CMC · California Mechanical Code

What requirements apply to underground piping installation and excavations?

Homeowner summary: Underground mechanical piping must be laid on a firm bed, buried to a minimum depth (usually 12 inches, 18 inches where damage is likely), protected from corrosion, fitted with a tracer if plastic, and left uncovered until the inspector approves it — these rules are in the California Mechanical Code, primarily **§ 1310.1** and the excavation sections **§ 317.3–.4** .

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

In plain English: underground piping must be buried to specified minimum cover depths (or placed in conduit if cover can't be provided), laid on a firm bed, protected from corrosion, and left exposed until inspected. The controlling California Mechanical Code provisions are § 1310.1 and its subsections (cover, trenching, and corrosion protection) and the general excavation/backfill/inspection rules in § 317.3 and § 317.4. For system-specific items (process piping, fuel gas, geothermal) the CMC applies the same keep-open-for-inspection rule in other chapters as well (see § 1405.1 and § 1303.2) .

The single most important rule: Keep excavations open until the underground piping has been inspected and approved — do not cover or conceal buried piping before inspection unless directed otherwise by the Authority Having Jurisdiction. This requirement appears repeatedly in the CMC (for example § 317.3, § 1405.1, § 1303.2) .

Requirements in detail

Minimum burial (cover)

Minimum cover: 12 inches (305 mm) of earth cover is required for underground piping as a baseline. If the piping is likely to experience external damage from external forces, the minimum cover increases to 18 inches (457 mm). If you cannot provide the minimum 12 in cover, the piping must be installed in conduit. See § 1310.1.1 for these rules .

Trench bottom / bedding / alignment

Piping must be laid on a firm, substantially continuous bearing along the trench bottom to prevent sagging and movement; the trench bottom must be graded for continuous bearing. See § 1310.1.2 and the general underground-installation support requirement § 313.5 .
For some systems (for example horizontal ground-loop geothermal piping) an embedment of not less than 6 inches (152 mm) of inert granular material above and below the pipe is required; check the system chapter for details (§ 1707.18.3) .

Backfill, compaction, and protection during consolidation

Trenches shall be backfilled promptly after inspection and backfilled in thin layers to 12 inches (305 mm) above the top of the piping with clean earth (no stones, boulders, frozen earth, debris, etc.) to avoid damage. Mechanical compaction to finish grade is permitted once the immediate surround is placed and compacted. See § 317.4 .
If flooding the trench to consolidate backfill, take care to prevent the pipe from floating off its bedding (see § 1310.1.2.1) .

Corrosion protection of metallic underground piping

Galvanizing is not adequate protection for underground steel pipe or tubing (explicit prohibition). See § 1310.1.3.1 .
Acceptable options (unless an approved technical justification shows protection unnecessary) include:
1. Use of corrosion-resistant material suitable for the environment.
2. Factory-applied electrically insulating coating (with compatible coating of fittings/joints per manufacturer instructions).
3. Installation of a cathodic protection system and ongoing monitoring per the listed test criteria in § 1310.1.3.2–.3 .
Cathodic protection monitoring must demonstrate one of the listed test criteria (examples): pipe-to-soil voltage of −0.85 V (Cu/CuSO4), −0.78 V (KCl calomel), or −0.80 V (Ag/AgCl) as referenced in § 1310.1.3.3 .

Tracer / locating aids

When plastic pipe is buried, an electrically continuous corrosion‑resistant tracer wire (not less than AWG 14) or detectable tape shall be buried with the pipe with one end brought aboveground at a building wall or riser for locating. See § 1707.11 for tracer requirements applied to buried plastic piping in the geothermal chapter (the requirement is illustrative of the CMC approach) .

Inspection and tests before concealment

Excavations for underground piping must be kept open until the piping has been inspected and approved. If piping is covered before approval it shall be exposed at the Authority Having Jurisdiction’s direction. This is repeated for process piping, fuel gas piping, and general mechanical installations in § 1405.1, § 1303.2, and § 317.3 respectively .
For systems that require pressure testing, final inspection typically includes a pressure test held for a minimum period (see the applicable piping chapter for test pressures and duration) — process piping final test criteria are in § 1405.2.2 (for example) .

Decision-relevant dimensions — quick reference table

Requirement / decision factor	Value(s) / threshold	Code Reference
Minimum cover (normal)	12 in (305 mm)	§ 1310.1.1
Increased cover when external damage likely	18 in (457 mm)	§ 1310.1.1
If < 12 in cover available	Install in conduit	§ 1310.1.1
Trench bedding requirement	Firm, substantially continuous bearing along trench bottom	§ 1310.1.2 and § 313.5
Backfill immediate surround	Backfill in thin layers to 12 in (305 mm) above top of pipe with clean earth	§ 317.4
Plastic buried pipe embedment (example — geothermal)	6 in (152 mm) above & below (inert granular)	§ 1707.18.3
Tracer wire	AWG 14 minimum electrically continuous	§ 1707.11
Galvanizing as corrosion protection	Not acceptable for underground steel	§ 1310.1.3.1
Cathodic protection test targets	−0.85 V (Cu/CuSO4) or −0.78 V (KCl calomel) or −0.80 V (Ag/AgCl)	§ 1310.1.3.3
Keep trench open until inspected	Must remain open until piping inspected & approved	§ 317.3, § 1405.1, § 1303.2

Exceptions & special cases

The code allows an approved technical justification to show corrosion protection is unnecessary for a particular installation; such justifications must be accepted by the Authority Having Jurisdiction (see § 1310.1.3.2) .
Geothermal ground-loop piping has additional, system‑specific trenching/bedding/insulation and setback rules (see § 1707.18 and related subsections) — do not assume the basic burial rules alone satisfy geothermal requirements .
Different chapters repeat the “keep open until inspected” requirement for different piping types (process piping § 1405.1, fuel gas § 1303.2) — follow the chapter that controls your system in addition to the general rules .

