SECTION P-919 PHILADELPHIA SINGLE-STACK WASTE & VENT SYSTEM 324

P-919.1 Scope. The City of Philadelphia has the oldest known model plumbing code in the country dating back to June 30, 1885. Since the inception of the Philadelphia Plumbing Code, one of the main characteristics and theories has been the single stack method of waste and vent. This code and the single stack theory has stood the test of time and continues today to be a model code copied by many other codes as a base line. Every building and structure in the City of Philadelphia as of this writing has been built incorporating this methodology of the single stack theory. This Section is intended to be used for any modification or rebuilding of any of these existing structures, homes or buildings or as an option for any planned new construction in the future. Systems utilizing this Section shall not be permitted to incorporate any other methods of design contained in other Sections of this Code.   325

P-919.2 Drainage System Sizing.

P-919.2.1 Fixture-unit values. The relative load weights of fixtures shall be determined in accordance with Table P-919.2(a).

P-919.2.2 Values for fixtures not listed. Fixture unit values for fixtures that are not listed in Table P-919.2(a) and cannot be determined by similarity to a fixture listed therein shall be determined by Table P-919.2(b).

P-919.2.2.1 Values for indirect waste receptor. The drainage fixture unit load of an indirect waste receptor receiving the discharge of indirectly connected fixtures shall be the sum of the drainage fixture unit values of the fixtures that discharge to the receptor, but not less than the drainage fixture unit value given for the indirect waste receptor in Table P-919.2(a) or 919.2(b).

P-919.2.2.2 Clear-water waste receptors. Where waste receptors such as floor drains, floor sinks and hub drains receive only clear-water waste from display cases, refrigerated display cases, ice bins, coolers and freezers, such receptors shall have a drainage fixture unit value of one half.

P-919.2.3 Values for continuous flow. For a continuous or semi-continuous flow in a sanitary drainage system, such as from a bilge pump, ejector, air conditioning equipment, commercial laundry, dishwashing equipment, or similar device, each gallon per minute flow shall be deemed to be two fixture-units.

P-919.2.4 Maximum fixture-unit load. The maximum number of fixture-units connected to a given size of house drain, horizontal branch, or vertical soil or waste stack, shall be determined by Table P-919.2(c).

P-919.2.5 Soil stack size. The size of a soil or waste stack is determined by the fixture-units on the stack plus the fixture-units on the horizontal branch from the base of the soil or waste stack connected to the building drain.

P-919.2.6 Horizontal branch size. The size of all horizontal branch lines including the horizontal branch from the base of the soil or waste stack connected to the building drain is determined by the fixture units and gradient fall.

P-919.2.7 Building drain/building sewer size. The size of the building drain is determined by its gradient fall and total number of fixture-units.

P-919.2.8 Fall for small piping. Horizontal drainage piping of 3-inch diameter and less shall be installed with a fall of not less than 1/4 inch per foot.

P-919.2.9 Fall for large piping. Horizontal drainage piping of more than 3 inches and up to and including 6 inches in diameter shall be installed with a fall not less than 1/8 inch per foot. Horizontal drainage piping larger than 6-inch diameter shall be installed with a fall of not less than 1/16 inch per foot.

P-919.2.10 High-rise buildings. If the building is 75 feet in height and not more than 160 feet in height, as measured from the lowest level of fire department vehicle access, the vertical soil or waste stacks connected to the house drain or to any of its branches shall be one size larger than given in Table P-919.2(c), and this shall also apply when the soil or waste stacks are connected to a horizontal branch pipe that discharges into a soil or waste stack. If the building is more than 160 feet in height, the vertical soil or waste stacks connected to the house drain or to any of its branches shall be two sizes larger than given in Table P-919.2(c), and this shall also apply when the vertical soil or waste stacks are connected to the horizontal branch pipe that discharges into a soil or waste stack. The size of the main soil stack shall be sized according to the largest branch entering the stack, except if the amount of fixture units requires a larger size. The developed length of the soil or waste stacks shall be determined by measuring the distance between the center line of the horizontal branch pipe and the roof. If a relief vent is installed on all horizontal branches below the top floor and between the soil or waste stacks and the first fixture on the horizontal branch, the soil or waste stack sizes shall be in accordance with Table P-919.2(c), regardless of the height of the building. The diameter of a relief vent shall not be less than one-half the diameter of the horizontal branch to which it is connected, with a minimum size of 1-1/2 inches (38 mm). The maximum number of fixture units connected to the relief vent shall be in accordance with Table P-919.9(a). The size of the branch line and its stack shall be determined by the developed length of the stack.

