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  • CHAPTER11
    STORM DRAINAGE 

    SECTION1101
    GENERAL 

    1101.1Scope.

    The provisions of this chapter shall govern the materials, design, construction and installation of storm drainage.

    1101.2Disposal.

    Rainwater from roofs and storm water from paved areas, yards, courts and courtyards shall drain to an approved place of disposal. For one- and two-family dwellings, and where approved, storm water is permitted to discharge onto flat areas, such as streets or lawns, provided that the storm water flows away from the building.

    1101.3Prohibited drainage.

    Storm water shall not be drained into sewers intended for sewage only.

    1101.4Tests.

    The conductors and the building storm drain shall be tested in accordance with Section 312.

    1101.5Change in size.

    The size of a drainage pipe shall not be reduced in the direction of flow.

    1101.6Fittings and connections.

    All connections and changes in direction of the storm drainage system shall be made with approved drainage-type fittings in accordance with Table 706.3. The fittings shall not obstruct or retard flow in the system.

    1101.7Roof design.

    Roofs shall be designed for the maximum possible depth of water that will pond thereon as determined by the relative levels of roof deck and overflow weirs, scuppers, edges or serviceable drains in combination with the deflected structural elements. In determining the maximum possible depth of water, all primary roof drainage means shall be assumed to be blocked. The maximum possible depth of water on the roof shall include the height of the water required above the inlet of the secondary roof drainage means to achieve the required flow rate of the secondary drainage means to accommodate the design rainfall rate as required by Section 1106.

    1101.8Cleanouts required.

    Cleanouts shall be installed in the storm drainage system and shall comply with the provisions of this code for sanitary drainage pipe cleanouts.

    Exception: Subsurface drainage system.

    1101.9Backwater valves.

    Storm drainage systems shall be provided with backwater valves as required for sanitary drainage systems in accordance with Section 715.

    SECTION1102
    MATERIALS 

    1102.1General.

    The materials and methods utilized for the construction and installation of storm drainage systems shall comply with this section and the applicable provisions of Chapter 7.

    1102.2Inside storm drainage conductors.

    Inside storm drainage conductors installed above ground shall conform to one of the standards listed in Table 702.1.

    1102.3Underground building storm drain pipe.

    Underground building storm drain pipe shall conform to one of the standards listed in Table 702.2.

    1102.4Building storm sewer pipe.

    Building storm sewer pipe shall conform to one of the standards listed in Table 1102.4.

    TABLE 1102.4

    BUILDING STORM SEWER PIPE

    MATERIALSTANDARD
    Acrylonitrile butadiene styrene (ABS) plastic pipeASTM D 2661; ASTM D 2751; ASTM F628; CSA B181.1; CSA B182.1
    Cast-iron pipeASTM A 74; ASTM A 888; CISPI 301
    Concrete pipeASTM C 14; ASTM C 76;CSA A257.1M; CSA A257.2M
    Copper or copper-alloy tubing (Type K, L, M or DWV)ASTM B 75; ASTM B 88;ASTM B 251; ASTM B 306
    Polyethylene (PE) plastic pipeASTM F 2306/F 2306M
    Polyvinyl chloride (PVC) plastic pipe (Type DWV, SDR26, SDR35, SDR41, PS50 or PS100)ASTM D 2665; ASTM D 3034;ASTM F 891; CSA B182.4; CSA B181.2; CSA B182.2
    Vitrified clay pipeASTM C 4; ASTM C 700
    Stainless steel drainage systems, Type 316LASME A112.3.1

    1102.5Subsoil drain pipe.

    Subsoil drains shall be open-jointed, horizontally split or perforated pipe conforming to one of the standards listed in Table 1102.5.

    TABLE 1102.5

    SUBSOIL DRAIN PIPE

    MATERIALSTANDARD
    Cast-iron pipeASTM A 74; ASTM A 888;CISPI 301
    Polyethylene (PE) plastic pipeASTM F 405; CSA B182.1;CSA B182.6; CSA B182.8
    Polyvinyl chloride (PVC)Plastic pipe (type sewer pipe, SDR35, PS25, PS50 or PS100)ASTM D 2729; ASTM D 3034,ASTM F 891; CSA B182.2;CSA B 182.4
    Stainless steel drainage systems, Type 316LASME A112.3.1
    Vitrified clay pipeASTM C 4; ASTM C 700

    1102.6Roof Drains.

