CSLB General Building (B) — All Questions
← Back to practice105 questions
What is the minimum slope for a 2 inch horizontal drainage pipe?
- a.1/4 inch per foot✓
- b.1/8 inch per foot
- c.1/16 inch per foot
- d.1/2 inch per foot
The CPC requires a minimum uniform slope of 1/4 inch per foot (about 2 percent) for horizontal drainage pipe 2-1/2 inches and smaller. The 1/8 inch per foot minimum is allowed only for pipe 3 inches and larger, so it is too flat for a 2 inch line. The 1/16 inch and 1/2 inch values are not the code minimum for this size.2022 California Plumbing Code (CPC) §708.1
A 4 inch building drain must be installed at a minimum slope of:
- a.1/4 inch per foot
- b.1/8 inch per foot✓
- c.1/16 inch per foot
- d.3/16 inch per foot
For drainage pipe 3 inches and larger, the CPC permits a minimum slope of 1/8 inch per foot (about 1 percent). The 1/4 inch per foot minimum applies to pipe 2-1/2 inches and smaller. The 1/16 and 3/16 inch values are not code minimums for a 4 inch drain.2022 California Plumbing Code (CPC) §708.1
Each fixture trap must have a water seal with a depth of not less than and not more than:
- a.1 to 2 inches
- b.1-1/2 to 3 inches
- c.2 to 4 inches✓
- d.3 to 5 inches
The CPC requires each trap to have a liquid seal of not less than 2 inches and not more than 4 inches, except for special deep-seal traps. A shallower seal is easily lost to evaporation or siphonage, and a deeper seal beyond code is only allowed for approved deep-seal designs. The other ranges fall outside the required 2 to 4 inch window.2022 California Plumbing Code (CPC) §1002.0
For a 1-1/2 inch trap arm, the maximum developed length from the trap weir to the vent is:
- a.30 inches
- b.60 inches
- c.72 inches
- d.42 inches✓
Per the trap-to-vent distance table, a 1-1/2 inch trap arm may run a maximum developed length of 42 inches (3 feet 6 inches) to its vent. The 30 inch value is for a 1-1/4 inch arm, 60 inches is for a 2 inch arm, and 72 inches is for a 3 inch arm. Exceeding the limit risks self-siphonage of the trap seal.2022 California Plumbing Code (CPC) §1002.2
Cleanouts in horizontal drainage lines must be spaced no more than:
- a.100 feet apart✓
- b.50 feet apart
- c.75 feet apart
- d.150 feet apart
The CPC requires cleanouts in horizontal drainage piping to be installed not more than 100 feet apart measured along the developed length. Spacing at 50 or 75 feet is stricter than required, and 150 feet exceeds the maximum, leaving a run that cannot be fully cleared with standard equipment.2022 California Plumbing Code (CPC) §707.4
The minimum diameter of a vent pipe must be:
- a.Equal to the diameter of the drain it serves
- b.Not less than one-half the diameter of the drain served, but never less than 1-1/4 inch✓
- c.Not less than one-third the diameter of the drain served
- d.Not less than 2 inches in all cases
The CPC requires a vent to be at least one-half the diameter of the drain it serves and never smaller than 1-1/4 inch. Requiring the vent to equal the drain wastes material, one-third is below the code floor, and a flat 2 inch minimum is not what the code specifies for all vents.2022 California Plumbing Code (CPC) §904.0
What is the minimum clearance required in front of a cleanout on a 4 inch drainage pipe?
- a.12 inches
- b.24 inches
- c.18 inches✓
- d.30 inches
Cleanouts on pipe 3 inches and larger require a minimum clearance of 18 inches in front of the cleanout for rodding. Cleanouts on pipe smaller than 3 inches require only 12 inches. The 24 and 30 inch figures are more than the code minimum.2022 California Plumbing Code (CPC) §707.9
A 4 inch building drain sloped at 1/4 inch per foot is permitted a maximum load of how many drainage fixture units (DFU)?
- a.180 DFU
- b.250 DFU
- c.160 DFU
- d.216 DFU✓
Table 703.2 permits a 4 inch building drain or sewer at 1/4 inch per foot to carry a maximum of 216 DFU. At 1/8 inch per foot the same pipe is limited to 180 DFU. The 250 and 160 values do not correspond to a 4 inch drain at this slope.2022 California Plumbing Code (CPC) §703.0 (Table 703.2)
A 3 inch building sewer sloped at 1/8 inch per foot is limited to a maximum of how many DFU?
- a.20 DFU✓
- b.27 DFU
- c.36 DFU
- d.42 DFU
Table 703.2 limits a 3 inch building sewer at 1/8 inch per foot to 20 DFU. At 1/4 inch per foot the 3 inch line rises to 27 DFU, and at 1/2 inch per foot to 36 DFU. A 3 inch line also may not receive more than two water closets regardless of DFU count.2022 California Plumbing Code (CPC) §703.0 (Table 703.2)
What is the maximum DFU load on a 2 inch horizontal fixture branch?
- a.3 DFU
- b.6 DFU✓
- c.12 DFU
- d.20 DFU
Table 703.1 limits a 2 inch horizontal fixture branch to a maximum of 6 DFU. A 1-1/2 inch branch carries 3 DFU, a 2-1/2 inch branch carries 12 DFU, and a 3 inch branch carries 20 DFU. Loading a 2 inch branch beyond 6 DFU requires upsizing the pipe.2022 California Plumbing Code (CPC) §703.0 (Table 703.1)
What is the maximum number of water closets permitted on a 3 inch horizontal fixture branch?
