Adding a New Bathroom: Permits, Drains, and Vents

You found a closet, a corner of the basement, or a spare room that could become a full bathroom—and then someone asked where the new toilet drain would tie in.

That is the moment many homeowners realize adding a bathroom where none existed is not the same project as refreshing an existing one. A new fixture group needs its own drain and vent path. On a second floor, you often cannot dump into the floor below’s vent and call it done.

PermitCove is an independent homeowner guide, not a government agency. The Spokane (WA), Portland (OR), and Pasadena (CA) examples below are concrete local rules from published handouts and permit pages. Your city or county Authority Having Jurisdiction (AHJ) may package building, plumbing, electrical, and mechanical permits differently, adopt a different code year, or limit who can pull the work. Confirm every step locally. See our disclaimer.

New Bathroom vs Bathroom Remodel

Shoppers and contractors sometimes say “bathroom remodel” for both projects. Plan reviewers do not. Start by naming what you are actually doing:

• Existing bathroom remodel keeps a wet room where one already is. Cosmetics may stay light; moving fixtures, opening walls for plumbing, or changing the tub/shower drain usually triggers permits. Our bathroom remodel permits guide covers that gray zone. If you are only turning an existing tub into a walk-in shower, see the tub-to-shower conversion guide.
• Adding a new bathroom creates a toilet, lavatory, and tub or shower group in space that was dry—closet, hallway slice, unfinished basement, attic bump-out, or an addition. You are introducing new drain, vent, water, electrical, and usually exhaust paths.

Portland’s residential bathroom pages frame the project as converting part of a home to a bathroom and walk applicants through research, prepare, apply, and inspect. They note that a remodel may need trade permits only (electrical, mechanical, plumbing), while a new bath has a building path—and some projects may qualify for Portland’s Simple Bathroom Program versus the standard process. That split is a Portland example, not a nationwide rule. Ask your AHJ which path applies before you buy fixtures.

If the new bath sits in unfinished basement space, also read Finishing a Basement: When You Need a Building Permit. Spokane’s SFR-14 notes that exposed exterior concrete walls in an unfinished basement area being remodeled need insulation (Spokane cites minimum R-21 and points to SFR-13)—attribute that figure to Spokane, not every U.S. city.

A new bathroom is a rough-in project: new drains, vents, supply, wiring, and exhaust before finishes hide the story.

The Permit Stack: Building, Plumbing, Electrical, Mechanical

Spokane’s SFR-14 bathroom addition/remodel guide sheet is blunt: adding or remodeling a bathroom normally requires building, plumbing, electrical, and mechanical permits. Attribute the following Spokane triggers to that handout:

• Building if you add or relocate walls, or remove wall/ceiling finish to the studs and joists.
• Plumbing if you add, replace, relocate, or reinstall plumbing fixtures.
• Electrical if you add a circuit or relocate switches, lights, or outlets.
• Mechanical for the exhaust fan path when the project requires outdoor ventilation.

Pasadena’s Residential Bathroom Remodel handout (2025 California code edition framing) similarly expects a completed building permit application—and plumbing, mechanical, and electrical applications when applicable—plus plans. Do not invent fees from either city’s packet language; ask the counter for current valuation and fee schedules.

For the broader “who pulls what” picture, see how to apply for a building permit and the printable 10-minute AHJ permit check. Plumbing and gas line questions that travel with a water heater move sit in our plumbing and gas line permits guide.

Drains, Vents, and the Second-Floor Trap

The lead problem on a new bath is not tile—it is drain, waste, and vent (DWV). Each fixture needs a trap and a vent path so the trap seal does not siphon. Spokane SFR-14 publishes concrete fixture sizes for its jurisdiction (attribute these to Spokane, not your city unless your AHJ matches them):

• Toilet (water closet): minimum 3-inch drain and minimum 2-inch vent.
• Lavatory (wash basin): minimum 1½-inch drain and vent.
• Bathtub: 1½-inch trap and trap arm; after the vent connection, horizontal drain runs must be minimum 2-inch with a 1½-inch vent.
• Shower: minimum 2-inch trap, trap arm, and drain with a minimum 1½-inch vent.
• Combining vents: Spokane allows vents to combine if they are more than 42 inches above the floor level.

