This standard covers the design, material selection, fabrication, installation, testing, and acceptance of sanitary drain, waste, and vent piping systems inside buildings, including piping below slabs on grade, and extending to the five-foot connection point with the building sewer outside the building foundation wall. The scope encompasses all sanitary drainage, waste, and vent (DWV) piping that conveys sewage and liquid waste from plumbing fixtures and floor drains by gravity to the building sewer, and all vent piping that protects trap seals and admits air to the drainage system.
Sanitary waste and vent piping is among the most consequential plumbing scopes on any project. Unlike pressure piping systems that fail dramatically, DWV failures are often slow and concealed — improper slope fills pipes with solids, inadequate venting destroys trap seals and admits sewer gas, and poorly supported piping sags over time to create chronic blockages. The consequences range from nuisance service calls to structural damage from chronic leakage, to occupant health hazards from hydrogen sulfide intrusion. This standard is written to close the gaps between code minimums and reliable, long-term performance.
This standard does not cover storm drainage or roof drainage systems. Where a combined sanitary and storm drainage system is present, the authority having jurisdiction governs the discharge arrangement; the materials and installation requirements of this standard apply to the sanitary portions of such systems. Coordinate floor drain and fixture locations with plumbing floor plans and fixture schedule and coordinate with Plumbing Fixtures for trap configuration, outlet size, and rough-in dimensions at each fixture.
Materials, equipment, and installation shall comply with the latest adopted edition of the following standards and codes unless a specific year is cited elsewhere in the contract documents. Where the contract documents or a referenced standard conflicts with the adopted building code, the more stringent requirement governs unless the Engineer of Record directs otherwise in writing.
| Standard | Title |
|---|---|
| IPC | International Plumbing Code (Chapter 7 — Sanitary Drainage; Chapter 9 — Vents) |
| UPC | Uniform Plumbing Code (Chapter 7 — Drainage Systems; Chapter 9 — Venting) |
| ASTM A74 | Standard Specification for Cast Iron Soil Pipe and Fittings (hub and spigot) |
| ASTM A888 | Standard Specification for Hubless Cast Iron Soil Pipe and Fittings for Sanitary and Storm Drain, Waste, and Vent Piping Applications |
| CISPI 301 | Standard Specification for Hubless Cast Iron Soil Pipe and Fittings for Sanitary and Storm Drain, Waste, and Vent Piping Applications |
| CISPI 310 | Specification for Coupling for Use in Connection with Hubless Cast Iron Soil Pipe and Fittings for Sanitary and Storm Drain, Waste, and Vent Piping Applications |
| ASTM C1277 | Standard Specification for Shielded Couplings Joining Hubless Cast Iron Soil Pipe and Fittings |
| ASTM C564 | Standard Specification for Rubber Gaskets for Cast Iron Soil Pipe and Fittings |
| ASTM D2665 | Standard Specification for Poly(Vinyl Chloride) (PVC) Plastic Drain, Waste, and Vent Pipe and Fittings |
| ASTM D3034 | Standard Specification for Type PSM Poly(Vinyl Chloride) (PVC) Sewer Pipe and Fittings |
| ASTM D2564 | Standard Specification for Solvent Cements for Poly(Vinyl Chloride) (PVC) Plastic Pipe and Fittings |
| ASTM F656 | Standard Specification for Primers for Use in Solvent Cement Joints of Poly(Vinyl Chloride) (PVC) Plastic Pipe and Fittings |
| ASME B16.12 | Cast Iron Threaded Drainage Fittings |
| MSS SP-58 | Pipe Hangers and Supports — Materials, Design and Manufacture |
| MSS SP-69 | Pipe Hangers and Supports — Selection and Application |
| ASSE 1072 | Barrier-Type Floor Drain Trap Seal Protection Devices |
| ASSE 1018 | Water-Supplied Trap Seal Primer Valves |
| NSF/ANSI 14 | Plastics Piping System Components and Related Materials |
Where the project is located in a jurisdiction that has adopted the Uniform Plumbing Code rather than the International Plumbing Code, references to IPC chapter and section numbers shall be understood to refer to the equivalent UPC provisions. The Contractor shall confirm the adopted edition with the Authority Having Jurisdiction prior to submitting the permit application.
Contractor shall submit the following for the Engineer's review and comment prior to fabrication, procurement, or installation of any portion of the work. No substitutions for specified materials shall be used until the substitution has been reviewed and accepted in writing.
Contractor shall provide the following at substantial completion before the sanitary waste and vent system is accepted.
All sanitary waste and vent piping shall be installed by a licensed plumbing contractor and by journeymen or apprentice plumbers working under the direct supervision of a licensed journeyman. The installing contractor shall have verifiable experience in commercial DWV piping installation on at least three projects of comparable size and complexity within the preceding five years.
Hubless cast iron piping shall be installed only by personnel who have been trained in the torquing and coupling-installation techniques required by the coupling manufacturer. Personnel who are installing couplings for the first time on a project shall demonstrate proper torque technique on sample connections before performing production work.