TABLE P-919.2(a)
FIXTURE UNIT VALUES

Fixtures	Private Installations	Public Installations	Minimum Trap Sizes (Inches)
Bathroom group consisting of 1 lavatory, 1 water closet, 1 bathtub or shower stall	6	–	–
Bathtub with 1-1/2 inch trap a	2	3	1-1/2
Bathtub with 2-inch trap a	3	4	2
Cup Sink	–	2	1-1/4
Dishwashers, domestic, automatic	4	–	1-1/2 c
Drinking Fountain	–	1/2	1-1/4
Floor Drain	3	3	3
Kitchen Sink with 1-1/2 inch trap b	3	3	1-1/2
Kitchen Sink with 2 inch trap b	–	4	2
Laundry tray with 1-1/2 inch trap (1 or 2 compartment)	3	3	1-1/2
Laundry tray with 2 inch trap	–	4	2
Lavatory with 1-1/4 inch or 1-1/2 inch trap	1	2	1-1/4
Lavatory, Barber, Beauty, Parlor, or Surgeons	–	3	1-1/2
Service Sink (slop sink), Mop Receptor	–	3	3
Service Sink, flushing rim with flush valve	–	6	3
Shower Stall with 1-1/2 inch or 2 inch trap	2	3	1-1/2
Shower Stall with required 3 inch trap	–	6	3
Urinal, stall and washout	–	2	1-1/2
Urinal, pedestal, siphon-jet and blow-out	–	4	2
Urinal, non-water	–	1	1-1/2
Wash Fountain, Duo	–	2	2
Wash Fountain, any other size	–	5	2
Washing Machine, domestic, automatic	4	–	2
Water Closet	3	6	3
Fountain Cuspidor (Dental Chair)	–	1	1-1/4
Sink, Soda Fountain or Bar	–	2	1-1/2

 

For SI: 1 inch = 25.4 mm

a.   With or without shower head over bathtub.

b.   With or without garbage grinder unit, or dishwasher, in sink with 1-1/2 or 2 inch trap.

c.   Commercial dishwasher shall include minimum 2-inch trap.

TABLE P-919.2(b)
OTHER FIXTURE VALUES

 

Required Fixture Drain or Trap Size	Fixture Unit Value
	Private Installations	Public Installations
1-1/4 inch	1	2
1-1/2 inch	2	3
2 inch	3	4
3 inch	4	6
4 inch	4	8

 

TABLE P-919.2(c)
MINIMUM PIPE SIZES ACCORDING TO FIXTURE LOAD
(Maximum Fixture-Units that may be connected)

House Drain or Horizontal Branch					Vertical Soil or Waste Stack
Pipe size (Inches)	1/16" Fall	1/8" Fall	1/4" Fall	1/2" Fall
1-1/4			2	2
1-1/2			4	6	6
2			10	18	20
2-1/2			27	36	36
3			48a	65 a	75 b
4		50	100	200	225
5		130	225	420	480
6		330	480	875	1,015
8	500	850	1,100	2,000	2,320
10	1,050	1,650	2,320	3,800	4,500
12	1,800	3,000	4,500	6,500	8,100
15	3,600	6,000	8,100	10,000	13,600

 

Note a:    Limit 2 water closets.

Note b: Limit 6 water closets.

P-919.2.11 Minimum size of soil and waste pipe. No soil or waste stack shall be smaller than the largest branch draining into it regardless of the height of the building. Soil stacks receiving the discharge of water closets shall not be less than 3 inches in diameter, as provided in Table P-919.2(c). Three-inch Soil stacks shall be limited to six water closets. No horizontal soil pipe or waste pipe draining water closets shall be less than 3 inches in diameter. When using 3-inch ideal bends (closet bends) to receive the discharge of water closets, this fitting shall be a blind bend containing no drainage connections for other fixtures. No waste pipe shall be less than 1-1/4 inches in diameter.

P-919.2.12 Building drain/building sewer. The minimum size of the main house drain receiving the discharge of water closets shall be 4 inches inside nominal diameter.

P-919.3 Venting.

P-919.3.1 Required. All fixtures shall be adequately vented to prevent syphonic action and to protect trap seals.

P-919.3.2 Connection. The seal of every fixture trap in a plumbing system shall be protected by being individually connected to a properly vented drain.

