This standard covers the materials, joining methods, fittings, valves, specialties, hangers and supports, pipe insulation, installation, disinfection, and pressure testing for domestic potable cold water, domestic hot water, and hot water recirculation piping systems within buildings. All materials and components in contact with potable water shall comply with NSF/ANSI 61 for health effects and NSF/ANSI/CAN 372 for lead-free content, a federal requirement under the Safe Drinking Water Act applicable to all plumbing components installed on or after January 4, 2014.
The scope of this standard begins at the downstream side of the building water service entrance, which is defined as the point immediately downstream of the water meter assembly and the main building shutoff valve. Piping covered by this standard terminates at fixture connection stops and equipment rough-in connections. The water service from the utility main to the meter vault is a separate scope.
Pipe sizes, routing, riser configurations, and fixture connection rough-in dimensions are as indicated on the plumbing floor plans, plumbing riser diagrams, and fixture rough-in schedule. This standard establishes the material, quality, and performance requirements that govern those drawings.
Water heaters, tankless heaters, storage tanks, domestic water booster pumps, heat trace systems, water softeners, filtration, and backflow prevention devices at point of connection to equipment are specified separately in Water Heaters and Backflow Prevention. This standard addresses only the piping, fittings, valves, water hammer arrestors, recirculation pump accessories, supports, insulation, and connecting accessories.
Materials, components, and installation shall comply with the latest adopted edition of the following standards and codes. Where the contract documents, the Authority Having Jurisdiction (AHJ), or a referenced standard impose conflicting requirements, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing. The applicable plumbing code — International Plumbing Code (IPC) or Uniform Plumbing Code (UPC) as adopted by the jurisdiction — shall take precedence over all other references on any matter directly addressed by that code.
| Standard | Title |
|---|---|
| ASTM B88 | Standard Specification for Seamless Copper Water Tube |
| ASTM B32 | Standard Specification for Solder Metal (lead-free) |
| ASTM B813 | Standard Specification for Liquid and Paste Fluxes for Soldering of Copper and Copper Alloy Tube and Fittings |
| ASTM B828 | Standard Practice for Making Capillary Joints by Soldering of Copper and Copper Alloy Tube and Fittings |
| ASTM F441/F441M | Standard Specification for Chlorinated Poly(Vinyl Chloride) (CPVC) Plastic Pipe, Schedules 40 and 80 |
| ASTM F442/F442M | Standard Specification for Chlorinated Poly(Vinyl Chloride) (CPVC) Plastic Pipe (SDR-PR) |
| ASTM F493 | Standard Specification for Solvent Cements for Chlorinated Poly(Vinyl Chloride) (CPVC) Plastic Pipe and Fittings |
| ASTM D2846/D2846M | Standard Specification for Chlorinated Poly(Vinyl Chloride) (CPVC) Plastic Hot- and Cold-Water Distribution Systems |
| ASTM F876 | Standard Specification for Crosslinked Polyethylene (PEX) Tubing |
| ASTM F877 | Standard Specification for Crosslinked Polyethylene (PEX) Hot- and Cold-Water Distribution Systems |
| ASTM F1807 | Standard Specification for Metal Insert Fittings Utilizing a Copper Crimp Ring, or Alternate Stainless Steel Clamps, for SDR9 Cross-linked Polyethylene (PEX) Tubing |
| ASTM F2080 | Standard Specification for Cold-Expansion Fittings with PEX Reinforcing Rings for PEX Tubing |
| ASTM F2098 | Standard Specification for Stainless Steel Clamps for Securing SDR9 Cross-linked Polyethylene (PEX) Tubing to Metal Insert Fittings |
| ASTM A312/A312M | Standard Specification for Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes |
| ASME B16.18 | Cast Copper Alloy Solder Joint Pressure Fittings |
| ASME B16.22 | Wrought Copper and Copper Alloy Solder Joint Pressure Fittings |
| ASME B16.51 | Copper and Copper Alloy Press-Connect Pressure Fittings |
| ASME B31.9 | Building Services Piping |
| NSF/ANSI 61 | Drinking Water System Components — Health Effects |
| NSF/ANSI/CAN 372 | Drinking Water System Components — Lead Content |
| ASSE 1010 | Performance Requirements for Water Hammer Arresters |
| ASSE 1013 | Performance Requirements for Reduced Pressure Principle Backflow Prevention Assemblies |
| ASSE 1015 | Performance Requirements for Double Check Backflow Prevention Assemblies |
| ASSE 1017 | Performance Requirements for Temperature Actuated Mixing Valves for Hot Water Distribution Systems |
| ASHRAE 90.1 | Energy Standard for Buildings Except Low-Rise Residential (Pipe Insulation Tables) |
| AWWA C651 | Disinfecting Water Mains |
| MSS SP-67 | Butterfly Valves: Face-to-Face Dimensions, Pressure-Temperature Ratings, Materials, Non-Destructive Test, Examination, and Marking |
| MSS SP-80 | Bronze Gate, Globe, Angle, and Check Valves |
| MSS SP-110 | Ball Valves Threaded, Socket-Welding, Solder Joint, Grooved and Flared Ends |
| ASCE 7 | Minimum Design Loads and Associated Criteria for Buildings and Other Structures (seismic restraint) |
Contractor shall submit the following for the Engineer's review prior to procurement and installation. Work shall not proceed on any system or zone until the corresponding submittals have been reviewed and returned.
Contractor shall provide the following at substantial completion before the domestic water system is accepted.
Domestic water piping installation shall be performed by journeyman plumbers licensed in the jurisdiction where the work is performed and supervised by a licensed plumbing contractor. The Contractor's license shall be current and shall cover the full scope of work. Soldering and brazing of copper piping shall be performed by plumbers who have demonstrated proficiency in the applicable joining methods, and where the AHJ requires individual certification for brazing, personnel shall hold current qualifying certification.