If a specific detail (for example, a special bedding-zone compaction value for a non-geothermal thermoplastic pipe) is needed but not present in the retrieved CMC excerpts, the code text for that narrow situation is not available in the files I searched — you should consult the applicable chapter in the full CMC or your local AHJ for that detail.

Common mistakes

Covering the trench before inspection — inspectors repeatedly flag pipes that were buried prior to rough inspection (the CMC requires trenches to be kept open until approval; § 317.3, § 1405.1, § 1303.2) .
Assuming galvanizing is adequate for underground steel — the code expressly says zinc coating is not adequate protection (§ 1310.1.3.1) .
Poor bedding or non‑continuous support — pipes must be laid on a firm, substantially continuous bearing; uneven bedding leads to sagging and early failure (§ 1310.1.2 and § 313.5) .
Using contaminated backfill directly around the pipe (rocks, debris, frozen earth) or failing to backfill in thin layers to the required elevation above the pipe (§ 317.4) .
Omitting tracer or detectable tape with buried thermoplastic pipe — makes locating later difficult and may violate the code chapter applying to that system (§ 1707.11) .

Worked example — driveway gas service across a residential lot

Scenario: You must install underground metallic gas piping across a residential driveway where the surface will receive vehicle loads and the pipe could be damaged by traffic.

Choose minimum cover: Because vehicle/traffic makes external damage likely, the minimum cover is 18 inches (457 mm) (not 12 in). Cite: § 1310.1.1 .
Trench preparation: Grade the trench bottom so the pipe has a firm, substantially continuous bearing along its entire length; use imported bedding if existing soil is unsuitable per § 1310.1.2 and § 313.5 .
Corrosion protection: Because the pipe is metallic and underground, provide correct corrosion protection — options include (a) use corrosion‑resistant material, (b) factory coating with properly coated fittings, or (c) cathodic protection. If you select cathodic protection, plan monitoring to demonstrate the required pipe-to-soil voltages (e.g., −0.85 V Cu/CuSO4) per § 1310.1.3.3 .
Tracer: If you use plastic service laterals, include AWG 14 tracer wire with one end brought above grade at a riser or building wall per § 1707.11 (applies to buried plastic examples in the CMC; follow system chapter if applicable) .
Inspection: Keep the trench open until the Authority Having Jurisdiction inspects and approves the installation — do not backfill until the rough piping inspection is passed (§ 317.3, also repeated in other chapters) .
Backfill: After inspection, backfill in thin lifts to at least 12 inches (305 mm) above the top of the pipe with clean earth (no stones, debris, frozen earth) and compact; then finish-grade with mechanical equipment as permitted (§ 317.4) .

This scenario demonstrates how the CMC’s burial depth, bedding, corrosion, tracer, inspection, and backfill rules work together in a practical installation under § 1310.1 and the excavation rules in § 317.3–.4 .

Related provisions (select CMC sections)

§ 1310.1 — Underground piping cover, trenching, and corrosion protection (primary controlling section)
§ 1310.1.1 — Cover requirements (12 in / 18 in / conduit option)
§ 1310.1.2 — Trenches; bedding and grading of trench bottom
§ 1310.1.3 — Protection against corrosion and cathodic protection criteria
§ 317.3 — Open trenches: keep open until inspected and accepted
§ 317.4 — Excavations: backfill, compaction, and clean‑earth requirement around pipe
§ 313.5 — Underground installation support: lay pipe on firm bed for entire length
§ 1405.1 — Process piping: excavations to remain open until inspected (applies to process piping chapter)
§ 1303.2 — Fuel gas piping inspection/excavation rule (applies in fuel gas chapter)
§ 1707.11 — Tracer wire and detectable warning tape requirement for buried plastic (geothermal chapter example)
§ 1707.18.3 — Geothermal horizontal piping embedment (6 in granular above/below)

Code references

Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:

CMC § 1401.0 High relevance — show source text
334 2025 CALIFORNIA MECHANICAL CODE

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CHAPTER 14

PROCESS PIPING

1401.0 General.

1401.1 Applicability. Except as otherwise addressed in this code, this chapter shall govern the installation of process piping in or in conjunction with a building or structure located upon the premises.

1402.0 Permit.

1402.1 General. It shall be unlawful to install, alter, or repair or cause to be installed, altered, or repaired process material piping without first obtaining a permit.

Permits for process piping shall show the total number of outlets to be provided for on each system and such other information as required by the Authority Having Jurisdiction.

Fees for process piping permits are included in Table 104.5.

1403.0 Plans Required.

1403.1 General. Plans, engineering calculations, diagrams, and other data shall be submitted in one or more sets with each application for a permit. The Authority Having Jurisdiction shall be permitted to require plans, computations, and specifications to be prepared and designed by a registered design professional.

Where plans or other data are submitted for review, a plan review fee shall be paid, as provided in Section 104.3.2.

1404.0 Workmanship.

1404.1 General. Process piping shall not be strained or bent, nor shall tanks, vessels, vats, appliances, or cabinets be supported by or develop strain or stress on the piping.

