Quick Answer: Adding a half bathroom (powder room — toilet and sink only, no tub or shower) to a San Jose home costs $8,000-$18,000 to convert an existing space (under-stair storage, coat closet, or unused utility room) into a powder room with new plumbing and finishes. Creating a new half bath as an addition or building out previously unfinished space costs $18,000-$40,000 depending on how far it is from existing plumbing. The minimum space required for a powder room is 20 sq ft, though 25-35 sq ft is more comfortable. Required utilities: one cold water supply, one drain, and ventilation (either operable window or exhaust fan with exterior duct). A plumbing permit from San José Building Division is required for all new fixture connections.
Half Bath Addition Cost by Scenario — San Jose 2025
| Scenario | Cost Range | Key Factor |
|---|---|---|
| Convert under-stair closet to powder room (near kitchen plumbing) | $8,000 – $15,000 | Best ROI — easiest plumbing run |
| Convert coat closet on main floor | $10,000 – $18,000 | Cost depends on distance to existing plumbing |
| Build out from unfinished garage space | $15,000 – $28,000 | Requires insulation, drywall, new plumbing run |
| New addition specifically for half bath | $20,000 – $40,000 | Most expensive — full construction |
| High-end finishes (designer tile, vessel sink, wallpaper) | +$3,000 – $8,000 | Powder rooms are seen as design statement rooms |
Quartz Construction adds powder rooms and half baths to San Jose homes regularly — often combined with kitchen remodel or room addition projects. CSLB #1003436 | Call (650) 749-7436.
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