All pipe, fittings, valves, solder, flux, gaskets, and components in contact with potable water shall be certified to NSF/ANSI/CAN 372, confirming that the weighted average lead content of the wetted surface area does not exceed 0.25 percent. This is a federal requirement under the Reduction of Lead in Drinking Water Act (Section 1417 of the Safe Drinking Water Act) and is not subject to project-level waiver. The Contractor shall maintain current NSF 61 and NSF 372 certification documentation on site throughout construction and shall make documentation available for inspection by the AHJ, the Engineer, or the Owner's representative upon request.
Where different pipe materials are joined in the same system — such as copper to CPVC, or copper to galvanized steel at the building water service entrance — appropriate transition fittings listed for the specific combination shall be used. At connections between copper and ferrous metals, dielectric unions, dielectric flanges, or listed dielectric transition couplings shall be provided to prevent the galvanic cell that forms between dissimilar metals in an electrolyte. Dielectric fittings shall be rated for the service pressure and temperature. The Contractor shall also verify the chemical compatibility of all materials that will contact CPVC — certain solvent-based adhesives, incompatible sealants, fire-stop materials, and some insulation adhesives cause environmental stress cracking in CPVC and shall not be used adjacent to CPVC pipe or fittings.
Rough piping, pressure test, and disinfection stages shall be available for inspection by the AHJ. The Contractor shall coordinate inspection timing and shall not conceal, insulate, or cover any portion of the piping system until inspections are complete and the work is released. Below-slab and underground piping shall be pressure-tested and inspected before backfill or concrete placement.
Every piece of pipe, tubing, and fitting shall bear the applicable ASTM standard designation, size, type or SDR designation, pressure rating, and NSF 61/372 certification mark, legibly printed or embossed on the product. Materials that do not bear these markings shall not be incorporated into the work.
The piping material shall be selected to suit the service conditions — temperature, pressure, water chemistry, installation environment (above-ground, below-slab, concealed, exposed), and the noise sensitivity of adjacent occupied spaces. The material selected for cold water piping and hot water piping on a given project should be consistent throughout to simplify installation, inspection, spare parts management, and future maintenance. Mixed-material installations are permitted but require additional attention to dielectric isolation, installer training, and compatible joining materials.
All piping materials specified in this section shall be NSF/ANSI 61 and NSF/ANSI/CAN 372 certified for potable water service.
Copper tube conforming to ASTM B88 is the established standard for commercial domestic water piping. ASTM B88 copper is available in Types K, L, and M, differentiated by wall thickness. Type K has the heaviest wall and is designated for underground and critical service. Type L has an intermediate wall and is the standard for above-ground interior commercial applications. Type M has the thinnest wall and is acceptable in low-pressure applications where permitted by the local plumbing code, but is generally not recommended for commercial service.
Copper is resistant to corrosion in most municipal water supplies, has a long service record, is joinable by multiple proven methods, and is compatible with all common joining temperatures. Its principal vulnerabilities are accelerated corrosion in water with low pH (below approximately 6.5), high dissolved oxygen, elevated chloramine levels, or aggressive flux residue left in the pipe after soldering. On projects with known aggressive water chemistry, the Engineer shall evaluate alternative materials or internal protective measures.
Hot water piping material shall match the cold water piping material throughout the building to reduce complexity in installation, maintenance, and spare parts. Where CPVC is used for hot water service, operating temperature shall not exceed 180°F and operating pressure shall not exceed 100 psi continuous per ASTM D2846.
Type K copper, conforming to ASTM B88, is the standard for underground and below-slab domestic water piping due to its heavier wall thickness, which provides additional resistance to external corrosion, soil loading, and incidental damage. Where soil conditions are known to be aggressive — low pH, high chloride content, high sulfate content, or the presence of corrosive fill material — Type K copper shall be sleeved in a continuous polyethylene protective sleeve conforming to AWWA C105 (polyethylene encasement), or stainless steel pipe shall be substituted. The protective sleeve shall extend at least 12 in. past all fittings and shall be lapped and taped at all joints.
Below-slab piping shall be installed with a continuous sand bedding and sand envelope of minimum 4 in. compacted depth beneath the pipe and 4 in. above the pipe, or as detailed on the plumbing site plan and underground utility details. Below-slab piping shall be pressure-tested before the slab is placed.
Chlorinated polyvinyl chloride (CPVC) pipe and tubing conforming to ASTM D2846 (for CTS-dimension tubing in sizes 1/2 in. through 2 in.) or ASTM F441/F441M (for IPS Schedule 40 and 80 pipe above 2 in.) is a corrosion-resistant, cost-effective alternative to copper for hot and cold water distribution. CPVC does not corrode in aggressive water chemistries that attack copper, does not support pinhole leak failures, and has a pressure rating of 100 psi at 180°F for ASTM D2846 CTS material, making it suitable for domestic hot water service temperatures.
CPVC is sensitive to chemical attack from a category of materials known to cause environmental stress cracking (ESC). Incompatible materials include certain solvent cements intended for standard PVC (not CPVC-specific), certain solvent-based pipe joint compounds, some fire-stop materials applied directly to the pipe, and some closed-cell foam insulation adhesives. Before using any sealant, adhesive, coating, or fire-stop product adjacent to or in contact with CPVC pipe or fittings, the Contractor shall confirm compatibility with the CPVC manufacturer's published chemical compatibility data.
CPVC shall not be installed where exposed to direct sunlight or ultraviolet light unless protected by an opaque UV-resistant cover. Outdoor or unconditioned space installations shall be evaluated for temperature range suitability; CPVC becomes brittle below its service temperature floor and shall not be installed in spaces subject to freezing without freeze protection.
