Rough plumbing is the floor, not the total
Most garage conversion cost guides give you a single line for bathroom plumbing, typically in the $6,000-$15,000 range depending on how far the new drain lines have to travel to reach the main sewer stack. That number covers the rough-in: pipes in the walls and under the slab, the toilet flange, and the shower drain. It says nothing about what the bathroom actually looks like when you’re done, and that finish layer is its own significant budget line.
Tile
Tile is usually the single biggest finish-level cost in an ADU bathroom. A tiled shower surround with a standard ceramic or porcelain tile runs $2,500-$6,000 installed for materials and labor, depending on shower size and pattern complexity. Natural stone or a more intricate layout, such as a herringbone pattern or a mosaic accent band, pushes that toward $6,000-$10,000. Floor tile for the rest of the bathroom adds $1,000-$2,500 for a typical ADU bathroom footprint. A tub-shower combo with a simple three-wall surround costs less than a curbless walk-in shower, which requires more precise waterproofing and slope work underneath the tile.
Fixtures
Toilet, sink, faucet, and shower valve and trim make up the fixture budget, and the range here is wide because it scales directly with quality tier. A functional, code-compliant fixture package, a standard two-piece toilet, a basic vanity with sink, and a mid-grade shower valve, runs $1,500-$3,000 total. Moving to a comfort-height toilet, a quartz or solid-surface vanity top, and a better shower valve with a rain head pushes that to $3,500-$6,000. High-end fixtures, a wall-mounted vanity, a freestanding tub, designer faucets, can push the fixture budget past $8,000 on its own.
Ventilation
Every ADU bathroom needs a working exhaust fan to manage moisture, and this is a smaller line item but not a trivial one, especially in a garage conversion where the fan has to duct through a roof or wall that wasn’t originally built with that penetration in mind. A standard bathroom exhaust fan installed with new ducting typically runs $400-$900. A quieter, higher-capacity fan with a humidity sensor, worth considering in a converted garage bathroom where moisture control matters more than in a room with better natural airflow, runs $700-$1,200 installed.
Putting the full picture together
Add it up and a complete, code-compliant ADU bathroom, finished, not just roughed in, typically runs $10,000-$20,000 in San Diego for a mid-range finish level, on top of the $6,000-$15,000 rough plumbing line most cost guides already quote. A builder-grade finish can land closer to $8,000-$12,000. A high-end finish with premium tile and fixtures can push past $25,000 for the finish work alone.
Lighting and electrical finish work
Beyond the rough electrical already priced into the plumbing and structural budget, a finished bathroom needs task lighting at the vanity, a ceiling fixture or recessed cans, a GFCI-protected outlet near the sink, and often a switch for the exhaust fan separate from the main light. Budget $500-$1,200 for this finish-level electrical work, more if the design calls for multiple light sources like sconces flanking a mirror plus overhead lighting, a common upgrade over a single centered ceiling fixture in a builder-grade bathroom.
Paint, trim, and the small details that add up
A finished bathroom also needs moisture-resistant paint on any non-tiled walls, baseboard and door trim to match the rest of the ADU, a mirror or medicine cabinet, towel bars, and a toilet paper holder. Individually these are small costs, typically $50-$300 each, but together they commonly add $800-$1,800 to the finish budget that a rough plumbing estimate never accounts for.
Where San Diego specifics change the number
Hard water is a real factor in fixture selection here. Shower valves, faucets, and glass shower doors all show mineral buildup faster in San Diego’s hard water than they would in a soft-water region, and cheaper fixtures tend to show it sooner and more visibly. Spending a bit more on a quality shower valve and considering a glass coating treatment on shower doors is a reasonable place to upgrade if the budget allows, since it affects how the bathroom looks in year three, not just on move-in day.
Why is my bathroom quote so much higher than the rough plumbing estimate I saw online?
Rough plumbing estimates cover pipes and drain lines only. Tile, fixtures, ventilation, paint, and any electrical for lighting and outlets are separate line items that typically add $10,000-$20,000 on top for a mid-range finish.
What’s the cheapest way to finish an ADU bathroom without it looking cheap?
Standard ceramic tile in a straightforward layout, a quality mid-tier toilet and faucet set rather than the absolute lowest-cost option, and a simple three-wall shower surround instead of a curbless design keep costs down while still looking finished and durable.
Can I phase the bathroom finish to spread out the cost?
Some homeowners rough in the plumbing and install basic, code-compliant fixtures and tile at move-in, then upgrade to higher-end finishes later once the ADU is generating rental income or the budget allows. This works structurally as long as the initial fixtures are genuinely functional and code-compliant, not a placeholder that will need to be torn out rather than simply swapped for a nicer version later on.
Do I need a permit for bathroom finish work in an ADU?
The rough plumbing and any new electrical for the bathroom require permits as part of the overall ADU conversion permit. Finish-level work like tile and fixture installation is typically covered under that same permit rather than needing a separate one, but confirm the specific scope with your contractor and San Diego Development Services.
For a detailed bathroom finish estimate based on your specific ADU layout, see our plumbing for ADU page or call (858) 400-4935.
Garage Convert SD connects San Diego homeowners with experienced, insured crews for full ADU conversions. Call (858) 400-4935 for a free consultation.