Mechanical and Electrical Systems Essay
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SanitaryDrainageVentandStormwaterDrainagePiping.ppsPowerPoint® Presentation
Chapter 3-*
PowerPoint® Presentation
Chapter 3
Sanitary Drainage, Vent, and Stormwater Drainage Piping
Sanitary Drainage Piping • Drainage Piping Installation • Sanitary Drainage Piping Venting • Stormwater Drainage Principles
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Horizontal and vertical pipes are used to construct sanitary drainage piping, vent piping, and storm water drainage piping.
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Horizontal and vertical pipes are used to construct sanitary drainage, vent, and stormwater drainage piping. A horizontal pipe is any pipe or fitting that makes an angle of less than 45° with the horizontal plane. A vertical pipe is any pipe or fitting that makes an angle of 45° or less with the vertical plane. See Figure 3-1.
Pipe sizes for sanitary drainage and vent piping are based on drainage fixture unit values.
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Wastewater discharge rates of plumbing fixtures have been established based on 1 dfu being equal to 7 1/2 gal. of water per minute of waste discharge. Drainage fixture unit values for various plumbing fixtures are typically found in a plumbing code, along with minimum fixture trap and drain size. See Figure 3-2. The minimum fixture trap and drain size is the smallest size pipe into which the fixture may drain. This size must be used even if another sizing table indicates that a smaller size pipe would convey an equal number of drainage fixture units of waste. Always refer to the plumbing code adopted in your particular area for accepted drainage fixture unit values and minimum size trap and drain sizes.
Properly sized horizontal drainage pipes can discharge a certain number of drainage fixture units of waste without subjecting the plumbing system to plus or minus pressure.
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Properly sized horizontal drainage pipes can discharge up to a certain number of drainage fixture units of waste without subjecting the plumbing system to plus or minus pressure. Changes in direction, materials, grades, and other factors affect the discharge capacities of drainage pipes and were considered in the design of sizing tables. See Figure 3-3.
The sizes of building sewer, building drain, and building drain branches from stacks are based on the slope of the pipe and the potential dfu discharge.
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Discharge capacities for different sizes of horizontal drainage pipes, including building sewers, building drains, and building drain branches from stacks, are typically found in plumbing codes. Based on sizing tables, a plumber can establish the total discharge of all the fixtures in a building in drainage fixture units and select a drain size to serve the demand. See Figure 3-4.
The size of horizontal branch drains is based on the grade of the drain.
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Horizontal branch drains are another type of horizontal drainage piping. A horizontal branch drain is drainage pipe extending horizontally from a soil or waste stack or building drain, with or without vertical sections or branches. A horizontal branch drain receives the discharge from one or more fixture drains on the same floor as the horizontal branch and conveys it to the soil or waste stack or to the building drain. Most plumbing codes require all underground drainage pipes to be at least 2″ in diameter. Similar to building sewers and building drains, horizontal branch drain sizes are determined using a sizing table. See Figure 3-5.
A branch interval equals one floor of plumbing fixtures but may exceed one story depending on the location of the fixtures.
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When sizing soil and waste stacks, branch intervals must be considered. A branch interval (BI) is a vertical length of stack at least 8′ high within which the horizontal branches from one story or floor of the building are connected to the stack. In general, one branch interval equals one floor of plumbing fixture drains. Depending on the location of the plumbing fixtures, some branch intervals extend more than one story of building height. See Figure 3-6.
Soil and waste stack diameter is based on the potential waste discharge and the branch intervals of the building.
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The Maximum Loads for Soil and Waste Stacks table, similar to other sizing tables, is based on the drainage fixture unit method. See Figure 3-7. The Maximum Loads for Soil and Waste Stacks table combines three tables into one and lists the maximum number of drainage fixture units that may empty into:
• stacks of not more than three stories, with a maximum of three branch intervals
• stacks of more than three stories or three branch intervals
• a stack on any one story or branch interval
When two sinks with 1 1/2″ traps and drains rated at 2 dfu each are located on different floors of a building, a 1 1/2″ diameter stack is required.
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Stack sizing varies depending on the floor on which the fixtures are installed in a building. For example, a 1 1/2″ diameter stack is required to serve a building with two domestic kitchen sinks with 1 1/2″ traps and drains, rated at 2 dfu each, and located on different floors of the building. See Figure 3-8.