Crosslinked polyethylene (PEX) tubing conforming to ASTM F876, assembled as a system per ASTM F877, is a flexible, corrosion-resistant, freeze-damage-tolerant tubing widely used in commercial branch distribution and manifold-based distribution systems. PEX is available in three crosslinking methods — peroxide (PEX-a), silane (PEX-b), and electron beam (PEX-c) — all of which meet ASTM F876 but which differ in flexibility, expansion memory, and fitting compatibility. The crosslinking method and fitting system are proprietary and not interchangeable between manufacturers; the Contractor shall use the tubing, fittings, and tools from a single manufacturer's system throughout each assembly.
PEX shall not be used in exposed locations where it will receive direct ultraviolet (UV) exposure, which degrades the material over time. PEX shall not be installed in mechanical rooms or other locations where sustained ambient temperature may exceed 140°F at the pipe surface. PEX is not suitable for steam or high-temperature hot water systems. PEX shall not be joined by solvent cement, adhesive, threading, or heat fusion — only mechanical fittings of the types described in this standard are approved.
PEX is particularly suited to manifold-and-branch ("home-run") distribution layouts in which individual tubing runs extend from a central manifold to each fixture, eliminating branch tees within the wall cavities. Home-run layouts reduce the number of joints inside walls, improve water delivery response time, and facilitate individual circuit isolation.
Type 316L austenitic stainless steel pipe conforming to ASTM A312/A312M is used in domestic water systems where extreme water quality aggressiveness, hygiene requirements, or corrosion resistance in high-chloride environments makes copper and thermoplastics unsuitable. Type 316L (low-carbon) is preferred over Type 304 or 316 for domestic water service because the lower carbon content provides superior resistance to sensitization and intergranular corrosion. Stainless steel is common in food service, pharmaceutical, semiconductor, and certain healthcare applications where water purity and cleanability are paramount.
Hot water recirculation piping is subject to continuous elevated temperature and constant flow throughout the building's occupied hours. These conditions accelerate corrosion in metallic piping and creep in plastic piping compared to the hot water supply piping, which may sit stagnant. Recirculation piping material shall be rated for the maximum recirculation temperature on a continuous duty basis. Where the recirculation temperature is maintained at 120°F or above (as required for Legionella control in most commercial facilities), the material shall be confirmed suitable for continuous service at that temperature.
Pipe sizes shall be as indicated on the plumbing floor plans, riser diagrams, and pipe schedules. The Engineer shall size piping to limit water velocity to protect against erosion-corrosion, water hammer, and noise. Maximum velocities shall be as follows: cold water mains and branches — 8 ft/s; hot water supply — 5 ft/s; hot water recirculation — 3 ft/s. In noise-sensitive locations — above occupied spaces, in corridors adjacent to patient rooms or classrooms, or within 10 ft of sound-sensitive occupancies — velocity shall be limited to 4 ft/s for all services regardless of pipe material.
Fittings shall be of a material compatible with the pipe material they join, shall comply with the applicable ASTM or ASME standard, and shall be NSF/ANSI 61 and NSF/ANSI/CAN 372 certified. Fittings shall be rated for the same service pressure and temperature as the adjacent piping. Dissimilar-material fittings used at transitions between pipe materials shall be listed for the specific combination and shall incorporate dielectric isolation where required.
Wrought copper fittings conforming to ASME B16.22 are the standard for solder-joint connections. Wrought fittings are preferred over cast bronze fittings because they are available in the full range of sizes, have tighter dimensional tolerances, and provide a slightly stronger joint due to their homogeneous material at the joint interface. Cast bronze fittings conforming to ASME B16.18 are acceptable as an alternative where wrought fittings are not available in the required configuration.
Press-connect copper fittings conforming to ASME B16.51 are approved as an alternative joining method that eliminates open flame during installation. Press-connect fittings shall incorporate a visual unpressed indicator — a leak-path feature that ensures an unpressed connection leaks visibly at system pressure during testing rather than appearing to hold pressure until the joint fails in service.
CPVC socket-type fittings conforming to ASTM D2846 shall be used with ASTM D2846 CTS-dimension tubing. For larger-diameter CPVC pipe conforming to ASTM F441/F441M (IPS Schedule 40 or 80), fittings shall conform to ASTM F437 (threaded) or ASTM F438/F439 (socket type, Schedule 40 and 80 respectively). All CPVC fittings shall be clearly identified as CPVC — standard PVC fittings shall not be used with CPVC pipe, as PVC fittings and PVC solvent cements are chemically incompatible with CPVC and will produce defective joints.
PEX fittings shall be selected to match the tubing's crosslinking method and shall be used with the manufacturer's specified tools only. The Contractor shall not mix fitting systems — use of a crimp tool to install an expansion-type fitting, or the use of one manufacturer's expansion ring on another manufacturer's fitting, shall not be permitted and shall be cause for rejection of the joint.
Cold expansion fittings conforming to ASTM F2080 use a PEX reinforcing ring that is expanded over the tubing end, and then both the ring and tubing are expanded over the fitting body and allowed to recover. The recovered tubing grips the fitting with the memory force of the crosslinked polyethylene, creating a full-flow connection with no reduction in internal bore. Cold expansion is the preferred fitting method for commercial PEX installations in 1/2 in. through 2 in. sizes.
Metal insert fittings with copper crimp rings conforming to ASTM F1807, or with stainless steel clamp rings conforming to ASTM F2098, reduce the internal bore at the fitting but are widely used in residential and light commercial branch circuits. The crimp or clamp is applied with a calibrated, go/no-go tool that provides a defined, verified joint geometry.
