Exam Cheat Sheet · Quick Reference
Idaho Plumbing Journeyman Exam
Idaho · PSI Services Contractor
Verified, not estimated. Every figure below is drawn from the official exam structure we maintain — question counts, passing standard and topic weighting. Practice questions are grounded in the source law with statute citations. We omit any figure we can't verify rather than guess at it.
Total questions
100
Passing score
70%
Exam time
180 min
Administered by
PSI Services Contractor
Format
Reference materials allowed
Idaho State Portion 100 questions
2015 Uniform Plumbing Code Chapter 3
6 Q · 6%
Material standards, listing requirements, and manufacturer marking of pipe, fittings, and componentsProhibited fittings and practices in drainage, vent, and waste piping systemsProtection of piping through walls, floors, and structural members including sleeves and nail platesHangers, supports, and pipe support intervals by material typeTrenching, excavation, backfill, and thermoplastic pipe bedding requirementsAlternate materials, alternative engineered design approval process, and equivalency testingFlood hazard area and coastal high hazard area plumbing installation requirementsTest gauge pressure ranges and incrementation requirements for pressure testing
2015 Uniform Plumbing Code Chapter 4
8 Q · 8%
Fixture installation requirements (clearances, spacing, and securing methods)Minimum number of required plumbing fixtures by occupancy type (Table 422.1)Water consumption limits and flow rates for fixtures (lavatories, showers, water closets, urinals, sinks)Shower compartment construction, lining materials, and waterproofing requirementsFixture-specific standards (water closets, urinals, lavatories, bathtubs, bidets, dishwashers, floor drains)Flushing devices (flushometer valves, flush tanks, and antisiphon requirements)Hot water temperature limitations for lavatories, bathtubs, and bidetsProhibited fixtures and special/alternative fixture requirements
2015 Uniform Plumbing Code Chapter 5
4 Q · 4%
Water heater location requirements and prohibited installationsTemperature, pressure, and relief valve requirementsCombustion air supply methods and sizing calculationsVenting system types and selection for Category I appliancesVent and chimney termination requirementsVent connector materials, sizing, clearances, and installationWater heater support, seismic strapping, and drainage pan requirementsSizing of Category I venting systems using tables and engineering methods
2015 Uniform Plumbing Code Chapter 6
8 Q · 8%
Backflow prevention devices, assemblies, and methods (types, components, and applicable standards)Cross-connection control and prohibited unlawful connectionsWater supply pipe materials, approved standards, and lead content requirementsPipe and tubing joining methods by material type (copper, CPVC, PEX, PE, PP, etc.)Water pressure regulation, pressure relief valves, and expansion tanksSizing water supply and distribution systems using fixture units and Table 610.4Identification and labeling of potable and nonpotable water systemsResidential fire sprinkler system installation, design, and pipe sizing
2015 Uniform Plumbing Code Chapter 7
9 Q · 9%
Drainage pipe materials, standards, and installation restrictions by location (above/belowground)Drainage fixture unit (DFU) values and sizing of drainage pipingJoints and connections for drainage piping by material typeCleanout requirements: location, spacing, clearance, and accessGrade and slope requirements for horizontal drainage piping and building sewersDrainage of fixtures below main sewer level: backwater valves, ejectors, sumps, and alarmsBuilding sewer materials, sizing, installation, separation from water pipes, and testingChanges in direction of drainage flow using approved fittings
2015 Uniform Plumbing Code Chapter 8
4 Q · 4%
Air gap and air break requirements for indirect waste pipingIndirect waste piping for food and beverage handling establishmentsIndirect waste receptor requirements and installation restrictionsCondensate waste disposal, pipe sizing, and overflow protectionChemical and industrial waste pretreatment and approved piping materialsSteam and hot water drainage condensers and sumpsPressure drainage connections and water softener discharge requirementsClear water wastes, swimming pool drainage, and cooling water connections
2015 Uniform Plumbing Code Chapter 9
9 Q · 9%
Vent pipe sizing based on fixture units and developed lengthVent termination requirements including roof and sidewall clearancesVent pipe grades, connections, and rise above flood-level rimWet venting requirements for vertical and horizontal bathroom groupsCircuit venting requirements and limitationsSpecial venting for island fixtures and air admittance valve restrictionsCombination waste and vent system requirements and limitationsVent stack and relief vent requirements for multi-story drainage stacks
2015 Uniform Plumbing Code Chapter 10