    Roof drains shall conform to ASME A112.6.4 or ASME A112.3.1.

    1102.7Fittings.

    Pipe fittings shall be approved for installation with the piping material installed, and shall conform to the respective pipe standards or one of the standards listed in Table 1102.7. The fittings shall not have ledges, shoulders or reductions capable of retarding or obstructing flow in the piping. Threaded drainage pipe fittings shall be of the recessed drainage type.

    TABLE 1102.7

    PIPE FITTING

    MATERIALSTANDARD
    Acrylonitrile butadiene styrene (ABS) plasticASTM D 2661; ASTM D 3311;CSA B181.1
    Cast-ironASME B16.4; ASME B16.12;ASTM A888; CISPI 301;ASTM A 74
    Coextruded composite ABS and drain DR-PS in PS35, PS50, PS100, PS140, PS200ASTM D 2751
    Coextruded composite ABS DWV Schedule 40 IPS pipe (solid or cellular core)ASTM D 2661; ASTM D 3311; ASTM F 628
    Coextruded composite PVC DWV Schedule 40IPS-DR, PS140, PS200 (solid or cellular core)ASTM D 2665; ASTM D 3311;ASTM F 891
    Coextruded composite PVC sewer and drain DR-PS in PS35, PS50, PS100, PS140, PS200ASTM D 3034
    Copper or copper alloyASME B16.15; ASME B16.18;ASME B16.22; ASME B16.23;ASME B16.26; ASME B16.29
    Gray iron and ductile ironAWWA C110/A21.10
    Malleable ironASME B 16.3
    Plastic, generalASTM F 409
    Polyethylene (PE) plastic pipeASTM F 2306/F 2306M
    Polyvinyl chloride (PVC) plasticASTM D 2665; ASTM D 3311;ASTM F 1866
    SteelASME B16.9; ASME B16.11; ASME B 16.28
    Stainless steel drainage systems, Type 316LASME A112.3.1

    SECTION1103
    TRAPS

    1103.1Main trap.

    Leaders and storm drains connected to a combined sewer shall be trapped. Individual storm water traps shall be installed on the storm water drain branch serving each conductor, or a single trap shall be installed in the main storm drain just before its connection with the combined building sewer or the public sewer. Leaders and storm drains connected to a building storm sewer shall not be required to be trapped.

    1103.2Material.

    Storm water traps shall be of the same material as the piping system to which they are attached.

    1103.3Size.

    Traps for individual conductors shall be the same size as the horizontal drain to which they are connected.

    1103.4Cleanout.

    An accessible cleanout shall be installed on the building side of the trap.

    SECTION1104
    CONDUCTORS AND CONNECTIONS

    1104.1Prohibited use.

    Conductor pipes shall not be used as soil, waste or vent pipes, and soil, waste or vent pipes shall not be used as conductors.

    1104.2Floor drains.

    Floor drains shall not be connected to a storm drain.

    SECTION1105
    ROOF DRAINS

    1105.1General.

    Roof drains shall be installed in accordance with the manufacturer’s instructions. The inside opening for the roof drain shall not be obstructed by the roofing membrane material.

    1105.2Roof drain flow rate.

    The published roof drain flow rate, based on the head of water above the roof drain, shall be used to size the storm drainage system in accordance with Section 1106. The flow rate used for sizing the storm drainage piping shall be based on the maximum anticipated ponding at the roof drain.

    SECTION1106
    SIZE OF CONDUCTORS, LEADERS
    AND STORM DRAINS

    1106.1General.

    The size of the vertical conductors and leaders, building storm drains, building storm sewers and any horizontal branches of such drains or sewers shall be based on the 100-year hourly rainfall rate indicated in Figure 1106.1 or on other rainfall rates determined from approved local weather data.

    100-YEAR, 1-HOUR RAINFALL (INCHES) EASTERN UNITED STATES

    For SI: 1 inch = 25.4 mm.

    Source: National Weather Service, National Oceanic and Atmospheric Administration, Washington D.C.

    FIGURE 1106.1

    100-YEAR, 1-HOUR RAINFALL (INCHES) EASTERN UNITED STATES

    100-YEAR, 1-HOUR RAINFALL (INCHES) EASTERN UNITED STATES

    For SI: 1 inch = 25.4 mm.

    Source: National Weather Service, National Oceanic and Atmospheric Administration, Washington D.C.