- a.1
- b.3
- c.2✓
- d.4
A 3 inch horizontal fixture branch is limited to a maximum of two water closets regardless of its 20 DFU capacity. This restriction exists because a 3 inch line cannot reliably carry the surge from more than two closets. Three or four water closets require a 4 inch branch.2022 California Plumbing Code (CPC) §703.0 (Table 703.1)
A vent terminating through a roof must extend above the roof surface at least:
- a.3 inches
- b.12 inches
- c.4 inches
- d.6 inches✓
Each vent pipe passing through a roof must extend at least 6 inches above the roof surface. A shorter extension can be blocked by debris or ponding water. Where the roof is used for purposes other than weather protection, the vent must extend at least 7 feet above the roof.2022 California Plumbing Code (CPC) §906.1
A vent terminal near an openable window or door must terminate at least:
- a.3 feet above or 10 feet horizontally away from the opening✓
- b.1 foot above or 5 feet away
- c.2 feet above or 6 feet away
- d.5 feet above or 15 feet away
A vent must terminate at least 3 feet above or at least 10 feet horizontally from any openable window, door, or air intake within 10 feet, to keep sewer gas out of the building. The other combinations are less than the code-required separation and could allow gas to re-enter.2022 California Plumbing Code (CPC) §906.2
For a 2 inch trap arm, the maximum developed length to the vent is:
- a.3 feet 6 inches
- b.5 feet✓
- c.6 feet
- d.8 feet
A 2 inch trap arm may run a maximum developed length of 5 feet (60 inches) to its vent. The 3 feet 6 inch value is for a 1-1/2 inch arm, 6 feet is for a 3 inch arm, and 8 feet is not a listed value. Exceeding the maximum risks siphoning the trap seal.2022 California Plumbing Code (CPC) §1002.2
For a 3 inch trap arm, the maximum developed length to the vent is:
- a.5 feet
- b.8 feet
- c.6 feet✓
- d.10 feet
A 3 inch trap arm may run a maximum developed length of 6 feet to its vent. The 5 foot value is for a 2 inch arm and 10 feet is for a 4 inch arm; 8 feet is not a listed value. Longer runs on this size require an additional or relocated vent.2022 California Plumbing Code (CPC) §1002.2
The minimum trap and trap arm size for a lavatory is:
- a.1-1/2 inch
- b.2 inch
- c.1 inch
- d.1-1/4 inch✓
A lavatory has a minimum trap and trap arm size of 1-1/4 inch and a DFU value of 1. A 1-1/2 or 2 inch trap is larger than required, and a 1 inch trap is smaller than the code minimum for any fixture. Kitchen sinks, by contrast, require a 1-1/2 inch trap.2022 California Plumbing Code (CPC) §702.0 (Table 702.1)
The minimum trap and drain size for a residential kitchen sink is:
- a.1-1/2 inch✓
- b.1-1/4 inch
- c.2 inch
- d.3 inch
A kitchen sink requires a minimum 1-1/2 inch trap and drain and carries 2 DFU. A 1-1/4 inch trap is too small for a kitchen sink and is used for lavatories. A 2 or 3 inch trap exceeds the minimum requirement for this fixture.2022 California Plumbing Code (CPC) §702.0 (Table 702.1)
The minimum trap size for a shower is:
- a.1-1/2 inch
- b.2 inch✓
- c.1-1/4 inch
- d.3 inch
A shower requires a minimum 2 inch trap and drain to handle its flow without backing up. A 1-1/2 or 1-1/4 inch trap is too small and would restrict drainage. A 3 inch trap exceeds the minimum for a single shower.2022 California Plumbing Code (CPC) §702.0 (Table 702.1)
The maximum vertical distance between a fixture outlet and the trap weir must not exceed:
- a.12 inches
- b.18 inches
- c.24 inches✓
- d.30 inches
The vertical distance from the fixture outlet down to the trap weir (the fixture tailpiece) must not exceed 24 inches. A longer drop increases discharge velocity and can self-siphon the seal. Values of 12 or 18 inches are within the limit but not the maximum, and 30 inches exceeds it.2022 California Plumbing Code (CPC) §1002.0
Under the CPC, installing two traps in series on a single fixture (double trapping) is:
- a.Required for floor drains
- b.Allowed if both are vented
- c.Allowed for kitchen sinks only
- d.Prohibited✓
The CPC prohibits double trapping because the air trapped between two seals blocks flow and causes sluggish, gurgling drainage. Each fixture is served by a single trap. Venting does not make double trapping acceptable, and no fixture type is exempted from this rule.2022 California Plumbing Code (CPC) §1002.0
Crown venting, where the vent connects at the top of the trap crown, is:
- a.Prohibited; the vent connection must be at least two pipe diameters from the trap weir✓
- b.Required on all P-traps
- c.Allowed on 2 inch traps only
- d.Required for floor sinks
Crown venting is prohibited because the vent opening at the crown quickly clogs with grease and debris. The vent must connect to the trap arm at a point at least two pipe diameters downstream of the trap weir. It is not required or allowed on any specific fixture as a crown vent.2022 California Plumbing Code (CPC) §905.0
The use of an S-trap on a fixture is:
- a.Permitted for all fixtures
- b.Prohibited✓
- c.Permitted if a deep seal is used
- d.Permitted for outdoor fixtures
S-traps are prohibited because the downward outlet directly below the trap makes the seal prone to self-siphonage. Fixtures must use a properly vented P-trap instead. A deeper seal or an outdoor location does not make an S-trap acceptable.2022 California Plumbing Code (CPC) §1002.0
A single wet vent may serve fixtures within a maximum of how many bathroom groups?
- a.1
- b.3
- c.2✓
- d.4
The CPC allows a wet vent to serve any combination of fixtures within a maximum of two bathroom groups on the same floor. Limiting it to one group is stricter than the code allows, and three or four groups exceed the wet-vent limit and require additional venting.2022 California Plumbing Code (CPC) §908.0
A circuit vent may serve a battery of not more than how many fixtures?
- a.4
- b.6
- c.10
- d.8✓
A circuit vent serves a horizontal branch (battery) of not more than eight fixtures that drain by gravity. Fewer than eight is allowed, but the code cap is eight; a battery larger than eight requires additional relief venting. Four, six, or ten are not the code maximum.2022 California Plumbing Code (CPC) §911.0
A combination waste and vent system is typically used for:
- a.Floor sinks and island sinks where a conventional vent is impractical✓
- b.Water closets in a public restroom
- c.Battery of urinals on a wall
- d.Roof drains
Combination waste and vent systems are designed for fixtures such as floor sinks, floor drains, and island sinks where structural conditions make a conventional vent impractical, relying on oversized horizontal piping for air movement. Water closets are excluded from combination waste and vent systems, and urinal batteries and roof drains use other methods.2022 California Plumbing Code (CPC) §910.0
Horizontal vent piping must be graded so that it:
- a.Runs perfectly level
- b.Drains any condensate back to the drainage pipe by gravity✓
- c.Slopes away from the drainage system
- d.Is installed only vertically
Horizontal vent pipes must maintain a slope back toward the drainage piping so condensate and any moisture drain back by gravity and do not pool inside the vent. A level or reverse-sloped vent allows water to collect and block airflow. Vents are not restricted to vertical runs.2022 California Plumbing Code (CPC) §905.0
A vent must rise vertically to a point above the flood-level rim of the highest fixture served before it may offset horizontally, by at least:
- a.At the flood-level rim
- b.3 inches above
- c.6 inches above✓
- d.12 inches above
A vent must rise to at least 6 inches above the flood-level rim of the highest fixture served before offsetting horizontally, so that any drainage backup cannot enter the horizontal vent. Offsetting at or 3 inches above the rim risks fouling the vent, and 12 inches is more than the code minimum.2022 California Plumbing Code (CPC) §905.0
What is the minimum diameter permitted for any vent pipe?
