Bathroom Addition Cost (2026): Half Bath vs Full Bath, Real Project Breakdowns

Adding a bathroom is one of the most requested projects I get — and one of the most misunderstood in terms of cost. I've added bathrooms in basements, converted closets into half baths, built full master bath additions, and everything in between. The cost range is enormous, and it all depends on one thing: how far are you from existing plumbing?

Let me break it all down.

Quick Cost Overview

These numbers include permits, plumbing, electrical, finishes, and labor. They assume typical conditions — no major structural work or foundation modifications.

Half Bath vs. Full Bath: What Makes Sense?

Half Bath (Powder Room)

A half bath has a toilet and sink. That's it. No shower, no tub.

Best for:

• Homes with only one bathroom (going from 1 to 1.5 baths is transformative)
• Near the kitchen or main living area for guest use
• Maximizing ROI at the lowest cost

Minimum space needed: 18 square feet (3' × 6'). Comfortable: 25–35 square feet.

Typical cost breakdown:

Full Bath

A full bath includes a toilet, sink, and tub or shower (or a tub/shower combo).

Best for:

• Homes with 2+ bedrooms sharing one bath
• Adding a master suite
• Basement finishing with a full apartment setup

Minimum space needed: 36 square feet (5' × 7.2'). Comfortable: 50–75 square feet.

Typical cost breakdown:

The #1 Cost Factor: Distance From Existing Plumbing

I cannot overstate this: the location of your new bathroom relative to existing plumbing lines is the single biggest cost variable. Everything else is secondary.

Scenario 1: Back-to-Back With Existing Bathroom (Best Case)

If your new bathroom shares a wall with an existing bathroom or kitchen, the plumber can tie into existing supply and drain lines through the shared wall. This is the cheapest option by far.

Plumbing cost: $1,500–$3,500 Why: Short runs, existing vent stack nearby, minimal demolition

I recently added a half bath in a closet that backed up to the master bathroom. Total plumbing cost: $2,200. The entire project came in at $11,500.

Scenario 2: Same Floor, 10–20 Feet From Existing Plumbing

Still manageable. The plumber runs supply lines through the floor or wall cavities and ties into an existing drain line. May need a new vent pipe through the roof.

Plumbing cost: $3,000–$6,000 Why: Longer runs, possible ceiling/floor demolition in the path, new vent pipe

Scenario 3: Basement Bathroom (Below Existing Sewer Line)

Here's where it gets expensive. In most homes, the main sewer line exits through the basement floor or wall. A basement bathroom's drains are at or below this line, so gravity doesn't help you.

Solution: An ejector pump system ($800–$2,000 for the pump, plus installation). The pump sits in a sealed pit below the bathroom floor and pumps waste up to the main sewer line.

Plumbing cost: $4,000–$8,000 Why: Concrete cutting/trenching for drain lines ($1,500–$3,000 alone), ejector pump, longer supply runs

I've done dozens of basement bathrooms. Budget a minimum of $15,000 for a half bath and $25,000 for a full bath in a basement with a concrete slab.

Scenario 4: New Addition (Extending the Home's Footprint)

If you're building a bump-out or room addition to house the new bathroom, you're in major [renovation](/blog/bathroom-renovation-cost-guide) territory.

Additional costs beyond the bathroom itself:

• Foundation work: $5,000–$15,000
• Framing and roofing: $8,000–$20,000
• Exterior finishing (siding, etc.): $3,000–$8,000
• HVAC extension: $2,000–$5,000

Total project cost: $40,000–$90,000+ for a full bath addition with new square footage.

Plumbing Deep Dive

Since plumbing is the big-ticket item, let's get specific about what's involved.

Supply Lines (Hot and Cold Water)

Running new copper supply lines costs $8–$15 per linear foot. PEX tubing (now allowed in most jurisdictions) costs $3–$8 per linear foot and is faster to install. PEX has largely replaced copper in residential work, and I recommend it for any new bathroom project.

