Can You Dig A Basement Deeper To Lower The Floor?

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You may be thinking of a home renovation and are wondering if you can dig your basement to lower your basement floor. To help you with the project, we have done the research to provide you with the best answer.

Yes, you can dig a basement deeper to lower the floor. The basic methods to do so include:

  • Underpinning
  • Bench-footing

You might be increasing the space for a tenant, for a family member, or to simply make the space more livable. Whatever reason you may have for lowering the basement floor, continue reading to learn more on the methods you can use and the factors to take into consideration to successfully do so.

A basement construction for a new house, Can You Dig A Basement Deeper To Lower The Floor?

How Do You Lower A Basement Floor?

Lowering your basement floor can be done either by underpinning or bench-footing. But which method should you use? If you are torn between the two, you are not alone. Each option has its benefits and drawbacks.

In a nutshell, if you want to increase the height of your basement without decreasing the square footage, then underpinning is your best bet. Otherwise, if you use bench-footing, the square footage of your basement will be reduced.

Ideally, you can go as low as you can, though your contractor will advise you on the best method to use. The factors they assess to decide on the best method include:

  • The new depth of the basement floor required
  • The soil condition on which your property is built on
  • The total cost of lowering the floor
  • The long-run maintenance costs
  • Any existing problems like cracks that need to be tackled before starting the job.

Both methods are briefly explained below so that you can make a sound choice.

Underpinning

Underpinning, as shown in the video above, is a method that involves digging up the existing floor and excavating the dirt out to lower the foundation. There are several underpinning methods. We have listed them below:

  • Pit or mass concrete - This is the most popular method whereby the existing foundation is deepened and then filled with concrete to create a new floor level.
  • Mini piles - In this method, piles are driven into the ground, bypassing the weak soil on which the existing foundation sits, and continues until it reaches more stable soil suitable for building a new foundation.
  • Pier and beam - This can be considered an advanced option to the pit method. The current footings are replaced by a concrete beam on which the weight of the house is dispersed.
  • Cantilever needle beam - This method is the best when you are satisfied with your basement and do not want to change anything about it. Rather, you need to access your basement externally.
  • Jet grouting - This method is used to strengthen weak soil under your property. Grout is mixed with the current soil using high-pressure jets.

Reasons To Underpin

The reason behind choosing this method is that it does more than just lowering a foundation and strengthening it. In the process, your contractor will be able to access the electrical, plumbing, and insulation systems to either repair or upgrade them, especially if your home is old.

In addition, if the waterproofing has a problem, it may be changed to prolong the life in the dry space of your basement. It also increases the value of your home.

But this method is expensive, and it takes a long time to complete the job.

Bench Footing

This method does not require you to dig beneath the foundation to lower your basement floor like in underpinning but is instead made possible by widening the foundation structure.

Normally, a contractor creates a perimeter all around on the inside of the wall in your basement, and then the foundation is dug up all around it, and new footings are constructed so that they extend deeper than your new floor level.

Finally, concrete is poured in so that the base of your basement looks like it has a bench all around it, which also provides extra support.

What Are The Benefits And Drawbacks Of Bench Footing?

If you are wondering whether to use this method, here below are the pros and cons of bench footing to help you make a sound decision:

Pros Cons
Consumes little time. The square footage of your basement is reduced.
Cheaper than underpinning. Not likely to add value to your home.
No changes are made to the foundation walls. Does not encompass fixing of cracks, if any.
Little excavation.  
Good option if your neighbor does not agree to you digging under the foundation.  
The new ‘bench’ created can be used as a space for display.  

How Much Does It Cost To Lower The Floor In A Basement?

Lowering a basement floor can cost thousands of dollars. Though underpinning is more expensive because a lot more work is required such as excavation, bench footing is not very involved and costs less.

Generally, it can cost between $20,000 and $50,000 to lower a basement floor. And even if you did the work yourself, it would cost you $80 per square to underpin, and $25 per square foot to bench foot.

The overall cost depends on the area surface of the floor being lowered, the number of walls to put up, and how complicated the job is.

How Deep Can You Dig A Basement?

A sectional view of a residential building with a view of the basement

It’s very important to consider how far deep you can dig because your foundation needs enough footage to reinforce a building without causing any potential risk of collapse. Your contractor will carry out an assessment and advise you how far low you can dig.

Legally, you can dig up to 25 feet down, but if you want to go beyond this, you will need to research and find out if anyone has mining rights in the area.  

How Safe Is Underpinning?

Underpinning, just like bench footing, is safe. Even though the methods are different, both strengthen the foundation. 

The safety of your basement largely depends on the workmanship done. It’s highly unlikely that qualified professionals would compromise on quality.

Is There An Alternative To Underpinning?

As mentioned, there are only two methods with which to lower your basement floor. But if your basement has weakened due to subsidence, an alternative to underpinning is the use of a non-disruptive method such as Geobear technology.

Underpinning is disruptive because the soil has to be excavated from the foundation. It also takes a long time to complete and requires the building to be vacated before starting on the job.

But with Geobear technology, geopolymer resin is injected into the foundation through holes dug in the ground and can take only a day to complete and does not require a building to be vacated.

Does Underpinning Devalue Property?

Underpinning adds value to your property. As explained above, this method has many benefits.

Your floor is not only lowered, but your contractor can access the hidden mechanisms in your basement like the electrical, insulation, and plumbing and correct anything that could be wrong.

Also, if the foundation is weak, any of the underpinning methods used will improve the strength of the foundation, subsequently increasing its value.

However, if underpinning is done in a shoddy manner, the value of your property can decrease. That is why it is important to hire only qualified professionals who will do a high-quality job for you.

In Closing

Lowering a basement floor is a good idea if you want to increase space in your basement. There are a variety of reasons for doing this, for example, creating space for an office, laundry, or rental.

There are only two methods to choose from, underpinning and bench footing. Each has its pros and cons which you need to carefully understand so that you can make the most suitable decision.

Finally, for a top-notch job to be done, hire qualified professional contractors and/or engineers to do the work for you. Even if the costs might be high, it will be worth it.  

Have a look at our previous posts on minimum requirements for a basement and how tall your basement ceiling can be:

Minimum Height For Basement Ceiling

How Tall Basement Ceiling Needs To Be

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