- a.2 inches
- b.1 inch
- c.3 inches
- d.1-1/4 inch✓
No vent pipe may be less than 1-1/4 inch in diameter regardless of the drain it serves. A 1 inch vent is below the code floor. The 2 inch and 3 inch values are minimums for larger drains, not the absolute minimum for any vent.2022 California Plumbing Code (CPC) §904.0
A horizontal branch serves two lavatories (1 DFU each), one kitchen sink (2 DFU), and one bathtub (2 DFU). What is the total DFU and minimum branch size?
- a.6 DFU, 2 inch branch✓
- b.4 DFU, 1-1/2 inch branch
- c.8 DFU, 3 inch branch
- d.6 DFU, 1-1/2 inch branch
The load is 1 + 1 + 2 + 2 = 6 DFU. A 2 inch horizontal branch is rated for exactly 6 DFU, so it is the minimum size. A 1-1/2 inch branch is limited to 3 DFU and is undersized, while a 3 inch branch is larger than needed for 6 DFU.2022 California Plumbing Code (CPC) §703.0 (Table 703.1)
A horizontal drain run is 80 feet long at 1/4 inch per foot slope. What is the total fall over the run?
- a.10 inches
- b.20 inches✓
- c.40 inches
- d.16 inches
Total fall equals slope times length: 80 feet times 1/4 inch per foot = 20 inches. Ten inches would be the fall at 1/8 inch per foot, and 40 inches would require 1/2 inch per foot. Sixteen inches does not match any standard slope for this run.2022 California Plumbing Code (CPC) §708.1
A 3 inch drain runs 48 feet at the minimum slope of 1/8 inch per foot. What is the total fall?
- a.12 inches
- b.3 inches
- c.6 inches✓
- d.9 inches
Total fall equals 48 feet times 1/8 inch per foot = 6 inches. Twelve inches would be the fall at 1/4 inch per foot, which is steeper than the minimum. Three and nine inches do not match a 48 foot run at 1/8 inch per foot.2022 California Plumbing Code (CPC) §708.1
Over its length, the total fall of a trap arm must not exceed:
- a.Two pipe diameters
- b.One-half pipe diameter
- c.There is no limit
- d.One pipe diameter✓
The trap arm may slope at 1/4 inch per foot, but its total fall from the trap weir to the vent must not exceed one pipe diameter. If it drops more than one diameter, the vent opening ends up below the trap weir, which allows self-siphonage. Two diameters exceeds the limit, half a diameter is stricter than required, and the fall is definitely limited.2022 California Plumbing Code (CPC) §1002.2
For a 1-1/4 inch trap arm, the maximum developed length to the vent is:
- a.30 inches✓
- b.42 inches
- c.24 inches
- d.36 inches
A 1-1/4 inch trap arm may run a maximum developed length of 30 inches (2 feet 6 inches) to its vent. The 42 inch value is for a 1-1/2 inch arm. Values of 24 and 36 inches are not the listed maximum for this smallest trap arm size.2022 California Plumbing Code (CPC) §1002.2
For a 4 inch trap arm, the maximum developed length to the vent is:
- a.6 feet
- b.10 feet✓
- c.8 feet
- d.12 feet
A 4 inch trap arm may run a maximum developed length of 10 feet to its vent, the longest listed. Six feet is the limit for a 3 inch arm. Eight and twelve feet are not the listed maximum for a 4 inch trap arm.2022 California Plumbing Code (CPC) §1002.2
A cleanout is required at:
- a.The top of the stack only
- b.No location if the pipe is new
- c.The base of each soil or waste stack✓
- d.Every other floor only
The CPC requires a cleanout at or near the base (foot) of each vertical soil or waste stack, where solids tend to accumulate as flow turns horizontal. Placing one only at the top or on alternating floors would leave the critical base of the stack inaccessible for rodding. New pipe still requires cleanouts.2022 California Plumbing Code (CPC) §707.4
A cleanout is required where an aggregate horizontal change of direction in a drainage line exceeds:
- a.45 degrees
- b.90 degrees
- c.22-1/2 degrees
- d.135 degrees✓
A cleanout is required where the aggregate horizontal change of direction exceeds 135 degrees, because sharp cumulative bends collect debris and are hard to rod through. Smaller thresholds such as 45 or 90 degrees would require far more cleanouts than the code intends, and 22-1/2 degrees is a single-fitting angle, not the aggregate limit.2022 California Plumbing Code (CPC) §707.4
A cleanout (often a two-way cleanout) is required at:
- a.The junction of the building drain and the building sewer✓
- b.Each individual fixture trap
- c.The midpoint of the roof vent
- d.No exterior location
A cleanout is required at or near the junction of the building drain and the building sewer, commonly installed as an accessible two-way cleanout, to allow rodding in both directions. Individual fixture traps and roof vents are not the required junction cleanout location, and an exterior cleanout is exactly what this rule provides.2022 California Plumbing Code (CPC) §707.4
The drainage fixture unit (DFU) value of a private bathtub is:
- a.1
- b.2✓
- c.3
- d.4
A private bathtub (with or without a shower over it) is assigned 2 DFU. A value of 1 corresponds to a lavatory, and 3 or 4 would overstate the discharge of a single tub. Correct DFU values are needed to size branches and drains properly.2022 California Plumbing Code (CPC) §702.0 (Table 702.1)
The DFU value assigned to a single lavatory is:
- a.2
- b.3
- c.1✓
- d.4
A lavatory is assigned 1 DFU, the smallest common value, with a 1-1/4 inch minimum trap. Values of 2, 3, or 4 belong to higher-discharge fixtures such as sinks, tubs, or water closets. Using the correct DFU keeps branch and drain sizing accurate.2022 California Plumbing Code (CPC) §702.0 (Table 702.1)
The DFU value of a residential kitchen sink is:
- a.1
- b.3
- c.4
- d.2✓
A residential kitchen sink is assigned 2 DFU with a 1-1/2 inch minimum trap. A value of 1 is for a lavatory, and 3 or 4 overstates a single kitchen sink. Correct DFU values ensure the connecting branch is neither undersized nor oversized.2022 California Plumbing Code (CPC) §702.0 (Table 702.1)
What is the minimum vent size for a 3 inch drain, using the half-diameter rule?