Soldering is the standard joining method for copper tube and fittings 2 in. and smaller. All solder shall be lead-free conforming to ASTM B32, with a tin-silver or tin-antimony alloy composition; solder containing lead is prohibited for potable water service and constitutes a federal violation under NSF/ANSI/CAN 372. Flux shall conform to ASTM B813 and shall be water-soluble type to facilitate thorough flushing after installation; petroleum-based, non-water-soluble fluxes shall not be used, as residue from non-water-soluble flux accelerates internal copper corrosion and cannot be fully removed by flushing alone.
Joints shall be made per ASTM B828: cut tube square with a wheel cutter or hacksaw, remove internal burrs and external sharp edges, clean both the tube exterior and the fitting socket interior to bright copper using emery cloth or a fitting brush (never use steel wool, which leaves ferrous particles), apply flux to both mating surfaces sparingly, and assemble immediately. Heat the fitting — not the tube — and apply solder at the back edge of the joint when the fitting is hot enough to melt solder on contact. Allow the fitting to cool undisturbed. Overheating burns flux, oxidizes copper surfaces, and produces a porous, weak joint. Quenching a hot joint with water can stress the metal.
Brazing shall be used for copper piping 2-1/2 in. and larger, and is required by many plumbing codes for these sizes. Brazing shall also be used for any copper piping subject to operating temperatures above 250°F or operating pressures above 100 psi where soldering is insufficient. Brazing filler metal shall be silver-bearing BCuP-series alloy per AWS A5.8, applied per ASTM B828. Flux is not required with self-fluxing BCuP alloys on copper-to-copper joints, but shall be used at copper-to-bronze joints to prevent oxide formation.
Personnel performing brazing shall have demonstrated proficiency. Where the AHJ requires qualification testing for brazing personnel, tests shall be current before the work begins.
Press-connect fittings conforming to ASME B16.51 create a permanent mechanical joint without heat, eliminating hot work permits, reducing fire risk, and significantly accelerating installation compared to soldering or brazing. The joint is formed by pressing an O-ring-equipped fitting onto the tube using a calibrated hydraulic pressing tool. Each fitting manufacturer specifies the compatible pressing tool jaw profiles and tool calibration intervals; the Contractor shall use only the specified tooling and shall maintain calibration records on site. Press-connect fittings shall incorporate a visible gap or leak-path feature on the O-ring that causes an unjoined fitting to leak at system test pressure, providing a visible quality verification during hydrostatic testing.
Press-connect joints are permanent and cannot be disassembled once pressed. Location of all press joints shall be accessible for inspection; press joints shall not be installed in poured-concrete or masonry chases where a failed joint cannot be repaired without structural damage.
CPVC joints shall be assembled using CPVC-specific two-step primer and solvent cement conforming to ASTM F493. PVC-specific solvent cement shall not be used on CPVC; the solvent formulations differ and a PVC cement will not produce an adequate bond in CPVC.
Assembly procedure: cut the tube square using a miter box saw or wheel cutter — do not use a hacksaw that leaves a ragged edge; deburr and bevel the cut end at approximately 10 to 15 degrees to ease insertion; dry-fit the joint and mark the insertion depth with a pencil; apply the primer to both the tube exterior and fitting socket interior, using a full-circle stroke; immediately apply the CPVC solvent cement to the tube first, then to the fitting socket, using a full-circle stroke with a slightly smaller applicator; insert the tube into the socket with a slight twisting motion and hold assembled for 30 seconds to resist pipe spring-back. A continuous bead of cement should be visible around the full circumference of the joint. Wipe excess cement from the surface. Do not disturb the joint until the manufacturer's cure time has elapsed for the ambient temperature at time of assembly — cure times increase dramatically below 60°F.
Do not apply CPVC solvent cement at ambient temperatures below 40°F unless the manufacturer provides specific cold-weather procedures. Do not apply solvent cement to wet pipe surfaces. Maintain the manufacturer's published cure time before pressure testing; premature testing causes joint failure.
PEX tubing shall be joined using the fitting method selected in the Fittings section. Joints shall be made per the fitting manufacturer's installation instructions using the manufacturer's specified and calibrated tools. Tool and fitting systems are proprietary and not interchangeable between manufacturers; do not use tools from one system to make connections with a different system's fittings.
For cold expansion fittings (ASTM F2080): cut the tube square, expand the PEX reinforcing ring over the tube end to the manufacturer's specified depth, expand the tube end over the fitting body using the expansion tool, and push the assembly together completely. The tube memory will recover and grip the fitting within 30 seconds at 65°F or higher; below 40°F recovery time increases significantly. The Contractor shall ensure full recovery before continuing work on the branch.
For crimp ring (ASTM F1807) and clamp ring (ASTM F2098) methods: cut the tube square, slide the ring onto the tube, insert the fitting body fully, position the ring at the correct setback from the tube end per the manufacturer's instructions, and crimp or clamp with the calibrated go/no-go tool. The go/no-go gauge shall be checked after each joint and shall be re-calibrated when it fails the verification check. Record tool calibration status in the installation log.
All valves installed in potable water service shall be NSF/ANSI 61 and NSF/ANSI/CAN 372 certified. Valve certification shall extend to all wetted surfaces including the body, trim, seat, and packing. Valves shall be full-port configuration to minimize pressure drop and to permit thorough flushing and pigging where applicable. Valve sizes, types, and specific locations are as indicated on the plumbing floor plans, riser diagrams, and valve schedule.
Isolation valves shall be provided at the following minimum locations: at the main building water service entry; at the base of each riser and the top of each downfeed; at the inlet and outlet of each water heater, pressure reducing valve, and backflow preventer; at each branch serving a group of three or more fixtures; at each individual fixture where shut-off without disrupting adjacent fixtures is required; and at the inlet and outlet of the recirculation pump. Additional valve locations shall be as indicated on the valve schedule.