5 Q · 5%
Trap installation requirements and fixture trap rulesTrap arm lengths and Table 1002.2 distance requirementsProhibited trap types and trap seal depth requirementsGrease interceptor types, sizing, and installation requirementsHydromechanical vs. gravity grease interceptor sizing methodsSand interceptor construction, sizing, and design requirementsOil and flammable liquid interceptor requirements and ventingFloor drain trap seals and trap seal primer requirements
2015 Uniform Plumbing Code Chapter 11
10 Q · 10%
Storm water drainage system materials and approved pipe typesSizing of roof drains, vertical conductors, and leaders using Table 1101.12Sizing of horizontal storm drains and sewers using Table 1101.8Primary and secondary (emergency) roof drainage requirementsSubsoil drain installation, sump requirements, and discharge optionsControlled-flow roof drainage system requirements and conditionsTraps on storm drains and leaders connected to combined sewersTesting methods for storm drainage systems (water test and air test)
2015 Uniform Plumbing Code Chapter 12
12 Q · 12%
Gas piping system design, sizing methods, and allowable pressure dropAcceptable piping materials, joining methods, and fittings (metallic and plastic)Underground and aboveground gas piping installation requirementsPressure testing, leak detection, and purging proceduresInspection requirements, certificates of inspection, and authority to disconnectGas meters, pressure regulators, and shutoff valvesAppliance connections, connectors, sediment traps, and shutoff valvesElectrical bonding and grounding of gas piping systems
2017 Idaho State Plumbing
25 Q · 25%
Testing and inspection of plumbing systems under Idaho's amended Section 105.3 (tests in the presence of the AHJ; exhibition and minor-work exceptions)Idaho definition of 'plumbing system' incorporated from Section 54-2604, Idaho Code (Section 218)Fixture amendments: qualities of fixtures (401.2), shower receptor floor slope 1/8 to 1/2 inch per foot (408.5), deleted Sections 403.3, 408.7.5 and 409.4Water heater amendments: Table 501.1(1) deleted, Category 3/4 vent air test at 5 psi for 15 minutes (503.1), seismic provisions deleted (507.2), 18-inch ignition-source height in garages (507.13)Backflow amendments: Table 603.2 changes, hose outlets and self-draining frost-proof hose bibbs (603.5.7), carbonated beverage dispensers (603.5.12), chemical dispensers (603.5.21)Water supply amendments: tracer wire exception (604.10.1), PE water service joints inside buildings (605.6.2), 42-inch cover for yard piping (609.1), plastic pipe testing (609.4), water hammer and pipe insulation (609.10, 609.11)Fixture unit and softener amendments: two fixture units for bathtubs and clothes washers (Tables 610.3, 702.1, 703.2), pre-plumbed softener loop in new residences (610.2), softener sizing footnote (611.4)Drainage amendments: 2-inch minimum underground drain and vent (703.1), double sanitary tees (704.2), one-step solvent cement (705.5.2), cleanout locations and 50-foot intervals (707.4), ejector and sump exceptions (710.3, 710.5), air testing of plastic DWV (712.1, 723.0), 4-inch building sewer (717.1)Indirect waste amendments: food-handling fixture air gaps and 1-inch minimum piping (801.3.3), water softener drain 3/4 inch to an approved location (805.4), domestic dishwasher high loop without an air gap (807.3)Venting, trap and gray water amendments: sidewall venting (906.1), horizontal wet vent (908.1), air admittance valve limits (909.0), trap arm 180-degree rule (1002.3), trap seal primers (1007.1), garage floor drain interceptors (1016.1), gray water inspection and IDEQ jurisdiction (1502.1)
Key Distinctions
ABS solvent cement jointvsPVC solvent cement joint
ABS surfaces need only be cleaned free of dirt and moisture before applying solvent cement per ASTM D2235 (no primer required), whereas PVC requires purple primer.
ISPC 2017 Section 705.1.2Shower receptor finished floor slope (Sec. 408.5)vsShower receptor lining pitch to weep holes (Sec. 408.7)
The finished floor must slope uniformly toward the drain not less than 1/8 in. per foot (max 1/2 in. per foot), while the waterproof lining material must be pitched 1/4 in. per foot to the weep holes in the subdrain.
ISPC 2017 Section 408.5Test gauge incrementation for tests of 10 psi or lessvsTest gauge incrementation for tests over 10 psi up to 100 psi
Tests of 10 psi or less require gauges of 0.10 psi incrementation or less; tests exceeding 10 psi but not more than 100 psi require gauges of 1 psi incrementation or less.
ISPC 2017 Section 318.2Maximum hot water from a bidetvsMaximum hot water from public-use lavatories / shower and tub-shower valves
Bidet discharge is limited to 110°F by an ASSE 1070 or CSA B125.3 device, while public-use lavatories and shower/tub-shower control valve settings are limited to 120°F (water heater thermostat does not count as the lavatory control).
