer. This method is commonly used for shallow foundations and provides increased strength and stability to the foundation.

Jet Grouting Method

The jet grouting method is a more advanced and less invasive approach to underpinning. It doesn’t involve extensive excavation. Instead, contractors inject a mixture of resin and cement deep into the soil at high pressure. This mixture solidifies and forms soil cement columns, providing additional support and stability to the foundation.

Reinforced Beam Base Method

The reinforced beam base method is an advanced form of underpinning. It involves excavating to a lower level around the perimeter of the foundation while bracing the property. Reinforcement beams are then positioned beneath the excavation area and filled with concrete. This method provides enhanced strength and stability to the foundation.

Mini Piles and Brackets Method

The mini piles and brackets method is commonly used to address subsidence issues. Trenches are dug around the affected area, and piles are driven into the ground until they reach stable soil. Brackets and plates are then used to brace the piles and support the existing foundation. This method helps restore the structure to its original position and provides long-term stability.

The Importance of Consulting a Structural Engineer

When it comes to house pinning and underpinning, consulting a structural engineer is crucial. A structural engineer has the expertise to assess the condition of your foundation, identify the underlying issues, and recommend the most appropriate method of underpinning. They can also provide guidance on the structural integrity of your property and ensure that the underpinning process is carried out effectively and safely.

Will House Pinning Provide a Permanent Fix?

Underpinning is considered a permanent solution to foundation issues. However, it’s important to note that the success and longevity of the underpinning process depend on various factors, including the specific method used, the soil conditions, and the expertise of the professionals involved. Proper planning, execution, and regular maintenance can significantly increase the lifespan of the underpinning and provide a long-term fix for foundation problems.


House pinning, or underpinning, is a critical process for strengthening the foundation of a building or structure. Whether your foundation has weakened over time, the soil conditions have changed, or you’re planning significant renovations, underpinning may be necessary to ensure the stability and longevity of your property. By understanding when and why house pinning is required, consulting a structural engineer, and choosing the appropriate underpinning method, you can protect your investment and enjoy a secure and durable home for years to come.