An underpinning kit is a system of steel components designed to stabilize or lift a building’s foundation by transferring its weight down to stronger soil or bedrock below. It typically includes steel piers (pipes or shafts), mounting brackets, and sometimes spreader beams, all engineered to work together as a permanent structural repair. If you’ve been told your home needs underpinning, understanding what’s in these systems and how they differ will help you evaluate quotes and ask better questions.
What’s Inside an Underpinning Kit
An underpinning kit isn’t a single product you buy off a shelf. It’s a coordinated set of steel components sized for your specific foundation. The core parts include:
- Steel piers: The vertical pipes or shafts driven into the ground. Industry guidelines require a minimum 3-inch outer diameter Schedule 40 steel pipe, though many systems use larger sizes depending on the load.
- Brackets: Heavy steel plates that sit against the foundation wall or footing and connect to the pier. These are the transfer point where your home’s weight moves from the foundation onto the pier system.
- Spreader beams: Steel beams (minimum 3 feet long) placed on each side of window and door openings to distribute lifting force evenly and prevent cracking. Openings wider than 6 feet typically require custom-engineered beams.
Some kits also include hydraulic lifting equipment used during installation to raise a settled foundation back toward its original position. After the structure is lifted into place, the brackets are permanently fastened to the pier pipes, and the excavated areas are backfilled to grade.
Helical Piers vs. Push Piers
The two main types of underpinning kits use fundamentally different pier designs, and the right choice depends on your soil and your structure.
Helical Pier Kits
Helical piers are steel shafts with screw-like plates welded along their length. They’re mechanically screwed into the ground using hydraulic equipment, much like a corkscrew into a cork. Because they don’t rely on the building’s weight for installation, they work well for both light and heavy structures. They’re the more versatile option, handling loose, wet, or expansive soils where other methods struggle. Installers can also control depth precisely, stopping at the exact layer of stable soil.
Push Pier Kits
Push piers are steel tubes that get hydraulically driven straight down into the ground, using the weight of the building itself as resistance. That makes them a natural fit for heavier structures like brick or concrete block homes where there’s enough downward force to drive the piers deep. They perform best in firm, stable soils and can reach greater depths than helical piers in some conditions. They also tend to cost less, which matters when you need a dozen or more piers around a foundation perimeter.
Your foundation contractor and engineer will recommend one type over the other based on a soil analysis and the weight of your structure. In some cases, a project uses both types at different points along the foundation.
How Engineers Decide What You Need
An underpinning kit isn’t one-size-fits-all. An engineer calculates how many piers your foundation needs and where they go based on the load your foundation carries and the spanning ability of the existing footing between piers. As a general rule, pier spacing can’t exceed twice the depth of the existing foundation and stem wall, because the concrete needs to be able to “arch” between support points without cracking.
The engineer also evaluates whether your existing foundation is strong enough to transfer loads to the new piers, or whether it needs reinforcement first. This is why underpinning projects vary so widely in cost. A home with a shallow footing and poor soil might need piers every 4 to 5 feet, while a deeper foundation on moderately stable ground might need them every 8 feet.
Signs Your Foundation May Need Underpinning
Most homeowners start researching underpinning kits because they’ve noticed something wrong. The clearest warning signs include stair-step cracks in brick or block walls (those zig-zag patterns that follow mortar joints), which indicate uneven settlement beneath the home. Horizontal cracks are more serious, signaling significant lateral pressure against the foundation wall. Any crack wider than 1/4 inch in walls or floor slabs warrants professional inspection.
Doors and windows that suddenly stick, jam, or won’t close completely are another common sign. Foundation shifts pull frames out of alignment, so a door that swings shut on its own or a window that lets in drafts where it didn’t before can point to settlement. Floors that slope noticeably or feel bouncy in spots suggest the foundation underneath has shifted unevenly. Inspectors typically use laser levels to measure exactly how much movement has occurred before recommending a repair plan.
How Long Underpinning Lasts
Steel pier underpinning systems are designed to be permanent. When properly installed, they last as long as the structure they support, often many decades. Steel piles and beams offer high tensile strength and resist moisture and temperature swings well. Most underpinning contractors back their work with warranties of around ten years, though the actual lifespan of the system far exceeds that.
The main variables that affect longevity are environmental: soil acidity, groundwater levels, and how much the surrounding soil expands and contracts with moisture changes. Homes in areas with reactive clay soils or fluctuating water tables face more ongoing stress on their foundations, which is partly why they needed underpinning in the first place. The pier system bypasses those unstable upper soil layers entirely, anchoring into competent ground below where conditions are more stable.
Industry Standards for Underpinning Kits
Not all underpinning kits meet the same engineering bar. Helical pier systems used in the United States are evaluated under ICC-ES Acceptance Criteria AC358, a standard maintained by the International Code Council’s Evaluation Service. This criteria covers helical pile systems and devices under the International Building Code, and products that carry an ICC-ES evaluation report have been independently tested for load capacity and structural performance. When comparing contractors, asking whether their pier system holds an ICC-ES evaluation report is a straightforward way to verify quality.
Florida’s sinkhole stabilization guidelines provide additional minimum standards, including requirements for pipe diameter, bracket attachment methods, and spreader beam placement. Your local building department may have its own requirements. Portland, Oregon, for example, publishes specific structural requirements for underpinning residential structures with helical piles and push piers. A permitted underpinning project will need to meet whichever local code applies.