What Is Underpinning & When Is It A necessity?

Underpinning is the strengthening of an existing building foundation. If the original foundation isn’t strong enough to support the house, then underpinning may be required. This usually happens due to changes in the soil structure.

What does the underpinning of a building mean?

Concrete Underpinning involves strengthening or supporting the foundations of an existing house, structure, or building. This can be accomplished by strengthening the existing foundation, adding expanding filler, or extending the foundation so that load is evenly distributed across a greater area.

When underpinning is necessary?

For most homeowners, the underpinning will be required if the foundation does not support the house. It’s usually due to:

The soil supporting foundation has changed in a way that is not obvious. Due to subsidence, moisture expansion and contraction, large trees nearby, and damaged plumbing left un-repaired.

The soil’s characteristics were not fully understood when the foundation was designed.

If the above reasons are not applicable, then underpinning may be required. New construction is happening nearby, which means that soil support for existing foundations will be excavated. To increase foundations existing, e.g. Adding another story to the building. Natural disasters such as earthquakes floods droughts cause the structure or other structures to become unstable.

Image is of equiptment used by our underpinning Adelaide team

Cracks found in floors or walls

Cracks are not always dangerous. Sometimes they’re just superficial cracks like minor or very small cracks in plaster, cornices, and skirting boards. It is possible to see bigger cracks, which can often indicate deeper issues such as uneven weight distribution from weak foundations.

It is best to watch the cracks over several weeks or even months to determine if they become larger, wider, or more severe. If they don’t change over a prolonged period, then subsidence is likely to have ended.

If you are doing a DIY appraisal of your property, here are some signs to watch out for. You should understand that subsidence is a common problem on many properties. If subsidence is occurring actively, underpinning is not required. Sometimes, once subsidence has occurred, the structure may reach equilibrium and no further danger. As with all things, it is best not to be unsure and ask a professional. That is why Adelaide Underpinning Groups offer a complimentary home checkup.

Does underpinning offer a permanent fix for this problem?

It will ultimately depend on where your home is located (the site classification) as well as the type and method of underpinning that you choose to address your problem. Not all types are suitable for every foundation problem. We let you know at the beginning of our complimentary home checkup if our underpinning method is suitable for you. If we can’t fix it permanently, we will tell you so and give you an alternative plan of action. Because it is the most reliable method of underpinning, we only use a screw pile.

What Are The Main Methods Of Underpinning?

Concrete Underpinning can be used to strengthen and repair the building foundations. In some cases, foundation failures or fittings can occur after the structure has been completed (sub and full-scale). If this happens, a solution must be found to restore structural stability. The way of concrete underpinning can be used to strengthen the foundations of buildings or other infrastructure. These methods involve the addition of permanent or temporary support to an existing foundation so that it can be enlarged and has a greater carrying capacity.

Most homeowners will need to underpin if the foundation is weak enough to support their homes. It is often due to:

The soil which supports the foundation may have changed in any manner, such as subsidence, moisture expansion/contraction, nearby large trees, or old, damaged plumbing that was not repaired. The soil’s properties were not properly understood in the initial design of the foundation, so the foundation was not appropriate for the conditions.

Underpinning may also be required in less-common cases. The structure’s use has changed, e.g. After a major renovation. New construction in the surrounding or locality will require excavation of soil to support existing foundations.

Structures have also been affected by natural disasters like earthquakes, floods, droughts, and other extreme weather conditions.

Methods of underpinning or some foundation strengthening methods: 
Mass concrete underpinning method (pit method)- The mass concrete underpinning method has been used for centuries. This method involves extending an existing foundation to create a stable stratum. The soil below the existing foundation will be excavated in stages or using pins. Once the strata are achieved, the excavation is filled in with concrete and stored for curing before the next excavation. To transfer the load from an old foundation to a new one, a new pin can be provided by placing dry sand and cement packs. This is a cost-effective method for foundations with shallow depths. 

Pier-and-Beam Underpinning Method- It is also known for the base and beam technique, which was introduced after the Second World War. Because mass concrete couldn’t be used for foundations with large depths, so this method evolved. It is feasible in almost all ground conditions. Reinforced concrete beams are used to transfer the load to concrete piers or mass concrete bases. The ground conditions applied loads and beam size will affect the beams’ depth and size. It is considered economical to drill below 6m.

Adelaide Underpinning Group providing underpinning services in Mendindie, Adelaide

Mini Pile Underpinning- This method can be used where loads from the foundation need to be transferred into strata at a distance greater than 5m. This method can adapt to the soil of variable nature. It is also possible to use it for soil that is hard to reach and could cause pollution issues. The driving of piles with a diameter between 150 and 300mm is possible. These piles can be a augured (or driven steel cased).

Method of Pre-testing- It can be used for stripping or Pad foundation. This can be used to build buildings with 5-10 stories. The subsoil is compacted and compressed in an excavation that applies predetermined loads to the soil before underpinning. This will cause less noise and disruption. This method is not suitable for floating foundations.