ISPC 2017 Section 410.3Public lavatory faucet flow ratevsShowerhead flow rate
Public lavatory faucets are limited to 0.5 gpm at 60 psi; showerheads are limited to 2.5 gpm at 80 psi.
ISPC 2017 Section 407.2.1Water closet center-to-side wall clearancevsWater closet center-to-center spacing and front clear space
A water closet or bidet may not be set closer than 15 in. from its center to a side wall or obstruction (paper dispensers and grab bars are not obstructions), while center-to-center spacing to a similar fixture must be at least 30 in. and clear space in front at least 24 in.
ISPC 2017 Section 402.5Double tee branch / double hub fitting (prohibited)vsDouble hub sanitary tapped tee (permitted exception)
Double hub fittings, single or double tee branches, tapped tee branches, side inlet quarter bends, running threads, bands and saddles are prohibited as drainage fittings, but a double hub sanitary tapped tee is permitted on a vertical line as a fixture connection.
ISPC 2017 Section 310.1Trench width formula 1 for thermoplastic sewer pipevsTrench width formula 2 for thermoplastic sewer pipe
Formula 1 is 1.25 × outside diameter plus 12 in.; formula 2 is outside diameter plus 16 in.; the code joins them with 'or' as alternative minimums (e.g., 4 in. OD yields 17 in. or 20 in.).
ISPC 2017 Section 314.4.145-degree offset constantvs22-1/2-degree offset constant
Travel for a 45° offset equals set × 1.414 (and run equals set × 1.000), whereas travel for a 22-1/2° offset equals set × 2.613.
Excavation where rock is encounteredvsBedding for thermoplastic piping
Where rock is encountered the trench must be excavated at least 6 in. below the bottom of the pipe with sand added so the pipe never rests on rock, while thermoplastic piping must be bedded in not less than 4 in. of granular fill.
ISPC 2017 Section 314.4Horizontal support spacing for Schedule 40 PVC/ABS DWVvsHorizontal support spacing for PEX 1 in. and smaller
Solvent-cemented Schedule 40 PVC and ABS DWV is supported at 4 ft intervals for all sizes (expansion allowance every 30 ft), while PEX 1 in. and smaller is supported at intervals not exceeding 32 in.
ISPC 2017 Table 313.3Manufacturer's mark on materialsvsField markings
Each length of pipe, fitting, trap, fixture, material and device must bear the manufacturer's mark or name cast, stamped or indelibly marked on it; field markings are expressly not acceptable.
ISPC 2017 Section 301.2.1Key Terms
Trap arm ISPC 2017 Section 202.0 (Definition of Trap Arm)
That portion of a fixture drain between a trap and the vent, as defined in 2017 ISPC Section 202.0.
Steel nail plate (pipe protection) ISPC 2017 Section 312.9
Protection required where plastic, copper or copper alloy piping penetrates framing members to within 1 in. of the exposed framing; the plate must be not less than No. 18 gauge (0.0478 in.) thick.
Hanger rod size ISPC 2017 Table 313.6
Per Table 313.6, hanger rods for pipes and tubes 5 in. through 8 in. shall be not smaller than 1/2 in.
Test gauge ISPC 2017 Section 318.5
A gauge used for required pressure tests whose pressure range shall not exceed twice the test pressure applied.
Tunnel (between open-cut trenches) ISPC 2017 Section 314.2
An excavation that must have a clear height of 2 ft above the pipe and be limited in length to one-half the trench depth, with a maximum length of 8 ft.
Trench paralleling a footing ISPC 2017 Section 314.1
A trench deeper than a building footing and running parallel to it must be located not less than 45 degrees from the bottom exterior edge of the footing, or as approved under Section 301.2.
Rodentproofing (strainer plates) ISPC 2017 Section 312.12
Strainer plates on drain inlets must be designed and installed so that no opening exceeds 1/2 in. in the least dimension.
Concealment of imperfections ISPC 2017 Section 309.2
It is unlawful to conceal cracks, holes or other imperfections in materials by welding, brazing or soldering, or by using paint, wax, tar, solvent cement or other leak-sealing or repair agent.
Drilling and tapping / threading of drainage piping ISPC 2017 Section 310.2
No drainage or vent piping may be drilled and tapped for making connections, and cast-iron soil pipe shall not be threaded.
Single-stack drainage and venting with unvented branch lines ISPC 2017 Section 310.4
A system prohibited by Section 310.4, with no exception for approval by the Authority Having Jurisdiction.