- a.1-1/2 inch✓
- b.2 inch
- c.1-1/4 inch
- d.3 inch
Half of a 3 inch drain is 1-1/2 inch, which is also above the 1-1/4 inch absolute minimum, so 1-1/2 inch is the minimum vent size. A 1-1/4 inch vent is below half the drain diameter here. A 2 or 3 inch vent is larger than the minimum this rule requires.2022 California Plumbing Code (CPC) §904.0
Using the half-diameter rule, the minimum vent size for a 4 inch drain is:
- a.1-1/2 inch
- b.2 inch✓
- c.3 inch
- d.4 inch
Half of a 4 inch drain is 2 inches, so the minimum vent is 2 inches (well above the 1-1/4 inch floor). A 1-1/2 inch vent is less than half the drain diameter and undersized. A 3 or 4 inch vent exceeds the minimum required, though developed length could increase the required size.2022 California Plumbing Code (CPC) §904.0
The required size of a vent pipe:
- a.May be reduced by half above the roof
- b.May be reduced one size above the highest fixture
- c.Shall not be reduced along its length✓
- d.May be reduced below the flood-level rim
A vent must not be decreased in size along its required length; reducing it would restrict airflow and could cause frost or debris closure. It may be increased but not reduced. Reducing it above the roof, above the top fixture, or below the flood rim all violate this rule.2022 California Plumbing Code (CPC) §904.0
In areas subject to frost closure, a vent extension through the roof must be increased to a minimum of 3 inches, and the change in size must be made at least:
- a.3 inches below the roof
- b.6 inches below the roof
- c.2 feet below the roof
- d.1 foot (12 inches) inside the building below the roof✓
Where frost or snow closure is a concern, the vent must be at least 3 inches in diameter through the roof, and the increase in size must be made at least 1 foot inside the building below the roof. Making the transition too close to the roof line (3 or 6 inches) leaves the enlarged section exposed to frost, and 2 feet is more than the code requires.2022 California Plumbing Code (CPC) §906.7
The horizontal drainage pipe between a fixture trap and its vent is called the:
- a.Trap arm✓
- b.Developed length
- c.Crown weir
- d.Fixture branch
The horizontal pipe between the trap weir and the vent is the trap arm, and its maximum length is set by pipe size in the trap-to-vent table. Developed length is a general measurement term, the crown weir is the top inside of the trap, and a fixture branch collects multiple fixtures. Only trap arm names this specific segment.2022 California Plumbing Code (CPC) §1002.2
A 5 inch building sewer sloped at 1/4 inch per foot is permitted a maximum load of how many DFU?
- a.390 DFU
- b.480 DFU✓
- c.575 DFU
- d.840 DFU
Table 703.2 permits a 5 inch building sewer at 1/4 inch per foot to carry 480 DFU. At 1/8 inch per foot it is limited to 390 DFU, and at 1/2 inch per foot to 575 DFU. The 840 value belongs to a 6 inch line at 1/4 inch per foot.2022 California Plumbing Code (CPC) §703.0 (Table 703.2)
A 6 inch building drain sloped at 1/8 inch per foot is permitted a maximum load of how many DFU?
- a.840 DFU
- b.1000 DFU
- c.700 DFU✓
- d.620 DFU
Table 703.2 permits a 6 inch building drain at 1/8 inch per foot to carry 700 DFU. At 1/4 inch per foot it rises to 840 DFU, and at 1/2 inch per foot to 1000 DFU. The 620 value is a 6 inch horizontal fixture branch capacity, not a building drain load.2022 California Plumbing Code (CPC) §703.0 (Table 703.2)
A 2 inch building drain sloped at 1/4 inch per foot is permitted a maximum load of how many DFU?
- a.26 DFU
- b.24 DFU
- c.6 DFU
- d.21 DFU✓
Table 703.2 permits a 2 inch building drain at 1/4 inch per foot to carry 21 DFU. At 1/2 inch per foot the same pipe carries 26 DFU. The 24 value corresponds to a 2-1/2 inch drain, and 6 DFU is the branch capacity of a 2 inch fixture branch, not the building-drain load.2022 California Plumbing Code (CPC) §703.0 (Table 703.2)
Loss of a trap seal from siphonage or back pressure is primarily prevented by:
- a.Proper venting of the drainage system✓
- b.Using a larger trap
- c.A deeper seal alone
- d.Adding a cleanout
Venting introduces air to equalize pressure in the drainage system, which prevents siphonage and back pressure from pulling or pushing out the trap seal. A larger trap or a deeper seal alone does not correct the pressure imbalance, and a cleanout serves maintenance, not seal protection.2022 California Plumbing Code (CPC) §901.0
Developed length of a pipe run is measured as:
- a.The straight-line distance between endpoints
- b.The total length along the centerline of the pipe and fittings✓
- c.Only the vertical portions
- d.Only the horizontal portions
Developed length is measured along the centerline of the pipe and fittings, following the actual path the water travels. A straight-line distance ignores bends and offsets, and counting only vertical or only horizontal portions understates the true run used for slope, vent, and trap-arm limits.
In a wet-vented bathroom group, a wet-vent section carrying 4 DFU must be at least what size?
- a.1-1/4 inch
- b.1-1/2 inch
- c.2 inch✓
- d.3 inch
For wet venting, a section carrying 3 to 4 DFU must be at least 2 inches. Sections carrying 1 to 2 DFU may be 1-1/2 inch. A 1-1/4 inch pipe is below the wet-vent minimum, and 3 inches is larger than required for 4 DFU.2022 California Plumbing Code (CPC) §908.0
An island sink, with no wall to run a vent up, is commonly vented using a:
- a.Circuit vent
- b.Relief vent only
- c.Common vent
- d.Island (loop) vent✓
An island sink is typically served by an island or loop vent, which rises as high as possible under the countertop, loops back down, and connects to the vent system to allow venting where no wall is available. A circuit vent serves a battery of fixtures, a relief vent supplements a stack, and a common vent joins only two fixtures at the same level.
A common vent may serve how many fixtures connected at the same level?
- a.2✓
- b.3
- c.4
- d.8
A common vent serves two fixtures that connect to the drainage system at the same level through a single vent. Three or four fixtures exceed the common-vent limit and need another venting method, and eight is the maximum for a circuit vent, not a common vent.2022 California Plumbing Code (CPC) §905.6
A fixture is 5 feet from its vent, but the trap arm is 1-1/2 inch, which allows only 3 feet 6 inches. The correct fix is to:
- a.Add a cleanout at the trap
- b.Increase the trap arm to 2 inch, which allows 5 feet✓
- c.Install a deeper-seal trap
- d.Slope the arm more steeply
Increasing the trap arm to 2 inch raises the allowable developed length to 5 feet, satisfying the trap-to-vent distance. Adding a cleanout or a deeper trap does not change the maximum trap-arm length. Increasing the slope beyond limits would drop the vent below the trap weir and promote siphonage.2022 California Plumbing Code (CPC) §1002.2
The minimum slope for a 2-1/2 inch horizontal drainage pipe is:
- a.1/8 inch per foot
- b.1/16 inch per foot
- c.1/4 inch per foot✓
- d.1/2 inch per foot
Pipe 2-1/2 inches and smaller requires a minimum slope of 1/4 inch per foot. The 1/8 inch per foot minimum applies only to pipe 3 inches and larger, so it is too flat here. The 1/16 inch value is below any code minimum, and 1/2 inch exceeds the required minimum.2022 California Plumbing Code (CPC) §708.1
The size of a building drain or sewer:
- a.May be reduced after each cleanout
- b.May increase then reduce
- c.May be reduced after a fixture branch
- d.Shall not decrease in size in the direction of flow✓
A drain or sewer must not decrease in size in the direction of flow, because a reduction creates a choke point where solids collect and clog. It may stay the same or increase downstream. Reducing after a cleanout or a branch still violates the no-reduction rule.
