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Adding bathroom plumbing to a detached garage starts with the basic line installation cost of $900 to $1,300. On top of this base expense, you'll need to budget for each fixture. A toilet costs  $250 to $550, sinks cost $150 to $800, and a shower or bathtub costs $400 to $1,900. The project will also require ventilation, moisture-resistant materials, and possibly electrical work. Remember that these costs reflect only the plumbing aspects—additional construction, finishing, and permitting expenses will apply to complete a functional bathroom space.

While certain aspects of garage renovation might be suitable for DIY enthusiasts, plumbing installation requires professional expertise. Connecting to water and sewer systems demands specialized knowledge and equipment, and improper installation can result in severe water damage, code violations, and potential health hazards. Most municipalities require permits for plumbing modifications, and these often stipulate that licensed professionals must perform work. Consider limiting your involvement to simpler tasks like painting or basic finishing work.

The timeframe for adding plumbing to a detached garage spans one to three days for the actual plumbing work. However, this represents only the active installation period. The complete project timeline must account for planning, obtaining permits (which can take weeks depending on your locality), coordinating multiple contractors if needed, and addressing any unexpected challenges that arise during installation. Weather conditions can also impact excavation and outdoor connection work.

Adding plumbing to a detached garage will likely increase your property taxes. Tax assessors consider plumbing an improvement that enhances property value and functionality. The specific tax impact varies by location and project scope. Converting a garage into living space with plumbing facilities can trigger significant reassessment in many jurisdictions. Before proceeding with your project, consult your local tax assessor's office to understand the potential tax implications and factor this ongoing expense into your decision-making process.