How to Add a Basement to a House

Can you add a basement to a house? Definitely. Do you want to build a basement under an existing house? Maybe. Do a lot of research before committing yourself to adding a basement under your home. This article will help you learn more about how to add a basement to a house.

You Can Put a Basement Under Most Buildings

How to Add a Basement to a House

Basements are built for many types of existing buildings. In most instances, the basement is constructed; then, the building is moved to the location and set on the basement. Finally, services are hooked up, and any required finishing is completed.

House-moving companies and foundation companies are very adept at coordinating these types of projects.

  • Modular Homes.
  • Trailers.
  • Houses moved to new locations.

Basement building permit

It is impossible to build basements in some locations. High water tables, underground streams and springs, and soil types are problems. (Many parts of Florida, for instance, have no basements.)

A call or visit to your local government building permit department will tell you if a basement under your existing house is possible.

Note: If you proceed with adding a basement, you will get to know city or county engineers, plumbing, sewer, heating, and construction inspectors better than you ever thought possible.

The Benefits of Adding a Basement Under your House 

Adding a basement under your home can improve your living arrangements. It could be worth the time, cost, and effort if you cannot move or do not want to move. Adding a basement is a good option if building an addition, garage, storage shed, or outbuilding is not feasible.

Increases Living Space

Ideally, adding a basement adds the same amount of floor area as you have on the main floor. Some possible uses for your newly finished basement include:

  • Mother-In-Law Suite.
  • Children’s Bedrooms.
  • Rental Suite.
  • Entertainment Theater.
  • Exercise Room.
  • Whatever You Desire.

Increases Storage Space

Hundreds of square feet in a new basement stores a lot of overflow. From six years of tax files to unused exercise equipment, getting it out of your living area is a relief. Other options, such as a storage shed–if available–may be more cost-effective.

Increases Resale Value

For resale purposes, agents only list the area of the floors above grade–not basements. Well-designed and finished basements are great selling points. Remodelling Magazine says the national average Return on Investment (ROI) for finishing a basement is over 70%.

The 70% does not factor in the cost of building the basement, but it is an indication that finished basements have significant value. Add to that the years of benefit and pleasure you derive from the extra space, and the investment may be well worth it.

The Cons of Adding a Basement Under Your House 

Living in a house with a basement has many benefits, but there are some cons to building the basement after the house.


Adding a basement under your house costs between $50.00 and $75.00 per square foot if you have an existing crawl space. More if your home sits on a concrete pad. (Breaking up and removing the pad while salvaging plumbing and sewer connections adds to the price.)

The entire project probably takes 9 – 12 months to complete. You will not be living in your home while it happens. Be prepared for the additional costs of renting or the annoyance of living with relatives.

Miscellaneous Concerns

Most other concerns like flooding, leaking, rodents, and pests are non-issues if you have a good contractor who ensures solid water-tight and pest-tight construction. Make sure you pay attention to the possibilities and ask questions.

How to Build a Basement Under Your House

If I haven’t convinced you to add space in another way–let’s get to it. Unless you are a general contractor by trade, this is not a DIY project. Start by getting quotes from reputable general contractors–preferably three who have experience with this type of project.

Ask for references, names, and addresses of previous customers. Get permission to see and talk to them. You are engaging in a major league contract. Be diligent with your money.

Adding a basement under a house involves almost as many trades as building a complete house – building movers, excavators, cribbers, plumbers, and electricians.  A general contractor is experienced in scheduling and supervising multiple tradesmen and obtaining all required permits.

Spend time with your contractor during the entire process. You may not know the difference between a 15 amp breaker and a tin basher, but you are writing the checks and will have to live with the result. Being on-site can prevent the temptation to take a shortcut.


Once you have chosen a contractor, get a plan drawn. The dimensions have to match your house. Plumbing rough-ins, electrical panel locations, footings, etc., must be clearly marked. Basement locations have to match the main floor locations.

Note: You will need detailed plans to get permits.


You are going to lift and/or move your house. Remove anything that might break and tie down everything else, drain all the water lines, and disconnect power.

Remove anything in your yard that might get in the way or get crushed – backhoes, gravel trucks, and concrete trucks need a lot of space. Make sure the neighbors are fully informed. Men and equipment may encroach on their property.

Moving the House

Most contractors prefer moving the house right off the basement location to make work easier and safer. In many situations, there is not enough space close by. They will then raise and block the house high enough to work under it. Make sure that you understand and approve of the method that will be used.


If the house is removed, they can dig a hole using a large track hoe, which is quick and efficient. If the house can only be raised in place, the excavation will have to be done with a tractor-mount backhoe and loader. A ramp is dug to allow the hoe to get under the house, and the process is a much slower operation.

Pouring the Walls

Before the footings are poured, contractors will install all water and sewer lines. They will pour the footings and post pads, then the walls. Then, they’ll install weeping tile around the footings and waterproof the exterior walls. (Pouring a $100,000.00 basement that leaks is not funny.) Finally, they’ll backfill the hole, ensuring proper grading for water drainage.

Replacing the House

The last step is to place the house on your new basement and secure it to the concrete. Once that’s finished, the contractor will hook up all of the services, pour the basement floor, install the HVAC system, and install stairs to the main floor. 

Is It a Good Idea to Build a Basement Under an Existing House?

It’s almost never a good idea to build a basement under an existing house if you have other options. If you do not have options or refuse to use them, make sure that you are adding the basement for your own needs and pleasure. There is a very good chance you will not recoup your investment in dollar value only.