Everything You Need to Know About Slab Underpinning


The construction business is hugely flourishing these days with buildings and apartments coming up in all corners of the streets. And, it is the structural engineers who are following various methods to make the firm foundation of the buildings. Recently, a prevalent method of strengthening the foundation of houses, has been the method of slab underpinning. In this article, you will know what the underpinning method is and when it is necessary.

What is a slab underpinning?

Slab underpinning is a method of strengthening the foundation of an existing building. This reinforcement is needed when the original foundation no longer provides the needed support to the house. That usually happens due to the change in the soil structure or some external influence on the soil.

Slab underpinning is achieved in various ways, such as

  • An expanding filler is introduced to the soil to make it stronger.
  • The foundation is extended so that the load is equally distributed over an area with large surface.
  • The screw pile underpinning method is applied in which sturdy metal pillars are used to underpin the building.

When do you need slab underpinning?

The footing of your house may move for different reasons, and not all footing movement needs slab underpinning. So, when do you need it?

  • Slab underpinning is required when the footing of your house has subsided for reasons which can’t be reversed. You can use this method to improve the house’s stability if the original footing installed is not deep enough. It helps in jacking up your house back to almost level.
  • You may need slab underpinning if you start spotting cracks in the walls and floor of your house. Also, in cases of a slanted floor, misaligned door frames, and windows, you require underpinning. The method is essential when you notice your house is slowly sinking into the ground.
  • Slab underpinning is vital in case of a damaged or aged foundation of a building. These foundations can no longer support the structure, be it an apartment block, a house, or other premises. Usually, the foundation of a building sinks due to changing soil structure or suboptimal work by previous contractors. It can even occur due to the unavoidable wear and tear of the foundation over time.
  • Sometimes, slab underpinning may be required due to damage in the building foundation caused by excavation on the neighbouring sites. It is widespread in crowded urban areas.
  • Underpinning a structure is also needed to add an extra story to the building.

How long does slab underpinning take?

The time required for slab underpinning of a house depends on the number of underpins specified by the structural engineer. The job will take approximately two weeks to finish for a building that needs up to 10 underpins. Moreover, if your house needs to be fully underpinned, you might have to look for a settlement outside for about a month.

Positive aspects of slab underpinning

Some of the benefits of slab underpinning that everyone gets include

  • Increase the integrity of the structure

The slab underpinning method retains the life of buildings standing as-is for a long time. This method opens up the mechanics of the house so that a structural engineer can inspect the house thoroughly for any corrections. The underpinning method also helps replace these houses’ old drainage and plumbing systems, if any.

  • Strengthening the base of the building

Sometimes, buildings are built on moist soil, which is difficult to hold on to. These houses are prone to collapse even with a slight tremor around in the area. Therefore, building strong support or foundation is essential for these houses. So, to increase the stability of these buildings, you usually resort to the slab underpinning method.


If you ever found any spot cracks in the walls and floor of your house, you should not ignore it. Therefore, you can notice that developing a robust foundation is essential to provide stability to your house. Thus, you resort to the method of slab underpinning to strengthen the foundation of your home.