A vent that terminates through a side wall must be located at least how far from a property line and from openings such as windows?
- a.10 feet✓
- b.3 feet
- c.5 feet
- d.1 foot
A sidewall vent termination must be at least 10 feet from the property line and at least 10 feet horizontally from any openable opening (unless 3 feet above it), and be protected against birds and rodents. Distances of 3, 5, or 1 foot are less than the required separation and could let sewer gas enter openings.2022 California Plumbing Code (CPC) §906.2
A trap primer is installed on a floor drain trap in order to:
- a.Clean the trap automatically
- b.Replenish water and maintain the trap seal✓
- c.Serve as the vent
- d.Increase the drain slope
A trap primer periodically adds water to a seldom-used trap, such as a floor drain, to replenish the seal that would otherwise evaporate and let sewer gas escape. It does not clean the trap, act as a vent, or change the pipe slope. Maintaining the seal is its sole purpose.
A residential clothes washer standpipe is assigned what DFU value and minimum trap size?
- a.1 DFU, 1-1/2 inch
- b.3 DFU, 2 inch
- c.2 DFU, 2 inch✓
- d.2 DFU, 3 inch
A domestic clothes washer standpipe is assigned 2 DFU and requires a minimum 2 inch trap and standpipe to handle its rapid pump-out discharge. A 1-1/2 inch trap is too small for a washer, and neither 1 DFU nor 3 inch matches the code value for a residential washer.2022 California Plumbing Code (CPC) §702.0 (Table 702.1)
A horizontal branch serves two water closets (3 DFU each), two lavatories (1 DFU each), and two showers (2 DFU each). What is the minimum branch size?
- a.2 inch
- b.4 inch
- c.1-1/2 inch
- d.3 inch✓
The load is (2 x 3) + (2 x 1) + (2 x 2) = 6 + 2 + 4 = 12 DFU. A 3 inch branch carries up to 20 DFU and allows a maximum of two water closets, so it fits both the 12 DFU load and the two closets. A 2 inch branch (6 DFU) and 1-1/2 inch branch (3 DFU) are undersized, and a 4 inch branch is larger than needed here.2022 California Plumbing Code (CPC) §703.0 (Table 703.1)
A plumber terminates a vent pipe through a residential roof that is used only for weather protection. What is the minimum height the vent must extend above the roof surface?
- a.At least 6 inches (152 mm) above the roof✓
- b.At least 3 inches above the roof
- c.At least 12 inches above the roof
- d.Flush with the roof surface
The CPC requires a vent terminal to extend not less than 6 inches above the roof. A terminal set too low can be blocked by roofing material, snow, or debris, defeating the vent. Some jurisdictions require more height for snow load, but 6 inches is the code minimum.2022 California Plumbing Code (CPC) §906.1
A vent penetrates a roof deck that is also used as a sun deck or walking surface. How high must the vent terminal extend above that roof?
- a.6 inches
- b.At least 7 feet (2134 mm) above the roof✓
- c.3 feet
- d.36 inches
When a roof is used for purposes other than weather protection (such as a deck or garden), a vent must terminate at least 7 feet above the roof surface. This keeps sewer gases well above the breathing zone of people using the roof.2022 California Plumbing Code (CPC) §906.1
A vent terminal is located 8 feet horizontally from an openable window. Under the CPC it must either terminate at least 10 feet away or…
- a.at least 6 inches above the window
- b.at least 12 inches above the window
- c.at least 3 feet (914 mm) above the top of the window✓
- d.at least 2 feet above the window
A vent terminal within 10 feet horizontally of a door, openable window, or air intake must extend at least 3 feet above that opening. At 8 feet away the plumber is inside the 10-foot zone, so the 3-foot rise applies to keep sewer gas from entering the building.2022 California Plumbing Code (CPC) §906.2
An air admittance valve (AAV) serving an individual fixture must be installed a minimum distance above the horizontal branch drain it serves. What is that minimum?
- a.At the same level as the trap weir
- b.1 inch above the flood-level rim
- c.2 inches above the fixture drain
- d.At least 4 inches (102 mm) above the horizontal branch drain✓
An AAV must be installed at least 4 inches above the horizontal branch drain it serves and above the trap weir of the fixture. This keeps the valve out of the wetted flow path so it can admit air freely when negative pressure occurs. AAVs must also remain accessible for replacement.2022 California Plumbing Code (CPC) §918.0
Where are air admittance valves (AAVs) prohibited from being installed?
- a.In a location where they could be exposed to a supply or return air plenum✓
- b.In an accessible attic space
- c.Within a wall cavity that has a ventilation grille
- d.Under a lavatory in a vanity cabinet
AAVs must not be installed in a supply or return air plenum, because a valve failure could draw sewer gas into the building's air distribution. They must be located in a ventilated, accessible space and installed above the fixtures they serve. Attics and vanity cabinets are commonly acceptable when accessible.2022 California Plumbing Code (CPC) §918.0
What term describes a vent that connects to the drain of a single fixture and extends independently to the outside air or to another vent?
- a.Wet vent
- b.Individual (back) vent✓
- c.Circuit vent
- d.Relief vent
An individual vent (sometimes called a back vent) serves the trap of one fixture and rises independently to open air or ties into another vent above the flood-level rim. It is the most basic vent type and directly protects a single trap seal from siphonage and back-pressure.2022 California Plumbing Code (CPC) §901.0
Two fixtures connected at the same level to a vertical drain and served by a single shared vent are using which venting method?
- a.Island vent
- b.Wet vent
- c.Common vent✓
- d.Yoke vent
A common vent serves two fixtures that connect at the same level to a shared vertical drain and are vented by one vent. The connecting drain and the vent must be sized for the combined fixture load. This is efficient for back-to-back fixtures such as two lavatories.
A horizontal wet-vent system under the CPC is limited to serving fixtures within…
- a.any group of fixtures on one floor
- b.a kitchen and laundry group
- c.up to eight fixtures of any type
- d.one or two bathroom groups on the same floor level✓
Wet venting under the CPC is limited to the fixtures of one or two bathroom groups located on the same floor level. The drain of an upstream fixture serves as the vent for a downstream fixture, so the arrangement is restricted to controlled bathroom-group layouts. Kitchen and laundry fixtures are not part of a wet-vented bathroom group.2022 California Plumbing Code (CPC) §908.0
In a bathroom-group wet vent, where is the dry vent connection typically made?