1405.0 Inspections.

1405.1 General. Upon completion of the installation, alteration, or repair of process piping, and prior to the use thereof, the Authority Having Jurisdiction shall be notified that such piping is ready for inspection.

Excavations required for the installation of underground piping shall be kept open until such time as the piping has been inspected and approved. Where such piping is covered or concealed before such approval, it shall be exposed upon the direction of the Authority Having Jurisdiction.

1405.2 Required Inspections. The Authority Having Jurisdiction shall make the following inspections and shall either approve that portion of the work as completed or shall notify the permit holder wherein the same fails to be in accordance with this code.

1405.2.1 Rough Piping Inspection. This inspection shall be made after process piping authorized by the permit has been installed and before piping has been cov

ered or concealed. This inspection shall include a determination that the piping size, material, and installation are in accordance with the requirements of this code.

1405.2.2 Final Piping Inspection. This inspection shall be made after piping authorized by the permit has been installed and after portions thereof that are to be covered or concealed are so concealed. This inspection shall include a pressure test, at which time the piping shall stand a pressure of not less than one-and-one-half times the maximum designed operating pressure where hydraulic testing is conducted or 110 percent where testing is conducted pneumatically. Test pressures shall be held for a length of time satisfactory to the Authority Having Jurisdiction, but in no case for less than 30 minutes with no perceptible drop in pressure. HPM drain, waste, and vent piping shall be tested in accordance with the plumbing code. Tests shall be made in the presence of the Authority Having Jurisdiction. Necessary apparatus for conducting tests shall be furnished by the permit holder.
CMC § 1405.2 High relevance — show source text
Excavations required for the installation of underground piping shall be kept open until such time as the piping has been inspected and approved. Where such piping is covered or concealed before such approval, it shall be exposed upon the direction of the Authority Having Jurisdiction.

1405.2 Required Inspections. The Authority Having Jurisdiction shall make the following inspections and shall either approve that portion of the work as completed or shall notify the permit holder wherein the same fails to be in accordance with this code.

1405.2.1 Rough Piping Inspection. This inspection shall be made after process piping authorized by the permit has been installed and before piping has been cov

ered or concealed. This inspection shall include a determination that the piping size, material, and installation are in accordance with the requirements of this code.

1405.2.2 Final Piping Inspection. This inspection shall be made after piping authorized by the permit has been installed and after portions thereof that are to be covered or concealed are so concealed. This inspection shall include a pressure test, at which time the piping shall stand a pressure of not less than one-and-one-half times the maximum designed operating pressure where hydraulic testing is conducted or 110 percent where testing is conducted pneumatically. Test pressures shall be held for a length of time satisfactory to the Authority Having Jurisdiction, but in no case for less than 30 minutes with no perceptible drop in pressure. HPM drain, waste, and vent piping shall be tested in accordance with the plumbing code. Tests shall be made in the presence of the Authority Having Jurisdiction. Necessary apparatus for conducting tests shall be furnished by the permit holder.

1405.3 Other Inspections. In addition to the inspections required by this section, the Authority Having Jurisdiction shall be permitted to require a special inspector, as specified in the building code, during installation of piping systems. In cases where the work authorized was installed in accordance with plans and specifications prepared by a registered design professional, the Authority Having Jurisdiction shall be permitted to require a final signed report stating that the work was installed in accordance with approved plans and specifications and the applicable provisions of this chapter.

1406.0 Pipe, Tubing, and Fittings.

1406.1 General. Process pipe, tubing, and fittings shall comply with ASME B31.3 and shall be installed in accordance with the manufacturer’s installation instructions. Materials shall be rated for the operating temperatures and pressures of the system, and shall be compatible with the type of liquid.

1406.2 Hazardous Process Piping (HPP). HPP supply piping or tubing in service corridors shall be exposed to view. HPP piping shall be identified in accordance with nationally recognized standards to indicate the material being transported. Liquid HPP piping shall have an approved means for directing spilled materials to an approved containment or drainage system.

Liquid HPP waste or drainage systems shall be installed in accordance with the plumbing code.

1406.2.1 Installation in Exit Corridors and Above Other Occupancies. Hazardous process supply pipe shall not be located within exit corridors, within a portion of a means of egress required to be enclosed in fire-resistive construction, or in concealed spaces in or above

2025 CALIFORNIA MECHANICAL CODE 335

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PROCESS PIPING

areas not classified as Group H Occupancies, except as permitted by this subsection.
CMC § 1.1.1.2 High relevance — show source text
(14)Installation of LP-Gas systems for railroad switch heating.

(15)Installation of LP-Gas and compressed natural gas (CNG) systems on vehicles.

(16)Gas piping, meters, gas pressure regulators, and other appurtenances used by the serving gas supplier in distribution of gas, other than undiluted LP-Gas.

(17)Building design and construction, except as specified herein.

(18)Fuel gas systems on recreational vehicles manufactured in accordance with NFPA 1192.

(19)Fuel gas systems using hydrogen as a fuel.

(20)Construction of appliances. {NFPA 54:1.1.1.2}

1303.0 Inspection. 1303.1 Inspection Notification. Upon completion of the installation, alteration, or repair of gas piping, and prior to the use thereof, the Authority Having Jurisdiction shall be notified that such gas piping is ready for inspection. 1303.2 Excavation. Excavations required for the installation of underground piping shall be kept open until such time as the piping has been inspected and approved. Where such piping is covered or concealed before such approval, it shall be exposed upon the direction of the Authority Having Jurisdiction.