    FIGURE 1106.1—continued

    100-YEAR, 1-HOUR RAINFALL (INCHES) CENTRAL UNITED STATES

    100-YEAR, 1-HOUR RAINFALL (INCHES) EASTERN UNITED STATES

    For SI: 1 inch = 25.4 mm.

    Source: National Weather Service, National Oceanic and Atmospheric Administration, Washington D.C.

    FIGURE 1106.1—continued

    100-YEAR, 1-HOUR RAINFALL (INCHES) WESTERN UNITED STATES

    100-YEAR, 1-HOUR RAINFALL (INCHES) EASTERN UNITED STATES

    For SI: 1 inch = 25.4 mm.

    Source: National Weather Service, National Oceanic and Atmospheric Administration, Washington D.C.

    FIGURE 1106.1—continued

    100-YEAR, 1-HOUR RAINFALL (INCHES) ALASKA

    100-YEAR, 1-HOUR RAINFALL (INCHES) EASTERN UNITED STATES

    For SI: 1 inch = 25.4 mm.

    Source: National Weather Service, National Oceanic and Atmospheric Administration, Washington D.C.

    FIGURE 1106.1—continued

    100-YEAR, 1-HOUR RAINFALL (INCHES) HAWAII

    1106.2Size of storm drain piping.

    Vertical and horizontal storm drain piping shall be sized based on the flow rate through the roof drain. The flow rate in storm drain piping shall not exceed that specified in Table 1106.2.

    TABLE 1106.2

    STORM DRAIN PIPE SIZING

    PIPE SIZE (inches)CAPACITY (gpm)
    VERTICAL DRAINSLOPE OF HORIZONTAL DRAIN
    1/16 inch per foot1/8 inch per foot1/4 inch per foot1/2 inch per foot
    23415223144
    387395579111
    418081115163231
    5311117165234331
    6538243344487689
    81,1175057141,0101,429
    102,0509271,3111,8552,623
    123,2721,4802,0932,9604,187
    155,5432,5083,5465,0167,093

    For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon per minute = 3.785 L/m.

    1106.3Vertical leader sizing.

    Vertical leaders shall be sized based on the flow rate from horizontal gutters or the maximum flow rate through roof drains. The flow rate through vertical leaders shall not exceed that specified in Table 1106.3.

    TABLE 1106.3

    VERTICAL LEADER SIZING

    SIZE OF LEADER (inches)CAPACITY (gpm)
    230
    2 × 230
    11/2 × 21/230
    21/254
    21/2 × 21/254
    392
    2 × 492
    21/2 × 392
    4192
    3 × 41/4192
    31/2 × 4192
    5360
    4 × 5360
    41/2 × 41/2360
    6563
    5 × 6563
    51/2 × 51/2563
    81208
    6 × 81208

    For SI: 1 inch = 25.4 mm, 1 gallon per minute = 3.785 L/m.

    1106.4Vertical walls.

    In sizing roof drains and storm drainage piping, one-half of the area of any vertical wall that diverts rainwater to the roof shall be added to the projected roof area for inclusion in calculating the required size of vertical conductors, leaders and horizontal storm drainage piping.

    1106.5Parapet wall scupper location.

    Parapet wall roof drainage scupper and overflow scupper location shall comply with the requirements of Section 1503.4 of the International Building Code.

    1106.6Size of roof gutters.

    Horizontal gutters shall be sized based on the flow rate from the roof surface. The flow rate in horizontal gutters shall not exceed that specified in Table 1106.6.

    TABLE 1106.6

    HORIZONTAL GUTTER SIZING

    GUTTER DIMENSIONSa (inches)SLOPE (inch per foot)CAPACITY (gpm)
    11/2 × 21/21/426
    11/2 × 21/21/240
    41/839
    21/4 × 31/455
    21/4 × 31/287
    51/874
    4 × 21/21/4106
    3 × 31/21/2156
    61/8110
    3 × 51/4157
    3 × 51/2225
    81/16172
    81/8247
    41/2 × 61/4348
    41/2 × 61/2494
    101/16331
    101/8472
    5 × 81/4651
    4 × 101/21055

    For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon per minute = 3.785 L/m, 1 inch per foot = 83.3 mm/m.

    1. a.Dimensions are width by depth for rectangular shapes. Single dimensions are diameters of a semicircle.

    SECTION1107
    SIPHONIC ROOF DRAINAGE SYSTEMS

    1107.1General.