- a.At the most upstream fixture drain, so the vent draws through the wet-vented section✓
- b.At the water closet only
- c.At the most downstream fixture
- d.At the bathtub trap arm exclusively
The dry vent for a wet-vented bathroom group is connected at the drain of the most upstream fixture (commonly a lavatory). Air is then drawn through the wet-vented drain to protect the downstream fixture traps. The water closet is usually the most downstream fixture on the wet-vented branch.2022 California Plumbing Code (CPC) §908.0
A circuit vent serving a battery of floor-mounted fixtures on a horizontal branch may serve a maximum of how many fixtures?
- a.6
- b.8✓
- c.10
- d.12
A circuit vent may serve a battery of up to 8 fixtures connected to a horizontal branch drain. A single vent rises between the last two fixtures to serve the whole battery, and a relief vent may be required where fixtures discharge above. This method suits banks of floor-mounted water closets or urinals.2022 California Plumbing Code (CPC) §911.0
A kitchen island sink with no adjacent wall for a conventional vent is best served by which venting arrangement?
- a.An air-break standpipe
- b.A common vent
- c.An island fixture (loop) vent✓
- d.A relief vent only
An island fixture vent, often called a loop vent, rises from the fixture drain, loops up as high as possible under the countertop, then returns down and back to the vent system. It is used where the sink is not against a wall, such as a kitchen island. A foot (relief) vent and accessible cleanouts are typically required.2022 California Plumbing Code (CPC) §909.0
What is the minimum diameter permitted for a vent pipe, regardless of the fixture it serves?
- a.1/2 inch
- b.3/4 inch
- c.1 inch
- d.1-1/4 inches (32 mm)✓
No vent pipe may be smaller than 1-1/4 inches in diameter. In addition, a vent must generally be at least one-half the diameter of the drain it serves. Undersized vents are prone to clogging and cannot relieve pressure fast enough to protect trap seals.
A tall drainage stack with five or more branch intervals generally requires what to protect trap seals from pressure changes?
- a.A vent stack (main vent) installed adjacent to the soil/waste stack✓
- b.An additional cleanout only
- c.A larger building trap
- d.A backwater valve at each branch
A vent stack, or main vent, runs parallel to a tall soil or waste stack and is cross-connected with relief vents at intervals. It equalizes air pressure so that the surge of water down the stack does not siphon or blow out trap seals. Vent stacks are typically required once a stack has several branch intervals.2022 California Plumbing Code (CPC) §904.0
In a cold climate subject to frost closure, a vent through the roof must be enlarged to a minimum of 3 inches. Where must that increase in size be made?
- a.6 inches before passing through the roof
- b.At least 12 inches (305 mm) inside the building before the vent passes through the roof✓
- c.24 inches above the roof
- d.Only at the roof line itself
In frost-closure climates, a vent terminal must be at least 3 inches in diameter to resist closing off from frost. The increase from the smaller vent size must be made at least 12 inches inside the building before the pipe penetrates the roof. This keeps the enlarged, warmer section below the freezing zone.2022 California Plumbing Code (CPC) §906.0
A sewage ejector receiving the discharge of a water closet must have a discharge pipe of not less than what diameter and be able to pass a 2-inch solid?
- a.1-1/4 inches
- b.1-1/2 inches
- c.2 inches (51 mm)✓
- d.4 inches
A pump or ejector handling water-closet discharge must have a discharge pipe of at least 2 inches and be capable of passing a 2-inch spherical solid. This prevents clogging by the solids typical of sanitary sewage. Smaller effluent-only pumps are permitted only where they handle liquid waste without solids.2022 California Plumbing Code (CPC) §710.0
A sump or receiving tank that collects sewage from fixtures located below the sewer level must be…
- a.open to the room for inspection
- b.vented only to the interior of the building
- c.left unvented if the pump is sealed
- d.gastight (sealed) and provided with a vent to the outside air✓
A sump that receives sewage must be gastight and vented to the outside air to control sewer gas and equalize pressure as the pump cycles. An open or interior-vented sump would release odors and gases into the building. Clear-water sumps that handle no sewage may have different requirements.2022 California Plumbing Code (CPC) §710.0
Fixtures with flood-level rims located below the elevation of the next upstream manhole cover must be protected from sewer backflow by…
- a.An approved backwater valve✓
- b.A deeper trap seal
- c.An air-admittance valve
- d.A larger vent
Fixtures whose flood-level rims are below the next upstream manhole cover can flood when the public sewer surcharges, so they must discharge through an approved backwater valve. Fixtures above that elevation must not drain through the backwater valve, so they still drain by gravity if the valve closes. This protects low fixtures without impeding normal flow from higher ones.2022 California Plumbing Code (CPC) §710.1
An installed backwater valve must be…
- a.buried and permanently sealed
- b.accessible for service and maintenance✓
- c.installed only in a vertical pipe
- d.located inside the building trap
A backwater valve must be installed so it remains accessible for inspection, cleaning, and repair, typically in a valve box or cleanout enclosure at grade. A buried or sealed valve cannot be serviced and will fail without warning. Accessibility is a core code requirement for any backwater device.2022 California Plumbing Code (CPC) §710.1
Under the CPC, rainwater (storm) drainage and sanitary sewage generally must…
- a.share the same building drain
- b.combine at the building trap
- c.be kept in separate piping systems and not combined unless a combined public sewer is approved✓
- d.combine only if the pipe is upsized
Storm and sanitary drainage must be kept separate; rainwater must not discharge into a sanitary sewer, and sanitary waste must not enter a storm drain, unless the jurisdiction has an approved combined sewer. Combining the systems can overload the sanitary sewer during storms and cause backups. Where a combined public sewer exists, connection rules are set by the local authority.2022 California Plumbing Code (CPC) §1101.0
The air gap for an indirect waste pipe discharging into a receptor must be at least…
- a.1/2 inch
- b.equal to the pipe diameter
- c.3 inches minimum
- d.twice the effective opening (diameter) of the indirect waste pipe, and not less than 1 inch✓
An indirect waste air gap must be at least twice the effective opening of the drain pipe, measured vertically, and never less than 1 inch. This physical separation prevents sewage from backing up into the equipment through the indirect drain. It is the same principle used for potable-water air gaps.2022 California Plumbing Code (CPC) §801.2
Food-handling equipment such as a commercial food-prep sink or an ice machine must discharge to the drainage system by means of…
- a.An indirect waste with an air gap to a floor sink or receptor✓
- b.A direct hard connection to the sewer
- c.A trap primer only
- d.An air-admittance valve
Equipment used to store, prepare, or serve food must drain indirectly through an air gap into a floor sink or other approved receptor. The air gap prevents sewage from ever backing up into food-contact equipment. A direct connection to the sewer is prohibited for such equipment.2022 California Plumbing Code (CPC) §801.0
A domestic dishwasher discharge, before it connects to the drainage system, must be protected against backflow by…
- a.a backwater valve
- b.an air gap (or an approved high loop where permitted) in the drain line✓
- c.a check valve at the pump
- d.a deep-seal trap
A dishwasher drain must be protected by an air-gap fitting, or by a high loop where the local code allows, so waste cannot siphon back into the machine. The air gap is the most reliable method and is required by many jurisdictions. This protects the dishwasher and the food washed in it from contamination.2022 California Plumbing Code (CPC) §807.0
Which establishment is most likely required to install a grease interceptor or grease trap?