For a bathroom 15 feet from the water heater:

• Copper: $240–$450 for materials and fittings
• PEX: $90–$240 for materials and fittings

Drain Lines

This is where the real cost lives. Drain lines must slope at 1/4 inch per foot (minimum) toward the main stack. A toilet requires a 3-inch drain; sinks need 1.5-inch; showers/tubs need 2-inch.

ABS/PVC drain pipe: $3–$6 per linear foot installed Concrete cutting for basement drains: $15–$25 per linear foot (plus $500–$1,000 for the trenching and patching)

Venting

Every drain fixture needs a vent pipe that connects to the roof vent stack. This prevents siphoning of the P-traps (which would let sewer gas into your home).

Options:

• Traditional vent: Run a new vent pipe through the wall and roof. $500–$1,500 depending on routing.
• Air admittance valve (AAV): A mechanical vent that fits inside the wall. $15–$30 for the valve. Allowed by most codes for individual fixtures, but not all jurisdictions approve them. Check local code.

Rough-In Labor Rates

A licensed plumber charges $75–$150/hour depending on your market. A complete bathroom rough-in (supply, drain, and vent for toilet, sink, and tub/shower) takes 16–32 hours.

Plumber rough-in labor: $1,200–$4,800

Location Strategies That Save Thousands

Based on hundreds of projects, here are the smartest locations for adding a bathroom:

1. Convert a Large Closet (Half Bath — $8,000–$15,000)

Walk-in closets adjacent to bathrooms are gold mines. You already have plumbing 6–12 inches away through the wall. Minimum closet size of 3' × 6' works. I've done this conversion at least 30 times, and it's consistently the most cost-effective bathroom addition.

2. Under the Stairs (Half Bath — $10,000–$18,000)

The space under a staircase is often 30–40 square feet of wasted space. With creative fixture placement (corner sink, compact toilet), this can become an elegant powder room. The challenge is usually headroom — you need a minimum of 6'8" at the toilet.

3. Garage Conversion (Full Bath — $20,000–$35,000)

If you're converting part of a [garage to living space](/blog/heloc-for-garage-conversion), adding a bathroom makes sense. The concrete floor allows for easy drain line installation (cut the concrete, lay pipes, patch). Just ensure the floor slopes away from the garage door, not toward it.

4. Bump-Out Addition (Full Bath — $35,000–$60,000)

A 6' × 8' bump-out addition is the minimum for a comfortable full bath without stealing interior square footage. This is the right choice when interior space is at a premium and the exterior wall is near existing plumbing.

Fixtures: Where to Spend and Where to Save

After 200+ bathroom projects, here's where I tell clients to allocate their budget:

Spend More On:

• Toilet: A quality toilet (Toto Drake, $350–$450) will outperform a $150 builder-grade toilet for decades. Comfort height, elongated bowl, and 1.28 GPF flushing is the sweet spot.
• Faucet: A $200 faucet from Delta or Moen will last 15+ years. A $50 faucet will drip within 3. I've replaced thousands of cheap faucets.
• Tile installation: Proper waterproofing (Schluter Kerdi or RedGard) in the shower is non-negotiable. Water damage from a leaking shower costs $5,000–$15,000 to remediate.

Save Money On:

• Vanity: A high-quality 24" or 30" vanity from Home Depot ($250–$500) is 90% as good as a $1,500 custom piece. The countertop matters more.
• Mirror: A simple frameless mirror ($40–$80) is perfectly fine. The fancy framed options ($200–$500) are pure aesthetics.
• Accessories: Towel bars, toilet paper holders, and robe hooks from Amazon ($30–$60 for a matching set) are identical to the $150 sets at specialty stores.

Permits and Code Requirements

You will need permits. Adding a bathroom involves plumbing and electrical work, both of which require permits in virtually every jurisdiction.

Typical permit costs:

• Plumbing permit: $100–$400
• Electrical permit: $75–$250
• Building permit (if structural work): $200–$600
• Total permit fees: $300–$800

Key code requirements:

• Minimum clearances: 15" from toilet center to any side wall or fixture. 21" clear in front of the toilet (24" is code in many areas now).
• Ventilation: An exhaust fan vented to the exterior is required (no, you can't just open a window in most jurisdictions). 50 CFM minimum for bathrooms under 100 sq ft.
• GFCI protection: All bathroom outlets must be GFCI protected.
• Waterproofing: Shower walls and floors must have a waterproof membrane behind the tile.
• Floor loading: If adding a tub on an upper floor, verify the floor joists can handle the weight. A full bathtub weighs 500+ pounds. Older homes with 2×8 joists may need sistering.

