CSLB General Building (B) — All Questions

Static pressure at the water meter reads 68 psi. The highest fixture served is 32 ft above the meter. Ignoring meter and friction losses, how much pressure remains at the elevation of that fixture?

• a.About 60.2 psi
• b.About 58.4 psi
• c.About 54.1 psi✓
• d.About 46.2 psi

Elevation loss is 0.433 psi for every foot of rise, so 32 ft x 0.433 = 13.86 psi, and 68 - 13.86 = 54.1 psi. The 60.2 and 58.4 answers come from using a smaller loss factor such as 0.25 or 0.3 psi per foot. The 46.2 answer wrongly applies 2.31 psi per foot, which is the inverse relationship (2.31 ft of head per psi).

How many feet of vertical head are equivalent to 22 psi of water pressure?

• a.About 50.8 ft✓
• b.About 9.5 ft
• c.About 45.4 ft
• d.About 22 ft

One psi equals 2.31 ft of head, so 22 x 2.31 = 50.8 ft. The 9.5 ft answer divides by 2.31 instead of multiplying, and 45.4 ft comes from using a rounded factor of 2.0 plus arithmetic error. Answering 22 ft ignores the conversion entirely and treats psi and feet as interchangeable.

A potable water supply outlet discharges over a receptor and the effective opening of the outlet is 1 in. What is the minimum required air gap?

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

The air gap must be at least twice the diameter of the effective opening, so 2 x 1 in = 2 in. The 1 in answer is only the code minimum floor that applies to very small openings, not the calculated value here. The 1-1/2 in choice uses a 1.5 multiplier and 3 in uses a 3x multiplier, neither of which the code uses.UPC §603.3.1

A supply outlet has an effective opening of 3/8 in. What minimum air gap must be provided above the flood level rim of the receiving vessel?

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

Twice the effective opening is 2 x 0.375 = 0.75 in, but the code sets an absolute minimum air gap of 1 in, so 1 in governs. The 3/4 in answer applies the 2x rule without checking the minimum. The 1-1/4 in and 2 in values are larger than anything the rule produces for a 3/8 in opening.IPC §608.15.1

A gauge on the building side of the meter shows a static street pressure of 96 psi with no flow. What does the plumbing code require?

• a.An approved pressure-reducing valve limiting downstream pressure to not more than 80 psi✓
• b.Nothing, because the pressure is still under 100 psi
• c.An increase of one pipe size on the water service
• d.An approved vacuum relief valve on the water service

Where static pressure exceeds 80 psi, an approved pressure-reducing valve must be installed to hold the downstream distribution system at 80 psi or less. The 100 psi threshold does not exist in the code; 80 psi is the trigger. Upsizing pipe lowers friction loss but does nothing to static pressure, and a vacuum relief valve protects against collapse or siphoning, not high pressure.UPC §608.2

A 40 ft horizontal run of 3/4 in copper water tube is installed in a ceiling. Using a maximum horizontal support spacing of 6 ft for copper 1-1/2 in and smaller, what is the minimum number of hangers required?

• a.5 hangers
• b.6 hangers
• c.7 hangers✓
• d.8 hangers

40 ft divided by 6 ft equals 6.67 spaces, and since a partial space still needs a hanger you round up to 7. Answering 6 truncates the fraction and leaves a span longer than 6 ft. The 5 hanger answer assumes 8 ft spacing, and 8 hangers assumes the 5 ft spacing used for cast iron, not copper.UPC §313.3

A 24 ft horizontal run of 1/2 in CPVC water distribution pipe is supported at the maximum spacing of 3 ft. What is the minimum number of supports required?

• a.6 supports
• b.8 supports✓
• c.9 supports
• d.12 supports

24 ft divided by 3 ft equals 8 supports at the maximum allowed spacing. The 6 support answer uses the 4 ft spacing allowed for larger plastic pipe, and 12 supports assumes 2 ft spacing, which is more than the code requires. The 9 answer adds an extra support that the calculation does not produce.IPC Table 308.5

PEX tubing runs horizontally for 16 ft above a suspended ceiling. Using the maximum horizontal support spacing of 32 in for PEX, what is the minimum number of supports?

