Basement Bathroom Addition in Bellevue, NE Below-Grade Baths Built Properly

Drainage below the sewer line

The defining constraint is elevation. A basement fixture generally sits below the level of the building drain leaving the house, so waste cannot flow by gravity. Two solutions exist. Break the slab, trench to a sump, and set a sealed sewage ejector basin with a pump that lifts waste up to the gravity line. Or install an above-floor macerating system behind the fixture, which avoids the slab but puts a pump and a cutting assembly in the room. The ejector approach is more work and more durable; the macerating approach is faster and has consumable parts. Either way the drain layout, vent connection and pump discharge get decided before the framing goes up, because both routes change where the walls can be.

Bellevue's flood record is a reason to inspect first

The City's flood information page documents that on April 23, 2019 Bellevue sent certified mail letters to all residents whose dwellings were deemed unsafe or unfit for human occupancy because of damage and contaminates from flood waters, and its updates name the Paradise Lakes and Green Acres developments among the areas addressed, per the City of Bellevue flood information page. At Offutt, flood water reached the installation on March 15, 2019 and the Air Force reported roughly 30 buildings affected within two days, per Offutt's own account of the response. Most basements in the city were never touched. The point is narrower: before an impermeable finish goes over a below-grade floor or a stud wall goes against a foundation wall, take a moisture reading on the slab, look at the base of any existing framing, and confirm nothing was covered up after a prior water event.

Radon: cutting the slab opens the path

Sarpy County's average pre-mitigation radon level is 5.3 picocuries per liter, drawn from 5,649 measurements taken between October 1, 2019 and September 30, 2024, per the Nebraska Department of Health and Human Services radon report. The EPA action level is 4.0. Every penetration a bathroom makes in that slab — the closet bend, the shower drain, the ejector pit, the lavatory trap arm — is a potential entry route, and where a mitigation system already exists, its performance depends on the slab staying sealed. Seal each penetration as it is backfilled, keep the suction pit and its piping intact, and test after the work is finished. A post-work test costs a fraction of the finish it would otherwise call into question.

Permits, and who files them

Bellevue's permit division states that no structure regulated by the division within the city and its two-mile jurisdiction may be altered, repaired or converted without a permit first obtained from the building official, and that unless otherwise exempted separate plumbing, mechanical and electrical permits are required, per the City's permit FAQ. A new below-grade bathroom is new work by every measure. Under § 27-58 the plumbing permit is applied for, signed and paid for by the master plumber, and Nebraska statute 18-1917 requires that plumber to hold a license from the nearest city or village with journeymen licensed by the same. Plumbing fees are $23.50 for issuance plus $9.80 per fixture or trap, with $4.75 per fixture where drainage or vent piping is altered, per the plumbing fee schedule. Building permit valuation runs $69.25 for the first $2,000 plus $14.00 per additional $1,000 under the 1997 Uniform Administrative Code table Bellevue still uses, per the building permit fee schedule.

Insulating a below-grade room in Climate Zone 5

Nebraska sits in Climate Zone 5, where the 2018 energy code Bellevue adopted alongside the IRC prescribes R-19 or R-15 continuous at a basement wall, R-49 at the ceiling and 3 air changes per hour at 50 pascals, per the state energy code summary. Sarpy County's 99 percent heating design temperature is 2 degrees Fahrenheit, per the county design temperature guide, and Omaha reached 16 below zero on January 14, 2024, per the National Weather Service annual summary. The assembly that survives that is continuous rigid foam against the concrete with the framing held off the wall, not fiberglass batts stuffed against masonry where warm interior air can reach a cold surface. Any supply line run in a rim joist cavity or against a foundation wall is a freeze candidate and belongs inside the insulation, not behind it.

Ventilation and heat for a room with no exterior window

Below grade there is usually no glazing, so natural ventilation under R303.3 is unavailable and mechanical exhaust is the only route: 50 cfm intermittent or 20 cfm continuous under IRC M1505.4.4, per this summary of the ventilation sections. The duct has to reach the exterior, which below grade means a longer run and often a rim-joist penetration, so size the fan for the actual run and insulate the duct. Basements also run cold, which makes an electric floor a reasonable addition here; see heated bathroom floor for the circuit and protection requirements. The services list shows how the pieces of a below-grade build fit together.