1303.3 Type of Inspections. The Authority Having Jurisdiction shall make the following inspections and either shall approve that portion of the work as completed or shall notify the permit holder wherein the same fails to be in accordance with this code.

1303.3.1 Rough Piping Inspection. This inspection shall be made after gas piping authorized by the permit has been installed before such piping has been covered or concealed, or before fixture or appliance has been attached thereto. This inspection shall include a determination that the gas piping size, material, and installation meet the requirements of this code. 1303.3.2 Final Piping Inspection. This inspection shall be made after piping authorized by the permit has been installed and after portions thereof that are to be covered or concealed are so concealed and before fixture, appliance, or shutoff valve has been attached thereto. This inspection shall comply with Section 1313.1. Test gauges used in conducting tests shall be in accordance with Section 1303.3.3 through Section 1303.3.3.4.

2025 CALIFORNIA MECHANICAL CODE 275

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FUEL GAS PIPING

1303.3.3 Test Gauges. Tests required by this code, which are performed utilizing dial gauges, shall be limited to gauges having the following pressure graduations or increments.

1303.3.3.1 Pressure Tests (10 psi or less). Required pressure tests of 10 psi (69 kPa) or less shall be performed with gauges of 0.10 psi (0.69 kPa) increments or less.

1303.3.3.2 Pressure Tests (greater than 10 psi to 100 psi). Required pressure tests exceeding 10 psi (69 kPa) but less than or equal to 100 psi (689 kPa) shall be performed with gauges of 1 psi (7 kPa) increments or less.

1303.3.3.3 Pressure Tests (exceeding 100 psi). Required pressure tests exceeding 100 psi (689 kPa) shall be performed with gauges of 2 percent increments or less of the required test pressure.
CMC § 1.1.1.1 High relevance — show source text
[NFPA 54:1.1.1.1(A)]

1302.2 Piping System Requirements. Requirements for piping systems shall include design, materials, components, fabrication, assembly, installation, testing, inspection, operation, and maintenance. [NFPA 54:1.1.1.1(E)]

1302.3 Applications. This chapter shall not apply to the following items:

(1) Portable LP-Gas appliances and equipment of all types that are not connected to a fixed fuel piping system.

(2) Installation of appliances such as brooders, dehydrators, dryers, and irrigation equipment used for agricultural

purposes.

(3) Raw material (feedstock) applications except for piping to special atmosphere generators.

(4) Oxygen-fuel gas cutting and welding systems.

(5) Industrial gas applications using such gases as acetylene and acetylenic compounds, hydrogen, ammonia, carbon monoxide, oxygen, and nitrogen.

(6) Petroleum refineries, pipeline compressor or pumping stations, loading terminals, compounding plants, refinery tank farms, and natural gas processing plants.

(7) Large integrated chemical plants or portions of such plants where flammable or combustible liquids or gases are produced by chemical reactions or used in chemical reactions.

(8) LP-Gas installations at utility gas plants.

(9) Liquefied natural gas (LNG) installations.

(10)Fuel gas piping in electric utility power plants.

(11)Proprietary items of equipment, apparatus, or instruments such as gas-generating sets, compressors, and calorime ters.

(12)LP-Gas equipment for vaporization, gas mixing, and gas manufacturing.

(13)LP-Gas piping for buildings under construction or renovations that is not to become part of the permanent building piping system—that is, temporary fixed piping for building heat.

(14)Installation of LP-Gas systems for railroad switch heating.

(15)Installation of LP-Gas and compressed natural gas (CNG) systems on vehicles.

(16)Gas piping, meters, gas pressure regulators, and other appurtenances used by the serving gas supplier in distribution of gas, other than undiluted LP-Gas.

(17)Building design and construction, except as specified herein.

(18)Fuel gas systems on recreational vehicles manufactured in accordance with NFPA 1192.

(19)Fuel gas systems using hydrogen as a fuel.

(20)Construction of appliances. {NFPA 54:1.1.1.2}

1303.0 Inspection. 1303.1 Inspection Notification. Upon completion of the installation, alteration, or repair of gas piping, and prior to the use thereof, the Authority Having Jurisdiction shall be notified that such gas piping is ready for inspection. 1303.2 Excavation. Excavations required for the installation of underground piping shall be kept open until such time as the piping has been inspected and approved. Where such piping is covered or concealed before such approval, it shall be exposed upon the direction of the Authority Having Jurisdiction.

1303.3 Type of Inspections. The Authority Having Jurisdiction shall make the following inspections and either shall approve that portion of the work as completed or shall notify the permit holder wherein the same fails to be in accordance with this code.

1303.3.1 Rough Piping Inspection. This inspection shall be made after gas piping authorized by the permit has been installed before such piping has been covered or concealed, or before fixture or appliance has been attached thereto.
CMC § 1707.10 High relevance — show source text
1707.10 Excavations and Open Trenches. Excavations required to be made for the installation of piping or tubing shall be in accordance with Section 317.3. Piping or tubing shall be supported to maintain its alignment and prevent sagging. Piping in the ground shall be laid on a firm bed for its entire length; where other support is otherwise provided, it shall be approved in accordance with Section 302.0. Piping or tubing shall be backfilled after an inspection in accordance with Section 317.4.