• a.3 supports
• b.4 supports
• c.5 supports
• d.6 supports✓

Convert first: 16 ft equals 192 in, and 192 divided by 32 equals 6 supports. The 4 and 3 answers come from using 48 in or 72 in spacing, which apply to rigid materials, not flexible PEX. Five supports would leave one span longer than 32 in and would allow the tubing to sag.IPC Table 308.5

To limit erosion-corrosion and noise, what is the generally accepted maximum design velocity in a copper hot water distribution line?

• a.5 feet per second✓
• b.8 feet per second
• c.10 feet per second
• d.12 feet per second

Hot water accelerates erosion of the copper tube wall, so hot lines are held to about 5 fps while cold lines are commonly designed to about 8 fps. The 8 fps answer is the cold water limit and is too aggressive for hot water. The 10 and 12 fps values are well above accepted design practice for any copper water line and would produce velocity noise and premature pinhole failures.

A commercial kitchen is being piped with solenoid-operated quick-closing valves on the dishwasher and ice machine supplies. What does the code require on those branches?

• a.A larger supply pipe to slow the water velocity
• b.Approved water hammer arrestors sized and located per the manufacturer's instructions✓
• c.A check valve immediately upstream of each valve
• d.A vacuum breaker on each supply branch

Quick-closing valves stop flow almost instantly and convert momentum into a pressure spike, so the code requires approved water hammer arrestors on those branches. Upsizing pipe reduces velocity somewhat but does not satisfy the arrestor requirement. A check valve does not absorb the shock wave, and a vacuum breaker addresses back-siphonage, which is a different problem entirely.IPC §604.9

A potable water line supplies makeup water to a chemically treated boiler system and the connection is under continuous pressure. Which backflow prevention device is required?

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

Treated boiler water is a high hazard (health hazard) contaminant and the connection is under continuous pressure, which calls for a reduced pressure principle assembly. A double check assembly is only acceptable for low hazard, non-health, continuous pressure applications. An atmospheric vacuum breaker cannot be used under continuous pressure at all, and a hose bibb vacuum breaker is for hose outlets and protects only against back-siphonage.IPC §608.13

A fire sprinkler system with no antifreeze or chemical additives is connected to the potable water supply under continuous pressure. Which assembly is the appropriate minimum protection for this low hazard connection?

• a.Atmospheric vacuum breaker
• b.Pressure vacuum breaker
• c.Reduced pressure principle assembly
• d.Double check valve assembly✓

A non-additive sprinkler system is a low hazard (pollutant, not contaminant) connection under continuous pressure, which is the exact application for a double check valve assembly. A reduced pressure assembly exceeds the minimum required here and adds an unnecessary relief discharge. An atmospheric vacuum breaker may never be used under continuous pressure, and a pressure vacuum breaker protects against back-siphonage only, not back-pressure.IPC §608.13

An atmospheric vacuum breaker serves a fixture whose flood level rim is 34 in above the finished floor. What is the minimum height above the floor at which the vacuum breaker may be installed?

• a.34 in
• b.40 in✓
• c.46 in
• d.37 in

An atmospheric vacuum breaker must be at least 6 in above the flood level rim, so 34 + 6 = 40 in above the floor. Installing it at 34 in puts it level with the rim with no clearance at all. The 37 in answer uses a 3 in clearance and 46 in uses the 12 in clearance required for a pressure vacuum breaker above its highest outlet.IPC §608.13

A pressure vacuum breaker protects a lawn irrigation zone whose highest sprinkler head is 42 in above grade. What is the minimum height above grade for the vacuum breaker?

• a.4 ft 6 in✓
• b.4 ft 0 in
• c.3 ft 6 in
• d.5 ft 6 in

A pressure vacuum breaker must be at least 12 in above the highest downstream outlet, so 42 in + 12 in = 54 in, or 4 ft 6 in. The 3 ft 6 in answer is simply the head height with no clearance added. The 4 ft 0 in answer adds only 6 in, which is the atmospheric vacuum breaker rule, and 5 ft 6 in adds 24 in, more than the code requires.IPC §608.13

Which condition makes a pressure vacuum breaker an unacceptable choice for a given cross-connection?

• a.The outlet is a hose thread connection
• b.The device would be located outdoors
• c.The supply piping is copper rather than steel
• d.A booster pump downstream could push water back toward the supply✓

A pressure vacuum breaker protects only against back-siphonage; a downstream pump creates back-pressure, which requires a double check assembly or reduced pressure assembly depending on the hazard level. Hose thread outlets, outdoor locations, and copper supply piping do not disqualify a pressure vacuum breaker. The distinction to remember is back-siphonage (negative supply pressure) versus back-pressure (higher downstream pressure).

