ADU & Addition Plumbing
California has made ADUs far easier to build. The plumbing connection is still where the schedule most often slips.
ADU plumbing covers the water supply, drain and vent, and sewer connection for an accessory dwelling unit. In California these are permitted and inspected, and the plumbing rough-in must pass inspection before walls close. Whether you tie into the existing house lines or run a separate service affects both cost and timeline substantially.
Accessory dwelling units are now a major part of California residential construction, and Salinas is no exception. The plumbing side involves supply, drain, waste and vent, and getting waste out to the sewer — plus a water heater and fixtures inside.
The decision that shapes the project is whether you tie into the existing house plumbing or run separate lines. Tying in is usually cheaper but depends on whether the existing service and sewer lateral have capacity. Separate service is cleaner but involves the utility and more excavation.
We are not your permit expediter and will not pretend to be. What we do is the licensed plumbing work, sized correctly, installed to code, and present for inspection. Requirements and fees are set by the City of Salinas and Monterey County, and you should confirm those with them rather than relying on a contractor's summary, ours included.
When this is likely your problem
- Planning an ADU, junior ADU, or garage conversion
- An addition that needs a bathroom or kitchen
- Uncertainty about whether existing lines can carry another unit
- A plan check comment about plumbing
- A contractor needing rough-in before drywall
- Deciding between shared and separate water service
What's included — and what isn't
Included in the quote
- Review of existing service and sewer capacity
- Supply, drain, waste, and vent rough-in for the unit
- Water heater connections
- Sewer connection or tie-in to the existing lateral
- Presence on site for rough-in and final plumbing inspection
- Fixture trim after finishes
Quoted separately
- Permit, plan check, and impact fees
- Architectural drawings and plan expediting
- Excavation and trenching beyond the plumbing scope
- Concrete, framing, drywall, and finishes
- Electrical and mechanical trades
- Utility meter installation, which is the provider's work
What drives the number
We quote after diagnosis, not before. These move the number most on this service:
- CONNECTIONTie-in to existing lines versus a separate service and lateral.
- DISTANCEHow far the unit sits from the existing connection point.
- CAPACITYWhether existing service and sewer can carry the additional load.
- FIXTURESFixture count in the unit.
- SITETrenching distance, obstructions, and what is on the surface.
Salinas note
The most common ADU delay we see is the rough-in inspection sequence. Plumbing has to be inspected before it is covered, and framing or insulation going in ahead of that inspection means opening it back up. Confirm the inspection order with the City of Salinas early — it costs nothing and prevents the most expensive kind of rework.
Related
What the visit involves
Assess what exists
Service size and sewer lateral condition decide the whole approach.
Price both connection paths
Tie-in and separate service, where both are viable.
Rough in for inspection
Supply, DWV, and connections installed and tested before close-up.
Trim and final
Fixtures connected after finishes, and we attend final inspection.
Questions about this service
Can my ADU share the existing water and sewer?
Often yes, if the existing service size and sewer lateral have capacity for the additional fixtures. That is an assessment rather than an assumption — an older undersized service may not carry it. We check before designing, because discovering it later is expensive.
Do I need a separate water meter?
That depends on local requirements and on whether you want the unit billed separately. It is a question for the City of Salinas and the water provider rather than for us. We will build to whichever arrangement you confirm with them.
When does plumbing happen in an ADU build?
Rough-in before walls close, then trim after finishes. The rough-in inspection is a hard gate — nothing can be covered until it passes. That single dependency drives more ADU schedule slips than anything else on the plumbing side.
Do you handle the permits?
We handle the plumbing work and are present for plumbing inspections. Permit applications, plan check, and fees are typically the owner's or general contractor's responsibility, and requirements are set by the city. We will tell you plainly what is ours and what is not so nothing falls between us.
Ready to get this looked at?
Call and describe what's happening. You'll get an honest read before anyone drives out.