CSLB General Building (B) — All Questions

A water closet is being roughed in against a side partition in a narrow alcove. Measuring from the finished face of the partition to the center of the closet outlet, what is the minimum dimension the model plumbing codes require?

• a.12 inches
• b.14 inches
• c.15 inches✓
• d.18 inches

The centerline of a water closet must be at least 15 inches from any side wall, partition, or vanity, which is what makes a 30 inch wide alcove the practical minimum for a single fixture. The 12 inch figure is the standard rough-in distance from the finished back wall to the closet flange center, not a side clearance. 14 inches and 18 inches are not code minimums; 18 inches is a common designer's comfort dimension and 14 inches is simply short of the requirement.IPC §405.3.1

Two water closets are to be installed side by side in a school restroom. What is the minimum distance between the centerline of one closet and the centerline of the adjacent closet?

• a.30 inches✓
• b.24 inches
• c.21 inches
• d.36 inches

Because each closet needs 15 inches of clearance on each side of its centerline, two adjacent closets require 15 plus 15, or 30 inches center to center. The 24 inch and 21 inches figures are front clearance numbers, not lateral spacing. 36 inches exceeds the requirement and would be an accessibility compartment width rather than the general fixture spacing minimum.

A framed water closet compartment measures 32 inches wide inside the finished surfaces, and the closet is set exactly on the center of that width. Does the installation satisfy the side clearance requirement?

• a.No, the centerline is only 15 inches from each side and 16 inches is required
• b.No, a compartment must be at least 36 inches wide in all cases
• c.Yes, but only because a compartment is exempt from side clearance rules
• d.Yes, the centerline is 16 inches from each side, which exceeds the 15 inch minimum✓

Half of 32 inches is 16 inches, so each side has 16 inches of clearance from the centerline, one inch more than the 15 inch minimum. The requirement is 15 inches, not 16, so the first choice reverses the numbers. Compartments are not exempt from clearance rules, and 36 inches is an accessible-stall dimension rather than a universal minimum.

Under the International Plumbing Code, what is the minimum clear space required in front of a water closet, measured from the front edge of the fixture to any wall or obstruction?

• a.15 inches
• b.21 inches✓
• c.24 inches
• d.30 inches

The IPC requires 21 inches of clear space in front of a water closet, lavatory, or bidet, although some jurisdictions and the UPC require 24 inches. 15 inches is the side clearance from the centerline, not a front dimension. 30 inches is the center-to-center spacing between two closets and has nothing to do with front approach space.IPC §405.3.1

A building owner replaces 40 old 3.5 gpf water closets with 1.28 gpf high efficiency models. If the fixtures are flushed a combined total of 2,000 times per day, how much water is saved per day?

• a.2,560 gallons
• b.3,500 gallons
• c.5,120 gallons
• d.4,440 gallons✓

The savings per flush is 3.5 minus 1.28, or 2.22 gallons, and 2.22 times 2,000 flushes equals 4,440 gallons per day. 2,560 gallons is 1.28 times 2,000, the new consumption rather than the savings. 5,120 and 3,500 gallons come from doubling the new usage or from using the old flush volume alone, neither of which is a difference calculation.IPC §604.4

A storage type water heater is being installed. Which device must be provided on the tank to protect against both excessive temperature and excessive pressure?

• a.A combination temperature and pressure relief valve✓
• b.A vacuum relief valve at the top of the tank
• c.A backflow preventer on the cold water inlet
• d.A pressure reducing valve on the building supply

Every storage water heater must be equipped with an approved combination temperature and pressure relief valve, typically rated to open at 210 degrees F and 150 psi. A vacuum relief valve prevents siphoning of the tank on bottom-fed heaters but does not relieve pressure or temperature. A backflow preventer and a pressure reducing valve address contamination and supply pressure, not tank overpressure or overheating.IPC §504.4

A temperature and pressure relief valve has a 3/4 inch outlet. Which discharge piping arrangement is acceptable?

