What Is Underpinning A Foundation And When Is It Necessary?

Searching for information about underpinning a foundation? If so, you’ve landed on the right page! In this article, we’re going to talk about what underpinning is, when it’s used, methods, what causes foundation problems, and things you can do to prevent trouble with your home’s foundation.

What is underpinning a foundation?

Underpinning a foundation stabilizes and reinforces a foundation that can no longer adequately support the structure built on top of it. Underpinning increases the depth of the foundation and transfers the structure’s weight to load-bearing soil or bedrock.


For more information about soil and construction see, How Missouri Soil Affects Your Kansas City Area Home.

When is underpinning a foundation necessary?

Foundation underpinning is necessary when the foundation can no longer support the building sitting on top of it. Foundations start to fail for various reasons, including,

  • Problems with the soil – These problems could include differential settlement (often caused by drainage problems), subsidence (when the ground sinks and takes your foundation with it), and problems related to erosion.
  • The foundation wasn’t constructed properly – Soils are not all alike. Perhaps the building contractor didn’t consider the soil conditions before constructing the foundation.  
  • A natural disaster has weakened the foundation, and it’s no longer stable.

Underpinning a foundation is not a cosmetic repair or temporary fix. It solves the root problem, which is that the foundation is sitting on unstable soil that cannot support it. If done correctly, underpinning should last for the life of the structure.

 
While foundation underpinning is usually used for failing foundations, it may also be necessary when the foundation is stable but conditions on top of and around the foundation change. These include,

  • Adding an extra story to the building – If you plan to add another floor to your house, you’ll probably need to strengthen the foundation via underpinning.
  • When there’s going to be heavy excavation next to the building – Heavy excavation next to a foundation can cause destabilization. Sometimes it’s necessary to underpin a foundation before excavation begins for new construction next door.   

Underpinning is not an inexpensive repair. However, it will increase the value of your property. 

photo of a push pier

Underpinning methods

Here at KC Waterproofing, we use the following three foundation repair methods to underpin a building:


Push piers – Heavy-duty steel push piers are the most common method for underpinning a foundation in trouble. The installation procedure involves attaching steel brackets to the foundation footer and then, using the building’s weight along with hydraulic pressure, driving the steel piers through the brackets until they reach load-bearing soil. Once they’re in place, synchronized hydraulic jacks lift the building.


Helical piers – While corkscrew-shaped helical piers are usually used for new construction projects requiring a deep foundation, they’re also used for underpinning foundations. Because of their shape, they’re turned into the ground until they reach load-bearing soil. (Determining the load capacity requires consultation with a geotechnical or structural engineer.) Once they’re in place, synchronized hydraulic jacks lift the building back to level.


Slab piers – Slab piers are helical or push piers installed through holes in the slab. They’re spaced 5 feet apart, and either pushed (push piers) or turned (helical piers) into the ground until they reach the load-bearing strata. At that point, the slab is lifted and leveled. 

What causes foundation problems?

Foundation problems are caused by various things, including,

  • Expansive clay soil – Expansive clay soils swell when they soak up moisture and shrink when they dry out. This causes movement under the foundation, which can, over time, lead to destabilization.
  • Soil that wasn’t adequately prepared before construction – Foundations are heavy. If they’re placed on soil that wasn’t adequately prepared, they will settle unevenly into the ground after being built, causing problems. Proper preparation prior to construction includes removing organic material such as leaves and compacting the fill soil.
  • Soil erosion under the foundation – This might be caused by an undetected leaking pipe or wetter than usual weather combined with poor drainage. 
  • Soil creep – This is something that happens to homes built on hillsides. Soil creep is something like a slow-moving, imperceptible landslide. Eventually, it can destabilize a foundation.
  • Large trees – If large trees have been “drinking” water from the soil around and under the foundation, it could dry out the soil and cause voids to form, which the house then sinks into.

For more information, see Is It Safe To Live In A House With Foundation Problems?