All pipe, fittings, couplings, and specialty drainage items shall be listed and marked by a nationally recognized testing laboratory for the applicable product standard. Cast iron soil pipe shall be marked with the applicable standard designation (ASTM A74 or ASTM A888/CISPI 301), the pipe weight class, and the manufacturer's identification. PVC DWV pipe shall be marked with the applicable standard designation (ASTM D2665), the material designation, the nominal pipe size, and the NSF/ANSI 14 listing mark.
Unlisted or unmarked pipe and fittings shall be rejected and removed from the project regardless of documentation provided by the supplier.
All fittings in the sanitary drainage system shall be drainage-pattern fittings designed for gravity flow. Sanitary drainage systems shall not use pressure-pattern tee fittings (standard tees, crosses, or straight-pattern tees) to connect drainage branches. Drainage-pattern fittings — including sanitary tees, wye fittings, combination wye-and-eighth-bends, and long-sweep bends — direct flow in the direction of drainage and minimize velocity-killing dead pockets. The use of pressure tees in drainage systems causes turbulence, solids deposition, and chronic blockage, and is not permitted regardless of the direction of flow being connected.
The Contractor shall schedule inspections by the Authority Having Jurisdiction for all below-slab and below-grade piping before placement of concrete, fill, or backfill. No concealment of any portion of the DWV system is permitted before the applicable rough plumbing inspection has been completed and released. The Contractor shall notify the Engineer of Record if any inspection rejection or required modification differs from the contract documents, before proceeding with corrective work.
The choice of pipe material shall be established by the contract documents. Where the contract documents permit more than one material for a given portion of the system, the Contractor shall submit the proposed material for each location and shall not mix materials within a continuous run without an approved transition fitting. The following materials are specified for the applications indicated.
Hubless cast iron is the preferred material for above-grade interior sanitary piping in commercial and institutional buildings. Its mass provides superior noise attenuation relative to plastic piping — an important consideration in hotels, multifamily residential, healthcare facilities, and office buildings where drain noise in occupied spaces is a chronic source of complaints. Cast iron also provides greater resistance to accidental impact, a longer service life, and superior fire resistance. The premium over PVC DWV is modest relative to the long-term performance advantages in occupied buildings.
PVC DWV is acceptable in applications where noise attenuation is not a significant concern, where the structure type or occupancy type makes it appropriate, and where it is permitted by the adopted plumbing code and the contract documents. PVC DWV shall not be used above grade in locations where acoustic performance is required, including in chase walls adjacent to occupied spaces in hotels, healthcare facilities, dormitories, and similar occupancies.
Hub-and-spigot (hub-and-spigot) cast iron with compression gasket joints is a robust and well-proven material for below-slab buried drainage in commercial buildings. The compression gasket joint tolerates minor differential settlement without losing water tightness, which is an important attribute in below-slab applications where post-construction access for joint repair is expensive and disruptive. PVC Schedule 40 DWV is also widely used below slab in commercial construction where soil conditions and structural design do not impose significant differential settlement; it shall be installed on a uniform granular bed and shall be supported and bedded per the requirements of the Buried and Below-Slab Piping section of this standard.
Hubless cast iron soil pipe and fittings shall conform to ASTM A888 or CISPI 301 and shall be manufactured from gray iron. Pipe and fittings shall be available in sizes as indicated on the drawings and shall comply with all dimensional, weight, and mechanical requirements of the applicable standard. The nominal wall thickness and dimensional properties shall comply with Table 1 of ASTM A888, which specifies service weight and extra-heavy weight pipe; service weight shall be used unless extra-heavy weight is specifically indicated on the drawings.
Service weight hubless cast iron is appropriate for the large majority of commercial DWV applications. Extra-heavy weight is warranted for underground installations subject to vehicular loading, for connections below heavy machinery, or where extra-heavy weight is specifically required by the structural engineer or the contract documents. The Contractor shall not substitute service weight for extra-heavy weight in locations where extra-heavy weight is indicated.
Hub-and-spigot cast iron soil pipe and fittings shall conform to ASTM A74 and shall be available in service weight and extra-heavy weight as indicated. Pipe shall be straight-length and shall be furnished in nominal 5-foot and 10-foot laying lengths. Hub-and-spigot cast iron shall be joined with compression-fit rubber gaskets conforming to ASTM C564; lead and oakum joints are obsolete, shall not be specified, and shall be used only where required to match existing lead-joint piping during renovation work under the direction of the Engineer. The compression gasket joint creates a watertight, root-resistant seal without the thermal cracking risk of lead or the rigidity of solvent-cemented joints.
Polyvinyl chloride drain, waste, and vent pipe and fittings shall conform to ASTM D2665 and shall be Schedule 40 wall thickness throughout. Pipe shall be manufactured from virgin PVC compound meeting the cell classification requirements of ASTM D2665. Pipe and fittings shall carry the NSF/ANSI 14 listing mark and shall be rated for drain, waste, and vent service. Cellular-core PVC pipe (foam-core) shall not be substituted for solid-wall Schedule 40 pipe unless specifically approved by the Engineer for above-grade vent-only applications where structural loading and joint pull-out are not concerns.
