Foundation underpinning is a construction process that aims to reinforce an existing or defective foundation. Read the excerpt below to learn more about underpinning and the various considerations you should make when underpinning your residential or commercial building.
When Do You Need Underpinning?
Below are some circumstances that may force you to underpin your building:
- If your foundation weakens due to poor construction or natural hazards such as floods or earthquakes. A weak foundation develops cracks and can warp in severe cases.
- If you need to add an upper storey or basement to the existing structure.
- You may also need to underpin the foundation if the soil underneath weakens.
- A change in the building code or zoning regulations may force you to underpin the foundation.
The Underpinning Process
Foundation underpinning should be conducted by trained and experienced personnel. Below is a guide on how to underpin foundations.
Ask a structural engineer to inspect the building before you commence underpinning works. The engineer will check the depth of your foundation and its current or intended load to determine how you should underpin the foundation. Further, they will create technical drawings to guide the contractor during underpinning works. In some cases, the engineer may rule out underpinning. For instance, take a situation where all the building's support structures have been compromised due to poor workmanship or a severe earthquake. In such a scenario, the engineer may ask you to demolish the structure since it could collapse anytime.
Types of Underpinning
There are several types of underpinning:
- Mass pour underpinning. It involves pouring concrete underneath the existing foundation. The method is popular because it is cost-effective.
- Beam and base underpinning. A concrete base is installed below the foundation. Concrete beams are built below the base to bear the load of the structure.
- Mini-piles underpinning. Concrete piles are constructed under the foundation to provide additional support. The method can be used to counter foundation weaknesses caused by waterlogging.
- Resin injection. A solution of resins and hardeners is injected into the foundation to seal cracks and strengthen the soil below. It is fast and effective since it does not require any excavation work.
Hire an experienced contractor to underpin your building. The contractor will work closely with the structural engineer to ensure the work is executed as per the blueprints. Preferably, work with a contractor that has general liability insurance and one that provides guarantees on their completed works.
Underpinning is a sure way to increase the longevity of your building. As a rule, you must consult a structural engineer and work with an experienced contractor.