A basement bathroom addition is usually the most plumbing-heavy part of a finished basement. The plan has to cover where the waste goes, how the fixtures are vented, the exhaust fan and enough headroom.
Permits for a basement bathroom
- Milwaukee: plumbing in a single-family, owner-occupied home needs a permit (414-286-8208), and a bathroom remodel is marked "Probably" [1].
- Brookfield: plumbing fixtures such as a tub, toilet, shower or sink need a plumbing permit, and an electrical permit may be required for certain projects [2].
- Shorewood: a bathroom remodel needs building, plumbing and electrical permits, with plans [3].
- Glendale: a bathroom remodel is "Probably," so call (414) 228-1708 [4].
Who can do the plumbing depends on the town. Franklin says plumbing and electrical work must be done by licensed contractors [5], and Waukesha issues those permits only to licensed contractors [6]. New Berlin lets an owner who lives in a single-family home do their own plumbing and electrical, but not hand it to a contractor under the owner's permit [7].
Getting waste up to the sewer
When the bathroom sits below the home's drain line, wastewater has to be pumped up. HomeGuide says ejector pumps and macerating toilet systems can do this without breaking up the slab, and that an ejector pump adds $2,000 to $5,500 [8]. Ask each plumber which method they'd use for your house and why.
Ceiling, venting and the fan
- Headroom. The general rule is 7 feet, but the ceiling may slope lower past the front edge of a toilet or sink, as long as it doesn't drop below 5 feet until beyond the back of the fixture. Lower ceilings are also allowed over the back or side of a tub or shower [9].
- Exhaust. Waukesha's basement page says rooms with a toilet, tub or shower need an exhaust fan rated for 50 cubic feet per minute if it runs on demand, or 20 if it runs continuously, vented outside [6]. Greendale's checklist asks for at least 50 at the outside termination and recommends a 70 CFM fan [10].
- Venting. New Berlin's guide says shower stalls must be vented and drained through a 2 inch trap with approved fittings [7].
Cost
National figures from HomeGuide: converting existing basement space runs $200 to $250 per square foot, or $3,000 to $12,500 for 15 to 50 square feet [8]. By size, a small half bath is $3,000 to $5,000, a medium full bath $8,000 to $12,500 and a large full bath $10,000 to $25,000 [8]. Angi lists toilet installation at $225 to $530, a sink at $215 to $660 and a shower at $1,100 to $8,500 [11].
More is in the cost guide. If the bathroom serves a basement bedroom, read egress windows too.
Request a quote for a basement bathroom.
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Sources
- City of Milwaukee DNS, Does It Need a Permit? (fetched Nov 11, 2026) https://city.milwaukee.gov/DNS/permits/PermitChecklist
- City of Brookfield, Items Requiring Permits (fetched Nov 11, 2026) https://www.ci.brookfield.wi.us/744/Items-Requiring-Permits
- Village of Shorewood, Permit Information Sheet (PDF) https://www.villageofshorewood.org/DocumentCenter/View/632/Permit-Informational-Sheet?bidId=
- City of Glendale, Permit Information Sheet (PDF) https://www.glendalewi.gov/DocumentCenter/View/201/Permit-Information-Sheet
- City of Franklin, One & Two Family Addition/Alteration Permit Applications (PDF, 2026) https://www.franklinwi.gov/Files/Inspection/One-and-Two-Family-Addition-Alteration-Permit-Application-2026.pdf
- City of Waukesha, Residential Basement Remodel (fetched Nov 11, 2026) https://www.waukesha-wi.gov/government/departments/residential-basement-remodel.php
- City of New Berlin, Recreation Rooms guideline (PDF, dated 08/26/2022) https://www.newberlin.org/DocumentCenter/View/500
- HomeGuide, "How Much Does It Cost to Put a Bathroom in the Basement? (2026)," Jennifer Carlson, Feb 6, 2026. https://homeguide.com/costs/cost-to-put-bathroom-in-basement
- Wis. Admin. Code SPS 321.06, Ceiling height (fetched Nov 11, 2026) https://docs.legis.wisconsin.gov/code/admin_code/sps/safety_and_buildings_and_environment/320_325/321/ii/06
- Village of Greendale, Basement Rec-Room Checklist for Plan Submittal (PDF) https://greendale.org/departments/inspection_services/docs/BASEMENT%20REC%20ROOM-PLAN%20REVIEW%20CHECKLIST-website.pdf
- Angi, "How Much Does It Cost to Finish a Basement? [2026 Data]," Rachel Hoffman, updated Oct 29, 2026. https://www.angi.com/articles/how-much-does-it-cost-finish-basement.htm