CSLB General Building (B) — All Questions

A wet-vented bathroom group discharges 5 DFU to a wet vent section. Wet vent capacity limits are 1-1/2 in = 1 DFU, 2 in = 4 DFU, and 3 in = 6 DFU. What is the minimum wet vent size?

• a.1-1/2 in
• b.2 in
• c.4 in
• d.3 in✓

The 5 DFU load exceeds the 4 DFU capacity of a 2 in wet vent, so the next size, 3 in (6 DFU), is required. A wet vent uses an oversized drain to also serve as a vent, but only up to the fixture-unit cap for its size. Exceeding the cap forces a larger wet vent or separate venting.UPC §908.0

A circuit vent serves a battery of floor-mounted fixtures on a horizontal branch. What is the maximum number of fixtures a single circuit vent may serve, and where is the vent taken off?

• a.Eight, between the two most upstream fixtures✓
• b.Two, downstream of the last fixture
• c.Four, at the last fixture
• d.Ten, at the base of the stack

A circuit vent may serve up to eight fixtures on a horizontal branch, and the vent is taken off the branch between the two most upstream fixtures. A relief vent is added when the branch also receives discharge from upper floors. Water closets in batteries are a classic circuit-vent application.IPC §911.0

A commercial kitchen installs a grease interceptor rated for a flow of 35 gpm. Using the common rule that grease capacity in pounds is about twice the gpm rating, what nominal grease retention does this unit provide, and what is its purpose?

• a.35 lb, to trap sand
• b.70 lb, to intercept fats, oils and grease✓
• c.150 lb, to neutralize acid
• d.300 lb, to settle solids

A hydromechanical grease interceptor rated at 35 gpm provides roughly 70 lb of grease retention and its purpose is to intercept fats, oils, and grease before they enter and clog the building drain and public sewer. Interceptors are sized by fixture flow and required retention. Sand interceptors and acid neutralizers serve entirely different wastes.IPC §1003.4

A building drain serving fixtures below the elevation of the public sewer manhole must be protected against sewer backflow. Which device is required on that low-level drainage?

• a.An air gap
• b.A vacuum breaker
• c.A backwater valve✓
• d.An air admittance valve

Fixtures below the next upstream manhole rim are subject to backflow from a surcharged sewer and must discharge through a backwater valve, which closes when flow reverses. Fixtures above that level must not drain through the backwater valve so they are not blocked when it closes. Vacuum breakers and air gaps protect potable water, not drainage.UPC §710.0

A basement floor drain sits 3 ft below the elevation of the upstream sewer manhole cover. During a main surcharge, how much backpressure head could push up through that drain if unprotected, using 0.433 psi per foot?

• a.0.43 psi
• b.3.0 psi
• c.13 psi
• d.1.3 psi✓

Backpressure = depth below the surcharge level x 0.433 = 3 x 0.433 = 1.3 psi. Even a modest 3 ft head can flood a basement, which is why fixtures below the manhole rim require a backwater valve. The valve seats against reverse flow while still passing normal drainage.UPC §710.0

A hot-water recirculation loop loses 4,000 BTU/hr to the piping. The pump must circulate enough water so it cools only 20 F while replacing that loss. Using Q (gpm) = BTU/hr / (500 x delta-T), what recirculation flow is required?

• a.0.4 gpm✓
• b.0.2 gpm
• c.0.8 gpm
• d.2.0 gpm

Q = 4,000 / (500 x 20) = 4,000 / 10,000 = 0.4 gpm. The 500 factor is the heat capacity of water in BTU per hour per gpm per degree F. A low recirculation flow is enough to offset standby losses and keep hot water instantly available without eroding the piping.UPC §608.0

A temperature-and-pressure (T and P) relief valve on a water heater is rated to open at 210 F and 150 psi. What is the required disposition of its discharge pipe?

• a.Trapped and vented to the drain
• b.Run full-size to within 6-24 in of the floor with no trap or valve✓
• c.Reduced one size and terminated outside above grade
• d.Connected to the recirculation return

The T and P discharge must be full pipe size, contain no valves or traps, and terminate 6 to 24 in above the floor or an approved receptor so a discharge is visible and cannot be blocked. A trap would hold water and corrode; a valve could be shut and defeat the safety device. This prevents a tank from becoming a pressure vessel.UPC §608.3

A closed water-supply system (with a backflow preventer or check valve at the meter) has a water heater but no expansion control. As the water heats and expands, what device is required to prevent pressure buildup?

