The reinforcing or strengthening of a building’s foundation. The original foundation may no longer be strong enough to hold the home. It is often the result of changes in the soil’s structure. This can be due to a soil type change or an external force. Continue reading for detailed information.

What are the underpinnings (of a structure)?

The process of underpinning involves supporting or strengthening an existing building, house or other structure. The foundation can be reinforced, the soil strengthened by adding expanding filler or the foundation extended to distribute the weight over a larger surface.

What is the need for underpinning?

Underpinnings are required by most homeowners when their original foundation is too weak to hold up the home. Underpinning is often required as a result:

The soil that supports the foundation may have changed. through subsidence, expansion/contraction due to moisture, large trees nearby, damaged plumbing left unrepaired.

The soil properties were not properly understood when the foundation was designed – this means that the foundation does not meet the requirements.

Underpinning may also be required in less frequent cases for these reasons:

The way in which the building is used, e.g. Following a major refurbishment

Excavation of soil to support existing foundations due to new construction in close proximity

To increase the capacity of foundations, e.g. Supporting another floor to the building

Natural disasters like earthquakes, flooding or droughts have made the building unstable or move.

Let’s look closer at some of the elements that affect a foundation to help determine if underpinning will be needed.

The classification of soil types and sites

In order to ensure the foundations are stable, it is important that you know what type of soil your building will be built on. Certain soil types can be more susceptible to structural changes (e.g. During prolonged periods of rain or drought, these soils can become unstable and cause structural problems. These soils are called “reactive”.

Underpinning your building will depend on the type of soil beneath it.

What causes foundation failure?

The foundations of a building can fail for a number of reasons.

Reactive Soils

The problem is usually caused by the soils that are highly reactive. The movement can be caused by shrinkage or expansion. As soils continue to dry out, they lose moisture and shrink. Moisture levels can rise, as they do during prolonged periods of rainy weather. Soils will swell, sometimes up to several hundred per cent.

The foundation can be compromised by both shrinkage and growth of soil. This will result in visible cracks in walls and foundations, as well as heaving and subsidence.

Unevenly Compacted Fill

Sometimes, when a filling was done on a building site, the materials used were not compacted enough to hold the weight. As a result, problems with foundations are common. Problems can arise from multiple fill materials or poorly compacted material.

Site Erosion

The soil can be worn away around the foundations to such an extent that the foundations are structurally compromised. The cause of erosion can be a variety of things, including a ruptured water pipe, uncontrolled flow or inadequate drainage.

The slope failure

The movement of the earth downward is what causes a slope to fail. Slow failure is known as “creep”, while sudden failures are called “landslides”. Underpinnings can help correct a problem where a slope fails due to creep. This is a site-specific issue that requires expert evaluation.

Foundation Design

The original design may not have been adequate to a certain extent. It could have been because the soil properties were not properly understood when the original foundation design was made – the foundation would not be suitable for the circumstances. Modern building codes have made this less problematic.

Do I need underpinning?

When evaluating your property yourself, there are a few signs you should look out for. It is vital to remember that many different properties experience subsidence to various degrees when reading this list. Subsidence is not required unless it is active. After subsidence occurs initially, sometimes the structure achieves a level of equilibrium where there is no danger. If you’re unsure about anything, always ask an expert. That is why our Home Checkup is free.

Cracks on walls or floors

It’s not always a bad thing to have cracks. They can be superficial such as hairline or minor cracks on plaster cornices, skirting boards, and other surfaces. The bigger cracks can be a sign of a more serious problem, like uneven foundations or faulty weight distribution.

You can find cracks in the interior of a building (inside, for example, on tiles, plaster, or walls and floors) as well as outside (outside, such a brickwork, rendered, or concrete slab).

Try to monitor the cracks for a few weeks to see if they get wider, longer or bigger. Or if any new ones appear. The house may have settled if the cracks remain the same for a period of time.

The floor is not level

Unleveled floors are not always as visible as cracks. A lean on one or several sides is an indication that your foundation may be causing problems.

We’ve witnessed cases where you could stand on one end of the hallway, and watch the entire house fall as you looked down. Unleveled floors can also cause misaligned doorways. You can generally use a leveling spirit to determine how uneven a space is. Place a ball into the room to see if you can get it to roll in one direction or remain still. To understand the significance of this, you will need a professional.

Look for irregular trenches that form in the upper layers of soil around the edges of the slab or building. Another sign of subsidence is the formation of irregular trenches around the edge or slab.

Alignment of doors and windows

Foundation problems can often be detected by the condition of your doors and windows. The gaps around windows and doors are getting bigger and wider. You may find it difficult to shut (or open) windows or doors, or you might not be able to secure them.

Door or window frames can begin to pull away from the surrounding wall in more advanced cases.