What Does Basement Underpinning Entail?

Within the construction niche, basement underpinning pertains to the process of repairing or re-strengthening an existing foundation of a building. Basement underpinning is usually referred to as a repair method but it is also advised by landscapers for prolonging the durability of a residential building. Homeowners planning to undertake basement underpinning should have a basic understanding of what it entails since it quite expensive.

Basement Underpinning Basics

The most established form of basement underpinning uses a combination of concrete and piers. Some people might refer to this as ‘traditional underpinning’ but this is actually a slight modification since the earliest form of underpinning didn’t use piers. While the concrete adds to the basement’s overall durability, the presence of piers increases its load-bearing strength.

Basement underpinning is recommended for many reasons, like:

  • The existing basement is showing signs of extensive cracking, moisture seepage or is sinking into the underlying soil bed.
  • The existing basement is leaking out the internal heat even after repeated, basic repairs with mortar and insulation treatment.
  • The existing basement needs to be strengthened for bearing additional weight as more floors are being added to the house.
  • Construction of large buildings in the vicinity along with moisture-friendly soil has caused large-scale soil compaction below the basement, causing overall instability of the house.

Basement Underpinning Entails:

1. Getting Started

At the time starting the project, a temporary support-like structure is created. This is done to ensure that the basement doesn’t collapse during underpinning. Further, it provides a base upon which heavy materials like piers can be moved.

2. Excavation

Excavation or removal of soil from under and around the basement is vital. This provides access to the underside of the basement, creating space that is used for installing the stabilizing additions (piers).

Before excavating the soil, you should have a detailed plan that explains the angles and spots wherein the piers would be inserted. Unnecessary excavation can lengthen the project and weaken the basement.

Basement underpinning requires the creation of rounded or squared holes depending upon the kind of excavation tools used and the shape of the piers. Ideally, the holes should be at least 24 inches apart.

Excavation tools include the use of backhoes and soil loaders that required for scooping-out and piling the dug-up soil. Some people prefer using shovels but this can make the entire process rather tiring.

3. Pier Piling

Once the excavation has created enough space, the extra support in the form of piers is introduced. This could be in the form of using:

  • Resistance Piers—they are installed using advanced machinery wherein they are driven through the soil without needing any screws or brackets. These are ideally suited for bigger homes.
  • Helical Piers—these are installed using the conventional system of screwing the piers upon a frame. These piers are difficult-to-manipulate once installed, since the framework secured with screws cannot be undone.

4. Pouring Concrete

Some landscapers prefer to pour concrete upon the pier frame too to make it more durable while some just like to pack some garden soil. The outer edge of the piers is secured along the perimeter of the basement by pouring concrete. The temporary support structure is removed. Concrete pouring is done in the traditional manner using tools like shovels, trowels and concrete rakes. The outer edge of the concrete-covered edge is smoothed with a concrete cutter.