• a.A pressure-reducing valve
• b.A vacuum breaker
• c.A thermal expansion tank✓
• d.A backwater valve

A closed system cannot push expanded hot water back into the main, so a thermal expansion tank (or similar expansion control) is required to absorb the volume increase and prevent the T and P valve from weeping. Water expands roughly 2 to 3 percent between cold and hot, which spikes pressure in a sealed system. The expansion tank is charged to system static pressure.UPC §608.5

A reduced-pressure principle (RP) backflow assembly is installed on a service subject to a health hazard. How must it be installed with respect to the ground and drainage?

• a.Below grade in a valve box
• b.Flush to a wall with the relief plugged
• c.Any orientation as long as it is accessible
• d.Above grade with the relief port able to discharge to atmosphere✓

An RP assembly must be installed above grade with an air gap below its relief port so the relief can discharge freely and be observed; it may not be submerged in a pit that could flood the relief. RP assemblies protect against both backsiphonage and backpressure of high-hazard (health) cross connections. Submerging or plugging the relief defeats the protection.UPC §603.0

A lawn irrigation system with chemical injection is connected to a potable supply. This is classified as a high health hazard under backpressure and backsiphonage conditions. Which backflow assembly is required?

• a.Reduced-pressure principle assembly✓
• b.Atmospheric vacuum breaker
• c.Dual check valve
• d.Hose-bibb vacuum breaker

Chemical injection creates a high health hazard and can occur under backpressure, so a reduced-pressure principle assembly is required because it protects against both backpressure and backsiphonage of a health hazard. An atmospheric vacuum breaker only protects against backsiphonage and cannot be under continuous pressure. Dual checks are for low-hazard applications only.UPC §603.0

An air gap is used to protect a potable outlet discharging over a flood-level rim. What is the minimum air gap for an effective opening of 1 in diameter, using the rule of two times the effective opening?

• a.1 in
• b.2 in✓
• c.1-1/2 in
• d.4 in

The minimum air gap is twice the effective opening diameter, so 2 x 1 in = 2 in, and never less than 1 in in any case. The air gap is the most reliable backflow protection because it is a physical break that cannot fail mechanically. Near a wall the multiplier increases to three times the opening.UPC §603.4.6

In a medical gas piping system, oxygen and other medical gases must use tubing that is cleaned and labeled for the service. What copper tubing is required for medical gas distribution?

• a.Type M copper, brazed
• b.PVC schedule 40
• c.Type L or K copper, cleaned for oxygen service, brazed with joints purged with nitrogen✓
• d.Galvanized steel, threaded

Medical gas distribution uses type L or K copper specifically cleaned and capped for oxygen service, brazed with a nitrogen purge to prevent internal oxide (copper scale) formation. The nitrogen purge keeps the interior clean so particles cannot enter patient equipment. Type M, plastic, and threaded steel are all prohibited for medical gas.NFPA 99

Medical gas piping must be tested before use. Which test verifies the system is free of leaks and cross connections at operating conditions?

• a.Hydrostatic test only
• b.Smoke test
• c.Slump test
• d.A pressure/leak test plus a cross-connection (crossover) verification at 1.5 times working pressure✓

Medical gas systems require an initial pressure test, a standing-pressure leak test, and a cross-connection test to confirm each outlet delivers only its labeled gas, typically at 1.5 times the working pressure. A crossover between oxygen and another gas is a lethal hazard, so verification of correct gas at every station outlet is mandatory. Hydrostatic water testing is not used on gas.NFPA 99

A water softener regenerates using 8 lb of salt per cubic foot of resin for a 3 cubic foot resin bed. How much salt is consumed per regeneration cycle?

