How Much Would It Cost to Add a Basement

How Much Does a Basement Cost?

Unfinished Basement, New Construction: $10-$25+ a Square Foot

Finished Basement, New Construction: $30-$100+ a Square Foot

Adding Basement to Existing House: $30,000-$70,000+

A basement can add additional storage, workshop or living space to a house, especially where it isn't possible to expand out or up. Although traditionally residents of tornado-prone areas have been told to take shelter in a basement if a storm shelter is not available, a basement does not necessarily function as a good tornado shelter unless the basement has been designed and reinforced for that purpose.

Typical costs:

Including a basement as part of new house construction can increase the cost of the house by $10-$25 or more a square foot for an unfinished basement, or about $10,000-$50,000 or more for an average house; and $30-$100 or more a square foot for a finished basement, or about $35,000-$175,000 or more for an average house; with costs depending on location, soil conditions, the size and shape of the basement area (unique shapes with more than four corners cost more), the materials/finishes used and additional features like a bathroom or laundry hook-ups.
Adding a basement to an existing house can cost $30,000-$70,000 or more, depending on the size of the existing crawlspace or half-basement or if the house is on a slab foundation, and how much of the work is do-it-yourself and how much is done by contractors. Many experts (like Bob Vila[1] ) estimate that it is less expensive and less risky to build an above-grade addition or an addition with a basement, next to the existing structure. However, house-moving companies like Klier Structural Movers[2] in Ohio assert that adding a basement to an existing house is a cost-effective addition.
A basement alone does not guarantee safety during a tornado. Building a structurally-reinforced safe room area inside a basement (whichit can double as a closet, bathroom or utility room) can add $6,660-$14,300 or more to the total cost, depending on size (the number of people expected to take shelter within it), materials used and location within the basement. Having a prefabricated safe room (a welded steel box, a steel skeleton with steel planks or a prefabricated unit that is bolted together on site) installed in a basement can cost $3,000-$20,000 or more, depending on materials and size.

Related articles: Basement Remodeling, Basement Waterproofing, Flooded Basement, Repairing and Sealing a Basement, Storm Shelter, Home Addition

What should be included:

Constructing an unfinished basement typically includes excavation, footings, walls, a concrete slab floor, utilities, waterproofing, drain tile, back fill and cleanup. A finished basement typically includes all of that plus flooring, walls, ceilings, drywall, windows, and additional waterproofing and more in order to provide the desired living space. Overall, a basement adds about 3-4 weeks to the new-house construction schedule. A video[3] illustrates the excavation process.
In some areas a basement is not feasible because of a high water table or unusual soil conditions (particularly in coastal or marshy areas, or in many parts of Texas, Oklahoma and Arkansas); the cost of excavating through solid rock; or because there is frequent earthquake activity.
In colder parts of the country, a home's foundation must be below the frost line, which can require digging down several feet (typically about 2.5'-5', depending on location). In those areas, adding a basement during new house construction may require only a few more feet of digging to create a usable basement area. In warmer climates where the foundation does not have to be as deep (typically 18"-20" for a crawlspace or a few inches for a slab foundation), including a basement adds more to the total cost of the house because it requires a lot more additional excavation, far beyond what would be done without a basement.
Adding a basement to an existing house requires: building permits and engineering plans; raising and supporting the house; excavating the basement space (and hauling away the dirt); re-grading and creating new drainage; and pouring concrete footers, floors and walls. A video[4] illustrates the process using a skid loader.

Shopping for a basement:

For new home construction, work with the architect to include a basement in the house design and blueprints.
For a remodeling project that includes adding a basement (either under the existing home or as part of an addition being built), the National Association of the Remodeling Industry offers tips for choosing a contractor[5] .
If possible, get several estimates. Request and check references from previous customers. Verify that the company is properly insured, bonded and licensed. Request a written contract or agreement that specifies the work to be done and the rates to be charged.

Post

Comments (1)

CostHelper News

What People Are Paying - Recent Comments

Posted by: Samthedog in brecksville, OH.	Posted: February 20th, 2016 07:02PM
Square Feet: 1000	Finished or Unfinished:
Contractor: jm design build

came home from work today to find the deck of my addition was installed and when standing in the room the joist height is 6'5", quite a bit lower than expected, I have a 6'2" son and this was to be his room, any suggestions?

External Resources: