What CALGreen requirements apply to ADU plumbing beyond fixture flow rates?

Low-flow fixtures get all the attention, but CALGreen reaches well beyond flush and faucet ratings. Several additional plumbing provisions are checked at plan review and at inspection, and overlooking them is a common source of corrections on ADU sets.

Hot water pipe insulation

CALGreen requires hot water supply piping to be insulated, particularly in unconditioned spaces such as attics, crawlspaces, and garages. Insulation reduces standby heat loss and shortens the wait for hot water at the fixture. The required insulation thickness scales with pipe diameter, and the requirement also typically covers the first run off the water heater and any piping buried in a slab.

Hot water delivery volume limits

CALGreen Section 4.303.1 limits the volume of water allowed to sit in the hot-water supply pipe between the heater and the fixture. The intent is to stop you from running gallons of cold water down the drain while waiting for hot. In practice this constrains how far a single water heater can be from the farthest fixture. Long runs in a spread-out ADU may require:

• A recirculation system (often demand-controlled to save energy), or
• A point-of-use water heater near the remote fixture, or
• Relocating the water heater more centrally during design.

This is why water heater placement is a design decision, not an afterthought — a heater tucked into a far corner can quietly force an expensive recirculation system that a more central location would have avoided entirely.

Other CALGreen plumbing touchpoints

• Greywater-ready provisions — some jurisdictions require new residential construction to be stubbed or designed so a future greywater (laundry-to-landscape or branched-drain) system can be added.
• Pressure and pressure-reducing valves — fixture flow ratings are tested at 60 psi; high static pressure may require a PRV to keep fixtures compliant and protect the system.
• Construction waste and pollution-prevention measures that touch the plumbing trades during the build.

How this ties into your plans

These requirements are easiest to satisfy when they are baked into the design rather than retrofitted. Water heater placement, pipe routing, and insulation notes all belong on the plumbing sheets from the start.

CALGreen has mandatory and optional ("Tier") measures, and many cities add local amendments. Confirm which apply to your project with your local building department.

Our plumbing plans call out insulation, hot-water delivery strategy, and CALGreen notes, and coordinate cleanly with our Title 24 energy reports so your water-heating and conservation requirements line up across the whole MEP set.