• a.1/2 inch copper reduced at the valve and terminating 30 inches above the floor
• b.3/4 inch pipe running by gravity to terminate 8 inches above the floor with a plain end✓
• c.3/4 inch pipe with a ball valve installed for service isolation
• d.3/4 inch pipe with a threaded cap installed on the terminal end

Discharge piping must be full size of the valve outlet with no reduction, must drain by gravity, must have no valve in the line, and must terminate between 6 and 24 inches above the ground or an approved receptor with no threads on the end. The 1/2 inch option reduces the pipe and terminates too high, the ball valve option installs a prohibited shutoff, and the threaded cap option both threads the end and blocks discharge entirely.IPC §504.6

A 50 gallon water heater is installed in the attic above a finished ceiling. A drain pan is required. What is the minimum size of the pan drain line?

• a.1/2 inch
• b.5/8 inch
• c.3/4 inch✓
• d.1 inch

Where leakage would cause damage to the structure, a pan is required and its indirect drain must be at least 3/4 inch in diameter, discharging to an approved location. 1/2 inch and 5/8 inch are undersized and would not carry the flow of a leaking tank. A 1 inch pan drain is permitted as an upsize but is not the code minimum being asked for.IPC §504.7

A gas fired water heater is installed in a residential garage in a seismic zone. It must be strapped in two places. Where must the lower strap be located relative to the heater's controls?

• a.Directly across the control housing
• b.At least 4 inches below the controls
• c.At the exact vertical midpoint of the tank
• d.At least 4 inches above the controls✓

The two straps go around the upper third and the lower third of the tank, and the lower strap must be at least 4 inches above the controls so the strap does not damage or obstruct the gas valve and thermostat. Strapping across or below the controls interferes with service and with the control housing itself. A single midpoint strap does not satisfy the two-point bracing requirement.

The same gas water heater is installed in that garage on a concrete slab. What is the minimum height that the source of ignition must be elevated above the garage floor?

• a.18 inches✓
• b.12 inches
• c.24 inches
• d.6 inches

Ignition sources in a garage must be at least 18 inches above the floor because gasoline vapors are heavier than air and pool at floor level. 12 inches and 6 inches leave the burner inside the vapor layer. 24 inches is higher than required and is not the code figure, although a taller platform would still comply.

A 120,000 Btu/h gas water heater draws all of its combustion air directly from outdoors through two vertical ducts. Using the 1 square inch per 4,000 Btu/h rule for vertical ducts, what is the required free area of each opening?

• a.15 square inches
• b.30 square inches✓
• c.60 square inches
• d.12 square inches

Dividing 120,000 by 4,000 gives 30 square inches, and that is the required free area for each of the two openings, one near the top and one near the bottom of the enclosure. 60 square inches is the combined area of both openings, not the size of each. 15 square inches halves the correct figure, and 12 square inches corresponds to no recognized ratio.

A 100,000 Btu/h water heater is placed in a closet and will take combustion air from inside the building only. Using the rule of thumb of 50 cubic feet of room volume per 1,000 Btu/h, what minimum volume of communicating space is needed?

• a.2,000 cubic feet
• b.3,000 cubic feet
• c.5,000 cubic feet✓
• d.10,000 cubic feet

Dividing 100,000 by 1,000 gives 100, and 100 times 50 cubic feet equals 5,000 cubic feet of communicating volume. 2,000 and 3,000 cubic feet come from applying a 20 or 30 cubic foot factor that the standard indoor air method does not use. 10,000 cubic feet doubles the requirement and would only be relevant if two such appliances shared the space.

Where an enclosure takes combustion air from an adjacent room through two permanent openings, where must those openings be located?

