Can You Build A Basement Under An Existing House?

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Basements are valuable areas of your home that are often built during the construction phase of your home. However, if you do not have a basement and you are considering adding one to your existing home, you will most likely ask yourself two questions: “Is it possible?” and “Is the project worth the costs?” Don’t worry because we have done our research to address all of your concerns.

Building a basement under an existing house is possible. The process would include underpinning or extending your home's foundation, excavating the ground underneath, and adding the walls and finishes. However, building a basement requires the right set of circumstances and is not recommended for areas prone to floods.

Knowing the possibility of building a basement underneath your existing home makes you ask more questions. How much does it cost? Is it cheaper than building a second story? Continue reading to learn everything you need to know about building a basement underneath your home.

An existing building making an extension on the basement, Can You Build A Basement Under An Existing House?

How Is It Possible To Build A Basement In An Existing House?

Yes, you can build a basement under an existing house. The process of building, however, is long and arduous. Building your basement can take at least 9 months to finish.

To begin, your contractors will have to move your existing home by raising it and bracing the foundations to keep your house from moving. Since the act of bracing keeps your home steady, it will reduce potential damages to your floors and walls.

Only then can the workers start digging and excavating the ground under your home. The price of excavation depends on various factors, which include your location and how wide your crawlspace is. Afterward, your contractors will extend your foundation through the process called underpinning.

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

If there is a wide enough space next to your home, contractors can use the help of large machinery to remove the soil underneath. Once the excavation is done, they will then install the necessary features of your basement such as drainage, plumbing, insulation, waterproofing, flooring, and walls.

Building a basement also requires getting necessary building permits and following your area’s building code. If you want to know the proper ceiling height for your future basement, check out our previous post to learn more: How Tall Does A Basement Ceiling Need To Be?

How Long Does It Take To Build A Basement Under An Existing House?

The time contractors will spend on your basement project depends on the location of your home and the complexity of your plans. According to Noble Structures, the planning stage can reach 6 months. The building phase, which includes the excavation, installation of new and extended foundations, and general waterproofing, can take 3 to 5 months. 

Adding the finishes to the basement can take anywhere from 4 weeks to 2 months to complete. In total, the whole process of making a basement under your home can take the better part of your year.

How Much Does It Cost To Build A Basement Under An Existing House?

The processes stated above previously can cost a lot of money. According to Home Advisor, building a basement under an existing house with a crawlspace can cost an average of $50 to $75 per square foot. 

This price includes the underpinning of your foundation and excavating the basement itself. If there is concrete poured underneath, taking it away may cost an additional $500 to $1,500.

Fixr says that the costs of adding a basement under an existing home can cost at least $50,000, depending on the area, size of the house, and type of soil underneath.

Finishing the basement, which includes installing windows, doors, the ceiling, lights, and other necessities, may cost as low as $1,000 and reach up to $100,000.

Is It Cheaper To Build A Basement Or A Second Story?

An excavator taking off dirt for a proposed residential building

On average, it might be cheaper to build a basement rather than add a second story to your home. As mentioned before, adding a basement to your home costs an average of $50 per square foot. 

In comparison, adding a second story may cost you an estimated $100 to $300 per square foot, according to Home Advisor and Home Guide. Another website called Fixr says that adding a second floor will cost you $300 to $500, with most jobs reaching a total of $200,000.

What Is The Benefit Of Having A Basement?

Modern basement with carpeted flooring recessed lighting and black sectional sofa

The benefits of having a basement are numerous. First and foremost, basements give you more storage space for important items, backup food, and items you will not use in a long time. Your basement can also serve as a shelter or safe room in case of extreme weather conditions like tornadoes and hurricanes.

You can also turn your basement into any kind of room you want. You can turn it into a private entertainment area for your recreational activities with your family, a bedroom for your children, extended family, or guests.

Can A Basement Be Added To A Slab House?

Yes, you can add a basement to your slab house. The process your contractors will follow to build your basement is highly similar to the process used for houses with crawlspaces. 

Since a slab house rests on a concrete slab foundation, workers will need to break it in order to excavate underneath. Contractors will lift the house and support it, remove the foundation, dig underneath, install a new foundation and the basement, restore all utilities, and then place your home back into its place. 

Although it is possible, it might be highly expensive due to the additional work your contractors have to do.

Is Building A Basement Possible Everywhere?

Building a basement depends on where you are. If your area is prone to flooding and heavy rainfall, it would be best to let go of any ideas of building a basement. High humidity and moisture will possibly crack basement walls, encourage the growth of mold and mildew, and attract pests.

If you have a basement, or you are living in a basement apartment in a humid area, and you see signs of pests, you will need to act fast. Read through this article to learn how to prevent bugs and pests from staying in your home: How To Prevent Bugs In A Basement Apartment.

How Much Value Does A Basement Add?

Interior of a wooden flooring basement and a small carpeted area for the guest bedroom

A basement may provide a myriad of benefits, but it does not add much value in terms of money. You could recoup an average of 79 percent of your expenses for a finished basement.

The 79 percent average return on investment only applies for finished basements, which Remodeling describes as a basement with insulated exterior walls, main area, bathroom, bar, and interior walls, and a ceiling with painted drywall. 

Are you planning on painting your basement ceiling? Look into our previous post: How Do You Prep A Basement Ceiling For Painting?

In Closing

Building a basement under your existing home is possible but the job requires a lot of forethought. You will have to consider if a long, expensive home renovation is worth it.

If you deem that a basement will add value to your day-to-day life and you are willing to spend time, money, and effort on it, contractors will be more than willing to help you build one to fit your needs.

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