Ball valves are the standard for 2 in. and smaller isolation service. They provide a tight, reliable shutoff with quarter-turn operation and minimal pressure drop in the fully open position. Bronze-body ball valves with PTFE (Teflon) seats are the standard for domestic water. Stainless steel body valves are required in highly aggressive water environments or where code requires them for hygienic applications. Gate valves conforming to MSS SP-80 remain code-acceptable but are being replaced in modern practice by ball valves; gate valves are prone to internal corrosion of the wedge and seat when left in one position for extended periods, and gate valves near full-closed can suffer erosion damage to the seat faces.
Butterfly valves are preferred for 2-1/2 in. and larger isolation service due to their lower cost, lighter weight, and easier manual operation compared to large ball or gate valves. Butterfly valve disc and body liner materials shall be rated for potable water service and confirmed NSF 61/372 certified. For hot water service, the EPDM or EPDM/stainless disc construction shall be rated for the maximum system temperature on a continuous basis. Butterfly valves shall be installed with sufficient straight pipe upstream and downstream to avoid turbulence-induced seat erosion; consult the valve manufacturer for minimum installation distances.
Check valves shall be provided at all pump discharges, at all locations where backflow through the check valve could cause contamination or system damage, and at all other locations indicated on the drawings.
Silent (spring-loaded, center-guided) check valves close without the slam associated with swing check valves because the spring begins closing the disc as soon as flow decelerates rather than waiting for flow reversal. They are the preferred type for pump discharge applications and for any location where water hammer from abrupt check valve closure is a concern. Swing check valves are acceptable in non-critical, gravity-drain, or low-velocity applications where water hammer is not a concern.
Hose-end drain valves shall be provided at all system low points, at the base of risers, and at any isolated zone or section that cannot drain back through the main distribution piping. Drain valves shall be full-port ball valve type with female hose thread outlet, NSF 61/372 certified, with a threaded cap on the outlet.
Where building water pressure exceeds 80 psi at the service entrance, a pressure reducing valve (PRV) shall be installed to limit system pressure to a level safe for the piping and fixtures served. PRV selection and sizing is the responsibility of the Engineer; this standard covers the installation requirements for the PRV piping assembly, which shall include isolation valves on the inlet and outlet, a strainer on the inlet, a pressure gauge on the outlet, and a union or flanged connection for PRV removal and replacement. An expansion tank downstream of the PRV shall be provided per the applicable plumbing code to accommodate the thermal expansion of water heated in a closed system. Consult Water Heaters for expansion tank requirements.
Water hammer is the hydraulic shock wave produced when fast-closing valves, solenoid valves, or dishwasher and washing machine fill valves abruptly stop or redirect flow. The resulting pressure spike can reach several times normal operating pressure, is transmitted throughout the connected piping, and over time causes fatigue cracking at fittings, joint failure, and valve seat damage. Water hammer arrestors absorb the pressure spike using a precharged gas chamber separated from the waterway by a piston; when the surge arrives, the piston compresses the gas cushion and dissipates the energy before it propagates.
Water hammer arrestors shall conform to ASSE 1010 and shall be sized using the Plumbing and Drainage Institute (PDI) fixture unit method, which assigns water supply fixture units (WSFU) to each fixture type and then determines the required arrestor capacity rating (PDI sizes A through F). Arrestors shall be installed as close as practical to the quick-closing valve that generates the surge, and in the orientation — vertical, horizontal, or multi-position — permitted by the manufacturer. Arrestors shall be located in an accessible position — behind an access panel if concealed in a wall — to permit inspection and replacement without demolition.
In commercial buildings, domestic hot water must be delivered to fixtures within a time that satisfies both the occupant comfort standard and the energy code. Without a recirculation system, water in long horizontal branches stagnates and cools; drawing hot water requires purging the cooled water to drain — wasting water, wasting the energy used to heat it, and failing to satisfy occupant expectations. ASHRAE 90.1 requires recirculation systems on all service hot water systems in commercial buildings with long supply piping, and the applicable energy code shall govern the specific threshold.
The recirculation system keeps water circulating continuously or on a timer-controlled schedule through a return loop from the distribution piping back to the water heater. The return piping shall be sized by the Engineer for a minimum recirculation flow rate sufficient to maintain the return temperature above the Legionella control threshold throughout the loop under worst-case heat loss conditions.
Legionella pneumophila, the bacterium that causes Legionnaires' disease, colonizes domestic water piping when water temperatures fall into the range of approximately 68°F to 122°F and stagnation occurs. Hot water storage shall be maintained at a minimum of 120°F, and the recirculation return temperature shall be maintained at a minimum of 110°F, to inhibit Legionella multiplication throughout the distribution system. Healthcare facilities shall comply with NFPA 99 and the applicable state health department requirements, which typically require higher storage and distribution temperatures and a formal water management program.
The operational conflict between energy codes (which encourage lower water heater temperatures) and Legionella prevention (which requires higher temperatures) is addressed through thermostatic mixing valves at point-of-use: the water heater stores and circulates water at 120°F to 140°F for Legionella control, and a certified thermostatic mixing valve conforming to ASSE 1017 blends down to a safe delivery temperature at the fixture. In healthcare applications and in facilities serving immunocompromised or high-risk populations, the Engineer shall coordinate with the Owner's infection control program to establish water management protocols.
The recirculation pump shall be a bronze or stainless steel wetted-parts, in-line centrifugal pump sized for the recirculation flow rate and head loss determined by the Engineer. The pump shall be NSF 61/372 certified for all wetted materials. The pump shall be controlled by a time clock, aquastat, or combination control to operate only during occupied hours or when the return temperature falls below the setpoint, as required by ASHRAE 90.1 and the applicable energy code.