1707.11 Protection of Piping, Materials, and Struc- tures. Piping and tubing passing under or through walls shall be protected from breakage in accordance with Section 316.1. Piping and tubing shall be installed in accordance with Section 316.2 to provide for expansion, contraction, and structural settlement. An electrically continuous corrosion-resistant tracer wire (not less than AWG 14) or tape shall be buried with the plastic pipe to facilitate locating. One end shall be brought aboveground at a building wall or riser.

1707.12 Sleeves. In exterior walls, annular space between sleeves and pipes shall be sealed and made watertight and shall not be subject to a load from building construction in accordance with Section 316.7 through Section 316.7.2.

2025 CALIFORNIA MECHANICAL CODE 351

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GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

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1707.18.5 Insulation. Insulation shall be provided on the piping where there is close proximity of all site services to prevent thermal interference between fluid-based onsite service systems. 1707.18.6 Pipe Bends. Sharp bending of pipe shall be prevented or approved elbow fitting shall be used with a bend-radius in accordance with the manufacturer’s

installation instructions.

1707.18.7 Closed Cell Insulation. Buried horizontal open-loop system pipes passing parallel within 5 feet (1524 mm) of a wall, structure, or water pipe shall be insulated with R-2 minimum closed cell insulation.

1707.18.8 Tracer Markings. Means shall be provided for underground detection or utility location of the buried pipe system. This shall include, but is not limited to, metallic detectable tape, with a thickness of not less than 11/64 of an inch (4.4 mm) and a width of 6 inches (152 mm).

This warning marking shall be permanent, conspicuous and resistant to the environmental conditions and shall be placed within 1 foot to 2 feet (305 mm to 610 mm) on top of the horizontal piping of the heat exchanger installation.

1708.0 System Start-Up. 1708.1 General. The following requirements shall be verified prior to system start-up:

(1) Piping shall be cleaned, flushed, and purged.

(2) The ground-heat exchanger and building piping shall be cleaned, flushed, and, where required, shall be filled with the heat transfer fluid medium. The ground loop system shall be tested at the design flow rate(s) and differential pressure(s) recorded. Where the actual pressure change at design flow is more than +/- 10 percent of the design flow pressure drop, the cause shall be identified and corrective action taken.
CMC § 7.1.1.1 High relevance — show source text
Underground plastic piping shall be installed with sufficient clearance or shall be insulated from any source of heat so as to prevent the heat from impairing the serviceability of the pipe. [NFPA 54:7.1.1.1, 7.1.1.2] 1310.1.1 Cover Requirements. Underground piping systems shall be installed with a minimum of 12 inches (305 mm) of cover. The minimum cover shall be increased to 18 inches (457 mm) if external damage to the pipe or tubing from external forces is likely to result. Where a minimum of 12 inches (305 mm) of cover cannot be provided, the piping shall be installed in conduit. [NFPA 54:7.1.2.1 – 7.1.2.1(B)]

1310.1.2 Trenches. The trench shall be graded so that the pipe has a firm, substantially continuous bearing on the bottom of the trench. [NFPA 54:7.1.2.2]

1310.1.2.1 Backfilling. Where flooding of the trench is done to consolidate the backfill, care shall be exer

cised to see that the pipe is not floated from its firm bearing on the trench bottom. [NFPA 54:7.1.2.3]

1310.1.3 Protection Against Corrosion. Steel pipe and steel tubing installed underground shall be installed in accordance with Section 1310.1.3.1 through Section 1310.1.3.9. [NFPA 54:7.1.3]

1310.1.3.1 Zinc Coating. Zinc coating (galvanizing) shall not be deemed adequate protection for underground gas piping. [NFPA 54:7.1.3.1] 1310.1.3.2 Underground Piping. Underground piping shall comply with one or more of the following unless approved technical justification is provided to demonstrate that protection is unnecessary:

(1) The piping shall be made of corrosion-resistant material that is suitable for the environment in

which it will be installed.

(2) Pipe shall have a factory-applied, electrically insulating coating. Fittings and joints between sections of coated pipe shall be coated in accordance with the coating manufacturer’s instructions.

(3) The piping shall have a cathodic protection system installed, and the system shall be maintained in accordance with Section 1310.1.3.3 or Section 1310.1.3.6. [NFPA 54:7.1.3.2] 1310.1.3.3 Cathodic Protection. Cathodic protection systems shall be monitored by testing and the results shall be documented. The test results shall demonstrate one of the following:

− (1) A pipe-to-soil voltage of 0.85 volts or more negative is produced, with reference to a saturated copper-copper sulfate half cell.

− (2) A pipe-to-soil voltage of 0.78 volts or more negative is produced, with reference to a saturated KCl calomel half cell.

− (3) A pipe-to-soil voltage of 0.80 volts or more negative is produced, with reference to a silversilver chloride half cell.

(4) Compliance with a method described in Appendix D of Title 49 of the Code of Federal Regulations, Part 192. [NFPA 54:7.1.3.3]
CMC § 1707.13 High relevance — show source text
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1707.13 Steel Nail Plates. Steel nail plates shall be installed for plastic and copper piping penetrating framing members to within 1 inch (25.4 mm) of the exposed framing in accordance with Section 316.6.

1707.14 Exterior Piping Protection. Exterior piping shall be fitted with end caps and protected from freezing, UV radiation, corrosion, and degradation. 1707.15 Heat Pump and Distribution System Instal- lation. The heat pump and distribution system shall be installed in accordance with the system’s design, with this code, and the manufacturer’s installation instructions.