When two sinks with
1 1/2″ traps and drains rated at 2 dfu each are located on the same floor, a 2″ diameter stack is required.
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If the same sinks and drains are installed on the same level of the building, a 2″ stack is required because only
2 dfu may drain into a 1 1/2″ pipe on any one story or branch interval. See Figure 3-9.
A stack that is offset 45° or less from the vertical plane is sized as a straight vertical stack.
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A stack that is offset 45° or less from the vertical plane is sized as though it is a straight vertical stack. See Figure 3-10.
A stack offset more than 45° from the vertical plane is sized in three parts—stack above the offset, offset, and stack below the offset.
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If a stack is offset more than 45° from the vertical plane, the procedure for sizing the stack is:
1. The portion of a stack above the offset is sized the same as a straight stack (based on the total number of drainage fixture units above the offset). See Figure 3-11.
2. The offset portion of the stack is sized like a horizontal building drain branch.
3. The portion of the stack below the offset is sized at least as large as the offset.
Trap seal loss due to back pressure is prevented when fixture drains near the base of the stack or stack offset are properly connected.
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In buildings of five or more stories with offset stacks or a building with a horizontal building drain branch from the stack, fixtures should not be installed on the floor in which the offset occurs if waste from fixtures four or more stories above the offset is discharged into the stack. Fixtures in these buildings that drain into the horizontal portion of an offset stack or horizontal building drain branch are subject to trap seal loss from back pressure. Trap seal loss due to back pressure is prevented if fixture drains near the base of the stack or stack offset
connect to the horizontal pipe at least 8′ from the offset (measured vertically or horizontally). See Figure 3-12.
When sizing offset stacks, the portion above the offset is sized first, followed by the offset, and then the portion below the offset.
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Assume that 11 dfu of waste empty into the stack on each floor for a total of 44 dfu (4 × 11 = 44) on the entire stack. See Figure 3-13. A 3″ stack is large enough for the section of the stack above the offset since the stack is more than three stories. The size of the offset section of the stack is based on the slope and number of drainage fixture units. For example, if the slope is 1/4″ per foot with 44 dfu draining into the stack, a 4′ pipe must be used. A 4″ pipe is used for the section of the stack below the offset since it must be at least as large as the offset.
Horizontal drainage piping must be properly graded to ensure adequate drainage and self-scouring action inside the pipe.
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Horizontal drainage piping is graded 1/4″ per foot of run to provide adequate drainage. See Figure 3-14. Horizontal pipes graded at 1/4″ per foot allow wastewater and waterborne waste to achieve the necessary velocity and discharge capacity so that the pipes can scour themselves and function properly without producing plus or minus pressures in the plumbing system. However, because of basement floor depth and inadequate sanitary sewer main depth, the building drain and/or building sewer grade may be less than 1/4″ per foot. In addition, a long sewer may require less grade because the accumulated or total pitch results in a deep building drain outlet. When laying pipe with a slight grade (1/16″–1/8″), a leveling instrument should be used. A leveling instrument, such as a transit level or laser transit level, ensures a consistent grade for pipe along its entire length and pipe that is free of sagging. A sagging pipe results in sections of the pipe being filled with water.
Various turns may be required for drainage piping. It is important that the appropriate fittings are used.
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Care must be taken in selecting the proper fittings for changes in direction in drainage piping to prevent waste stoppages. See Figure 3-15.
Changes in direction of pipes are common in sanitary drainage piping.
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Long-sweep fittings lessen the probability of waste stoppage. Short-sweep 1/4 bends may be used for changes of direction from a horizontal plane to the vertical plane. Long-sweep 1/4 bends, two 1/8 bends, or a combination wye and 1/8 bend may be used where the change of direction is from the vertical plane to the horizontal plane or from the horizontal plane to the horizontal plane. See Figure 3-16. Fittings that are not illustrated but have the equivalent sweep of the changes in direction fittings can be used for the same type of changes in direction.
Cleanouts provide access to the piping for removing stoppage and cleaning the interior of the pipe.
