What are the gas line requirements when an ADU uses gas appliances?

Where natural gas is permitted — meaning your city has not adopted an all-electric ordinance for new construction — gas piping in an ADU must be properly sized, valved, trapped, tested, and inspected before any wall is closed. Gas work is unforgiving, so the code requirements are specific and strictly enforced.

Core gas piping requirements

• Proper sizing for aggregate demand. The piping must deliver the combined BTU/hr load of every gas appliance running simultaneously while maintaining adequate pressure (commonly about 7 inches water column for standard residential appliances). Sizing depends on the total connected load, the developed length of pipe, and the pipe material.
• A manual shutoff valve at each appliance, accessible and within sight of the unit.
• A sediment trap (drip leg) ahead of each appliance gas valve to catch moisture and debris before it reaches the burner controls.
• A pressure (leak) test before concealment — typically holding air or inert gas at around 30 psi for a minimum period (often 30 minutes or more) with no pressure drop.
• Inspection of all joints by the building department before the piping is covered.

Common ADU gas appliances

The usual gas loads in an ADU are a tankless or tank water heater, a furnace or wall heater, a range/cooktop, and occasionally a gas dryer. Each adds to the BTU total the line must carry. Note that as California pushes toward electrification, many homeowners now choose a heat-pump water heater and heat-pump HVAC instead, which can eliminate the gas line entirely — often the cheaper and faster path.

The utility's role

The gas meter and the service connection belong to your gas utility (SoCalGas, PG&E, Southwest Gas, etc.), not your plumber. Adding ADU gas load may require a meter upgrade or relocation, which means a separate utility application, its own timeline, and its own fees. Start that coordination early — utility lead times routinely outlast construction.

A California Public Utilities Commission (CPUC) ruling eliminated certain gas line-extension subsidies for some mixed-fuel new construction. All-electric ordinances and gas-infrastructure cost rules vary by city and utility and continue to change — confirm current requirements with your building department and gas provider.

Our plumbing plans show gas piping, sizing, shutoffs, and sediment traps where gas is used, and our mechanical and electrical sheets coordinate the all-electric alternative when that is the better route for your project.