- a.A single-family residential kitchen
- b.A retail clothing store restroom
- c.A restaurant with commercial food preparation producing fats, oils, and grease (FOG)✓
- d.An office break room with only a coffee maker
Grease interceptors are required where fats, oils, and grease are generated in quantity, such as restaurants and commercial kitchens. FOG cools and hardens in the sewer, causing blockages and backups if not intercepted. Single-family homes and low-grease uses are generally exempt.2022 California Plumbing Code (CPC) §1014.0
A gravity grease interceptor (the large in-ground type) commonly has a minimum liquid capacity of…
- a.50 gallons
- b.100 gallons
- c.500 gallons
- d.750 gallons (2839 L)✓
Gravity grease interceptors are large in-ground tanks with a typical minimum liquid capacity of 750 gallons, sized upward based on the drainage load (DFU or seating). Their large volume and long retention time let grease float and settle before the effluent leaves. Small hydromechanical units serve lower-flow applications instead.2022 California Plumbing Code (CPC) §1014.0
The size of a hydromechanical grease interceptor is primarily selected based on…
- a.the flow rate (GPM) of the fixtures it serves and its rated grease retention capacity✓
- b.the color of the discharge
- c.the length of the drain line only
- d.the number of restrooms in the building
A hydromechanical (point-of-use) grease interceptor is selected by the flow rate in GPM it must handle and its rated grease capacity in pounds. A flow-control fitting limits flow to the rated GPM so grease can separate. Undersizing lets grease pass straight through to the sewer.2022 California Plumbing Code (CPC) §1014.0
The required size of vertical and horizontal storm (rainwater) piping is determined from code tables based on the projected roof area and…
- a.the number of floor drains
- b.the local rainfall rate in inches per hour✓
- c.the building trap size
- d.the sanitary DFU count
Storm drain and leader sizing is based on the horizontally projected roof area served and the local design rainfall rate in inches per hour. A higher rainfall rate or larger roof area requires larger pipe. Local jurisdictions publish the design storm intensity used for these calculations.2022 California Plumbing Code (CPC) §1101.0
A vent must rise vertically to at least what point before it may offset horizontally, to keep waste water out of the dry vent?
- a.2 inches above the trap weir
- b.the center line of the drain
- c.at least 6 inches (152 mm) above the flood-level rim of the fixture served✓
- d.12 inches above the floor
A vent must rise vertically to at least 6 inches above the flood-level rim of the fixture it serves before it may run horizontally. Below that height the pipe could carry or hold waste water, which would obstruct the vent. Keeping the horizontal offset above the flood-level rim keeps the dry vent dry.2022 California Plumbing Code (CPC) §905.0
For a 2-inch trap arm, the maximum developed length from the trap weir to the vent (per the CPC trap-to-vent table) is approximately…
- a.2 feet
- b.3 feet 6 inches
- c.3 feet
- d.5 feet (for 2-inch pipe)✓
The maximum trap-to-vent distance grows with pipe size: about 2 ft 6 in for 1-1/4 inch, 3 ft 6 in for 1-1/2 inch, and 5 feet for 2-inch pipe. Exceeding the distance risks self-siphoning the trap because the vent is too far to relieve pressure. The trap arm must also maintain proper slope within this length.
Besides not being directly beneath a door, openable window, or air intake, a side-wall (through-wall) vent termination must also maintain required clearance from…
- a.the lot/property line and building openings, per code✓
- b.the water meter
- c.the gas meter only
- d.the electrical panel
A through-wall vent terminal must keep the code-required distances from building openings and the property/lot line so sewer gas does not drift back indoors or onto a neighbor's lot. Through-wall terminations are also protected against birds and rodents with a screen or cap. Roof termination is preferred where a through-wall vent cannot meet the clearances.
An air admittance valve for an individual or branch fixture vent must be a listed device complying with which standard?
- a.ASSE 1017
- b.ASSE 1051✓
- c.ASSE 1070
- d.ASME A112.6
Individual and branch-type air admittance valves must be listed to ASSE 1051. Stack-type AAVs are covered by a different listing (ASSE 1050). Using a valve listed to the correct standard ensures it seals against sewer gas and admits air reliably.2022 California Plumbing Code (CPC) §918.0
Where a vent penetrates the roof, the plumber must provide…
- a.a backwater valve
- b.a cleanout at the roof
- c.a flashing (jacket) to make the roof penetration watertight✓
- d.a pressure-reducing valve
Every vent that passes through the roof must be made watertight with a proper flashing or roof jacket. Without it, rainwater would leak into the structure around the pipe. The flashing is sealed to both the roofing and the vent pipe.