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Cleanouts consist of tee or wye fittings installed in a drainage line and the unused opening capped with the appropriate removable cap or plug. See Figure 3-17. In general, a cleanout is the same size as the drainage pipe it serves (up to 4″ maximum). A 4″ cleanout is typically the largest size cleanout installed in a sanitary drainage system regardless of the size of the drain line it serves. Cleanouts should be provided in the following locations:
• front main cleanout—at the outside wall of the building at the connection of the building sewer and building drain
• stack base cleanout—at the base of all vertical soil or waste stacks
• at all 90° changes in direction
• at the upper terminal of all horizontal branch drains
• every 50′ on 3″ and smaller horizontal drainage pipe; every 100′ on 4″ and larger horizontal drainage pipe
A front main cleanout is placed at the outside wall of a building and may be placed either inside or outside of the building.
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A front main cleanout is always placed at the outside wall of the building and may be placed either inside or outside of the building. See Figure 3-18. A front main cleanout should be a full wye fitting placed in the direction of flow of the drain and should extend a minimum of 2″ above the finished floor or grade level so the cleanout opening cannot be used for a drain. The cleanout should be placed flush with the floor if the cleanout is in a traffic area. Stack base cleanouts should be located at least 6″ above the floor for easy access and to prevent their use as floor drains. Cleanouts at the upper terminals of horizontal branch drains can be eliminated if there is a plumbing fixture trap or a plumbing fixture with an integral trap that can be easily removed and used for a cleanout.
Developed length of vent pipe is measured along the centerline of the pipe and fittings.
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Vent pipes are sized based on the drainage fixture units connected to the vent pipe and the developed length of vent pipe. Developed length is the length of vent pipe measured along the centerline of the pipe and fittings. See Figure 3-19. Developed length must be considered when sizing vent piping because friction between air in motion within vent pipes and the interior surface of the pipe reduces the flow and the volume of air moving through the vent pipe. Pipe smaller than 1 1/4″ in diameter is unsuitable for venting. Although air flow within a smaller pipe may be adequate, the vent can easily become plugged.
A stack vent extends above the highest horizontal drain connected to a soil
or waste stack.
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A stack vent is the extension of a soil or waste stack above the highest horizontal drain connected to the stack. See Figure 3-20. Stack vents admit air to the plumbing system and provide an outlet for sewer gases. A stack vent is usually the terminal for other vent pipes, such as individual and group fixture vents and vent stacks.
Stack vent size is based on the total number of drainage fixture units draining into the waste portion of a stack and the developed length of the vent.
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Vents are sized according to the Size and Length of Individual, Branch, Circuit, and Stack Vents table. Stack vent sizing is based on the total number of drainage fixture units draining into the waste portion of the stack and the developed length of the vent. See Figure 3-21. Even though the Size and Length of Individual, Branch, Circuit, and Stack Vents table indicates that 2 1/2″ pipe may be used to vent drainage systems, 2 1/2″ pipe is never installed since no drain, waste, or vent fittings are made for use with 2 1/2″ pipe.
The vent and soil stacks are installed at the same time and are usually located close to one another.
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The vent stack is usually located close to the soil pipe stack, but its actual location depends on the building construction. See Figure 3-22. A vent stack is installed when the soil pipe stack is installed. Openings are left at the correct height and proper floors to accommodate fixture trap vents. A vent stack or main vent begins at the base of the soil stack and relieves back pressure that might occur at this location. A vent stack is connected to the waste stack at the lower end with a wye and 1/8 bend and connects with the stack vent (uppermost portion of the soil stack). However, if the vent stack or main vent is not run within a few feet of the soil stack, the vent may continue through the roof separately.
A yoke vent is connected to the waste stack below the horizontal fixture branch drain for that floor and to the vent stack at least 3′ above the floor.
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A yoke vent is connected to a soil stack with a wye and 1/8 bend. When connected to a waste stack, a yoke vent is connected to the waste stack below the horizontal fixture branch drain for that floor and to the vent stack at least 3′ above the floor level. See Figure 3-23. Sufficient space must be allowed between the soil or waste stack and the vent stack so that the connection between the yoke vent and soil or waste stack can be easily made.
Vent stack and main vent sizing is based on the size of soil or waste stack, number of drainage fixture units connected to the stack, and the developed length of the vent.