PVC sewer pipe conforming to ASTM D3034 (Type PSM, SDR 35) is permitted only for the below-grade building drain from the building foundation to the five-foot connection point with the building sewer, where so indicated on the drawings. ASTM D3034 sewer pipe shall not be used inside the building or above grade; it is a sewer-service material not rated for the chemical and temperature exposure of the interior building waste system.
Pipe sizes shall be as indicated on the drawings. No reduction in pipe size shall be made in the direction of drainage flow. The Contractor shall verify that the pipe sizes shown on the drawings comply with the drainage fixture unit (DFU) loading calculations in accordance with the adopted plumbing code, and shall report any discrepancy to the Engineer of Record before installation.
Hubless cast iron soil pipe and fittings shall be joined with shielded couplings conforming to CISPI 310 and ASTM C1277. Couplings shall consist of a stainless steel outer shield, stainless steel worm-drive clamp bands, and a neoprene sleeve gasket conforming to the elastomeric requirements of CISPI 310. All metallic coupling components shall be Type 301 or 304 stainless steel; couplings with carbon steel components are not acceptable for interior DWV service.
Couplings shall be installed with a torque wrench calibrated for the manufacturer's specified torque setting. The torque specification shall be obtained from the coupling manufacturer's published installation instructions and shall be verified as part of the submittal process. Under-torqued couplings leak; over-torqued couplings cut into the neoprene sleeve and create stress concentrations that eventually crack the gasket. Torquing by feel alone is not acceptable. The Contractor shall maintain at least one calibrated torque wrench on site for every two plumbers installing hubless couplings, and shall demonstrate proper technique to the Engineer's inspector if requested.
When joining hubless cast iron, pipe ends shall be clean and free of burrs, and shall be fully inserted into the coupling so that the pipe ends butt squarely against each other in the center of the gasket sleeve. The coupling shall be centered over the joint before band screws are tightened in a cross-pattern to achieve uniform compression, and the final torque pass shall confirm all screws are at the specified value.
The torque value shall be taken from the coupling manufacturer's current published installation instructions. The default value of 60 in-lbs is representative of standard CISPI 310 couplings for 1-1/2-inch through 4-inch pipe; larger pipe and heavy-duty couplings may require higher torque. The Contractor shall verify the manufacturer's current specification before commencing installation.
Hub-and-spigot cast iron soil pipe shall be joined using compression rubber gaskets conforming to ASTM C564. Gaskets shall be seated uniformly in the hub socket before the spigot end is inserted. The spigot end shall be clean and free of burrs, and a thin film of lubricant furnished or approved by the pipe manufacturer shall be applied to the spigot and the exposed face of the gasket before assembly. The joint shall be completed by driving the spigot into the hub until the gasket is fully compressed and the spigot shoulder contacts the hub face; partial insertion that leaves the gasket partially compressed is not a completed joint and shall be rejected.
Lead and oakum caulked joints shall not be used in new construction. Where lead and oakum joints exist in renovation work being connected to, a lead-to-hubless transition coupling shall be used to make the connection; the lead coupling shall be listed for joining lead-to-iron connections and installed per the manufacturer's instructions.
PVC DWV pipe and fittings shall be joined by solvent cement welding per ASTM D2564. All joints shall be made using a two-step process: a listed PVC primer conforming to ASTM F656, applied with a dauber of appropriate size and worked into the socket and onto the spigot until the surface softens; followed immediately by a medium-bodied or heavy-bodied solvent cement conforming to ASTM D2564, applied to both the socket and the spigot. The primer is not optional; joints made without primer on PVC pipe rely solely on solvent-cement adhesion without the surface dissolution that creates the true chemical weld, and such joints do not meet the standard. Purple primer is required unless a clear primer that meets ASTM F656 is specifically permitted by the authority having jurisdiction.
After applying cement, the spigot shall be inserted into the socket with a quarter-turn twist and held in place for a minimum of 30 seconds to prevent the joint from pushing apart while the cement is still fluid. A uniform bead of cement shall appear around the full circumference of the socket face; a joint that shows gaps in the bead or that has the bead on one side only shall be cut out and remade. Joints shall cure undisturbed for the time period specified by the cement manufacturer before the system is subjected to any load, movement, or pressure testing. Minimum cure times are temperature-dependent and shall be observed; cold ambient temperatures significantly extend required cure times.
Mechanical couplings (rubber-gasket slip couplings) may be used for repair joints and for connections to existing PVC piping where solvent cement joints cannot be made, subject to the Engineer's approval and the authority having jurisdiction's acceptance.