1707.16 Pressurizing During Installation. Ground source heat pump ground loop piping to be embedded in concrete shall be pressure tested prior to pouring concrete. During pouring, the pipe shall be maintained at the proposed operating pressure. 1707.17 Horizontal Geothermal Piping - Materials and Methods. Horizontal geothermal piping shall be in accordance with Section 1707.17.1 through Section 1707.18.8.

1707.17.1 Piping Material. Piping materials and joining methods for horizontal piping from the ground-heat exchanger shall be in accordance with Section 1703.2, Section 1703.3, Section 1703.4, Section 1703.5 and Section 1715.3.

1707.17.2 Dissimilar Materials. Transition fittings between dissimilar materials shall be inside or accessible.

1707.17.3 Protection of Piping. Pipes passing through walls shall be sleeved and sealed in accordance with Sec tion 316.0.

1707.18 Trenches, Excavation, and Backfill. Excavation for horizontal piping shall comply with Section 1707.18.1 through Section 1707.18.8, Section 1707.8 through Section 1707.11, and in accordance with the requirements of the Authority Having Jurisdiction. Prior to any excavation, trenching, or drilling, all buried utilities including drainage, and irrigation systems shall be located and flagged by the appropriate utility and ground source heat pump system contractor representative.

1707.18.1 Trenches. Trenches for underground piping or tubing shall be excavated in accordance with the setback requirements in Section 1712.4. 1707.18.2 Buried Systems. Buried open-loop system piping, shall be installed not less than 3.3 feet (1006 mm) below the finished grade.

1707.18.3 Pipe Installation. Piping in horizontal trenches shall be embedded with not less than 6 inches (152 mm) of inert granular material above and below, or in accordance with the Authority Having Jurisdiction and project specifications.

Horizontal piping trenching shall be backfilled with approved material and shall be compacted. 1707.18.4 Separation. The horizontal piping shall be separated from fluid-based onsite service systems to prevent excessive short-circuiting heat transfer between such systems.

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(6) Vertical and horizontal ground-heat exchangers shall maintain the following setbacks:

(a) Ten feet (3048 mm) horizontally from a pressuretested sewer lateral into a building.

(b) Twenty feet (6096 mm) horizontally from a nonpressure tested sewer lateral into a building.
CMC § 316.8 High relevance — show source text
316.8 Firewalls. A pipe sleeve through a firewall shall have the space around the pipe or tubing completely sealed with an approved fire-resistive material in accordance with other codes.

316.9 Structural Members. A structural member weakened or impaired by cutting, notching, or otherwise shall be reinforced, repaired, or replaced so as to be left in a safe structural condition in accordance with the requirements of the California Building Code or California Residential Code .

316.10 Rodentproofing. Mechanical system shall be constructed in such a manner as to restrict rodents or vermin from entering a building by following the ductwork from the outside into the building. 316.11 Metal Collars. In or on buildings where openings have been made in walls, floors, or ceilings for the passage of ductwork or pipes, such openings shall be closed and protected by the installation of approved metal collars securely fastened to the adjoining structure.

317.0 Trenching, Excavation, and Backfill.

317.1 Trenches. Trenches deeper than the footings of a building or structure, and paralleling the same, shall be located not less than 45 degrees (0.79 rad) from the bottom exterior edge of the footing, or as approved in accordance with Section 302.0.

317.2 Tunneling and Driving. Tunneling and driving shall be permitted to be done in yards, courts, or driveways of a building site. Where sufficient depth is available to permit, tunnels shall be permitted to be used between open-cut trenches.

Tunnels shall have a clear height of 2 feet (610 mm) above the pipe and shall be limited in length to one-half the depth of the trench, with a maximum length of 8 feet (2438 mm). Where pipes are driven, the drive pipe shall be not less than one size larger than the pipe to be laid.

317.3 Open Trenches. Excavations required to be made for the installation of a mechanical system or part thereof, within the walls of a building, shall be open trench work and shall be kept open until it has been inspected, tested, and accepted.

317.4 Excavations. Excavations shall be completely backfilled as soon after inspection as practicable. Precaution shall be taken to ensure compactness of backfill around piping without damage to such piping. Trenches shall be backfilled in thin layers to 12 inches (305 mm) above the top of the piping with clean earth, which shall not contain stones, boulders, cinderfill, frozen earth, construction debris, or other materials that will damage or break the piping or cause corrosive action. Mechanical devices such as bulldozers, graders, etc., shall be permitted to then be used to complete backfill to grade. Fill shall be properly compacted. Precautions shall be taken to ensure permanent stability for pipe laid in filled or made ground.

318.0 Scope. 318.1 Applicability. This part is applicable to health facil- ities regulated by OSHPD.

Note: This section has no corresponding provisions in the UMC. For the scope and authority of each state agency, refer to Chapter 1. 318.2 Services/Systems and Utilities. Refer to Section 1224.4.1, 1225.2.1 and 1228.4.1.1 of the California Building Code.
CMC § 313.1 High relevance — show source text
313.1 General. . . . . . . . . . . . . . . . . . . . . . 59