• a.24 lb✓
• b.8 lb
• c.16 lb
• d.32 lb

Salt per regeneration = dosage x resin volume = 8 lb/ft^3 x 3 ft^3 = 24 lb. The salt dose sets both the operating cost and the chloride load in the brine discharge, which must terminate through an air gap to a receptor. Higher salt doses increase capacity but also increase brine strength.UPC §611.0

A water heater is installed in a garage where flammable vapors may be present. What installation requirement addresses ignition of those vapors?

• a.Install a drip leg only
• b.Elevate the ignition source at least 18 in above the floor, or use an approved flammable-vapor-ignition-resistant unit✓
• c.Provide combustion air from the attic
• d.Add a second T and P valve

In a garage the pilot or ignition source must be at least 18 in above the floor, because gasoline vapors are heavier than air and pool low, unless the heater is listed as flammable-vapor-ignition-resistant (FVIR). Modern FVIR heaters are designed to prevent flame rollout from igniting floor-level vapors. Combustion air and relief valves do not address vapor ignition.UPC §507.0

A key difference between the Uniform Plumbing Code and the International Plumbing Code affects where the building drain becomes the building sewer. Which statement correctly pairs the codes?

• a.UPC 30 in, IPC 2 ft outside the wall
• b.Both use 5 ft outside the wall
• c.UPC 2 ft, IPC 30 in outside the wall✓
• d.Both use the property line

The UPC places the building drain to building sewer transition 2 ft outside the building wall, while the IPC uses 30 in. This boundary determines which code chapter, permit, and sometimes trade governs the piping. Knowing which model code the local jurisdiction adopted is essential before sizing or permitting.IPC vs UPC

An indirect waste pipe has an effective outlet opening of 3/4 in. The required air gap above the receptor flood-level rim is two times the effective opening. What is the minimum air gap?

• a.3/4 in
• b.1 in
• c.3 in
• d.1-1/2 in✓

Air gap = 2 x effective opening = 2 x 3/4 in = 1-1/2 in. The two-times rule sets the vertical separation that prevents waste from siphoning back into the indirect-wasted equipment. Near a wall the multiplier increases to three times the opening, which would give 2-1/4 in here.UPC §807.0

A sewage ejector serving fixtures below the sewer must discharge upward and then into the gravity building drain. What fitting protects the pump from gravity backflow when it is off?

• a.A check valve and a gate valve on the discharge✓
• b.A vacuum breaker
• c.A backwater valve on the inlet
• d.An air admittance valve

The pump discharge must have a check valve to prevent effluent from draining back into the sump when the pump stops, and a gate (shutoff) valve downstream of the check so the check can be serviced. Without the check valve, each cycle would refill the sump and short-cycle the pump. This is standard for ejector and sump pump discharge piping.UPC §710.13

A medical gas distribution system has a working pressure of 50 psi. The installation acceptance test is performed at 1.5 times the working pressure. What is the required test pressure?

• a.50 psi
• b.75 psi✓
• c.65 psi
• d.100 psi

Test pressure = 1.5 x working pressure = 1.5 x 50 = 75 psi. Medical gas piping is proven at 1.5 times its operating pressure to confirm joints and cross connections hold under a margin above service conditions. The standing-pressure and cross-connection tests are performed at this elevated pressure before the system is placed in service.NFPA 99

A thermostatic mixing valve blends 140 F stored water with 60 F cold water to deliver 110 F tempered water at a public lavatory. Using a mass balance, what fraction of the delivered flow must be the 140 F hot water?

• a.37.5%
• b.50.0%
• c.62.5%✓
• d.75.0%

Set 140f + 60(1 - f) = 110, so 80f = 50 and f = 0.625, or 62.5% hot water. The mixing valve holds storage at 140 F to control Legionella while blending down to a safe 110 F delivery. The cold fraction is the remaining 37.5%.UPC §608.0

A public toilet room fixture count is based on occupant load. If a code table requires one water closet per 40 occupants and the occupant load is 210, how many water closets are the minimum required?

• a.4
• b.5
• c.7
• d.6✓

Divide occupants by the ratio and round up: 210 / 40 = 5.25, which rounds up to 6 water closets. Fixture counts always round up because you cannot install a fraction of a fixture and the code sets a minimum. The occupant load is typically split by sex before applying the ratio in many codes.UPC §418.0

An oil-water separator serves three garage floor drains each rated at 20 gpm. The code allows sizing at 75 percent of the total connected flow for diversity. What design flow sizes the separator?

