What Does Underpinning A House Mean?

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Are you wondering what underpinning a house means? If so, don’t hit that back button because that’s what we’re going to talk about in this article.

Underpinning a house means supporting and strengthening the structure’s foundation using piers. These might be push piers, helical piers, drilled concrete piers, or slab piers. Foundation underpinning is a reliable foundation repair technique used for centuries to strengthen foundations and ensure their structural integrity over time.

This article will explore what underpinning is, why a house might need underpinning, how underpinning is done, and more.

What Is Underpinning A House? 

In simple terms, underpinning is the process of strengthening the foundation of a building by adding additional support below the structure. This is typically necessary when a home is built on unstable soil or when the existing foundation has become damaged. Underpinning is done to ensure the stability and longevity of your home.

The most common reason a house needs to be underpinned is differential settlement.

What Is Differential Settlement? 

Differential settlement happens when different parts of the foundation sink into the ground at different rates. This puts a lot of stress on the foundation and will cause cracks, uneven floors, and other problems.

At the first sign of differential settlement, it’s essential to seek professional help right away to assess the situation and develop a plan of action. With timely intervention, you can prevent further damage and preserve your home’s structural integrity.

In simple terms, underpinning is the process of strengthening the foundation of a building by adding additional support below the structure.

What Causes Differential Settlement? 

Differential settlement is caused by various things, including the following:

  • Expansive soil – If the soil under a foundation contains a lot of clay, it will expand as it soaks up moisture and then shrink as it dries out. This is usually seasonal, and it creates movement in the ground under the foundation. Over time, this can cause differential settlement.
  • Erosion-prone soil – Some soil types are prone to erosion. If you have this type of soil under your home, along with poor drainage, the soil could wash away, leading to the formation of voids. If the house settles into the voids, there will be differential settlement.
  • Inadequate soil preparation – Before anything gets built on top of it, the soil must be adequately tamped down. If this isn’t done correctly, the structure will settle into the ground after it’s built, usually unevenly.
  • Excavation – If your neighbor digs a big hole too close to your home’s foundation, this can be enough to destabilize the soil under your foundation, leading to differential settlement.
  • Weather changes – An example would be building a house on top of expansive soil during the dry season. When it starts to rain again, the soil will expand and push against the foundation. This can lead to differential settlement.
  • Seismic events – Any ground movement can potentially cause differential settlement.

While differential settlement is not always preventable, it is essential to be aware of its potential causes and to take measures to mitigate it. We’ll talk more below about how you can help prevent differential settlement.

How Is Underpinning A House Done?  

Underpinning a house to correct differential settlement usually involves installing push or helical piers. The type of pier used will depend on the weight of the building, the kind of foundation, etc.

Push piers are driven into the ground underneath the foundation until they reach load-bearing soil. Helical piers – which look something like giant corkscrews – are turned into the ground until they reach the required depth and capacity. If necessary, the foundation is then raised to maximum practical level, which means the foundation will be raised as much as possible without causing damage.

For push piers, the general installation process is as follows:

  • The soil in the area to be underpinned is excavated down to the footing.
  • Steel brackets are attached to the footing at various intervals. These brackets will provide support for the push piers.
  • The push piers are driven into the ground through the brackets using hydraulic pressure and the house’s weight.
  • Once the piers are in place, they’re attached to the brackets, and a synchronized hydraulic lifting system raises the foundation to maximum practical level.
  • The final step involves replacing the excavated soil.

Common Signs A House Might Need Underpinning Because Of Differential Settlement 

Common signs of differential settlement include the following:

  • Doors and windows that don’t open and close properly
  • Stair step cracks in brick or masonry
  • Cracks in walls, floors, and ceilings
  • Uneven floors
  • A chimney or porch that’s leaning away from the house
  • Torn or wrinkled wallpaper (The wall behind the wallpaper might be cracked.)
  • Diagonal cracks from the corners of windows and doors
  • Moldings that are separating from the wall or ceiling
  • A ceiling or floor separating from the wall

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

Underpinning Cost 

The cost to underpin a foundation varies according to your geographical area, what type of foundation you have, the severity of the problem, etc. For more information, see Foundation Repair Cost.

We also have a handy pricing calculator that will help you estimate the cost of foundation repair.

Of course, the only way to get an exact quote is to contact a foundation repair contractor and ask for an estimate.

How You Can Help Prevent Foundation Trouble 

Since most foundation problems are caused by excess moisture in the ground around a foundation, you can help prevent trouble by getting groundwater under control. Here are some ways to do that:

  • Make sure your gutters aren’t clogged with dead leaves and other debris. You don’t want runoff spilling over the side of the house and soaking the ground around the foundation.
  • Use downspout extensions to carry runoff away from the house before releasing it.
  • If you have any water-hungry vegetation planted next to your house, consider relocating it.
  • If necessary, regrade the yard around your house so it slopes away from the foundation. This will keep groundwater from draining toward the foundation.
  • Install a drain tile system. This is the best foundation waterproofing system in use today. Instead of putting up a barrier to keep water out, a drain tile system prevents excess soil moisture from building up in the first place.

If you think your house might need underpinning, contact us today to schedule a foundation evaluation. We serve Southern California, Arizona, and Nevada.


Brian Dalinghaus

Brian is one of the Co-Founders of Dalinghaus Construction. He has been in the foundation repair industry since 2005. During his career, he has been associated with helping over 4,000 homes and structures throughout California and Arizona.

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