Exception: Leader traps, area drain traps, and yard drain traps.

P-919.3.3 Stack vents. Every soil or waste stack shall be extended vertically, full size, as a stack vent to open air.

P-919.3.4 Vent stacks. A vent stack or main vent shall be installed with a soil or waste stack when relief vents or other branch vents are required in more than five branch intervals. The vent stack shall terminate independently in the open air above the roof or shall be connected with the stack vent at least 6 inches above the flood level rim of the highest fixture and shall connect with the soil or waste stack through, at, or below the lowest horizontal soil or waste branch, or with the house drain, in such manner as to prevent the accumulation of rust scale. When water closets are installed on this lowest horizontal branch, they shall be connected to the side of the horizontal branch.

P-919.3.5 Vent required. Every building in which plumbing is installed shall have at least one stack vent or vent stack which shall run undiminished in size and as directly as possible from the building drainage system through to the open air above the roof. The minimum size of the stack vent or vent stack shall be 3 inches.

P-919.4 Velocity Breaks in Buildings over 30 Stories.

P-919.4.1 Required. Velocity breaks shall be required in soil stacks in buildings more than 30 stories above grade to impede the velocity of the waste. At each velocity break, the stack shall be offset by two 45-degree breaks. A relief vent one-half the size of the soil stack shall be installed at the top of the second 45-degree break and shall be connected to the nearest vent stack.

P-919.4.2 Intervals. Velocity breaks shall be installed at maximum 10-story intervals above the 30th floor.

P-919.4.3 Relief vent. A relief vent pipe shall be installed on the main drain before the main house trap inside the building and be connected to the nearest vent line for any building 75 feet or higher. On main drains of 8 inches or less, the vent shall be a minimum of 4 inches. On main drains 10 inches and over, the relief vent shall be a minimum of 5 inches.

P-919.5 Ventilation of Branch or Horizontal Pipes.

P-919.5.1 Vent required. Every branch, horizontal soil pipe, or waste pipe to which a group of two or more fixtures is to be connected shall have a vent of the same size as the branch by: extending the branch full size as through the roof; connecting to the stack vent 6 inches above the highest fixture; or connecting to the vent stack 6 inches above the highest fixture connected to the branch. The horizontal branch from the base of a stack shall be connected to the building drain.)

P-919.5.2 Alternatives. Where the center of a water closet outlet is not more than 48 inches in developed length from the center of 4-inch vented soil pipe on a vertical line, or through a wye or wye and 1/8 bend on a vented horizontal line, connection of small fixture wastes - not exceeding two that are 1-1/2 inches or less in diameter - to the side of an ideal bend (closet bend) above the center line without an additional vent, or by using no-hub, copper, ABS or PVC pipe and fittings. Where the center of a water closet outlet is not more than 18 inches from the center of a 3-inch vented soil pipe and the 4-inch ideal bend (closet bend) is connected directly to a sanitary tee on a vertical line, connection of small fixture wastes - not exceeding two that are 1-1/2 inches or less in diameter - to the sides of the bend above the center line without an additional vent and in accordance with Section P-919.2.11. As an alternative to increasing the size of a stack from 3 inches to 4 inches, a merion/stack tee fittings shall be used to receive the discharge of a water closet and small fixture wastes.

P-919.5.3 Merion/stack tee fittings. The water closet soil line connected to a merion/stack tee fittings shall be a maximum of 8 feet developed length. The ideal bend (closet bend) shall not be less than 4 inches nominal diameter when receiving the discharge of small fixture wastes. When using 3-inch ideal bends (closet bend) to receive discharges of water closets, this fitting shall be a blind bend containing no drainage connections for other fixtures.

P-919.5.4 Existing stacks in buildings where the center of a water closet outlet is more than 4 feet but not more than 8 feet from the center of a vented soil pipe, an additional 1-1/2 inch vent will be permitted if the vent is no longer than 30 feet, provided the conditions are the same as in Section P-919.5.3.

P-919.6 Fixture Venting.

P-919.6.1 Minimum vent size. Any single water closet branch more than 8 feet in length or waste branch for fixtures other than water closets more than 12 feet in length shall have a vent sized at least one-half the diameter of the branch pipe. Depending on its length, the number of fixture units connected shall be in accordance with Table P-919.9(a).

P-919.7 Venting of Offsets.