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Vent stack and main vent sizing is based on the size of the soil or waste stack, number of drainage fixture units connected to the stack, and the developed length of the vent. See Figure 3-24. For example, a 3″ vent stack (90′ developed length) is required in an 8-story apartment building when a 4″ size soil stack is used to serve 88 dfu. Based on the Size and Lengths of Vent Stacks table, a 4″ stack with 240 dfu or less connected to it requires a 3″ vent stack.
Roof jackets or roof flanges are installed around vent terminals to prevent rainwater from leaking into the building.
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Roof terminals for vents must be sealed to the roof surface to prevent rainwater, snow, and other moisture around the pipe from leaking into the building. See Figure 3-25. Roof jackets or roof flanges are installed around the vent terminals to make the roof watertight. Some roof jackets are adjustable for different roof pitches and stack height variations caused by expansion and contraction of the stack or settling of the building.
Individual venting eliminates trap seal loss because the plumbing system is relieved of minus and plus pressure at every fixture trap.
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An individual vent is the most practical method of venting a fixture trap. Trap seal loss is virtually eliminated when an individual vent is used since the plumbing system is pressure-balanced at every fixture trap. See Figure 3-26. The most common individual vent is a continuous vent. A continuous vent is a vertical vent that is a continuation of the drain to which it connects.
Trap-to-vent distance is based on the fixture drain size.
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The maximum distance between the fixture trap and its vent is based on the fixture drain size. See Figure 3-27. Individual vents and other fixture trap vents should be connected as close to the trap as possible, usually to the fixture drain pipe directly below and in back of the fixture. Dirt, rust, or other foreign material in the vent drops into the waste line and is carried away by the discharge of the fixture, thus maintaining a clear vent. If an individual vent is to be reconnected to the vent stack, it should be connected at least 6″ above the flood level rim of the fixture served by the vent so that the vent will not serve as a waste line for the fixture if the fixture waste pipe is clogged. A flood level rim is the top edge of a fixture from which water overflows.
Floor-set water closets in a basement must be properly vented to provide adequate ventilation and air circulation.
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Individual vents can also be installed for floor-set fixtures, such as urinals, shower baths, and bathtubs. The fixture trap discharges into the side opening of a sanitary drainage tee, with the top opening serving as an individual vent connection. The vent stack connection must be at least 6″ above the flood level rim of the fixture served by the vent. Floor-set water closets in a basement must be properly vented to provide adequate ventilation and air circulation. See Figure 3-28. Flat venting of water closets should be avoided since stoppage of the fixture drain can result in waste backing into the vent and plugging it.
Common vent fittings include no-hub sanitary and tapped crosses and no-hub figure 1 fittings.
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A common vent, or unit vent, connects two fixture drains and serves as a vent for both fixture drains. The fixtures discharge waste into a sanitary cross, tapped cross, or figure 1 fitting. The top opening of the cross or fitting is used for a common vent connection, which is completed in the same manner as an individual vent. See Figure 3-29. Common venting is used on two similar fixtures with the same vertical drain heights, which are installed on opposite sides of a partition, and is common for fixture traps serving apartment and hotel bathrooms. Apartment and hotel bathrooms are usually located back to back and the waste, vent, and water pipes are run in a common wall between the rooms. Common vent design and principles are similar to individual venting.
Common venting is used for lavatory, bathtub, and water closet installations in back-to-back rooms.
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Common venting is used for lavatory, bathtub, and water closet installations in back-to-back rooms. See Figure 3-30.
When water closets are the highest fixtures on a stack, they may be common vented to that stack.
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It may be inconvenient to common vent bathtubs, showers, and other floor-set fixtures due to space limitations. When water closets are the highest fixtures on a stack, they may be common vented to that stack. In this installation, the stack vent also serves as a common vent. See Figure 3-31.
A basic wet vent
is a common vent with two fixtures whose horizontal drain openings are at different heights and installed back to back.