313.2 Material. . . . . . . . . . . . . . . . . . . . . . 59

313.3 Suspended Piping . . . . . . . . . . . . . 59

313.4 Alignment . . . . . . . . . . . . . . . . . . . . 59

313.5 Underground Installation . . . . . . . . 59

313.6 Hanger Rod Sizes . . . . . . . . . . . . . 59

Table 313.6 Hanger Rod Sizes . . . . . . . . . . . . . 59

313.7 Gas Piping . . . . . . . . . . . . . . . . . . . 59

314.0 Balancing . . . . . . . . . . . . . . . . . . . . 59

314.1 General. . . . . . . . . . . . . . . . . . . . . . 59

315.0 Louvers in Hurricane Prone

Regions . . . . . . . . . . . . . . . . . . . . . 59

315.1 General. . . . . . . . . . . . . . . . . . . . . . 59

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316.0 Protection of Piping, Tubing, Materials, and Structures . . . . . . . . 59

316.1 General. . . . . . . . . . . . . . . . . . . . . . 59

316.2 Installation . . . . . . . . . . . . . . . . . . . 59

316.3 Corrosion, Erosion, and Mechanical Damage. . . . . . . . . . . . 59

316.4 Protectively Coated Pipe . . . . . . . . 59

316.5 Fire-Resistant Construction . . . . . . 59

316.6 Steel Nail Plates . . . . . . . . . . . . . . . 60

316.7 Sleeves. . . . . . . . . . . . . . . . . . . . . . 60

316.8 Firewalls . . . . . . . . . . . . . . . . . . . . . 60

316.9 Structural Members . . . . . . . . . . . . 60

316.10 Rodentproofing . . . . . . . . . . . . . . . . 60

316.11 Metal Collars. . . . . . . . . . . . . . . . . . 60

317.0 Trenching, Excavation, and

Backfill . . . . . . . . . . . . . . . . . . . . . . 60

317.1 Trenches. . . . . . . . . . . . . . . . . . . . . 60

317.2 Tunneling and Driving. . . . . . . . . . . 60

317.3 Open Trenches. . . . . . . . . . . . . . . . 60

317.4 Excavations . . . . . . . . . . . . . . . . . . 60
CMC § 314.3 High relevance — show source text
Tunnels shall have a clear height of 2 feet (610 mm) above the pipe and shall be limited in length to one-half the depth of the trench, with a maximum length of 8 feet (2438 mm). Where pipes are driven, the drive pipe shall be not less than one size larger than the pipe to be laid.

314.3 Open Trenches. Excavations required to be made for the installation of a building drainage system or part thereof, within the walls of a building, shall be open trench work and shall be kept open until the piping has been inspected, tested, and accepted.

314.4 Excavations. Excavations shall be completely backfilled as soon after inspection as practicable. Precaution shall be taken to ensure compactness of backfill around piping without damage to such piping. Trenches shall be backfilled in thin layers to 12 inches (305 mm) above the top of the piping with clean earth, which shall not contain stones, boulders, cinder fill, frozen earth, construction debris, or other materials that will damage or break the piping or cause corrosive action. Mechanical devices such as bulldozers, graders, etc., shall be permitted to be then used to complete backfill to grade. Fill shall be properly compacted. Precautions shall be taken to ensure permanent stability for pipe laid in filled or made ground.

Underground thermoplastic pipe and fittings for sewers and other gravity flow applications shall be installed in accordance with this code and Section 314.4.1.

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GENERAL REGULATIONS

314.4.1 Installation of Thermoplastic Pipe and Fittings. Trench width for thermoplastic sewer pipe shall be not less than 1.25 times the outside diameter of the piping plus 12 inches (305 mm) or the outside diameter of the piping plus not less than 16 inches (406 mm). Thermoplastic piping shall be bedded in not less than 4 inches (102 mm) of granular fill supporting the piping. The backfill for thermoplastic piping shall be compacted along the sides of the piping in 6 inch (152 mm) layers and continue to not less than 12 inches (305 mm) above the piping. Compaction shall be not less than an 85 percent standard proctor density.

315.0 Joints and Connections.

315.1 Unions. Approved unions shall be permitted to be used in drainage piping where accessibly located in the trap seal or between a fixture and its trap; in the vent system, except underground or in wet vents; at any point in the water supply system; and in gas piping as permitted by Section 1212.6.

315.2 Prohibited Joints and Connections. A fitting or connection that has an enlargement, chamber, or recess with a ledge, shoulder, or reduction of pipe area that offers an obstruction to flow through the drain shall be prohibited.

316.0 Increasers and Reducers.

316.1 General. Where different sizes of pipes and fittings are to be connected, the proper size increasers or reducers or reducing fittings shall be used between the two sizes. Copper alloy or cast-iron body cleanouts shall not be used as a reducer or adapter from cast-iron drainage pipe to iron pipe size (IPS) pipe.
CMC § 1707.18 High relevance — show source text
1707.18 Trenches, Excavation, and Backfill. Excavation for horizontal piping shall comply with Section 1707.18.1 through Section 1707.18.8, Section 1707.8 through Section 1707.11, and in accordance with the requirements of the Authority Having Jurisdiction. Prior to any excavation, trenching, or drilling, all buried utilities including drainage, and irrigation systems shall be located and flagged by the appropriate utility and ground source heat pump system contractor representative.

1707.18.1 Trenches. Trenches for underground piping or tubing shall be excavated in accordance with the setback requirements in Section 1712.4. 1707.18.2 Buried Systems. Buried open-loop system piping, shall be installed not less than 3.3 feet (1006 mm) below the finished grade.

1707.18.3 Pipe Installation. Piping in horizontal trenches shall be embedded with not less than 6 inches (152 mm) of inert granular material above and below, or in accordance with the Authority Having Jurisdiction and project specifications.