Critical Spokane rule for second-floor new baths: you cannot connect the new drain line to the vent from a main-floor bathroom, even if that vent is a 3- or 4-inch line. A new, minimum 3-inch drain line must connect to the building drain. That one sentence saves homeowners from a rough-in rejection when they try to “tap the existing bath stack vent” upstairs.

For sizing framing only—not as a substitute for your adopted code—IRC 2024 Chapter 30 (sanitary drainage) Table P3004.1 lists a full-bath group with a 1.6 gallons-per-flush water closet at about 5 drainage fixture units (d.f.u.). Horizontal drainage slope in P3005.3 is not less than ¼ inch per foot for 2½-inch diameter and less, and not less than ⅛ inch per foot for 3-inch and larger. Your local code year may differ; say which edition your AHJ uses before you argue from a book you bought online.

New baths need a real drain path to the building drain—not a clever tie into someone else’s vent.

What Plans Usually Show

Spokane wants a floor plan of the bathroom with dimensions and proposed fixture locations, plus a key plan showing where the bathroom sits on its floor level inside the house—and an approximate total cost (labor and material; materials-only if the owner provides labor, with labor estimated by the department). Pasadena asks for a site plan highlighting the work area, a floor plan with dimensions about the remodeled area (adjacent rooms shown), and—if the layout changes—existing plus proposed floor plans, with framing notes if walls come out.

Portland’s “fill out your forms” page shows Type of Work as Alteration on the building permit application and gives a sample description of work for a new full bath in an unfinished basement (toilet, sink, shower; no load-bearing wall changes; trade work by licensed contractors; exhaust fan to the exterior; remaining basement unfinished). Adapt the description to your house—do not copy Portland’s sample blindly, and do not invent fees from valuation tips on that page.

Label fixtures, show the floor level on a key plan, and note new walls—packet clarity beats a pretty mood board.

Electrical, Exhaust, and Scald Protection

Spokane: if a bathroom outlet is added or relocated, it must be on a GFCI circuit with nothing else on the circuit except bathroom outlets. At least one GFCI-protected outlet is required on the counter by the sink, and all bathroom outlets must be GFCI-protected. Light and exhaust fan may use separate switches.

Pasadena examples (2025 CEC framing in their handout): at least one 20-amp GFCI-protected receptacle within 36 inches of the outside edge of each bathroom sink basin; a minimum one 120 V / 20 A branch circuit for bathroom receptacle(s) with no other receptacles on that circuit; all 125 V, 15- and 20-amp bathroom receptacles GFCI-protected. For outlet and circuit permit habits more broadly, see our electrical permit guide.

Exhaust: Spokane requires a minimum 50 CFM exhaust fan vented outdoors with a positive outdoor connection for a new bathroom, a bathroom with the ceiling opened, or an existing bath without an exterior window. If the fan uses a 3-inch exhaust, Washington State Ventilation and Indoor Air Quality rules in Spokane’s handout require upsizing the duct to a minimum of 4 inches; ducts leaving heated space or going above insulation need minimum R-4 insulation. Pasadena’s exhaust section also cites a minimum 50 CFM outdoor exhaust for baths with a tub, shower, spa, or similar moisture source (with continuous-operation and humidistat details in that California handout)—attribute those extras to Pasadena / the codes it cites.

Scald protection: Spokane requires the shower or tub/shower valve to meet ASSE A1016, with water not exceeding 120°F, and says the water heater thermostat alone is not a suitable control. Pasadena similarly requires pressure-balance / thermostatic / combination valves conforming to ASSE 1016 / ASME A112.1016 / CSA B125.16 (or listed alternatives in the handout), with handle positions limited to a maximum mixed setting of 120°F. Pasadena also notes shower stalls with a minimum interior finished area of 1,024 square inches able to encompass a 30-inch diameter circle—Pasadena / CPC examples, not a free pass for every city.

