Gas Line Burial Depth Rules in Each Valley City

Section 404.12 of the International Fuel Gas Code (IFGC) sets the depth, and Section 404.12.1 sets the outdoor appliance exception. The base text Phoenix uses says underground piping goes "a minimum depth of 12 inches (305 mm) below grade, except as provided for in Section 404.12.1," which allows 8 inches for "Individual lines to outdoor lights, grills and other appliances" where the work is approved and "not susceptible to physical damage."

Most East and West Valley cities rewrote it. Tolleson's version is typical: "Underground piping systems shall be installed at a minimum depth of 12 inches (305mm) below grade for metal piping and 18 inches (457mm) for plastic piping." Tolleson, Mesa, Gilbert, Queen Creek, Surprise and the county then deleted 404.12.1 outright.

Homes can fall under the residential code's twin section, IRC G2415.12, which several cities amend the same way.

Five terms come up on every buried gas line.

• Below grade. Measured down from the finished ground surface to the pipe.
• Metal piping. Coated steel or other metal pipe. Chandler wants it factory coated and at least schedule 40.
• Plastic piping. Polyethylene (PE) gas pipe, joined by heat fusion or listed fittings. The base code allows it "outdoors underground only."
• Tracer wire. A copper wire laid with plastic pipe so the line can be found later, at least 18 AWG.
• Individual outdoor appliance line. One line serving one outdoor light, grill or similar appliance, the only case the 8-inch exception covers.

Anyone burying gas piping on private property, natural gas or propane, home or business. That includes restaurant patio heaters, fire features, pool heaters, generators and yard lines between buildings.

The utility's side is different. Maricopa County says it does not "inspect installations upstream from the main electrical service or gas meters"; the rules here cover the owner's piping past the meter.

Depth is only one line on the inspection. The base code requires "A yellow insulated copper tracer wire or other approved conductor" beside buried plastic pipe, not less than 18 AWG, with access at each end. Gilbert and Chandler repeat the 18 gauge rule.

Plastic stays out from under buildings. The base code says plastic pipe "shall not be used within or under any building or slab," with one exception: "Plastic pipe shall be permitted under outdoor patio, walkway and driveway slabs provided that the burial depth complies with Section 404.12." Chandler is stricter; it says PE "is not allowed for use beneath any building slab or structure." Gilbert's residential amendment limits piping under buildings to "corrugated stainless steel tubing installed without joints."

Chandler also bans galvanized pipe underground: "Galvanized fittings or piping are prohibited in underground gas systems." The county wants the pipe exposed at inspection on "a firm bed of soil, free of rocks and debris."

The same job changes depth from one city line to the next.

A restaurant adds one patio heater line in Phoenix. A single outdoor appliance line can be approved at 8 inches if it's out of harm's way. The same line in Mesa, Gilbert, Surprise or Tolleson goes 12 inches for metal or 18 for plastic.

A Gilbert office park runs plastic pipe to a second building. It goes 18 inches deep with an 18 AWG tracer, and it can't pass under either building.

A Queen Creek homeowner adds a fire pit. Town Code 7.1.1.4.6 applies the fuel gas code to residential gas appliances, and that code's outdoor appliance exception is gone, so the line goes 12 inches for metal or 18 for plastic.

Settle the depth before the trench is dug, because the inspector sees it open.

1. 1Find who inspects the address. City limits decide it; unincorporated addresses go to Maricopa County.
2. 2Pick the pipe material and look up its depth for that city in the table.
3. 3Show the depth and tracer on the permit drawing. Chandler and Buckeye ask for trench depth on the plans; see the gas line permit rules by city.
4. 4Call 811 before digging. Southwest Gas says the call gets "underground utility-owned lines marked." Piping past the meter belongs to the owner, so keep a drawing of where the new line runs.
5. 5Leave the trench open until the inspector approves the pipe, tracer and bedding.

Most failed underground inspections come from one of these.

• "Eight inches is fine for any outdoor line." Only for a single line to one outdoor appliance, and not at all in Mesa's fuel gas code, Gilbert, Queen Creek, Surprise, Tolleson or the unincorporated county.
• "Plastic and metal go the same depth." Seven jurisdictions here send plastic to 18 inches.
• "Tracer wire is optional." Buried plastic gas pipe needs an 18 AWG tracer.
• "Plastic can run under a building slab." The base code keeps it out from under buildings and allows it only under outdoor patio, walkway and driveway slabs at full burial depth; Chandler bars it under any building slab or structure.

The inspection fails and the pipe gets reburied before cover. The county won't let gas into the system until it is "tested, inspected and approved," so a shallow line holds up turn-on as well.

This page explains the rules; each city's adopted code and inspectors govern. HQ runs and replaces buried gas lines for homes and businesses across the Valley, with free estimates and 24/7 service.