Many houses in Australia are built on top of a concrete slab in the earth underneath, providing them with a steady foundation to rest upon. Sometimes this slab can become unstable, and your house will need underpinning to make it secure. Signs of foundation problems include windows and doors that get stuck in their frames. Alternatively, you may notice cracks creeping along the walls.
Contractors can use different residential underpinning methods. Some involve pouring new concrete to reinforce the slab. Other techniques involve inserting long concrete pilings into the ground to hold up the house. Another possibility is injecting resin into the soil to make it firmer.
You may wonder what causes foundations to fail and need help. Here are several possibilities.
Obviously, concrete foundation slabs sit within the earth, which needs to be firm for the concrete slab to be secure. Sometimes the ground can sink, which is termed subsistence. This may be, for example, because the clay content of the soil dries out so that it shifts. Otherwise, the soil around your home may be sandy and thus not particularly stable. Sometimes, the ground expands and contracts due to fluctuating water content, which can also cause problems.
Another reason your house may need underpinning is building work, either for your own place or for nearby homes. For example, if you're building a second story on top of your house, the foundation may need reinforcement. The existing concrete slab foundation would have been originally built to carry a one-storey structure, and now it will have to bear almost double the load. Alternatively, nearby construction work involving excavation may affect the soil around your home.
Another possible cause of house instability is natural events. For example, drought can dry out the soil and make it contract. Conversely, floods can have the reverse effect and cause the earth to shift. Of course, earthquakes can also shake the concrete foundation slab of a home, as the land is trembling underneath.
Thus, if you notice the doors or windows sticking or cracks in the walls of your home, you should have an expert check the foundations. If the building needs residential underpinning, they can use various methods depending on what caused the problem. They may pour extra concrete around the existing slab to bolster it. Or they may sink long concrete pilings into the earth to find stable deeper ground. Another method that needs less excavation and is not so intrusive is resin soil injection.