Basements can be useful rooms for either storage or for use as a media room, entertainment room or even spare bedroom. They're also safe spaces to escape to during severe storms. However, some houses may not come with basements, prompting some homeowners to look into installing a basement under a completed house. This is a costly endeavor, however, that will typically run well into tens of thousands of dollars.
The overall cost of constructing a basement under an existing home will vary widely depending on a number of factors, including the size of the basement, the labor required, the materials and the paperwork required. Expect to pay no less than $30,000 to $50,000 to build yourself a basement. That number could be greatly increased, depending on your location and local fees.
Building a basement is not just a matter of digging a hole under the house. The house must be placed on a temporary foundation while tons of soil are removed from underneath in a process that could take several weeks to several months, during which time you will most likely be required to leave your home. So you'll have to factor in what it will cost to move into a hotel for a while or live with someone else.
The other factors that go into the extravagant cost of building a basement include details such as paperwork and zoning laws. Some cities may not let you build basements because of unstable soil conditions or may charge a hefty fee. The contractor fee will also come into the equation, as some will charge more than others. Electrical lines in your home will need to be moved as well as plumbing pipes, so electricians and plumbers will be involved, as well. The shape of the basement is also a factor, as the more complex the shape, the more expensive the building project.
One less expensive approach to building a basement is to build it not under your house but next to it. This will alleviate the need to dig under your house or physically move it. Building an adjacent basement, possibly with stairs leading down to it from somewhere in your home, could save you thousands of dollars as opposed to a basement underneath the home. However, the numbers will fluctuate depending on the aforementioned factors.