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What Is Foundation Underpinning?

Table of Contents


1. What Is Foundation Underpinning?
2. What Causes Differential Settlement?
3. Why Would A Foundation Need Underpinning?
4. How Is Underpinning Done?
5. Signs Your Home Might Need Underpinning
6. Will Underpinning Permanently Fix A Failing Foundation?
7. How Much Does Underpinning Cost?
8. Is It Safe To Buy A House That Has Been Underpinned?

Searching for information about foundation underpinning? If so, don’t hit that back button because you’ve landed on the right page. In this article, we’re going to go over what foundation underpinning is, why a foundation might need to be underpinned, how underpinning is performed, and more.

What Is Foundation Underpinning?

Foundation underpinning is a foundation repair procedure that strengthens and stabilizes foundations experiencing problems. Usually, foundation underpinning is done to repair differential settlement. This is when a foundation is sinking into the ground unevenly. Differential settlement puts a lot of stress on the foundation and can lead to severe structural damage. Foundation underpinning raises that area of the foundation again.

What Causes Differential Settlement?

Various things, including the following, cause differential settlement:

  • Expansive soil – Expansive soil contains a high percentage of clay, and because of this, it swells as it absorbs water and shrinks as it dries out. This creates movement in the soil under the house and, over time, can lead to differential settlement.
  • Erosion-prone soil – Soil prone to erosion can wash away and leave voids under the foundation. If the foundation sinks into the voids, you’ll have differential settlement.
  • Thirsty tree roots – Tree roots looking for water can “drink” moisture from the soil leaving behind voids.
  • Soil that wasn’t adequately compacted – Soil needs to be tamped down before anything gets built on top of it. If this isn’t done correctly, the structure will settle into the ground after it’s built, which could lead to differential settlement.
  • Downhill creep – This is when the soil at the top of a hill slowly ends up at the bottom of the hill. This can cause problems for a foundation leading to differential settlement and structural damage.
  • Natural disasters – Earthquakes, floods, hurricanes, sinkholes, etc., can all cause differential settlement.
  • Excavation next to the foundation – If your neighbor starts digging a big hole next to your home, it could destabilize the foundation and lead to differential settlement.
  • Improper Drainage – Having downspouts lead rain water away from the foundation is important. Assuring that proper drainage is installed around your home will help with foundation issues if this is the case.

Why Would A Foundation Need Underpinning?

As we just noted, the main reason for underpinning is differential settlement . However, that isn’t the only reason a foundation might need to be underpinned. Other reasons include when you’re planning to add a story to a building, remodeling the home, or even addings additions.

Lifting, leveling and stabilizing a foundation by installing piers around the foundation that is experiencing settlement will assure you that your home’s foundation is stabilized for many years to come.

How Is Underpinning Done?

The two most common underpinning methods are push piers and helical piers . Which one is chosen depends on various factors, including the structure’s weight, condition of the foundation, and so forth. Push piers are driven into the ground using the weight of the building, and installed to load bearing soil. Helical piers are installed, monitored, and recorded as they are screwed into the ground beneath the house. The brackets are installed to the foundation and the helical pier is installed once all of the piers have reached the specified depth and capacity capacities. Thereafter, loads are transported to the pier system installed; if required, lifting can also be done at this time. Helical piers can also be installed for new construction, additions to homes, and in some cases porches to assure the new foundation being poured will rest upon these helical piers and not clay or weak soil.

The General Installation Process For Push Piers Is As Follows:

  • First, the soil around the foundation is excavated down to the footing in the affected area.
  • Heavy-duty steel brackets are attached to the foundation at intervals in the area that’s going to be underpinned. These brackets will support the piers.
  • The push piers are driven into the ground using hydraulic pressure and the structure’s weight until they reach load-bearing soil.
  • Once the piers are in place, they’re attached to the steel brackets, and then a synchronized hydraulic lifting system raises the building to maximum practical level. This means the building is raised as much as possible without causing damage.
  • The excavated soil is replaced, and the repair is complete.

Check Out Our Animation Video Of How We Install Push Piers!

The General Installation For New Construction Helical Piers Is As Follows:

  • Helical piers for new construction (and repairing settled foundations) don’t require heavy excavation, installation is quick and causes minimal disruption.
  • They’re turned into the soil via a helical drive motor until they reach the depth and/or torque requirement specified by the geotechnical engineer. Starting with a helical pier that looks much like a giant screw and adding extensions as necessary.
  • This depth could be anywhere from 10 to 30 feet below ground or even up to 150 feet deep, if necessary.
  • Helical piers come in many different sizes and configurations, so a detailed soils report is used to design the piers per the load requirements recommended by the geotechnical engineer.
  • The diameter of the helices depends on the soil type, with clay soil requiring larger helices. Sometimes, depending on the soil conditions, piers with more than one helix might be necessary.
  • Once all the helical piers are installed to the determined depth. We cut and cap the tops. Allowing the concrete foundation to begin installation of being poured onto the newly installed helical piers.

Signs Your Home Might Need Underpinning

Your home might need underpinning if it’s experiencing differential settlement. The most common signs of differential settlement include:

  • Doors and windows that don’t open and close properly
  • Stair step cracks in brick or masonry
  • Wall, floor, and ceiling cracks
  • Uneven floors
  • Torn or wrinkled wallpaper (The wall behind the wallpaper might be cracked)
  • Floors and ceilings that are separating from the wall
  • Moldings that are separating from the wall or ceiling
  • Porches or chimneys that are pulling away from the house

If you see any of the above or anything else that looks suspicious, contact a foundation repair contractor right away and ask for a foundation inspection.

Will Underpinning Permanently Fix A Failing Foundation?

Provided the underpinning was done correctly, it should be good for the structure’s life. In other words, you shouldn’t have to do it again.

How Much Does Underpinning Cost?

The cost of foundation underpinning depends on various factors such as your geographical location, the problem, the chosen repair solution, ease of access, etc. Without doing a foundation inspection, it’s impossible to say.

Is It Safe To Buy A House That Has Been Underpinned?

Yes, it’s generally safe to buy an underpinned house. However, that doesn’t mean you should walk into it blindly. You’ll want to make sure the repair is under warranty and that the warranty is transferable. You’ll also want to check out the foundation repair contractor that did the repair. Are they still in business and likely to stay in business? The warranty is only as good as the company standing behind it. For more information, see, Buying An Underpinned House – What You Need To Know.

If you’re in Northern California and think your home might need foundation underpinning, contact us today to schedule a foundation evaluation and receive a repair estimate.

Steve Egloff

Steve Egloff

Founder of Bay Area Underpinning

Steve is the Founder of Bay Area Underpinning, a foundation repair company serving the San Fransisco Bay Area, California. Bay Area Underpinning was founded in 2005 with the goal of providing a cost-effective, engineered solution to foundation settlement problems with an emphasis on educating customers to make them feel comfortable with the various methods of foundation repair.

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