Where the recirculation loop serves multiple branches or multiple risers, balancing valves or pressure-independent automatic balancing valves shall be provided at each branch take-off or riser base on the return circuit to ensure that flow is proportional to the heat loss of each branch rather than taking the path of least resistance. Without balancing, the shortest-path branches circulate at excess flow while the longest branches stagnate, defeating Legionella control in the dead legs. Balancing valve locations shall be as indicated on the plumbing riser diagrams.
Piping shall be supported in accordance with ASME B31.9 and the applicable plumbing code. Support shall be provided at sufficient intervals to prevent sagging, which creates undrainable low points; excessive deflection, which stresses fittings and joints; and vibration transmission to the building structure, which generates noise. Hangers and support materials shall be compatible with the pipe material — direct contact between copper tube and bare steel or bare galvanized steel hangers shall not be permitted, as the galvanic cell between dissimilar metals in a humid environment consumes the zinc coating and then the steel rod and hanger hardware.
Where copper, CPVC, or PEX piping is supported by carbon steel or galvanized steel hangers, a full-length dielectric isolation liner, isolator insert, or neoprene-lined copper pipe clamp shall be provided between the pipe and the hanger or support to electrically isolate the dissimilar metals and prevent abrasion to plastic piping.
The Contractor shall not exceed the following maximum horizontal pipe support spacings. Larger pipe sizes within each material group follow the longer spacing where a range is given.
| Pipe Material | Nominal Pipe Size | Maximum Horizontal Spacing |
|---|---|---|
| Copper tube — Type K, L, or M | 3/4 in. and smaller | 6 ft |
| Copper tube — Type K, L, or M | 1 in. | 6 ft |
| Copper tube — Type K, L, or M | 1-1/4 in. through 2 in. | 8 ft |
| Copper tube — Type K, L, or M | 2-1/2 in. and larger | 10 ft |
| CPVC | 1 in. and smaller | 3 ft |
| CPVC | 1-1/4 in. and larger | 4 ft |
| PEX | 1/2 in. through 1 in. | 32 in. |
| PEX | 1-1/4 in. and larger | 48 in. |
| Stainless steel | All sizes | Per ASME B31.9 |
CPVC and PEX require significantly shorter support spacing than copper because thermoplastics creep under sustained load — the pipe will sag between inadequately spaced supports over time under its own weight plus the water weight, stressing joints and potentially forming undrainable pockets.
Vertical risers shall be supported at each floor penetration and at the base of the riser. A riser clamp or pipe clamp welded to the structure shall carry the full weight of the riser at each floor. PEX and CPVC risers shall be guided at each floor penetration to permit axial thermal movement without lateral deflection.
Domestic hot water piping expands along its length when heated to operating temperature. Copper tube has a coefficient of linear thermal expansion of approximately 9.4 × 10⁻⁶ in./in./°F; a 100 ft copper run heating from a 70°F installation temperature to 140°F operating temperature will elongate approximately 0.79 in. per 100 ft of run. CPVC has a coefficient of approximately 3.8 × 10⁻⁵ in./in./°F — approximately four times that of copper — and will elongate approximately 3.3 in. per 100 ft under the same conditions. PEX has a still higher coefficient.
Straight runs of piping shall incorporate thermal expansion provisions — expansion loops, offset L or Z configurations, or mechanical expansion joints — at the following intervals: metallic piping (copper), every 50 ft of straight run; CPVC piping, every 30 ft of straight run; PEX, every 20 ft on continuous horizontal runs or as directed by the manufacturer. In addition, all piping shall be installed with sufficient freedom of movement at anchors, guides, and wall penetrations that the piping can expand and contract without binding. The Contractor shall not anchor both ends of a long straight run of hot water piping without providing a mid-run expansion device.
Expansion loop, expansion offset, and mechanical expansion joint locations shall be as detailed on the plumbing riser diagrams and expansion detail drawings.
Where required by the applicable building code (IBC and ASCE 7), piping shall be braced for seismic loads. Seismic bracing requirements depend on the Seismic Design Category (SDC) of the building, the importance factor of the facility, and the pipe size. In SDC C and above, domestic water piping 2-1/2 in. and larger generally requires lateral and longitudinal seismic restraint. The Contractor shall confirm the project's SDC and the applicable threshold pipe size with the Engineer before beginning installation.
Pipe insulation on domestic water piping serves three distinct functions depending on the service: on hot water supply and recirculation piping, insulation reduces heat loss to the surrounding space, maintains acceptable delivery temperature at fixtures, reduces the energy consumed by the water heating system, and is required by ASHRAE 90.1 and the applicable energy code. On cold water piping in conditioned spaces, insulation prevents condensation on the pipe exterior when the pipe surface temperature is below the space dew point — uninsulated cold water piping in humid conditioned spaces drips condensate that damages ceilings, supports biological growth, and triggers mold complaints. All pipe insulation in air plenums and in rated assemblies shall have a flame spread index not exceeding 25 and a smoke developed index not exceeding 50 when tested per ASTM E84, as required by the applicable building code.
All domestic hot water supply and hot water recirculation piping shall be insulated continuously from the water heater through all distribution piping. Insulation shall be provided on all fittings, valves, flanges, and accessories as well as straight pipe sections; bare fittings and valve bodies are the most common source of excessive heat loss and condensation in partially-insulated systems.
Insulation thickness shall be the greater of the ASHRAE 90.1 minimum and the project-specified minimum. Where the energy code adopted by the jurisdiction imposes greater thicknesses than ASHRAE 90.1, the energy code governs. For operating temperatures above 140°F (such as systems maintained at higher temperatures for Legionella control), the Contractor shall confirm that the selected insulation material and adhesive are rated for the continuous service temperature.