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A basic wet vent is a common vent with two fixtures whose horizontal drain openings are at different heights and installed back to back. In this installation, the vertical drain is sized one pipe size larger than the upper fixture drain, but in no case is it smaller than the lower fixture drain. See Figure 3-32. For example, a 1 1/2″ vertical drain is required when the lavatory waste is above the kitchen sink waste. The wet vent of the vertical drain pipe would be 1 1/2″ pipe instead of the 1 1/4″ that would normally be required for a lavatory drain. However, if the kitchen sink drain is above the lavatory drain, the wet vent portion is sized as 2″ pipe instead of 1 1/2″ pipe, which is the normal size for a kitchen sink drain. As a general rule, not more than 1 dfu may drain into a 1 1/2″ wet vent or more than 4 dfu into a 2″ wet vent.
The vertical portion of the lavatory waste is the wet vent for the bathtub drain.
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A typical wet vent installation is a residential bathroom. See Figure 3-33. In this installation, the vertical portion of the lavatory waste is the wet vent for the bathtub drain. In this case, the lavatory waste is increased to 1 1/2″ pipe, but the lavatory vent, which vents 3 dfu, remains 1 1/4″ pipe.
In this installation, the waste pipe for the kitchen sink and lavatory is the wet vent for the bathtub.
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Another wet vent application is an installation in which the kitchen sink and lavatory are back to back and the waste pipe for these two fixtures is the wet vent for the bathtub. See Figure 3-34. In this installation, the wet vent portion of the vertical drain must be 2″ pipe because it drains 3 dfu, and the branch vent to the stack is 1 1/2″ pipe because it vents 5 dfu (lavatory [1 dfu] + kitchen sink [2 dfu] + bathtub [2 dfu] = 5 dfu).
When the lavatory drain is the wet vent for the water closet, it is not necessary to increase the wet vent size.
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Wet vents are often used in residential basement bathroom installations. See Figure 3-35. In this installation, the lava-tory drain is a wet vent for the water closet. The size of the wet vent portion of the pipe is not increased because the 2″ pipe required for a water closet vent is more than one pipe size larger than a lavatory waste, which is usually 1 1/4″.
A stack group is located next to a stack so vents may be kept to a minimum.
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Another type of wet vent is a stack group. A stack group is a group of fixtures located next to a stack so vents may be reduced to a minimum using the proper fittings. See Figure 3-36. A stack group is commonly used in one-story homes or when the bathroom is located on the top floor of a building. When a stack group is sized, the individual fixture drains are their normal size, but the stack vent is the same size as the soil stack. If the individual fixture trap arms exceed the maximum distance cited in the Fixture Trap-to-Vent Distance table, the fixtures must be revented.
Roof drains receive rainwater collecting on a roof surface.
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A roof drain receives rainwater collecting on a roof surface and discharges it into a rainwater leader. Roof drain bodies are available for a variety of applications. See Figure 3-37. Most roof drains have no-hub outlet connections.
Storm drain traps should be used when drain bodies or conductors are located within 10′ of a door, window, or other opening.
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In most applications, storm drain traps are not required when a storm drainage system connects to municipality storm sewer mains. Storm drain traps should be used when a roof drain body is located within 10′ of a door, window, or any other opening to a building. See Figure 3-38.
Projected roof area and horizontal storm drain slope determine the size of horizontal storm drains.
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Projected roof area is the primary factor in determining size of building storm drains and rainwater leaders. The projected roof area is the area (in sq ft) of a portion of the roof drained by a particular pipe. In addition to the projected roof area, the size of the building storm drains is based on the horizontal storm drain slope. See Figure 3-39.
Projected roof area is used to determine the size of building storm drains and rainwater leaders. 10′ of a door, window, or other opening.
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A greater slope allows rainwater to move quickly and efficiently through the system, allowing more rainwater to be conveyed. Based on the Horizontal Storm Drain Size table and using a slope of 1/8″ per foot, 4″ branch drain pipes are used to drain areas up to 1880 sq ft, a 5″ pipe drains areas up to 3340 sq ft, a 6″ pipe drains areas up to 5350 sq ft, and an 8″ pipe drains areas up to 11,500 sq ft. See Figure 3-40.
Rainwater leader size is based on the maximum projected roof area.
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All vertical rainwater leaders drain 1500 sq ft of projected roof area and require 3″ pipe. See Figure 3-41. With a 1/8,″ per foot slope, it is not uncommon for horizontal pipe to be larger than the leader into which it drains.
A reducer is used to transition from a rainwater leader to a storm drain.
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The underground pipe is reduced on the vertical rise. See Figure 3-42.