Signs you might have a foundation problem that requires underpinning

Here are some of the most common signs of foundation problems that might require underpinning:

  • Wall cracks – Look for horizontal wall cracks and vertical wall cracks that are wider at the top. Hairline vertical cracks are usually caused by shrinkage during the concrete curing process and do not affect your home’s structural integrity. However, that doesn’t mean hairline vertical cracks are harmless. Hairline vertical cracks in a foundation wall can allow water to enter your basement. Therefore, they should be inspected by a professional foundation repair contractor
  • Unlevel floors – If you drop a marble on the floor, does it always roll toward a specific area? If so, you might have an unlevel floor.
  • Floor cracks – Look for floor cracks that go from wall to wall across the room. A crack limited to one or two tiles probably happened when something fell on the floor.
  • Gaps between the crown molding and the wall or between the baseboard and the wall – Molding sections can separate from each other, form gaps between the molding and the ceiling/floor, or pop off the wall due to structural movement and settlement.
  • Gaps between the wall and the ceiling or between the wall and the floor – Again, even slight separations should get your attention.
  • Doors and windows that no longer open and close properly – If it’s just one door or window, it might not be foundation-related. However, that doesn’t mean it should be ignored. If the problem is being caused by a foundation issue, there will probably be other signs as well. Problems with multiple doors and windows are an obvious cause for concern.
  • Torn or wrinkled wallpaper – This could indicate the wall behind the wallpaper is cracked.
  • Wall rotation – Wall rotation happens when the soil along the outside of the wall is dry, while the soil along the inside of the wall has moisture. Wall rotation usually happens with shorter walls.
  • Diagonal wall cracks over 1/10 inch – If the diagonal cracks are hairline (i.e., less than 1/10 inch), they might not be related to a foundation problem. However, they should still be inspected by a professional foundation repair contractor.
  • Stair step cracks in brickwork or masonry – This is a sure sign the foundation has moved.
  • Chimneys or porches that are starting to pull away from the house – This could be related to problems with the foundation under the chimney or porch. However, it could also be related to a problem with the house’s foundation.

Things you can do that may prevent foundation problems

The following may help you prevent foundation problems:

  • Regrade your yard – Your yard should slope away from the foundation so that water doesn’t drain toward the foundation.
  • Clean your gutters regularly – Clogged gutters can cause water to spill over the side of the home and into the soil next to the foundation.
  • Install downspout extensions – If your downspouts are too short, they’ll release water too close to the foundation. Extensions channel the water away from the foundation before releasing it.
  • Install an underground downspout and bubbler pot – Water from the gutters flows into the underground downspout and from there into a bubbler pot located several feet from the foundation. When the bubbler pot fills with water, it pops up and releases the water away from your foundation.
  • Install an exterior or interiordrain tile system – A drain tile system is installed either around the outside perimeter of the foundation at the footing level (exterior) or around the inside perimeter of your basement (interior). Both types of drain tile systems work by preventing excess water from building up in the soil around the foundation. A drain tile system is a gold standard for waterproofing a basement foundation.
  • Install a French drain in your yard –  A French drain is a way to keep water from pooling around your home’s foundation. It involves digging a shallow trench somewhere in your yard, filling it with gravel, and then adding a perforated pipe. Water enters, flows through the pipe, and drains away from the foundation.
  • Keep large trees at least 20 feet away from the foundation – As we pointed out above, large trees will “drink” moisture from the soil around the foundation. 
  • Make sure you don’t have any undetected plumbing leaks – Over time, plumbing leaks can lead to soil erosion under and around the foundation.

Have you noticed a problem and think you might need underpinning for your home’s foundation? If you’re in our service area in Kansas or Missouri, contact us today for a free inspection and repair estimate. 


We can also create a benchmark report complete with measurements and a topographical map of the house. A benchmark report enables you to monitor if your home is settling and by how much.