A sewage sump that receives water-closet discharge and is served by a pump must be provided with a vent that…
- a.may be omitted if the pump is sealed
- b.is 1/2 inch minimum
- c.connects to the pump discharge line
- d.is sized per code and connects to the building vent system or extends independently to open air✓
A sealed sewage sump requires a vent, sized per code, that either ties into the building vent system or runs independently to the outside. The vent equalizes pressure as the sump fills and the pump discharges, and releases sewer gas outdoors. It must never connect to the pump discharge or be omitted.2022 California Plumbing Code (CPC) §710.0
For a building where sewage must be pumped and continuity of service is essential (such as public use), the CPC generally requires…
- a.duplex (two) pumps or ejectors so one can operate if the other fails✓
- b.a single large pump only
- c.a gravity bypass to the roof
- d.no pump, only a holding tank
Where interruption of pumping would create a health hazard, such as buildings used by the public, duplex pumps are required so that a standby unit takes over if one fails. The pumps typically alternate and can run together during peak flow. A single pump risks a sewage backup during any failure.2022 California Plumbing Code (CPC) §710.0
Sub-soil drains, foundation drains, and other clear-water drainage collected below sewer level should discharge to…
- a.the sanitary sewer directly
- b.a separate sump that pumps clear water to an approved point of disposal, kept separate from sewage✓
- c.a grease interceptor
- d.the vent stack
Clear-water drainage such as foundation and sub-soil drains must be collected in its own sump and pumped to an approved disposal point, not mixed with sanitary sewage. This avoids overloading the sanitary system with ground water and keeps a clean-water pump from handling sewage. The clear-water sump does not need to be gastight like a sewage sump.2022 California Plumbing Code (CPC) §710.0
An interior rainwater leader (a vertical storm pipe that carries storm water through a building) must be…
- a.vented like a sanitary stack
- b.trapped with a grease interceptor
- c.installed and, where it connects to a horizontal storm drain, sized to handle the roof area served✓
- d.connected to the sanitary building drain
An interior rainwater leader (conductor) must be sized for the roof area it drains and connected to a properly sized horizontal storm drain, kept separate from sanitary piping. Because storm systems carry no sewage, they are not vented like sanitary stacks, though offsets and connections still follow the storm-drainage rules. Where a leader could receive sewer gas, a trap is required.2022 California Plumbing Code (CPC) §1101.0
When a primary roof drain could become blocked and allow water to pond on the roof, the code requires…
- a.a larger sanitary vent
- b.a backwater valve on the roof drain
- c.no additional provision
- d.a secondary (overflow) roof drainage system or scuppers with independent discharge✓
Roofs must have a secondary (overflow) drainage system, such as overflow drains or scuppers, in case the primary roof drains clog. The overflow discharges independently so that a blockage does not let water accumulate to a structurally dangerous depth. This protects the roof structure from collapse under ponding loads.2022 California Plumbing Code (CPC) §1101.0
A hydromechanical grease interceptor is typically installed…
- a.as close as practical to the fixtures served, with a flow-control device limiting flow to its rated GPM✓
- b.after the building trap
- c.on the vent line
- d.inside the water closet
A hydromechanical grease interceptor should be located as close as practical to the fixtures it serves so grease is captured before it cools and adheres to piping. A flow-control fitting restricts flow to the unit's rated GPM, giving grease time to separate. It must remain accessible for regular cleaning.2022 California Plumbing Code (CPC) §1014.0
A small under-the-sink hydromechanical grease trap rated to PDI standards commonly has a flow rating such as…
- a.100 GPM
- b.20 or 25 GPM with a matching grease capacity✓
- c.5 GPM
- d.500 GPM
Point-of-use grease traps are commonly rated at low flows such as 20 or 25 GPM, matched to a corresponding grease-retention capacity in pounds. A flow-control fitting holds the flow at that rating so grease can separate. Larger loads require larger hydromechanical units or a gravity interceptor.2022 California Plumbing Code (CPC) §1014.0
An indirect-waste standpipe receiving a domestic clothes washer must have a trap, and the standpipe height above the trap weir must generally be within what range?
- a.6 to 12 inches
- b.12 to 16 inches
- c.18 to 30 inches (457–762 mm)✓
- d.36 to 48 inches
A clothes-washer standpipe must be trapped and vented, and the standpipe usually extends between 18 and 30 inches above the trap weir. Too short a standpipe can overflow during the wash pump-out; too tall creates back-pressure and slow draining. The trap is set at an accessible height below the standpipe.2022 California Plumbing Code (CPC) §804.0
What distinguishes an 'air break' from an 'air gap' in an indirect waste installation?
- a.They are identical terms
- b.An air break always has a larger separation than an air gap
- c.An air gap allows the indirect pipe to be submerged
- d.An air break lets the indirect pipe terminate below the receptor's flood-level rim (the pipe may touch the receptor), while an air gap keeps a physical separation above the flood-level rim✓
An air gap is an unobstructed vertical separation above the flood-level rim of the receptor, giving full protection against back-siphonage. An air break allows the indirect drain to end below the flood-level rim, even touching the receptor, but not submerged. Higher-hazard equipment (like food equipment) requires the full air gap, while lower-hazard drains may use an air break.2022 California Plumbing Code (CPC) §801.0
A combination waste-and-vent system is chiefly intended for…
- a.floor drains, sinks, and similar fixtures where conventional venting is impractical, using oversized horizontal piping✓
- b.a battery of water closets
- c.roof (storm) drainage
- d.water-heater relief piping
A combination waste-and-vent system uses oversized horizontal drain piping that carries both waste and air, providing venting for fixtures like floor drains and sinks in large open areas where a conventional vent cannot be run. Water closets and other high-discharge fixtures are generally not permitted on this system. The oversized pipe flows only partially full so air can move above the waste.2022 California Plumbing Code (CPC) §910.0
As a vent extends upward toward its terminal, its required diameter…
- a.may be reduced by half at the roof
- b.must not be reduced (no decrease in size in the direction of the terminal)✓
- c.may be reduced to 1/2 inch above the roof
- d.must double at every branch
A vent may not be reduced in size in the direction of flow toward the outlet; the required diameter is maintained or increased, never decreased, up to the terminal. Reducing the vent would restrict airflow and could allow frost or debris to close it. This is separate from the frost-closure rule that enlarges the terminal in cold climates.
Two fixtures set on the same floor level and connecting to a common vertical drain within the required distance may share…
- a.a single trap for both
- b.one backwater valve
- c.a common vent, provided the drain and vent are sized for both fixtures✓
- d.one cleanout only
Two fixtures at the same level connecting to a shared vertical drain within the code distance may be served by a common vent, with the connecting drain and vent sized for the combined load. Each fixture still has its own trap; a single trap serving two fixtures is generally prohibited. Common venting saves piping for back-to-back layouts.
Where a building (house) trap is installed on the building drain, it is commonly accompanied by…
- a.a grease interceptor
- b.a backwater valve on the vent
- c.a sump pump
- d.a fresh-air inlet on the upstream (building) side to ventilate the drainage system✓
A building (house) trap isolates the building drainage from the public sewer, and when used it is paired with a fresh-air inlet on the building side so the drainage system stays ventilated. Because a house trap can collect debris and block flow, many modern codes discourage or prohibit it. The fresh-air inlet terminates in open air, screened against pests.
In a horizontal wet-vent system, how must the wet-vented pipe (which carries both waste and air) be sized?
- a.Per the DFU load of the wet-vented section, and at least 2 inches where a water closet drains through it✓
- b.at 1-1/4 inch minimum only
- c.the same as the smallest fixture drain
- d.at 4 inches regardless of load
The wet-vented pipe must be sized for the drainage fixture unit (DFU) load of the fixtures it serves, and must be at least 2 inches where a water closet discharges into it. Adequate size keeps the pipe partially full so air can pass above the waste to vent the group. Undersizing would let the pipe flow full and lose its venting action.2022 California Plumbing Code (CPC) §908.0