P-919.7.1 Stack offsets. Offsets in soil or waste stacks at an angle greater than 45 degrees from the vertical serving fixtures above the offset shall be vented as provided in Sections P-919.7.2 or P-919.7.3.

P-919.7.2 Yoke venting offsets. Such offsets shall be provided with a yoke vent equal to one-half the diameter of the vent stack or soil stack but not less than 1-1/2 inches. The lower end of the yoke vent shall connect to the soil or waste stack through a wye below the offset and above the next lower horizontal branch, and the upper end shall connect to the stack vent or the vent stack not less than 6 inches above the highest fixture. The yoke vent may connect to a vent stack on the floor level above or higher provided the connection is a minimum of 6 inches (152 mm) above the flood level rim of the next fixture on the stack above the offset.

P-919.7.3 Separate Venting. Such offsets shall be vented as two separate soil or waste stacks, with the stack section below the offset and the stack section above the offset.

P-919.7.4 Venting not required. All buildings of not more than three stories having a soil or waste stack with one offset at an angle greater than 45 degrees from the vertical and which does not exceed 10 feet in length shall not require additional venting. No fixtures shall be permitted above the offset, except that one small fixture may be installed for a heel wash.

P-919.8 Vent Headers.

P-919.8.1 Vent header permitted. Stack vents and vent stacks shall be permitted to connect into a common vent header at the top of the stacks and extend to the open air above the roof at one point. Such header shall be sized in accordance with the requirements of Table P-919.9(a). As per Section P-919.5, the size of the horizontal branch entering a stack shall have a vent of the same size; therefore, one of the stacks entering into a common vent header shall be of the same size as the branch entering the stack and shall maintain that size through the roof. Other sizes of the header can then be sized as per Table P-919.9(a).

P-919.8.2 Sizing. The number of fixture units considered in sizing the vent header shall be the sum of all fixture units on all stacks connected thereto. The developed length shall be the longest vent length from the intersection at the base of the most distant stack to the vent header terminal in the open air above the roof. The latter shall be extended to the open air above the roof as a direct extension of one stack.

P-919.9 Size and Length of Vents.

P-919.9.1 Length of vents. The length of a vent shall be its developed length from the lowest connection of the vent with the soil stack, waste stack, or house drain to the vent terminal above the roof.

P-919.9.2 Size of stack vent. The diameter of a stack vent shall not be less than the diameter of the soil or waste stack of which it is an extension.

P-919.9.3 Size of vent stacks. A vent stack or main vent connecting relief vents, circuit vents, or loop vents shall have a diameter of at least one-half the diameter of the soil or waste stack to which the vent stack or main vent is connected, but in no case less than 1-1/2 inches (38 mm). The maximum number of fixture units connected to the vent stack shall be in accordance with Table P-919.9(a). The vent stack or main vent shall not be less in size than the branch, circuit, or loop vent it is servicing. Where fixtures are installed on the house drain behind the line of vent, a minimum vent stack of 1-1/2 inches (38 mm) shall be required for small fixtures having a fixture unit value not greater than 10 drainage fixture units and a minimum of a 2 inch (51 mm) vent for one or more water closets and other fixtures, except if a larger size is required according to Table P-919.9(a).

P-919.9.4 Size of relief vent. The diameter of a relief vent shall not be less than one-half the diameter of the horizontal branch to which it is connected, with a minimum size of 1-1/2 inches. The maximum number of fixture units connected to the relief vent shall be in accordance with Table P-919.9(a).  326

TABLE P-919.9(a)  327 SIZE AND LENGTH OF VENTS

Fixture Units Connected	Diameter of Vent (inches) – Maximum Length of Vent (feet)
	1-1/2"	2"	2-1/2"	3"	4"	5"	6"	8"
13	75	310
26	70	300
47	35	140	450
72	23	85	260	650
98	18	75	240	600
195		30	95	240	1000
293		22	70	180	750
390			28	70	320	1000
624			20	50	240	750
969				20	95	240	1000
1320				18	70	180	750
2165					30	80	350	1000

 

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Notes

324	Amended, Bill No. 230653 (approved December 20, 2023), effective April 1, 2024.
325	Amended, Bill No. 190713 (approved December 30, 2019), effective February 3, 2020. See note 313 for effective date provisions.
326	Enrolled bill read "P-P-919.9(a)".
327	Enrolled bill read "Table 919.9(a)"; prefix "P-" added at the discretion of the Code editor.