Horizontal piping trenching shall be backfilled with approved material and shall be compacted. 1707.18.4 Separation. The horizontal piping shall be separated from fluid-based onsite service systems to prevent excessive short-circuiting heat transfer between such systems.

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(6) Vertical and horizontal ground-heat exchangers shall maintain the following setbacks:

(a) Ten feet (3048 mm) horizontally from a pressuretested sewer lateral into a building.

(b) Twenty feet (6096 mm) horizontally from a nonpressure tested sewer lateral into a building.

(c) Three feet (914 mm) horizontally from buried utilities such as electrical, gas, or water.

(d) Fifty feet (15 240 mm) from a water well.

(e) Fifty feet (15 240 mm) from a septic tank and 100 feet (30 480 mm) from a subsurface sewage leaching field.

(f) One hundred feet (30 480 mm) from a spring; or at distances specified by the Authority Having Jurisdiction.

(7) Wells and boreholes shall be sealed in accordance with the Authority Having Jurisdiction. Where grout is required, it shall be applied in a continuous operation from the bottom of the borehole by pumping through a tremie pipe.

1707.8 Trenching, Excavation, and Backfill. Prior to excavation, trenching, or drilling, buried utilities, drainage, water, and irrigation systems shall be located. Prior to excavation, trenching, or drilling, the contractor, and owner shall agree in writing to site restoration requirements and submit to the Authority Having Jurisdiction for approval. Prior to any excavation, trenching, or drilling, all buried utilities including drainage and irrigation systems shall be located and flagged by the appropriate utility and ground source heat pump system contractor representative.

1707.9 Trenches, Tunneling, and Driving. Trenches shall comply with Section 317.1. Tunneling and driving shall comply with Section 317.2.
CMC § 1.1.1.2 High relevance — show source text
(17)Building design and construction, except as specified herein.

(18)Fuel gas systems on recreational vehicles manufactured in accordance with NFPA 1192.

(19)Fuel gas systems using hydrogen as a fuel.

(20)Construction of appliances. {NFPA 54:1.1.1.2}

1203.0 Inspection.

1203.1 Inspection Notification. Upon completion of the installation, alteration, or repair of gas piping, and prior to the use thereof, the Authority Having Jurisdiction shall be notified that such gas piping is ready for inspection.

1203.2 Excavation. Excavations required for the installation of underground piping shall be kept open until the piping has been inspected and approved. Where such piping is covered or concealed before such approval, it shall be exposed upon the direction of the Authority Having Jurisdiction.

1203.3 Type of Inspections. The Authority Having Jurisdiction shall make the following inspections and either shall approve that portion of the work as completed or shall notify the permit holder wherein the same fails to be in accordance with this code.

1203.3.1 Rough Piping Inspection. This inspection shall be made after gas piping authorized by the permit has been installed and before such piping has been covered or concealed or fixture or appliance has been attached thereto. This inspection shall include a determination that the gas piping size, material, and installation meet the requirements of this code.

1203.3.2 Final Piping Inspection. This inspection shall be made after piping authorized by the permit has been installed, and after portions, thereof that are to be covered or concealed are so concealed, and before fixture, appliance, or shutoff valve has been attached thereto.

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FUEL GAS PIPING

This inspection shall comply with Section 1213.1. Test gauges used in conducting tests shall be in accordance with Section 318.0.

1203.4 Inspection Waived. In cases where the work authorized by the permit consists of a minor installation of additional piping to piping already connected to a gas meter, the preceding inspections shall be permitted to be waived at the discretion of the Authority Having Jurisdiction. In this event, the Authority Having Jurisdiction shall make such inspection as deemed advisable to be assured that the work has been performed in accordance with the intent of this code.

1204.0 Certificate of Inspection.

1204.1 Issuance. Whereupon final piping inspection, the installation is found to be in accordance with the provisions of this code, a certificate of inspection shall be permitted to be issued by the Authority Having Jurisdiction. 1204.2 Gas Supplier. A copy of the certificate of such final piping inspection shall be issued to the serving gas supplier supplying gas to the premises. 1204.3 Unlawful. It shall be unlawful for a serving gas supplier, or person is furnishing gas, to turn on or cause to be turned on, a fuel gas or a gas meter or meters, until such certificate of final inspection, as herein provided, has been issued.

1205.0 Authority to Render Gas Service.

Frequently asked questions

Can I cover the pipe and backfill before an inspector sees it?

No. The CMC requires excavations for underground piping to be kept open until the piping has been inspected and approved; if covered before approval, it must be exposed at the direction of the Authority Having Jurisdiction (see § 317.3, § 1405.1, § 1303.2) .

Is galvanized (zinc‑coated) steel acceptable for underground piping?

No. The code states zinc coating (galvanizing) is not adequate protection for underground gas piping; choose a corrosion‑resistant material, a factory-applied insulating coating, or properly designed cathodic protection per § 1310.1.3 .

What if I can’t get 12 inches of cover over the pipe?

If you cannot provide the minimum 12 in (305 mm) cover, the piping must be installed in conduit as an alternative per § 1310.1.1 .

How should I prepare the trench bottom?

The pipe must be laid on a firm, substantially continuous bearing for its entire length (grade the trench so the pipe rests continuously) — see § 1310.1.2 and § 313.5 .

What does the code require for cathodic protection monitoring?

Cathodic protection systems must be monitored and documented; test results must show one of the enumerated pipe-to-soil voltage criteria (e.g., −0.85 V Cu/CuSO4) or compliance with certain federal methods as listed in § 1310.1.3.3 .

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