Which copper tube designation has the heaviest wall thickness and is the type commonly required for an underground water service?

• a.Type M
• b.Type L
• c.Type K✓
• d.Type DWV

Wall thickness runs K heaviest, then L, then M, so Type K is specified where the tube is buried and exposed to soil and backfill loading. Type L is the common choice for interior water distribution and Type M is the thinnest pressure type, often restricted to above-ground use. Type DWV is not a pressure-rated water tube at all and is limited to drain, waste, and vent service.UPC §604.0

What is the maximum lead content permitted in solder and flux used on a potable water piping system?

• a.0.2 percent✓
• b.0.25 percent
• c.2 percent
• d.8 percent

Solder and flux used in potable water piping may not exceed 0.2 percent lead, which is why 50/50 tin-lead solder is prohibited. The 0.25 percent figure is a different limit, the weighted average lead content allowed on the wetted surfaces of pipe, fittings, and fixtures. The 2 percent and 8 percent values are far above any lead-free standard and describe legacy alloys no longer permitted.UPC §604.0

What is the maximum weighted average lead content permitted on the wetted surfaces of pipe, fittings, and fixtures used to convey water for human consumption?

• a.0.2 percent
• b.0.05 percent
• c.0.25 percent✓
• d.8 percent

The lead-free standard limits the wetted surfaces to a weighted average of not more than 0.25 percent lead. The 0.2 percent value is the separate limit that applies to solder and flux, not to the wetted surfaces of the components. The 0.05 percent figure is stricter than the code requires, and 8 percent describes older leaded brass that may no longer be installed in potable systems.

Static pressure at the main is 72 psi. Meter loss at design flow is 9 psi, the highest fixture is 26 ft above the meter, and 15 psi residual is required at that fixture. How much pressure is available to overcome friction loss in the piping?

• a.About 41.2 psi
• b.About 36.7 psi✓
• c.About 48.0 psi
• d.About 25.5 psi

Elevation loss is 26 x 0.433 = 11.26 psi, so 72 - 9 - 11.26 - 15 = 36.7 psi available for friction. The 48.0 psi answer forgets the required residual pressure, and 41.2 psi forgets part of the elevation loss. The 25.5 psi answer subtracts the residual twice or uses a 20 psi flushometer residual that this problem did not specify.UPC §610.0

A flushometer water closet on the top floor requires 20 psi residual. Static pressure is 65 psi, combined meter and backflow preventer loss is 10 psi, and the flush valve is 34 ft above the meter. How much pressure remains for friction loss in the piping and fittings?

• a.About 35.0 psi
• b.About 25.3 psi
• c.About 14.7 psi
• d.About 20.3 psi✓

Elevation loss is 34 x 0.433 = 14.72 psi, so 65 - 10 - 14.72 - 20 = 20.3 psi for friction. The 35.0 psi answer ignores the elevation loss, and 25.3 psi uses a 15 psi residual instead of the 20 psi a flushometer needs. The 14.7 psi choice is the elevation loss itself, not the friction allowance.UPC §610.0

A sizing problem leaves 24 psi available for friction loss. The measured developed length to the most remote fixture is 160 ft, and fittings are estimated to add 50 percent to that length. What is the allowable friction loss per 100 ft of pipe?

• a.About 15 psi per 100 ft
• b.About 6.7 psi per 100 ft
• c.About 10 psi per 100 ft✓
• d.About 24 psi per 100 ft

Total equivalent length is 160 x 1.5 = 240 ft, so 24 psi / 240 ft x 100 = 10 psi per 100 ft. The 15 psi answer divides by the measured 160 ft and skips the fitting allowance. The 6.7 psi answer overstates the equivalent length, and 24 psi per 100 ft simply restates the total budget without dividing by length.UPC §610.0

A dwelling unit contains one flush tank water closet (2.5 WSFU), two lavatories (1.0 WSFU each), one bathtub with shower (4.0 WSFU), one kitchen sink (1.5 WSFU), one dishwasher (1.5 WSFU), and one clothes washer (4.0 WSFU). What is the total water supply fixture unit load?

