Installing a bathroom in a basement costs more than installing a bathroom above ground. Costs can range from $2,500 to $5,000 on average, depending on the number of fixtures and whether the plumbing must be installed from scratch or if it’s roughed in already. Basement plumbing requires special considerations to ensure proper drainage and tie-in with the main sewer line, which may not be deep enough to allow the basement bathroom plumbing to use gravity the way above-ground plumbing does. Virgil Miranda’s Construction subcontracts all plumbing work. Miranda says that sometimes the toilet alone in a basement can cost up to $2,500 because sometimes homeowners need to invest in a toilet that does not use gravity but instead a macerating function to grind waste down to prevent clogging. Miranda estimates that each bathroom fixture in a basement costs $800–$900 on average, so a full, three-piece bath could cost $3,000 for the fixtures alone. Adding a kitchenette or wet bar sink adds more to overall refinishing costs. In addition, some basements require a French drain with one or more sump pumps, which can cost up to $10,000 on average, depending on how much ground the drain covers.

Unless you install a plywood subfloor, your basement floor is likely to be a concrete slab. Fortunately, concrete accepts most common flooring choices, from paint to vinyl, laminate, tile, and carpet. Most solid wood flooring is not recommended for below-grade installations, however, because it shrinks and expands, resulting in gaps or warping. Engineered wood is a good alternative because it shrinks and expands a little less.
You can fit a full bathroom with tub/shower combination in a room that measures 40-square feet. However, on average, a smaller bath (with just a stand-up shower) or a half-bath usually needs to be about 30-square feet for comfort and functionality. Depending on the basement space and layout, you may be able to go with a larger 60-square feet or more bathroom space. Creating bathroom with a separate water closet may require 100-square feet or more.