Obstruction to flow (closet bend exception) ISPC 2017 Section 310.5
Enlargement of a 3 in. closet bend or stub to 4 in. shall not be considered an obstruction under Section 310.5.
Leaders/conductors ISPC 2017 Section 1101.16
Storm piping that shall not be used as soil, waste or vent pipes, nor may soil, waste or vent pipes be used as leaders or conductors — an absolute prohibition regardless of sizing.
Shower compartment ISPC 2017 Section 408.6
Regardless of shape, it must have a minimum finished interior of 1024 square inches and be capable of encompassing a 30 in. circle; the waste outlet and fixture tailpiece must be not less than 2 in. in diameter.
Whirlpool pump access ISPC 2017 Section 409.6
Where located in a crawl space, the whirlpool pump access shall be not more than 20 ft from an access door, trap door or crawl hole.
Air test (DWV and storm drainage) ISPC 2017 Section 712.3
Air is forced into the system to a uniform gauge pressure of 5 psi, or enough to balance a 10 in. column of mercury, held for not less than 15 minutes.
Continuous or semi-continuous discharge (storm drain sizing) ISPC 2017 Section 1104.1
For building storm drain computations, 1 gpm of such discharge is equivalent to 24 square feet of roof area, based on a rainfall rate of 4 in. per hour.
Water hammer arrestor requirement (Idaho amendment) Idaho Rules Governing Plumbing (IDAPA 24.39.20), Section 600.23, Page 9
Per ISPC Section 609.10 as amended by Idaho rule, the water hammer provision does not apply to residential construction.
UV protection of exposed PVC ISPC 2017 Section 312.14
PVC piping wrapped with not less than 0.04 in. thick tape, or otherwise protected from UV degradation, is permitted to be exposed to sunlight (Section 312.14 Exception 2).
Formulas to Know
Offset travel and run using constants
45° offset: travel = set × 1.414 and run = set × 1.000; 22-1/2° offset: travel = set × 2.613 (e.g., 16 in. set at 45° = 22.62 in. ≈ 22-5/8 in.; 10 in. set at 22-1/2° = 26.13 in. ≈ 26-1/8 in.)Total fall, downstream invert, and percent slope of a graded drain
Fall = run × grade (48 ft × 1/4 in./ft = 12 in. = 1.00 ft; 32 ft × 1/8 in./ft = 4 in.); downstream invert = upstream invert − fall (100.00' − 1.00' = 99.00'); percent slope = (rise in inches per foot ÷ 12) × 100 (0.25 ÷ 12 × 100 = 2.08%)Cut length of threaded pipe between two fittings
Cut length = center-to-center − (fitting takeoff × 2) + (thread engagement × 2); e.g., 42 − (2 × 2-1/4) + (2 × 1/2) = 38-1/2 in.; 36 − (2 × 2) + (2 × 1/2) = 33.00 in.Cylindrical tank/pipe volume and gallon capacity
V = π × r² × h (use radius = half the diameter); gallons = cubic feet × 7.48; e.g., 4 ft dia × 6 ft = π × 2² × 6 = 75.4 cu ft = 564 ≈ 565 gal (half full: π × 2² × 3 = 37.7 cu ft = 282 gal); 100 ft of 2 in. ID pipe = π × (1/12)² × 100 = 2.18 cu ft = 16.3 galMinimum trench width for underground thermoplastic sewer pipe
(1.25 × outside diameter) + 12 in., or outside diameter + 16 in.; 4 in. OD = 17 in. or 20 in.; 6 in. OD = 19.5 in. or 22 in.Combustion air — one permanent opening method (outdoor air)
Free area = total input Btu/h ÷ 3,000 Btu/h per square inch; 60,000 ÷ 3,000 = 20 sq in. minimumOil/flammable liquid interceptor capacity (non-rated)
6 cubic feet minimum for not more than 3 vehicles, plus 1 cubic foot for each additional vehicle up to 10 vehicles; 7 vehicles = 6 + 4 = 10 cu ft; 8 vehicles = 6 + 5 = 11 cu ftMinimum number of controlled-flow roof drains
Not less than 2 drains for roof areas of 10,000 sq ft or less, plus not less than 1 additional drain for each 10,000 sq ft (or portion) exceeding 10,000 sq ft; 25,000 sq ft = 2 + 2 = 4 drainsMaximum test gauge pressure range
Gauge range ≤ 2 × test pressure applied; 60 psi test = 120 psi max range; 5 psi air test = 10 psi max rangeSizing pressure downstream of a pressure regulator (2015 UPC)
Design pressure = 80% of the reduced pressure when using the fixture unit table (Table 610.4); 0.80 × 70 psi = 56 psi