Pro tip: Pull your own permits online (many jurisdictions offer this) and save $200–$500 that contractors charge as a permit markup. Just make sure inspections happen on schedule.

Project Timeline

The typical delay: Tile. Custom tile orders take 2–4 weeks. Tile installation takes 3–5 days (including setting, grouting, and curing). Plan ahead.

ROI: The Numbers That Matter

Adding a bathroom delivers strong returns, but the specifics depend on what you're adding:

Going from 1 bath to 1.5 baths:

• Average cost: $12,000–$18,000 (half bath)
• Average value increase: $15,000–$25,000
• ROI: 100–140%

This is the highest-ROI bathroom addition scenario. Homes with only one bathroom sell at a significant discount in most markets.

Going from 1 bath to 2 baths (adding a full bath):

• Average cost: $25,000–$40,000
• Average value increase: $25,000–$45,000
• ROI: 80–115%

Going from 2 baths to 2.5 baths (adding a powder room):

• Average cost: $10,000–$18,000
• Average value increase: $10,000–$15,000
• ROI: 60–85%

Going from 2 baths to 3 baths:

• Average cost: $25,000–$45,000
• Average value increase: $15,000–$30,000
• ROI: 50–70%

The diminishing returns are clear. Adding a bathroom when you only have one is almost always worth it financially. Adding a third or fourth bathroom is about lifestyle, not investment.

Money-Saving Strategies

1. Keep it close to existing plumbing. I said it before, I'll say it again. Every foot of distance from existing pipes adds $50–$150 to the plumbing bill.

2. Use a prefab shower/tub unit instead of custom tile. A one-piece fiberglass shower ($300–$800) costs $3,000–$5,000 less than a custom tile shower when you factor in materials, waterproofing, and labor. It's not as pretty, but it's watertight and maintenance-free.

3. Do your own demolition. If you're converting a closet or space that needs gutting, demo the drywall, pull the carpet, and haul debris yourself. Saves $500–$1,500 in labor.

4. Install your own accessories. Towel bars, mirrors, toilet paper holders, paint — all easy DIY. Save $300–$800 in handyman charges.

5. Shop fixture sales. Kohler, Moen, and Delta all run major sales around Presidents' Day, Memorial Day, and Black Friday. A $600 toilet/vanity/faucet combo on sale drops to $350–$400.

6. Consider a three-quarter bath instead of full. Skipping the tub and installing a shower-only saves $1,000–$3,000 and requires less floor space. Most people prefer showers anyway.

Red Flags When Getting Quotes

• Quote doesn't mention permits. Either they're not pulling them (illegal and risky for you) or they'll add them later.
• No separate line items for plumbing and electrical. These should be clear, not buried in a lump sum.
• "We'll figure out the tile when we get there." Tile selection needs to happen before the quote. Materials vary from $2/sq ft to $25/sq ft.
• No mention of waterproofing. If the [contractor](/blog/diy-vs-contractor) doesn't discuss shower waterproofing methods, find someone who does.
• Timeline under 1 week for a full bath. It's not possible to do quality work that fast. Tile alone needs 48 hours of curing time.

Final Thoughts

A bathroom addition is a significant investment, but it's one that pays for itself — especially if you're going from one bathroom to two. The key is location. Spend time planning where the bathroom will go relative to existing plumbing, and you'll save thousands.

Get at least three quotes from licensed contractors. Make sure each quote specifies fixture brands, tile selections, and whether permits and inspections are included. And whatever you do, don't skip the waterproofing in the shower. I've ripped out more water-damaged bathrooms from cut-rate installations than I can count.

Planning a bathroom addition? Share your situation in the comments and I'll help you figure out the best approach for your home.

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