What is Underpinning?
When adding new stories to a property or repairing a faulty foundation, “underpinning” is the process used to improve and strengthen an existing foundation and allow for more load-bearing capabilities. It is common in restoring old buildings, “pop-top” renovations (adding stories to a property), and condo conversion (subdividing a property into multiple units – meaning additional load-bearing is needed for multiple kitchens, bathrooms, etc.). If you see cracks in a foundation or plans for a taller building, there’s a good chance that property needs to undergo underpinning.
Reasons for Underpinning
Most cases of underpinning are associated with faulty or unstable foundations. Such foundations are often the result of the age of the building or changes in the ground surrounding or under the existing structure.
You’ll also see the need for underpinning in the renovation and rehabbing industry as real estate investors plan to add additional stories to a property. For example, if you purchased a two-story building and want to add a third or even fourth floor, the foundation needs to compensate for that extra weight. The underpinning process makes such renovations possible, all while maintaining the integrity of both the foundation and the above-ground structure.
Types and Cost of Underpinning
There are several different methods of underpinning, though most require structural engineers to plan and execute properly.
Mass Concrete Underpinning a.k.a. “Pit Method”
The most popular method is the traditional concrete underpinning also called the “pit method” which has been around for over a century. This method utilizes hand-dug pits that are strategically dug under the existing foundation (typically 8-12 feet apart) and filled with concrete. This method is the most popular due to the ease of engineering and the low cost of labor.
Needle Beam and Pile Underpinning Method
Beam and base underpinning is a more advanced (and often expensive) method that involves integrating a cast concrete beam that is reinforced with rebar that extends into additional concrete piles below the beam. This method spreads the load-bearing stress across multiple points.
Why is Underpinning Important?
Underpinning is important in cases where the existing foundation of a property is either damaged and therefore compromised, or if additions will be made to the structure that require additional load-bearing abilities. In both cases, underpinning is used to remedy the issue and maintain the structural integrity of the property. Without undergoing the process of underpinning, the structure itself could begin either slowly or rapidly collapsing – causing additional damage and costing much more to repair than underpinning would have.
Whether the existing foundation was damaged from an earthquake, erosion, or you simply want to add more weight to a property, underpinning should always be done with the consultation of an experienced structural engineer. Furthermore, you will want to use a contractor that has experience in underpinning projects, as this is not a repair that you should take a gamble on.
If you’re considering a renovation project that may require underpinning, contact us today to see how we can offer you financing for the project, but also guidance as you navigate the process.