What Is Underpinning a Foundation and When Is It Needed?

If you’re running into issues with your foundation and your home is showing signs of instability, you might have heard the term “underpinning” online or from a foundation repair company. Underpinning is one of the most expensive but longest-lasting types of foundation repair, so it’s a good process to understand. In this guide, we’ll be explaining what underpinning is, when you might need it, the different kinds of underpinning, and more.

What Is Foundation Underpinning?

Underpinning is a way to provide additional support for foundations that have lost the support they need from the ground underneath them. It’s useful in areas where the soil at the typical foundation depth is expansive or subject to freezing, which can cause instability under your home.

The process of underpinning involves a contractor excavating under your foundation, installing long pins called piles that reach further down to a point where there’s no risk of soil movement, and then attaching the foundation to the pin to transfer the load to the support.

When Do You Need to Underpin a Foundation?

It’s often necessary to underpin foundations that are sinking or aren’t getting the support they need from the soil to support the structure above properly. There are a bunch of signs and issues you can look for in and around your home that can indicate that foundation stabilization through underpinning would be a possible solution.

Foundation Cracks

If you notice cracks in your slab or on your concrete block walls around the corners of your home, that could be a good indication of uneven support below. Not all foundation cracks are indicative of poor soil conditions, though, so you may need to contact a foundation repair company near you to assess them. All foundations crack naturally, and some cracks suggest a different type of issue.

Sinking Foundation

If you notice any portion of your foundation sinking down into the ground, underpinning will probably be necessary. Most homeowners only notice this if they have access to a crawl space or basement and can see the floor pulling away from the walls above in certain areas.

Cabinets/Countertops Pulling Away From the Wall

Since your home relies on your foundation for even support, any areas that lose support from underneath could result in problems with walls shifting above that. This can cause cabinets and countertops to pull away from the walls behind them, leaving visible gaps between the two. This can also indicate other foundation issues, like bowing foundation walls, so you might want to get a professional opinion to assess the underlying cause.

Sloping Floors

Sloping or uneven floors in your living area can be a direct result of the foundation sinking under your home. The floors will typically angle downward toward the area that requires underpinning.

Drywall Cracks

Drywall cracks—particularly around the corners of wall openings like windows, doors, and archways—can indicate foundation movement. This is another type of problem that can indicate other foundation issues, so you should have a professional take a look and determine if underpinning is the best foundation repair method.

Windows and Doors That Get Stuck

Finally, when your foundation loses support from underneath, it can’t provide the rigid structure it’s meant to for the rest of your home, so the framing around your windows and doors can shift, making it challenging for them to open and close. This issue can result from increased humidity in the home as well, so again, it’s best to have a foundation repair company inspect and determine the underlying problem.

Causes of Foundation Damage That Requires Underpinning

Understanding the underlying problem that leads to the need for underpinning is crucial because installing supportive piles under your home is only the first step. You’ll also need to fix the actual cause of the issue to prevent it from happening again.

Shifting Soil

Foundations most often lose support from underneath from shifting soils, usually when they expand and contract in response to moisture. Clayey soils are particularly problematic, as they absorb water and change in volume more readily than loamy and sandy soil. The best solution to this issue is usually installing a gutter system, grading soil away from your home, and considering a foundation drainage system.

Earthquakes

Earthquakes can cause sudden shifts in the earth under your home, which can leave portions of your foundation without the support they need. Damage might not be immediately apparent, but the shifting can eventually cause imbalances and demand underpinning.

Karst Landscape

Your foundation relies on the soil underneath, which, in turn, relies on the bedrock below for support. A karst landscape is one where the bedrock is primarily limestone and dolomite, both of which dissolve in the presence of water. Runoff can eventually create holes and channels in the bedrock, creating sinkholes in the soil above. In the case of sinkholes, underpinning might not be a permanent solution.

Improper Construction

When a home builder is constructing a house, one of the most important things they need to do is compact the soil properly after excavating. Too much compaction can cause issues with upward movement and foundation damage if it expands in the presence of water. Not enough compaction and the soil will settle unevenly under your home, leading to a sinking foundation and the need for underpinning.

Types of Foundation Underpinning

There are a few different styles of piles used in foundation underpinning, with the soil quality and the location of your home determining which is ideal.

• Push piers/steel piers: These reach down to hard bedrock for support, so they’re best in areas with expansive soil where the bedrock isn’t too deep.

• Helical piers: These act like screws and spread the load out to treads along the length of the pier. These work particularly well in areas with sandy soil and where the bedrock is prohibitively deep to use steel piers.

• Concrete piers: Concrete piers are an affordable option, but they often aren’t a permanent solution. They usually transfer the load a few feet into the ground. Contractors pour concrete piers on site.

• Segmented piers: These work the same as concrete piers and have the same issues with longevity, but they’re even more affordable, as the concrete is precast and installed in sections.

How Much Does Underpinning Cost?

Underpinning a foundation costs around $25,000 in most cases, and most jobs fall between $15,000 and $50,000. The total depends on the type of piers that are required and how many are necessary. Most piers cost between $1,400 and $3,500 each, and the average home requires 10 piers total.

The table below includes some more specific foundation repair costs based on the type of piers you need:

Unfortunately, homeowner’s insurance usually doesn’t cover foundation repair, so these totals will usually be out-of-pocket. The only exception would be if your foundation sinking is a result of an earthquake (and you have earthquake insurance) or a plumbing leak.

Alternative Solutions to Underpinning a Foundation

Depending on the severity of your damage and the type of foundation you have, there might be some other foundation repair methods that could stand in for underpinning. Keep in mind that none of these are applicable for raised foundations, like pier and beam foundations.

Mudjacking or Slabjacking

This process involves cutting a hole in your slab and pumping a cementitious material underneath to raise the slab back into place. Unlike underpinning, this is not a permanent solution, although it could be a suitable stand-in if you’ve only experienced a small amount of foundation sinking.

Polyjacking

Polyjacking is similar to mudjacking, but the foundation repair specialist will pump a different material—an expanding polyurethane foam—under your foundation. The foam expands and lifts your slab back into place. Again, this is not as permanent of a solution as underpinning, but it could work if you only have a little unwanted foundation movement.

Self-Leveling Concrete

Self-leveling concrete is a way to fix minor sinking that isn’t expected to continue getting worse, so it’s usually best for homes where normal settlement has gone a bit further than it usually would and left you with a slightly uneven slab. A foundation repair professional will pour self-leveling concrete over an uneven slab, and it will dry level with respect to gravity.

DIY vs. Hiring a Pro to Underpin a Foundation

Underpinning a foundation isn’t a project to tackle on your own. Hire a foundation repair contractor who specializes in underpinning to ensure the job is done right. Your home’s structural integrity depends on a stable foundation, and underpinning requires specialized equipment and expertise for a safe and long-lasting result. 

Attempting DIY foundation repair can pose safety risks, potentially further damage your home, and lead to foundation problems in the future. When deciding who to hire for foundation repair like underpinning, look for a contractor with experience working on foundations with similar issues, ask about warranties, and get several quotes.