Where hubless cast iron is connected to hub-and-spigot cast iron, an appropriately sized hubless shielded coupling shall be used. Where cast iron is connected to PVC DWV, a listed mechanical transition coupling of the appropriate nominal size and configuration — with a neoprene gasket of sufficient wall thickness to accommodate the outside diameter difference between cast iron and PVC pipe — shall be used. Solvent-cemented adapters are acceptable for connecting PVC DWV to cast iron hub-and-spigot fittings where the adapter is listed for the joint type and the spigot-to-hub fit is within tolerance. Incompatible materials shall never be joined without a listed transition fitting; taping, gluing, or caulking dissimilar materials is not a recognized joint method and shall not be used.
All fittings within the sanitary drainage system shall be drainage-pattern fittings. The following drainage-pattern fitting types are acceptable and shall be used in the configurations indicated:
Sanitary tees shall not be used for horizontal-to-horizontal connections under any circumstances. The sanitary tee places the branch connection at 90 degrees to the direction of flow in the main drain, which creates an abrupt pocket that immediately fills with solids. This is one of the most common sources of chronic blockage in commercial buildings and is a violation of the IPC (Section 706) and UPC requirements for drainage fittings. The Contractor shall specifically verify that all horizontal branch connections shown on the drawings use wye-pattern fittings, and shall notify the Engineer if any condition requires a different approach.
Fittings shall be of the same material as the pipe to which they are connected, unless a transition fitting is required. Cast iron DWV fittings shall conform to ASTM A888 (hubless) or ASTM A74 (hub-and-spigot) as applicable. PVC DWV fittings shall conform to ASTM D2665 and shall be Schedule 40 throughout. ASME B16.12 cast iron threaded drainage fittings may be used for threaded connections to equipment where drainage-pattern sanitary fittings are not available in the required thread size.
Closet flanges for water closets shall be as indicated on the fixture rough-in drawings for the applicable fixture type. Closet flanges shall be of cast iron for cast iron piping systems. PVC closet flanges conforming to the applicable material standard may be used with PVC DWV piping. Closet flanges shall be set level at the finished floor elevation and shall be secured to the pipe and to the floor framing or slab. Closet flanges set below the finished floor level are a common source of water closet seal failures; the flange face shall be flush with or not more than 1/4 inch above the finished floor.
Cleanouts shall be provided at locations and intervals as required by IPC Chapter 7 (Section 708) and as indicated on the drawings. At minimum, cleanouts shall be provided at the following locations:
Cleanout spacing at 100-foot intervals is a code maximum, not a target. In practice, 50-foot maximum spacing is better for maintenance in long runs of 4-inch drain, and 75-foot maximum spacing is reasonable for larger pipes where rodding equipment has greater reach. The Contractor shall provide cleanouts at code-minimum spacing unless the drawings indicate closer spacing.
Each cleanout shall be accessible without removing permanent construction and shall have not less than 18 inches of clear working space directly in front of the cleanout opening for drain-cleaning equipment to enter. Cleanouts located in concealed spaces — above ceilings, in crawl spaces, behind walls — shall be provided with an access panel or cover that is permanently hinged or removable and that is labeled "PLUMBING CLEANOUT" on the visible face. Cleanouts in finished floors shall have a flush cover rated for the applicable floor loading.
Cleanout plugs in cast iron soil pipe cleanouts shall be cast iron or brass. Plastic plugs in cast iron cleanouts are not acceptable for permanent installation. Cleanout plugs in PVC DWV cleanout fittings shall be PVC or ABS conforming to the fitting manufacturer's specification. Cleanout plugs shall have a nut or slotted head that allows them to be removed with standard plumbing tools; plugs recessed below the cleanout body face shall be accompanied by a lift-out recessed cover sized to fit the cleanout opening.
Floor drains shall be provided at locations indicated on the drawings. Each floor drain shall be connected to the sanitary drainage system, shall include an integral or separate trap of the required depth, and shall be sized to handle the design drainage flow. Floor drain body sizes, grate types, outlet sizes, and connections shall be as indicated on the plumbing floor plans and the fixture schedule.
Cast iron floor drain bodies are the standard for commercial and institutional buildings. Stainless steel floor drains are appropriate in food service, healthcare, and other high-sanitation environments where corrosion resistance and cleanability are priorities. PVC floor drain bodies are acceptable only in lightly loaded utility spaces.
Every floor drain trap shall be provided with a means of maintaining the trap seal against evaporation. Floor drains that are subject to regular water discharge — in mechanical rooms with equipment drains, in restrooms, in service corridors receiving mop sink discharge — may rely on that regular discharge to maintain trap seals. Floor drains that are infrequently used, including those in storage rooms, electrical rooms, elevator pits, and similar spaces, shall be provided with a trap seal primer system or a listed barrier-type trap seal protection device. Failure to maintain trap seals allows sewer gas (hydrogen sulfide) to enter occupied spaces and is one of the most commonly cited plumbing deficiencies in occupied buildings.
