What Is Underpinning?

Today you will learn what underpinning actually is, how to determine what type and methods best fit your situation best. Also, We'll talk about the methods of underpinning, with a quick review of the most important options. Read this article all the way to the end, and I tell you why you (as a homeowner or not) should get involved in choosing the best underpinning option for you.

Learn all the Secrets before you Hire a Building Contractor

By now you know that Underpinning is a method to reinforce existing foundations. Most likely these methods of underpinning are recommended by engineers to fix sinking buildings and other foundations issues.

In California, that we have earthquakes and liquefaction areas among many other unstable hillsides along with receding soils, Underpinning may be the only salvation for your sinking home. Underpinning as a foundation repair solution, basically consists of supporting failing foundations, sinking or settling concrete slabs, all done from underneath using lots of concrete.

Among the 4 major types of underpinning, which are a pit, mass pouring, beam and base, and pile, are usually recommended to lift and stabilize existing structures, so pay attention to it. Although I will point out and explain only 4 types of underpinning here, there are many other types and ways of underpinning to stabilize your home.

Additionally, we'll go over the three types of piles that are commonly used in the underpinning pile method. Because we know that you are looking for it on the internet, I will show you some drawings to help you visualize them.

Jesus loves you and so do I, by the way, a house built on rocks will not need underpinning! So if you are a Jesus freak you will never need underpinning.

Let's talk about the most important methods of underpinning:

I want to tell you the 4 most common types of underpinning because if you need to raise or repair any building, the right choice is paramount to successful outcomes. In the four choices that I’ll give you, you will find the ideal one for your situation.

1 - Pit Method or Hole Method

This is the most common and the easiest kind of underpinning. An engineer will evaluate your foundation system, and mark sections where your foundation will receive the underpinning method.

To help you understand a little more about these methods and important rules, watch below one of the videos from our Youtube Channel XPlanNation. We explain this one in detail there, with drawings and designs…

Usually, the foundation is divided into regular 3’ to 4’ sections, unless the structural engineer stipulates otherwise. Next, one section at the time is excavated under the foundation wall just above the plinth level.

Are you asking what is a plinth? Here is an example…

Plinth Method Sample

This is just one shoring solution. You can use other shoring methods if you like. But following the engineer's recommendations is always best. Then, the foundation pit is dug and the new foundation is laid underneath according to engineering recommendations. Use steel, hardware, and proper Concrete PSI as per plans. The work for this kind of underpinning is done in sections.

If you watched the video above, you know already how this is made.

2 - Mass Pouring Method

This type of underpinning is used in situations that require shallow underpinning but not a lot of digging. In this method, the weak soil under the surface is excavated and concrete is poured in its place to strengthen the base.

Check out this drawing here.

Mass Pouring Method Sample

3 - Beam and Base Method

This method utilizes a traditional mass concrete base along with supportive beams to ensure the foundation is stable. The weight of the foundation is supported by beams constructed below or above the foundation.

These beams distribute the foundation weight and transfer it evenly to a massive concrete base. Engineers go balls deep into this design.

Beam and Base Method Sample

4 - Pile Method

This is the method commonly used by foundation companies that invested in the right reusable hardware.

In the pile method, foundation piles, also known as foundation piers, are installed at equal distances along the foundation to lift it and transfer the weight of the home off of the unsteady concrete. This method is particularly useful in expansive, erosive, or waterlogged soils.

Though this is a common solution performed by foundation repair companies, there is a lot of variation between repair jobs based on the type of piers used.