• a.Both within 12 inches of the ceiling of the enclosure
• b.Both within 12 inches of the floor of the enclosure
• c.One at the ceiling and one at any convenient height on an outside wall
• d.One within 12 inches of the top of the enclosure and one within 12 inches of the bottom✓

The two-opening method requires one opening within 12 inches of the top and one within 12 inches of the bottom of the enclosure so that heated air can exhaust high while replacement air enters low. Placing both openings high or both low defeats the convective loop that drives the air exchange. Locating the lower opening at any convenient height does not satisfy the 12 inch dimension.

A shower compartment is framed 32 inches by 32 inches inside the finished walls. Does it meet the minimum area and minimum dimension requirements for a shower?

• a.Yes, 1,024 square inches meets the area minimum and 32 inches exceeds the 30 inch dimension minimum✓
• b.No, the area is 1,024 square inches but 1,200 square inches is required
• c.No, the minimum interior dimension is 36 inches in every direction
• d.Yes, but only if a 30 inch wide door is installed

32 times 32 equals 1,024 square inches, which is exactly the minimum area, and each interior dimension of 32 inches clears the 30 inch minimum. The area minimum is 1,024 square inches, not 1,200, and there is no universal 36 inch interior dimension for a standard shower. Shower doors must provide a 22 inch clear opening, so a 30 inch door is not the condition that makes the stall compliant.

An indirect waste pipe from a commercial ice machine is 1-1/2 inches in diameter and discharges into a floor sink. What is the minimum required air gap?

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

The air gap for an indirect waste must be at least twice the effective diameter of the discharge pipe, so 2 times 1-1/2 inches equals 3 inches measured from the pipe outlet to the flood level rim of the receptor. 1 inch is only the absolute minimum air gap for very small pipes. 2 inches and 1-1/2 inches apply the wrong multiplier to the pipe size.IPC §802.2

A 3/8 inch indirect waste tube from a beverage dispenser discharges over an open receptor. Applying the air gap rule, what is the required air gap?

• a.3/4 inch
• b.1 inch✓
• c.1-1/2 inches
• d.3/8 inch

Twice the pipe diameter would be only 3/4 inch, but the code also sets an absolute floor of 1 inch, so the required air gap is 1 inch. The 3/4 inch answer applies the multiplier and ignores the minimum. 1-1/2 inches and 3/8 inch are not produced by either part of the rule.IPC §802.2

A laundry standpipe for a residential clothes washer is roughed in with the top of the standpipe 14 inches above the trap weir. Is the installation acceptable?

• a.Yes, any height is acceptable as long as the trap is vented
• b.Yes, 14 inches is within the allowable range
• c.No, the standpipe must extend at least 18 inches and not more than 42 inches above the trap weir✓
• d.No, the standpipe must be at least 24 inches and not more than 60 inches above the trap weir

A clothes washer standpipe must be a minimum of 18 inches and a maximum of 42 inches above the trap weir, so 14 inches is too short and the discharge is likely to back out of the pipe. Height is regulated regardless of venting, so the first choice is wrong. The 24 to 60 inch range in the last choice is not the code window.

A showerhead is rated at the maximum allowable flow. A user showers for 8 minutes. Assuming the head flows at its rated maximum, how much water is used?

• a.12.0 gallons
• b.17.6 gallons
• c.24.0 gallons
• d.20.0 gallons✓

The maximum showerhead flow rate is 2.5 gpm at 80 psi, and 2.5 times 8 minutes equals 20 gallons. 17.6 gallons would result from a 2.2 gpm lavatory faucet rate, which does not apply to showerheads. 12 gallons uses a 1.5 gpm rate and 24 gallons uses 3.0 gpm, neither of which is the code maximum for a shower.IPC §604.4

A public restroom is fitted with metering faucets. What is the maximum volume of water each faucet may deliver per metering cycle?

• a.0.25 gallon✓
• b.0.5 gallon
• c.1.0 gallon
• d.0.125 gallon

Public metering faucets are limited to 0.25 gallon per metering cycle, which is a volume limit rather than a flow rate limit because the valve shuts itself off. 0.5 gallon and 1.0 gallon are urinal flush volumes, not faucet cycle volumes. 0.125 gallon is half the allowance and is not a code figure.