Water-supplied trap seal primer valves conforming to ASSE 1018 shall discharge to the trap inlet side of the drain, above the water seal, through a connection that prevents back-siphonage. The primer valve shall be connected to the domestic cold water system with an appropriate backflow prevention device in accordance with the requirements of Domestic Water Piping and the adopted plumbing code. Barrier-type trap seal devices conforming to ASSE 1072 are acceptable where water supply connection is not practical; they shall be installed in the trap inlet and maintained on the schedule recommended by the device manufacturer.
Floor drain grates shall be the type and finish indicated on the drawings and shall be secured against accidental displacement in any area accessible to the public. In food service and healthcare areas, grates shall be removable for cleaning without tools. In areas subject to fork lift or other wheeled vehicle traffic, grates shall be rated for the applicable live load. The drain body and grate shall be set level and flush with the finished floor surface; drains set proud of the floor surface create trip hazards and prevent effective floor mopping.
Every plumbing fixture connected to the sanitary drainage system shall be provided with a liquid seal trap. Each trap shall have a liquid seal of not less than 2 inches and not more than 4 inches in depth. Traps shall be self-cleaning — that is, designed so that the fixture discharge velocity carries waste cleanly through the trap without requiring separate flushing or priming.
Drum traps, bell traps, and crown-vented traps are prohibited in new sanitary drainage systems. S-traps (P-traps that discharge downward into the floor) shall not be used where they create an unvented trap arm that can lose its seal by siphonage; where a downward connection must be made, it shall be properly vented per the adopted plumbing code. Each fixture shall have its own independent trap; one trap serving two or more fixtures (a shared or common trap) is not permitted unless the fixture configuration is specifically recognized by the adopted plumbing code.
The distance from the trap weir to the vent connection (the trap arm) shall not exceed the maximum distance permitted by the adopted plumbing code for the pipe size used. The IPC Table 909.1 establishes maximum trap-to-vent distances ranging from 5 feet for 1-1/4-inch traps to 10 feet for 3-inch traps and 12 feet for 4-inch traps. Trap arms that exceed these distances cannot be adequately protected from siphonage by the vent connection; any such condition shall be reported to the Engineer of Record for resolution before the rough-in is concealed.
All pipe shall be supported continuously so that it cannot sag, deflect, or move under the weight of the pipe, the fluid it carries, and construction loads. Piping shall not rely on adjacent pipe, conduit, ductwork, or building insulation for support. Every hanger and support shall be capable of carrying the weight of the pipe, fittings, couplings, and the water weight of the pipe when full, without yielding or deflecting more than 1/16 inch per 10 feet of supported span.
Hangers and supports shall conform to MSS SP-58 for materials and design, and shall be selected and spaced in accordance with MSS SP-69. The hanger types listed in MSS SP-58 are accepted by the major plumbing codes; field-fabricated hangers are not permitted.
Maximum hanger spacing shall comply with the adopted plumbing code and with the pipe manufacturer's recommendations. In the absence of more stringent requirements from the contract documents, the following maximum spacing applies:
Cast iron soil pipe — both hubless and hub-and-spigot — shall be supported at every coupling and at not more than 5-foot intervals between couplings. Supporting at every joint is the recommended practice because it prevents the joint from experiencing any bending moment from span loads, which could work the coupling gasket loose over time. This practice adds modest cost but substantially extends the service life of the coupling joints.
PVC DWV pipe shall be supported at not more than 4-foot intervals for 3-inch and smaller pipe, and at not more than 4-foot intervals for 4-inch and larger pipe, unless the pipe manufacturer's literature or the contract drawings specify closer spacing. PVC pipe is subject to thermal expansion and contraction, and also to creep under sustained load. Hangers for PVC pipe shall not be cinched tightly against the pipe wall; the hanger shall support the pipe from below without constricting it, allowing the pipe to move longitudinally as it expands and contracts with temperature changes.
Vertical soil and waste stacks shall be supported at the base and at each floor penetration. Stack support at floor penetrations shall prevent downward movement of the stack and shall transfer the stack weight to the building structure, not to the piping connected to the stack at that floor. Riser clamps sized for the pipe diameter shall be installed below each floor slab or on pipe sleeves through each floor. Where a stack passes through a floor without a branch connection at that level, a mid-story guide may be used in lieu of a riser clamp, provided that a support clamp is installed within 18 inches above or below the floor.
Where the project is located in a seismic design category requiring seismic restraint of nonstructural systems, lateral bracing and longitudinal restraint for the sanitary DWV piping system shall be designed and installed per the requirements of the adopted building code, the applicable seismic design category, and the contract documents. Seismic restraint of piping systems is a specialized engineering scope; the Contractor shall not proceed with seismic restraint installation without reviewed shop drawings prepared by or reviewed by a licensed structural engineer for the restraint locations, hardware, and attachment points. Coordination between the seismic restraint design and the pipe hanger layout shall be completed before hangers are installed so that restraint hardware does not require field relocation.
