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Cost guide · 2026

How Much Does It Cost to Add a Bathroom in Washington?

Adding a bathroom is one of the highest-impact projects a growing household can take on — and one where the budget depends almost entirely on where the new bathroom goes. Here is what it actually costs to add a bathroom around Lynnwood, Seattle, and Snohomish County in 2026, from a powder room tucked under the stairs to a full addition.

The three ways to add a bathroom — and what each costs

A powder room carved out of existing space — under a staircase, out of a large closet, or off a hallway — is the least expensive route. A half bath needs only about 15–20 square feet, a sink, and a toilet, and in this market typically runs $15,000–$35,000 depending on how far the new plumbing has to travel to reach the existing drain and vent stacks.

A full bathroom within your existing footprint — converting part of a bedroom, a laundry room, or an oversized closet into a bath with a shower or tub — usually lands between $30,000 and $70,000. The room itself costs about what a full bathroom remodel does; the difference is the new supply, drain, and vent runs, the electrical circuits, and the ventilation that all have to be built from scratch.

A bathroom that rides on a home addition — a bumped-out primary bath, or a new bath inside a larger addition — is priced like the addition it lives in. Additions around Puget Sound run roughly $300–$550 per square foot, and bathrooms sit at the top of that band because they are the most plumbing- and finish-dense rooms in a house. Budget $75,000–$150,000 for a dedicated bathroom addition, and see our primary suite addition guide if the bath is part of a bedroom-and-bath suite.

What moves the number most

  • Distance to existing plumbing. A new bath that stacks over or backs onto an existing wet wall saves thousands. One on the far side of the house — or over a slab that needs trenching — costs real money before a single tile goes in.
  • Drain, waste, and vent logistics. Sewer line depth and venting paths decide how invasive the rough-in is. Basement baths sometimes need a sewage ejector pump; that is a line item worth knowing about early.
  • Upstairs vs. downstairs. Second-floor additions of any kind carry structural review, and wet rooms upstairs need careful attention to framing deflection and waterproofing.
  • Finish level. The same 40-square-foot room can be finished for $12,000 or $40,000. Tile, glass, stone, and fixtures are where taste meets budget — our bathroom remodel cost guide breaks down those tiers.
  • Permits and inspections. A new bathroom is never a cosmetic project — plumbing, electrical, and often structural permits apply in every city we serve, and the right contractor builds them into the price rather than around them.

Is it worth it?

Around Puget Sound, going from one bathroom to two is one of the strongest value moves in remodeling — it changes how a house functions for a family and how it shows at resale. Going from two to three matters most in larger homes and multigenerational setups. If the goal is an in-law arrangement or rental flexibility, it may be worth reading about attached ADUs before settling on a bathroom alone — sometimes the smarter project is slightly bigger.

Get a real number for your house

Where the new bathroom can go — and what it will cost — comes down to your home’s plumbing layout, framing, and panel capacity. Go Far Construction gives free, no-obligation estimates across Lynnwood, Seattle, and Snohomish & King County, with itemized written pricing that shows exactly where each dollar goes.

Bathroom addition questions

How much does it cost to add a bathroom in Washington?

In the Lynnwood–Seattle area in 2026, a powder room built within existing space typically runs about $15,000–$35,000, a full bathroom converted from existing space about $30,000–$70,000, and a bathroom that is part of a new addition roughly $75,000–$150,000, priced with the addition at about $300–$550 per square foot.

Can I add a bathroom anywhere in my house?

Almost anywhere — but placement drives cost. The most affordable spots back onto or stack above existing plumbing walls. Locations far from the main drain and vent stacks, or over a concrete slab, need longer runs, trenching, or an ejector pump, all of which add cost. A feasibility look at your plumbing layout answers this quickly.

Do I need a permit to add a bathroom?

Yes. A new bathroom always involves plumbing and electrical work, and often framing changes, so permits and inspections are required in every city in Snohomish and King County. Go Far Construction prepares the permit application for your jurisdiction and includes fees in the itemized estimate.

How long does it take to add a bathroom?

A powder room or a full bath within existing space typically takes 3–6 weeks of construction once permits and materials are in hand. A bathroom that is part of a larger addition follows the addition timeline — usually several months door to door including design and permitting.

Keep reading

How Much Does a Bathroom Remodel Cost in the Seattle Area? How Much Does a Home Addition Cost in Washington? How Much Does a Primary Suite Addition Cost in Washington? How Much Does a Small Bathroom Remodel Cost in Washington?

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