Cold water piping in conditioned spaces, and any cold water piping exposed to conditions where pipe surface temperature may fall below the dew point of the surrounding air, shall be insulated with a vapor-retarder-jacketed system. Closed-cell elastomeric foam is preferred because the closed-cell structure provides an inherent vapor retarder, eliminating the need for a separate vapor barrier. Fiberglass insulation with ASJ jacket is acceptable but requires that every seam, longitudinal cut, end cap, fitting insulation, and valve cover be properly sealed with the manufacturer's adhesive and foil tape to maintain vapor retarder integrity; any unsealed gap allows water vapor to migrate to the cold pipe surface, condense, saturate the insulation, and eventually drip.
Insulation shall be continuous and uninterrupted at all hangers, supports, valve bodies, flanges, and fitting insulation covers. Insulation shall not be cut back or omitted at structural penetrations. Where pipe passes through sleeves in walls and floors, the annular space between pipe insulation and sleeve shall be packed with a compressible, non-combustible filler and sealed at fire-rated assemblies per Firestopping. Insulation shall not be installed until pressure testing and the AHJ inspection are complete.
Install piping in accordance with ASME B31.9, the applicable plumbing code, and the manufacturer's installation instructions for the specific pipe material and joining method. Install all piping to permit complete drainage when required. Horizontal piping shall be pitched at a minimum of 1/8 in. per foot toward drain valves unless the pipe is kept completely full and air venting is provided at high points; where horizontal piping is installed level, provide air vent valves at all high points and drain valves at all low points. Install drain valves at the low point of each zone, branch, or section that can be hydraulically isolated.
Cap or plug all open pipe ends at the end of each workday, without exception. Potable water piping that is left open accumulates construction debris, insects, standing water, and contamination that is extremely difficult to fully remove during flushing and disinfection. This requirement applies from first installation through final pressure test.
Cut pipe and tube squarely using appropriate tools: wheel cutters for copper tube (ensures a square, burr-free cut with minimal deformation); miter saw or fine-tooth hacksaw for CPVC (hack saw is acceptable for CPVC but leaves a rougher edge than a saw with fine teeth); tubing shear or scissors for PEX (specialized tools ensure a square cut without crushing the tube). Remove all burrs and sharp edges from cut ends. Copper tube cut with a wheel cutter will have an internal raised burr from the cutter wheel — remove completely with the cutter's reamer or an external chamfering tool. Unremoved internal burrs cause velocity noise, turbulence, and erosion of downstream fittings and valves.
Pipe penetrations through walls, floors, and roofs shall be sleeved. Sleeves shall be sized to allow free movement of the pipe (and its insulation) within the sleeve and to accommodate the expected thermal movement. Sleeves through fire-rated assemblies shall be sealed with listed fire-stop systems in accordance with the fire-stop system listing and as directed by Firestopping. Exterior wall sleeves and below-grade sleeve entries shall be sealed watertight with a mechanical link seal or equivalent system to prevent water and air infiltration.
The Contractor shall coordinate pipe routing with structural, HVAC, electrical, and fire protection trades before installation to avoid conflicts. Plumbing piping shall not be installed above electrical switchgear, panelboards, motor control centers, or transformers without prior written approval from the Engineer. Where conflicts are identified, the Contractor shall request a routing modification from the Engineer before cutting or installing structure-penetrating sleeves. Piping crossing expansion joints in the building structure shall be provided with flexible connections or expansion loops that permit the required differential movement without imposing force on the piping or the structure.
Install horizontal piping with adequate slope to facilitate complete drainage when required. The minimum slope for drainable horizontal piping is 1/8 in. per foot toward the nearest drain valve. Where horizontal piping serves as a standing supply main that is never drained, install piping level with air vents at all high points to prevent air locking.
Protect open pipe ends with factory-supplied or field-fabricated caps or plugs. Protect installed piping from physical damage from other trades. Where mechanical equipment or material will be staged or moved through areas containing installed piping, provide temporary physical protection (lumber, protective barriers) around the piping. PEX piping installed above ceilings shall be protected from UV exposure if the ceiling will remain open during an extended construction period; cover exposed PEX with an opaque wrapping.
All domestic water piping shall be flushed and disinfected after pressure testing and before being placed in service. Disinfection destroys bacteria introduced during construction from handling, pipe cutting, soldering flux residue, standing water, and construction debris. The applicable plumbing code (IPC Section 610 or UPC Section 610) mandates disinfection of potable water piping before it is placed in service, and this requirement cannot be waived. The procedure used shall be coordinated with the local water utility, which may impose additional requirements.
Before chlorination, flush the entire system with clean potable water at the highest achievable velocity to dislodge and remove particulate debris, solder flux residue, CPVC primer and cement residue, cutting oil from pipe threads, and any standing construction water. Flushing shall continue from the most upstream inlet through each branch and riser until the discharge water at all outlets runs visually clear and has the appearance, odor, and taste of the supply water. Document flushing by branch or zone. Do not proceed to chlorination until flushing is complete.
The chlorination procedure shall be in accordance with AWWA C651, adapted for building piping systems, and the applicable plumbing code. Fill the system with a chlorine solution at a free chlorine concentration of not less than 50 mg/L (50 ppm). The chlorinating agent shall be sodium hypochlorite (liquid, typically 5 to 12.5 percent available chlorine concentration) or calcium hypochlorite tablets or granular. All chlorinating agents shall be food-grade or potable-water-grade. Retain the chlorinated water in the system for a minimum of 24 hours. During the contact period, operate all valves and specialty devices through their full range to expose all wetted surfaces to the chlorine solution.
After the 24-hour contact period, measure the residual free chlorine concentration at representative points throughout the system, including all zone ends and all branches most remote from the fill point. A minimum residual free chlorine concentration of 25 mg/L shall remain throughout the system at the end of the retention period. If the residual falls below 25 mg/L at any sample point, re-dose the system to restore the 50 mg/L initial concentration and repeat the 24-hour retention period.