The Contractor shall install sanitary waste and vent piping in coordination with structural framing, mechanical and electrical trades, and architectural finishes so that the required pipe sizes and slopes can be achieved without conflicts. Rough-in dimensions for fixtures, cleanouts, and floor drains shall be confirmed against the fixture schedule and the approved fixture rough-in sheets before any slab penetrations are made or below-slab piping is installed. Dimensions that cannot be confirmed from the drawings shall be referred to the Engineer of Record before proceeding.
The Contractor shall conduct a coordination review of the piping routing against the structural framing drawings before installation of below-slab or embedded piping. Floor penetrations through structural members shall not be made without approval from the structural engineer of record. Piping routed between structural bays shall be routed at the indicated invert elevations; where adequate slope cannot be achieved without conflicts with structural members or other systems, the Contractor shall immediately notify the Engineer and shall not deviate from the drawn routing or reduce pipe slope below code minimums without written direction.
All horizontal sanitary drainage piping shall be installed at a uniform slope in the direction of drainage flow. The pipe shall maintain the specified slope along its full length without dips, sags, or reverse grades. Slope shall be verified during installation and before concealment using a digital level or torpedo level on each pipe section; visual inspection alone is not sufficient for slope verification.
The minimum slopes above reflect the IPC requirements (Section 704.1) and represent the minimum gradients at which drainage velocity is adequate to keep solids in suspension and prevent settlement. For 3-inch and 4-inch pipe — which constitute the bulk of commercial building drain piping — 1/8-inch-per-foot slope is the code minimum. Where 1/4 inch per foot can be achieved without conflicts, it is preferred and produces more reliable self-cleaning velocity in short runs and at low flow rates. Slopes less than those indicated above are not permitted under any circumstances; a contractor who discovers that the indicated routing cannot achieve code-minimum slope without structural conflicts shall stop work on that run and report the condition to the Engineer of Record.
The maximum slope for horizontal drain piping shall not exceed 1/2 inch per foot (slope 45 degrees) for pipe 2-1/2 inches and smaller; steeper pitches can be used for vertical piping only. An excessively steep horizontal drain will allow liquid to run ahead of solids, stranding the solids and creating a blockage; this is the "too steep" failure mode that is as problematic as the "too flat" failure mode.
All vent piping shall be installed so that it drains by gravity to the sanitary drainage system. Horizontal vent pipes shall be graded not less than 1/4 inch per foot toward the drain, sloping downward in the direction of the drainage connection. Vents that cannot drain by gravity to the drainage system — because of building geometry, or because the vent runs back toward the structure — will accumulate condensate and liquid waste in the vent, which blocks the vent's function. A blocked vent is indistinguishable from a properly functioning vent until the trap seals it serves begin to siphon and sewer gas enters the building.
Where a vent pipe must take a horizontal offset below the flood level rim of the fixture it serves, the vent shall leave the drain pipe in a vertical or near-vertical direction before taking the horizontal offset; a vent taken as a horizontal branch from a horizontal drain below the fixture flood level rim functions as a drain, not a vent.
Where a soil or waste stack must be offset horizontally, the offset shall be made using appropriate drainage-pattern fittings. A stack offset that occurs below the lowest branch connection shall be treated as a horizontal drain at the offset location. A stack offset that occurs above the lowest branch connection shall be vented per the adopted plumbing code requirements for stack offsets, which may require an additional vent connection at the offset.
Pipes penetrating floor slabs, rated walls, and rated partitions shall be sleeved with a steel pipe sleeve of sufficient diameter to allow free passage of the insulated or bare pipe. Sleeves shall be set by the Contractor before concrete is placed; drilling or coring of structural slabs after concrete placement requires structural engineer approval and is done at the Contractor's risk. After pipe installation is complete, all sleeves in fire-rated assemblies shall be fire-stopped with a listed firestop system appropriate to the pipe material, the slab or wall assembly rating, and the annular space dimensions. Plastic (PVC) pipe penetrating fire-rated floor assemblies shall be fire-stopped with a listed intumescent firestop system that has been tested and listed for plastic pipe in the applicable fire-rated assembly.
Intumescent collars are the most common firestop method for plastic DWV pipe through floor slabs because they are pre-fabricated, easy to inspect, and well-listed for a wide range of pipe sizes and slab assemblies. The Contractor shall verify that the selected collar is listed for the specific pipe OD, the slab thickness, and the required fire-resistance rating, and shall submit the UL or FM listed assembly number as part of the firestop submittal.
Waste connections to plumbing fixtures shall be made with drainage-pattern fittings at the stub-out location shown on the fixture rough-in drawings. Fixture waste connections shall be made at the correct elevation so that the trap arm slope, trap seal depth, and vent-arm connection comply with the adopted plumbing code. No fixture shall be connected to the sanitary system through a fitting that creates an unvented trap or a trap arm that exceeds the maximum length for the trap size.