    Siphonic roof drains and drainage systems shall be designed in accordance with ASME A112.6.9 and ASPE 45.

    SECTION1108
    SECONDARY (EMERGENCY) ROOF DRAINS

    1108.1Secondary (emergency overflow) drains or scuppers.

    Where roof drains are required, secondary (emergency overflow) roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason. Where primary and secondary roof drains are manufactured as a single assembly, the inlet and outlet for each drain shall be independent.

    1108.2Separate systems required.

    Secondary roof drain systems shall have the end point of discharge separate from the primary system. Discharge shall be above grade, in a location that would normally be observed by the building occupants or maintenance personnel.

    1108.3Sizing of secondary drains.

    Secondary (emergency) roof drain systems shall be sized in accordance with Section 1106 based on the rainfall rate for which the primary system is sized. Scuppers shall be sized to prevent the depth of ponding water from exceeding that for which the roof was designed as determined by Section 1101.7. Scuppers shall have an opening dimension of not less than 4 inches (102 mm). The flow through the primary system shall not be considered when sizing the secondary roof drain system.

    SECTION1109
    COMBINED SANITARY AND
    STORM PUBLIC SEWER

    1109.1General.

    Where the public sewer is a combined system for both sanitary and storm water, the storm sewer shall be connected independently to the public sewer.

    SECTION1110
    CONTROLLED FLOW ROOF DRAIN SYSTEMS

    1110.1General.

    The roof of a structure shall be designed for the storage of water where the storm drainage system is engineered for controlled flow. The controlled flow roof drain system shall be an engineered system in accordance with this section and the design, submittal, approval, inspection and testing requirements of Section 316.1. The controlled flow system shall be designed based on the required rainfall rate in accordance with Section 1106.1.

    1110.2Control devices.

    The control devices shall be installed so that the rate of discharge of water per minute shall not exceed the values for continuous flow as indicated in Section 1110.1.

    1110.3Installation.

    Runoff control shall be by control devices. Control devices shall be protected by strainers.

    1110.4Minimum number of roof drains.

    Not less than two roof drains shall be installed in roof areas 10,000 square feet (929 m2) or less and not less than four roof drains shall be installed in roofs over 10,000 square feet (929 m2) in area.

    SECTION1111
    SUBSOIL DRAINS

    1111.1Subsoil drains.

    Subsoil drains shall be open-jointed, horizontally split or perforated pipe conforming to one of the standards listed in Table 1102.5. Such drains shall not be less than 4 inches (102 mm) in diameter. Where the building is subject to backwater, the subsoil drain shall be protected by an accessibly located backwater valve. Subsoil drains shall discharge to a trapped area drain, sump, dry well or approved location above ground. The subsoil sump shall not be required to have either a gas-tight cover or a vent. The sump and pumping system shall comply with Section 1113.1.

    SECTION1112
    BUILDING SUBDRAINS

    1112.1Building subdrains.

    Building subdrains located below the public sewer level shall discharge into a sump or receiving tank, the contents of which shall be automatically lifted and discharged into the drainage system as required for building sumps. The sump and pumping equipment shall comply with Section 1113.1.

    SECTION1113
    SUMPS AND PUMPING SYSTEMS

    1113.1Pumping system.

    The sump pump, pit and discharge piping shall conform to Sections 1113.1.1 through 1113.1.4.

    1113.1.1 Pump capacity and head.

    The sump pump shall be of a capacity and head appropriate to anticipated use requirements.

    1113.1.2 Sump pit.

    The sump pit shall be not less than 18 inches (457 mm) in diameter and not less than 24 inches (610 mm) in depth, unless otherwise approved. The pit shall be accessible and located such that all drainage flows into the pit by gravity. The sump pit shall be constructed of tile, steel, plastic, cast iron, concrete or other approved material, with a removable cover adequate to support anticipated loads in the area of use. The pit floor shall be solid and provide permanent support for the pump.

    1113.1.3 Electrical.

    Electrical service outlets, when required, shall meet the requirements of NFPA 70.

    1113.1.4 Piping.

    Discharge piping shall meet the requirements of Section 1102.2, 1102.3 or 1102.4 and shall include a gate valve and a full flow check valve. Pipe and fittings shall be the same size as, or larger than, the pump discharge tapping.

    Exception: In one- and two-family dwellings, only a check valve shall be required, located on the discharge piping from the pump or ejector.

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