• a.15.5 WSFU✓
• b.14.5 WSFU
• c.16.5 WSFU
• d.13.0 WSFU

Adding the listed values gives 2.5 + 1.0 + 1.0 + 4.0 + 1.5 + 1.5 + 4.0 = 15.5 WSFU. The 14.5 answer counts only one lavatory, and 13.0 drops the dishwasher. The 16.5 answer adds an extra fixture unit that is not in the list; the total load is then carried into the sizing table to pick the service and distribution sizes.

Using the standard fixture unit to gpm conversion curve, what happens to the estimated demand when the total water supply fixture unit load on a system is doubled?

• a.The demand in gpm exactly doubles
• b.The demand in gpm increases by less than double✓
• c.The demand in gpm more than doubles
• d.The demand in gpm stays the same

The conversion curve is probability based: as more fixtures are added, the chance that all of them run at once drops, so gpm rises more slowly than fixture units. This diversity is why a 200 WSFU building does not need twice the flow of a 100 WSFU building. Assuming a straight-line doubling oversizes the service, and the more-than-double and no-change answers contradict how the curve behaves.IPC Appendix E

What is the minimum nominal size normally permitted for a water service pipe serving a building?

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

The water service pipe may not be smaller than 3/4 in regardless of what the fixture unit calculation produces. A 1/2 in service is below the code floor even for a very small single-fixture building, and 5/8 in is a meter size designation, not a standard pipe size. Requiring 1 in as the minimum is stricter than the code and would be a design choice, not a code requirement.

The highest fixture in a building is 28 ft above the meter and requires 15 psi residual. Meter loss is 5 psi and calculated friction loss in the piping is 12 psi. What minimum static pressure is needed at the meter?

• a.About 44.1 psi✓
• b.About 32.0 psi
• c.About 55.1 psi
• d.About 40.0 psi

Add every loss to the required residual: 28 x 0.433 = 12.12 psi elevation, plus 5 psi meter, plus 12 psi friction, plus 15 psi residual equals 44.1 psi. The 32.0 psi answer omits the elevation loss, and 40.0 psi rounds the elevation loss down to about 8 psi. The 55.1 psi answer double counts one of the losses and would call for a booster that is not actually needed.UPC §610.0

Using velocity (fps) = 0.408 x flow (gpm) divided by the square of the inside diameter (in), what is the velocity of 12 gpm flowing in 3/4 in Type L copper with an inside diameter of 0.785 in?

• a.About 4.4 fps
• b.About 6.0 fps
• c.About 7.9 fps✓
• d.About 10.2 fps

0.408 x 12 = 4.896, and 0.785 squared is 0.616, so 4.896 / 0.616 = 7.9 fps, right at the practical 8 fps cold water limit. The 4.4 and 6.0 answers come from dividing by the diameter instead of the diameter squared or from using the nominal 3/4 in size. The 10.2 answer uses a smaller inside diameter such as 0.69 in, which belongs to a heavier wall tube.

A 60 ft straight run of CPVC hot water pipe will see a 70 degree F temperature change. Using a coefficient of thermal expansion of 0.000034 in per in per degree F, approximately how much will the run expand?

• a.About 0.6 in
• b.About 1.0 in
• c.About 2.4 in
• d.About 1.7 in✓

Convert to inches first: 60 ft = 720 in, and 720 x 0.000034 x 70 = 1.71 in of movement, which is why an offset or expansion loop is needed. The 0.6 in and 1.0 in answers come from using only part of the temperature change or forgetting the foot-to-inch conversion. The 2.4 in answer uses a temperature change near 100 degrees F rather than the 70 degrees stated.

An existing galvanized steel water line is being extended with copper tube. What must be installed at the point where the two materials join?

• a.A brass compression coupling
• b.An approved dielectric fitting or dielectric union✓
• c.A soldered joint made directly to the steel pipe
• d.A rubber sleeve coupling with stainless steel clamps

Copper and galvanized steel are far apart on the galvanic scale, so a dielectric fitting is required to break the metallic path and prevent accelerated corrosion at the joint. A brass coupling still conducts and only shifts the corrosion cell rather than stopping it. Copper cannot be soldered directly to galvanized steel, and a rubber sleeve coupling is a drainage fitting that is not rated for water distribution pressure.IPC §605