Trenches for below-slab and below-grade drainage piping shall be excavated to the dimensions required by the pipe size, the bedding type, and the cover depth. The trench bottom shall be graded to the pipe slope and shall be free of rocks, rubble, frozen material, or soft spots that would cause non-uniform bearing. Where the native soil is not competent to provide uniform pipe bearing — in fill areas, disturbed soil zones, or soft clay — the trench shall be over-excavated and a granular bedding layer of compactable sand or fine gravel shall be placed and shaped to provide continuous, uniform bearing under the pipe barrel. The Contractor shall report any trench bottom condition that is softer or more variable than the soil conditions assumed in the structural drawings to the geotechnical engineer of record before installing any piping.
Granular bedding shall be provided for all below-slab piping in new construction unless the native soil is unambiguously undisturbed and of competent bearing capacity, and the structural engineer of record has confirmed that native soil bearing is acceptable. Granular bedding is cheap insurance against differential settlement, which creates sags in the piping that immediately become solids collection points.
Minimum cover over the top of below-slab pipe to the underside of the slab shall be sufficient to provide the required haunch bedding support without disturbing the pipe during backfill compaction, and shall be not less than 6 inches above the pipe crown unless the structural engineer of record specifies otherwise. Backfill placed around the pipe shall be compacted by hand or with small mechanical equipment in thin, uniform lifts; large compaction equipment shall not operate within 3 feet of the pipe until sufficient cover has been placed. Backfill placed on one side before the other side is backfilled can roll the pipe off grade; both sides shall be backfilled simultaneously in lifts.
The required cover over buried piping shall be as indicated on the plumbing drawings or the civil drawings, and shall not be less than 6 inches from the top of the pipe to the underside of the slab. Where conflicts with other below-slab utilities require reducing pipe cover, the Engineer of Record shall be consulted before proceeding.
Hub-and-spigot cast iron pipe installed below slabs shall have the pipe barrel in continuous contact with the bedding for its full length between hubs. Bell holes shall be excavated at each hub location so that the hub does not bear on the bedding material; the pipe must be supported on the barrel, not on the hub. Bedding under the bell holes shall be removed and replaced with hand-packed granular bedding after the joint is made and inspected.
Where drainage piping is required to pass under footings, through highly loaded areas of the slab, or in locations where the structural drawings indicate concrete encasement, the Contractor shall encase the pipe in concrete per the details on the structural drawings. Concrete encasement for drainage piping shall be placed only after the piping has been successfully tested; encasing untested piping makes post-encasement repair effectively impossible without demolition. The Contractor shall schedule the concrete encasement pour separately from the piping test to ensure that testing is completed before any piping is encased.
The transition from the interior below-slab building drain to the exterior building sewer shall be made at the point indicated on the drawings, typically 5 feet outside the building foundation wall. The connection shall use a listed transition fitting appropriate to the pipe materials being connected. The exterior building sewer is outside the scope of this standard; the Contractor shall coordinate the building sewer installation and the connection point elevation with the civil drawings, the site plumbing drawings, and the applicable utility authority requirements.
The entire sanitary drain, waste, and vent system — all above-grade piping, below-slab piping, and branches to fixtures — shall be tested after rough-in is complete and before any piping is concealed by insulation, finishes, or other construction. No piping shall be covered, backfilled, or enclosed within fire-rated assemblies before the applicable test has been completed and accepted. The Contractor shall provide test notices to the Engineer and to the Authority Having Jurisdiction in sufficient time to allow witnessing; in most jurisdictions, the rough plumbing inspection must be witnessed by the building department inspector.
All tests shall be performed in the presence of the Engineer's inspector and, where required by the authority having jurisdiction, the building department inspector. Any portion of the system that shows evidence of leakage, loss of test head, or loss of pressure shall be repaired and re-tested until the section demonstrates compliance.
The water column test is the reference test method for sanitary DWV systems and shall be used unless air testing is selected per the criteria below.
For the water test, all openings in the system — including stack tops, cleanout plugs, fixture stub-outs, and any other openings — shall be plugged with expandable test plugs. The section under test shall be filled with water to a point not less than 10 feet above the highest fitting connection in the section, or to the top of the vent stack if the stack is shorter than 10 feet. The water shall be maintained at that level for not less than 15 minutes and the system shall remain free of visible leakage by inspection throughout the test period.
The water test makes leaks immediately visible and self-evident; even small joint failures show as wet spots or drips during the test hold period. This is the most reliable test method for identifying defective joints, and it is strongly preferred over air testing for initial acceptance. Air testing, while convenient, can mask slow leaks that would be found by the water column test.
Where the water test cannot be performed — due to the absence of adequate water supply, freezing ambient temperatures, or structural limitations on loading the piping with water weight — an air pressure test may be substituted.
For the air pressure test, all openings shall be plugged as described above. The system shall be pressurized to 5 psi (34 kPa) gauge using compressed air or an inert gas. Pressure shall be held for not less than 15 minutes without the introduction of additional air. The system shall demonstrate no pressure loss during the hold period by observation of a calibrated pressure gauge. The Contractor shall verify that all test plugs and end caps are rated for the test pressure and are appropriately restrained before pressurizing the system; plug blow-out from an unrestrained plug under 5 psi is a safety hazard.