If you tile the tub/shower area, Spokane wants cementitious backer board—not blue or green gypsum wallboard.

Exhaust belongs outdoors—50 CFM examples in Spokane and Pasadena handouts are local figures to confirm with your AHJ.

How to Describe the Work at the Counter

Write one honest paragraph before you apply. Portland’s sample for a basement full bath is a useful pattern: name the fixtures, say whether load-bearing walls change, state that plumbing/mechanical/electrical will be permitted as required, note exterior exhaust, and say what stays unfinished. Spokane wants cost honesty up front. Pasadena wants existing versus proposed when the layout moves.

Bad description: “Bathroom remodel.” Better: “Add new full bathroom on second floor in former closet/hall space; new 3-inch drain to building drain; new vents; new GFCI bath circuit; 50 CFM (or local) exhaust to exterior; no change to exterior walls.” Then let the counter tell you which permits stack.

Checklist Before You Open the Wall

1. Name the project: new bathroom where none existed—not a cosmetics remodel of an existing bath.
2. Ask which permits: building, plumbing, electrical, mechanical—and who may pull them.
3. Trace the drain: path to the building drain; if upstairs, do not plan to dump into a main-floor bath vent (Spokane’s published trap).
4. Size fixtures and vents per your AHJ; use Spokane’s inch sizes and IRC DFU/slope figures only as attributed examples.
5. Draw the packet: floor plan, key plan with floor level, existing/proposed if layout changes, site highlight if required.
6. Plan GFCI and the bath receptacle circuit per local electrical rules.
7. Plan outdoor exhaust (CFM, duct size, insulation, termination) before you cut the ceiling.
8. Specify scald-protection valves and backer board for wet walls.
9. Write the description of work in one clear paragraph; schedule rough inspections before cover.

Bottom Line

Adding a new bathroom is a multi-trade permit project: new drains and vents, often a dedicated bath receptacle circuit, outdoor exhaust, and plan sheets that show where the room sits in the house. Use Spokane’s second-floor drain rule, Portland’s alteration / Simple Bathroom framing, and Pasadena’s GFCI–exhaust–scald examples as real published patterns—attribute every inch, CFM, and temperature figure to the jurisdiction that printed it—and confirm your AHJ’s adopted code year before the first saw cut.

Last checked: October 31, 2026.

Official Sources

• City of Spokane — SFR-14 Bathroom Addition or Remodel in a Residence (PDF) (permit stack; fixture drain/vent sizes; 50 CFM exhaust and duct notes; GFCI; ASSE A1016 / 120°F; cementitious backer; second-floor drain cannot tie to main-floor bath vent)
• City of Portland — Residential bathrooms (convert space to a bathroom; Simple Bathroom Program vs standard; remodel may be trade permits only)
• City of Portland — Residential bathrooms: fill out your forms (Type of Work: Alteration; sample description for new full bath in unfinished basement)
• City of Pasadena — Residential Bathroom Remodel handout (PDF) (GFCI within 36"; dedicated 20A bath receptacle circuit; 50 CFM outdoor exhaust; scald protection; shower 1,024 sq in / 30" circle; plan submittal notes)
• IRC 2024 Chapter 30 — Sanitary Drainage (UpCodes viewer) (Table P3004.1 full-bath group ~5 DFU with 1.6 gpf WC; P3005.3 slope ¼ in/ft ≤2.5", ⅛ in/ft ≥3"—local code year may differ)

PermitCove is an independent guide for homeowners, not a government agency and not a substitute for your local building, plumbing, electrical, or mechanical department. Always confirm permit requirements, fees, licensing, and inspection sequencing with your AHJ before starting work.

Edited by Ahmed Khalifa, founder of PermitCove. Sources are linked inline; see our Editorial Policy.