A closet flange is set on a wood subfloor before the finished tile is installed, and the installer plans to seal the closet to the flange. Which practice is correct?

• a.Set the flange below the finished floor and shim the bowl with wood blocks
• b.Set the flange on top of the finished floor, secure it to the structure with fasteners, and seal with a wax or approved gasket✓
• c.Seal the flange to the bowl with structural adhesive instead of fasteners
• d.Rely on the closet bolts alone to hold the flange to the floor

The closet flange must rest on and be mechanically secured to the finished floor or structure, and the joint between the bowl horn and the flange is sealed with a wax ring or an approved elastomeric gasket. A flange set below the finished floor leaves a gap that the seal cannot reliably bridge, and shimming with wood blocks is not an approved support method. Adhesive does not replace fasteners, and closet bolts secure the fixture to the flange rather than the flange to the floor.

A restaurant installs a grease interceptor sized for 30 minutes of retention. If the connected fixtures produce a peak flow of 25 gallons per minute through the flow control device, what liquid capacity does the retention rule call for?

• a.250 gallons
• b.500 gallons
• c.750 gallons✓
• d.1,500 gallons

Retention volume equals flow rate times retention time, so 25 gpm times 30 minutes equals 750 gallons. 250 gallons corresponds to only 10 minutes of retention and 500 gallons to 20 minutes, both short of the design basis stated in the question. 1,500 gallons would represent a full hour of retention, twice what was specified.

A grease interceptor is inspected and found to contain accumulated grease and settled solids filling 25 percent of the total liquid depth. What action does the common maintenance standard require?

• a.No action; cleaning is required only at 50 percent
• b.Add an enzyme treatment and re-inspect in six months
• c.Install a larger flow control device to slow the incoming flow
• d.Pump and clean the interceptor, since the 25 percent threshold has been reached✓

The widely used 25 percent rule requires that an interceptor be pumped when grease and solids occupy a quarter of the liquid depth, because beyond that point retention efficiency falls off sharply. Waiting for 50 percent allows grease carryover into the building drain. Enzyme or chemical treatments emulsify grease so it passes through the unit rather than being retained, and changing the flow control does not remove the accumulated material.IPC §1003.3

A residence has a pressure reducing valve with a check on the incoming water service, and the 40 gallon water heater's relief valve has begun weeping each evening. What is the most likely cause and the correct correction?

• a.Thermal expansion in a closed system; install an expansion tank sized for the system✓
• b.The relief valve is set too high; replace it with a 250 degree F valve
• c.The heater is oversized; reduce the thermostat to 90 degrees F
• d.The discharge line is too long; shorten it and add a threaded cap

A check or pressure reducing valve makes the system closed, so water expanding as it heats has nowhere to go and pressure rises until the relief valve lifts, which is corrected with a properly sized thermal expansion tank. Replacing the relief valve with a higher setting defeats the safety device rather than solving the pressure problem. Lowering the thermostat to 90 degrees F creates a bacterial growth risk, and capping the discharge line is expressly prohibited.

A three compartment pot sink and a food prep sink are being connected in a commercial kitchen. How must the waste from food handling equipment such as a food prep sink be connected to the drainage system?

• a.Directly connected through a P-trap with no air gap or air break
• b.Indirectly connected through an air gap to an approved receptor✓
• c.Directly connected but only through a grease interceptor
• d.Indirectly connected through an air break, which is acceptable for all food equipment

Waste from equipment in which food is stored, prepared, or handled must be indirectly connected by means of an air gap so that sewage cannot back up into food contact surfaces. A direct connection provides no physical break at all, even when a trap or interceptor is present. An air break relies on the pipe extending below the flood rim and is permitted for some indirect wastes but not for food handling equipment.IPC §802.1