Positive air pressure testing of PVC plastic piping is discouraged in favor of the water test because PVC pipe can shatter under pressure if it contains a manufacturing defect or has been damaged. Where air testing of PVC piping is required, personnel shall be kept clear of the pressurized system and pressure shall be built gradually while the system is inspected for plug and joint defects before full test pressure is applied.
After fixtures are set, all fixture traps shall be filled with water and fixtures shall be flushed simultaneously from the highest floor down, with each floor group flushed while the floor below is observed for leaks at all accessible joints. This operational flush test confirms that all fixture connections are leak-free under normal flow conditions.
The Contractor shall maintain a test log recording each test section, the date and time, the test method, the names of the inspector and building department inspector if present, the measured head or pressure at the start and end of the hold period, and the pass/fail determination. Test reports shall be submitted as part of the closeout submittal package. Any section requiring repair and re-test shall have both the failure record and the successful re-test documented.
The sanitary waste and vent piping Contractor shall coordinate the routing of all drainage piping with the structural engineer for slab openings and framing penetrations, with the mechanical contractor for conflicts with HVAC duct and hydronic piping, with the electrical contractor for conflicts with conduit runs and lighting fixture locations, and with the general contractor for ceiling height verification. Coordination shall be completed and conflicts resolved before any rough-in begins; field-resolved conflicts that reduce pipe slope below code minimums or that require improper fittings are not acceptable.
Where the DWV piping must cross other systems, the preferred arrangement is to route ductwork above the pipe, as gravity drainage piping cannot be routed around obstructions without compromising slope. The Contractor shall not deviate from the drawn routing or reduce slope to avoid a conflict without written authorization from the Engineer of Record.
The vent piping system serves two functions: protecting fixture trap seals from positive and negative pressure transients in the drainage system, and providing escape paths for sewer gases that accumulate in the drainage system. The vent system shall be designed as an integrated part of the DWV system, not added after the drain layout is fixed. The Contractor shall install the vent configuration shown on the contract drawings and shall not substitute one vent configuration for another without the Engineer's approval, because the hydraulic behavior of the drain system is affected by the vent configuration.
Air admittance valves (AAVs) shall not be used as a substitute for open-stack venting of main stacks that terminate through the roof. AAVs may be used for individual fixture venting where permitted by the adopted code edition, where no local amendment prohibits them, and where they are installed at accessible locations above the fixture flood level rim. AAVs shall be listed by a nationally recognized testing laboratory for the application in which they are used.
Sanitary waste and vent piping shall be identified in accessible locations to allow maintenance personnel to distinguish sanitary waste piping from storm drainage, domestic water, and other piping systems. In concealed spaces and mechanical rooms, piping shall be identified with pipe markers conforming to ASME A13.1, indicating the pipe contents (SANITARY WASTE or SANITARY VENT) and the direction of flow for horizontal drain lines. Pipe marker spacing shall be not greater than 25 feet in straight runs, plus at each change of direction, at each side of wall and floor penetrations, and at each valve and cleanout.
Pipe and fittings shall be delivered in the manufacturer's original bundling or packaging with identification markings intact and legible. The Contractor shall inspect each shipment upon delivery for visible defects including cracks, spalled ends, damaged hubs, and deformed sockets. Damaged material shall be segregated and returned to the supplier; damaged material shall not be installed.
Pipe shall be stored on a flat surface, supported continuously along its length to prevent permanent bending, and free of contact with rocks or sharp objects that could damage the pipe wall. Plastic pipe shall be stored out of direct sunlight; UV exposure degrades PVC and reduces service life. PVC solvent cement and primer shall be stored in a cool location away from heat sources and shall not be used past the shelf life date printed on the container. Shielded coupling gaskets shall be stored dry and protected from ozone exposure, which causes gasket cracking.
Long pipe sections shall be carried, not dragged, across rough surfaces. Cast iron pipe dropped onto concrete or onto its own ends can crack without visible external indication; any pipe subjected to impact loading shall be tapped with a hammer and examined for the ring-test crack indication. PVC pipe subjected to impact in cold weather is susceptible to brittle fracture; PVC stored below 40°F shall be allowed to warm before installation.
The Contractor shall warrant all materials and installation covered by this standard against defects in workmanship and against leakage for the project warranty period following substantial completion. The warranty shall cover all joints, connections, hangers, supports, and specialty drainage items installed under this scope.
Manufacturer warranties for floor drain bodies, trap primer valves, and electronic trap seal devices shall be passed through to the Owner as part of the closeout documentation. Where a manufacturer warranty extends beyond the Contractor's installation warranty period, the Contractor shall assign and transfer the manufacturer warranty to the Owner at closeout.
The warranty shall not limit or replace the Contractor's obligation to comply with all applicable code requirements and the requirements of this standard. A system that does not leak but was installed with incorrect slopes, improper fittings, or inadequate supports shall still be corrected at the Contractor's expense if deficiencies are discovered within the warranty period.