After satisfactory retention test, flush the system completely with clean potable water until the free chlorine concentration at all outlets equals or is less than the maximum residual disinfectant level of the incoming water supply. Do not discharge chlorinated flushing water to sanitary drain without dechlorination where required by the local municipality.
After chlorination flushing is complete, collect bacteriological water samples from representative discharge points distributed throughout the system. At a minimum, provide one sample per building floor, or one sample per zone if the system is divided into isolated zones, with a minimum of three samples for any system. Samples shall be collected in sterile sample bottles and submitted to a state-certified or accredited laboratory for total coliform analysis. The system shall not be placed in service until bacteriological test results confirm the absence of total coliform bacteria (zero total coliform colonies per 100 mL).
If bacteriological testing reveals total coliform presence, the system shall be re-chlorinated and re-tested before being placed in service. Identify the possible source of contamination — commonly a cross-connection, a skipped branch, or a valve that was not operated during chlorination — before re-disinfection. Do not place a system with confirmed positive coliform results in service under any circumstances.
Where the superheated water thermal disinfection method is used — which is common in healthcare facilities per NFPA 99 where chemical residuals are unacceptable — heat all domestic water piping and storage to a minimum of 180°F and maintain that temperature at all outlet points for a minimum of 30 minutes. This method effectively pasteurizes the system without chemical residuals. Restrictions: CPVC piping systems shall not be subjected to superheated water disinfection above the ASTM D2846 maximum rated temperature of 180°F continuous; verify that all components — including valves, seals, and arrestors — are rated for the thermal disinfection temperature before proceeding. PEX tubing rated for maximum 140°F service shall not be subjected to the superheated water method.
All domestic water piping shall be hydrostatically pressure tested after installation, after all joints are complete, and before insulation is applied, ceilings are closed, or piping is otherwise concealed. Testing demonstrates that all joints are leak-free and that the system can withstand pressures significantly above the normal operating range. The test shall be witnessed by the Contractor's superintendent and shall be available for observation by the AHJ and the Engineer.
The test pressure shall be sufficient to confirm joint integrity without damaging the piping. The test pressure shall not exceed the pressure rating of the lowest-rated component in the test section — this is particularly important where valves, backflow preventers, or other rated components are installed.
Fill the system slowly from the lowest point, opening all high-point air vents and all fixture outlet stops or temporary drain connections as required to purge air from the system completely. Air in the test water compresses and creates a false pressure reading, and a pressure drop from air dissolution does not indicate a leak. Allow the system to stabilize for at least 15 minutes after reaching test pressure to account for thermal expansion or contraction of the test water before beginning the test period. Record the gauge pressure at the beginning and end of the test period and at 30-minute intervals during the test. A test is satisfactory when the gauge pressure does not drop during the test period and there are no visible leaks at any joint, fitting, valve, or component connection.
Test gauges shall have a maximum range not exceeding twice the test pressure, a minimum dial diameter of 4 in., and shall have been calibrated within the 12 months immediately preceding the test. Include gauge identification number and calibration expiration date in the pressure test report.
Do not apply test pressure to CPVC piping until the solvent cement joints have achieved the minimum cure time specified by the cement manufacturer for the ambient temperature at the time of assembly. Pre-mature testing of partially-cured CPVC joints will cause joint failure — the joint will appear to fail structurally rather than leak, and the failed section must be cut out and remade. Follow the manufacturer's cure time table precisely; cure times may be two to four times longer at 40°F than at 75°F.
Below-slab and underground piping shall be pressure-tested before backfill or concrete placement. Conduct the test at the same pressure and duration as above-ground piping. Document the test with dated photographs showing the pressure gauge reading and the exposed piping at all joints, and include the photographs in the pressure test report.
Pipe and fitting materials shall be delivered in original packaging with labeling, ASTM standard designations, and NSF 61/372 certification marks intact. Inspect all deliveries immediately upon receipt; reject and return any pipe or fitting that arrives without legible ASTM and NSF markings, with visible physical damage, with end caps missing (open ends), or that cannot be confirmed as the correct material and type for the service application. Substitution of a lower-grade material — for example, substituting Type M copper for specified Type L — shall not be accepted even when packaging appears identical.
Store pipe and tubing indoors or under weatherproof cover, elevated a minimum of 4 in. off the ground on wood dunnage, and supported at sufficient intervals to prevent sag. Copper tube shall be stored with original end caps or field-applied caps to prevent moisture, insect, and debris entry. CPVC and PEX shall be stored completely out of direct sunlight and away from artificial UV sources such as UV cure lamps; UV exposure degrades both materials and creates brittle failure risk even before installation. PEX shall be stored coiled at the manufacturer's minimum recommended coil diameter or in straight lengths — overly tight coiling creates memory bends that are difficult to straighten during installation.
Handle pipe and tube to avoid dents, kinks, scratches, and deformation. Do not drop pipe, drag pipe across rough surfaces, or use pipe as a lever or fulcrum. Damaged or kinked sections — particularly PEX, which can develop interior micro-cracks at kinks — shall be cut out and discarded. Do not install damaged material.
The Contractor shall warrant the domestic water piping installation against defects in materials and workmanship for the warranty period. The warranty shall cover pipe joint failures, valve packing and seat leaks attributable to manufacturing defects or workmanship, fitting failures, and failures of water hammer arrestors under normal operating conditions. The warranty shall not cover: damage from freezing caused by inadequate building heat maintenance; water hammer damage caused by system design, equipment selection, or operational conditions outside the Contractor's scope; damage caused by water quality conditions outside the material manufacturer's published limits; or physical damage from other trades or building users.
Manufacturer warranties for certified pipe and fitting systems, where applicable, shall be transferred to the Owner at substantial completion and included in the closeout submittal package. Where manufacturer warranty documentation requires Owner registration, the Contractor shall initiate registration before substantial completion.