Reinforcing an existing foundation is called underpinning. When the foundation of the building is not strong enough, it is necessary to reinforce the structure. The soil may have changed due to external influences or a change in soil composition. For more information, read here!
What’s the foundation (of an building)?
It is the act of strengthening or supporting the foundations of a house, building or structure. It is possible to achieve this by strengthening an existing foundation or by adding expanding soil filler.
Underpinning is required when?
Most homeowners will need to underpin their house if the foundation of the house is weak. It is typically caused by:
The foundation soil has been altered in some manner, e.g. through subsidence, expansion/contraction due to moisture, large trees nearby, damaged plumbing left unrepaired.
When the foundation design was first done, the properties of soil weren’t fully understood. This means the foundation wasn’t designed to suit the circumstances.
It is not uncommon to need underpinning for other reasons.
After a major renovation, the way that the structure has been used, for example. After a major renovation
New construction near excavations of the soil that supports existing foundations
Increase the strength of existing foundations (e.g. To support an additional story on the building
Natural disasters (such as floods, earthquakes and droughts) that cause the structure to shift or become instabile.
Take a look at these key factors that can impact the foundation.
There are two main soil classifications: Types of soil and site classifications
It is the soil type that determines how stable foundations will be. Certain types of soil are more susceptible to significant changes in structural conditions. This can lead to foundation issues during prolonged wet and dry periods. Reactive soils can be described as such.
It is important to know the soil type beneath your home to determine the damage it has sustained and which underpinning method will be most effective in stabilizing your home.
Why do foundations of buildings fail?
It is possible for the foundations to fail on a structure.
Reactive soils
The most common problem involves the movement of soils with high reactiveness. This involves either shrinkage (which can lead to settlement), or expansion (which can cause heaving). When soils are dry, they gradually lose water and shrink. If moisture is high, like during long periods of heavy rain, soils can swell by up to 100 percent.
It is possible for soil shrinkage or expansion to compromise the integrity and strength of a foundation. These conditions can lead to visible cracking and heaving in the walls and foundations.
Compacted fill that is not properly compacted
When a construction site has been filled, it is possible that the fill material was not properly compacted. This can lead to foundation problems. In such cases, it is common to have foundation issues. This problem may be caused by poorly compacted or multiple fill material.
Site Erosion
It is possible for erosion to wear down the soil surrounding foundations so much that they become structurally weak. It can come from many sources such as burst pipes, excessive water, poor drainage or similar.
A Slope Failure
It is the downward movement of soil that causes slope failure. This could be a slow, or “creep” failure. If a slope begins to fail due to creeping, you can use underpinning to correct the issue. It is important to consult an expert for a specific assessment.
Foundation Design
In a less extreme way, it is possible that the foundation design was inadequate. The soil properties may not have been properly considered when designing the foundation, resulting in a foundation that is inadequate for the current conditions. Due to the modern building code, this issue is much less prevalent.
Do I need underpinning?
You can use some indicators to evaluate your property on your own. As you read through the list, remember that there are many types of subsidence. Only where there is an active subsidence, is it necessary to install underpinning. Sometimes, after the initial subsidence has occurred, the structure is in a stable state and no longer poses a danger. It is always best to consult a professional when in doubt. This is why Home Checkup offers a free service.
Cracks in walls and floors
Cracks don’t have to be scary. Cracks can appear superficially, as in minor hairline fractures or cracks that are only visible on cornices, plaster and skirting. Larger cracks, however, are a different story. They usually indicate a bigger problem such as an uneven distribution of weight due to weak foundations.
The cracks you should look out for can be either interior (plaster and wall tiles), or exterior (brickwork rendered concrete slab)
If possible, observe cracks in the house over several weeks or even months. This will allow you to notice if cracks get larger or wider. They will likely remain the same over time, indicating that the subduction has run its course.
Not levelled floor
Uneven floors can be just as problematic as cracked walls. Leaning to one side or another of your house is not always obvious, but it can be an indicator that you have foundation problems.
You can see, in some cases that we have seen before, the collapse of a house when you stand at the end of a hall and look towards the other side. Sometimes, uneven floors are the cause of misaligned or crooked doors. Use a spirit-level to gauge the level of a room. You can also place a small ball inside the room and watch to see whether it stays still or rolls. It is often necessary to consult a professional in order to determine the importance of this.
You should also look out for any irregular trenches in the soil, around the perimeter of a building or slab. It is another indication of subsidence.
Door and window alignment problems
The condition of doors and windows may indicate foundation issues. Your windows and door frames are becoming more and larger with gaps. Not being able or willing to lock your windows and doors.
The frames of the door and windows may start to separate from surrounding walls in cases where there is a more noticeable lean.