• a.45 gpm✓
• b.30 gpm
• c.60 gpm
• d.80 gpm

Total connected flow = 3 x 20 = 60 gpm, and at 75 percent diversity the design flow is 60 x 0.75 = 45 gpm. The separator must be large enough to let oil rise and separate before the water passes on to the sewer. Undersizing lets oil carry through and creates an explosion hazard in the sewer.UPC §705.0

A laboratory discharges 10 gpm of acid waste that must be diluted with water at a 5-to-1 ratio (water to acid waste) before it enters the neutralizing tank. How much dilution water is required?

• a.10 gpm
• b.50 gpm✓
• c.25 gpm
• d.60 gpm

Dilution water = ratio x waste flow = 5 x 10 = 50 gpm. Diluting acid waste before the neutralizing tank lowers the concentration so the tank can raise the pH into the permitted discharge range. The combined flow of 60 gpm then passes to the neutralizer before the sanitary sewer.UPC §814.0

An air admittance valve (AAV) is used to vent an island fixture. Which condition must be met for the AAV to be acceptable?

• a.It may serve as the only vent for the building
• b.It may be buried in the wall permanently
• c.It must be located in a ventilated, accessible space and at least 4 in above the horizontal branch drain✓
• d.It replaces the need for any trap

An AAV must be installed in a ventilated, accessible location and rise at least 4 in above the horizontal branch drain it serves, and it can never be the sole vent for a building. It admits air to relieve negative pressure but seals against sewer gas escaping. At least one vent must still open to atmosphere for the overall system.IPC §917.0

A boiler feed with chemical treatment connects to potable water. This is a high-hazard connection. Which assembly protects the potable supply against backpressure from the pressurized boiler?

• a.Atmospheric vacuum breaker
• b.Dual check valve
• c.Hose-bibb vacuum breaker
• d.Reduced-pressure principle backflow assembly✓

A chemically treated boiler is a high health hazard under backpressure, so a reduced-pressure principle assembly is required because it alone protects against backpressure of a health hazard. Atmospheric vacuum breakers cannot be used under continuous pressure or against backpressure. The RP relief port provides a visible, fail-safe break.UPC §603.5.7

A single-family residence has an underground lawn sprinkler system with no chemical injection and no downstream pressure. This is a low-hazard, backsiphonage-only condition. Which is the minimum acceptable backflow device?

• a.Atmospheric vacuum breaker installed at least 6 in above the highest head✓
• b.Reduced-pressure principle assembly
• c.Air gap only
• d.No device required

For a residential sprinkler with no chemicals and no backpressure, an atmospheric vacuum breaker installed at least 6 in above the highest downstream head (sprinkler) is the minimum acceptable device. It protects only against backsiphonage and must not be under continuous pressure for more than 12 hours. Adding chemicals or downstream pumps would escalate the requirement to an RP assembly.UPC §603.0

A water heater relief-valve discharge, softener drain, and condensate line all terminate at the same floor-level receptor. What must be true of the receptor and each connection?

• a.All lines hard-connected
• b.Each discharges by air gap into the receptor, which is trapped and vented✓
• c.Lines share one trap
• d.Lines terminate below the receptor rim

Each indirect line must discharge through an air gap into the receptor, and the receptor itself must be trapped and vented so it drains to the sanitary system without allowing sewer gas back. The air gaps keep the potable-related discharges from cross connecting. Hard connections or below-rim terminations would defeat the required physical break.UPC §501.0

An air gap at a lavatory faucet must be maintained above the flood-level rim. If the effective opening of the faucet is 1/2 in and the outlet is near a single wall, the required gap is three times the opening. What is the minimum air gap?

• a.1-1/2 in✓
• b.1 in
• c.2 in
• d.3 in

Near a single wall the multiplier is three times the effective opening, so 3 x 1/2 in = 1-1/2 in. Away from walls the standard multiplier is two times the opening, but a nearby wall disrupts the free fall of air and requires the larger gap. The air gap is the most reliable backflow protection because it is a fixed physical break.UPC §603.4.6