14.3 High-Yield Number Review, Classic Traps, and a Final Readiness Checklist
Key Takeaways
DWV tests use a 10-foot water head or 5 psi air for 15 minutes, water supply tests use working pressure or 50 psi air, and plastic is never air tested.
Water closet front clearance in Washington is 24 inches, reduced to 21 inches in dwelling and sleeping units; the side clearance is 15 inches and the center-to-center spacing 30 inches.
A T&P relief valve's pressure setting may not exceed 150 psi, and its discharge ends 6 to 24 inches above the floor or grade, unthreaded, and never into the heater pan.
UPC Table 1002.2 limits trap arms to 30, 42, 60, 72, and 120 inches for 1-1/4 through 4-inch arms, and a water closet to 6 feet from its vent.
A common distractor is the IPC or unamended UPC value; in Washington, choose the amended 2015 UPC value.
Numbers by Chapter
Administration and testing (Chapter 1, 609, 712)
- Permit void 180 days after issue if work has not started, or after 180 days of suspension. Renewal within 1 year costs half the fee.
- Inspection notice: 1 working day (105.2.3) or 24 hours (105.2.4). Correction notices must be complied with in 10 days.
- DWV: 10-foot head, 15 minutes, or 5 psi air, 15 minutes. No air on plastic.
- Water: working pressure, 15 minutes, or 50 psi air (not on plastic). Disinfection (Washington): 50 ppm for 24 hours or 200 ppm for 3 hours.
General regulations (Chapter 3)
- Nail plates No. 18 gauge, where pipe is within 1 inch of the framing face, extending 1-1/2 inches past the pipe.
- Backfill in thin layers to 12 inches over the pipe. Thermoplastic sewer bedding 4 inches, with side compaction in 6-inch lifts.
- Hangers: copper 6 ft (1-1/2 inch and smaller) or 10 ft; PVC and ABS 4 ft; PEX 32 in; hubless cast iron at every other joint, or each joint if over 4 feet.
Fixtures (Chapter 4, Washington)
- 15 / 30 / 24 (21) inches for water closets; 12 / 24 inches for urinals.
- Shower 900 sq in plus a 30-inch circle to 70 inches; threshold 2 to 9 inches; liner 3 inches above the dam; pan test filled to the rough threshold.
- Waste outlets: lavatory 1-1/4, tub and sinks 1-1/2, shower and service sink 2 inches.
- Temperature limits: showers 120°F (ASSE 1016), tubs and public lavatories 120°F (ASSE 1070), bidets 110°F.
Water heaters (Chapter 5, 608)
- Washington first hour ratings 42–80 gallons. Straps in the upper and lower thirds, 4 inches from the controls. Garage ignition sources 18 inches up. Pan 1-1/2 inches deep with a 3/4-inch drain.
- Pressure relief setting 150 psi or less. Discharge full size, 6 to 24 inches above grade, not threaded, not into the pan.
Water supply (Chapter 6)
- Copper at least Type L; Type M only aboveground in buildings or underground outside structures. Lead: 0.25% wetted surfaces, 0.2% solder.
- Velocity 8 ft/s cold, 5 ft/s hot. Pressure 15 psi minimum residual, 80 psi maximum static, with 80% of the regulator setting used for sizing.
- Booster cutoff 10 psi, within 5 feet. PEX kept 18 inches from the water heater. Unions within 12 inches of equipment.
Backflow (Chapter 6, Washington, DOH)
- AVB 6 inches, no downstream valve, not over 12 hours of pressure in 24. PVB and SVB 12 inches. RP and DC 12-inch clearance below, with a platform above 5 feet.
- Boilers: air gap or RP; carbonators: RP. Test by a DOH BAT at installation and annually.
- Air gaps 1, 1-1/2, 2 inches, or 2 × D (sidewalls: 1-1/2, 2-1/4, 3 inches, or 3 × D).
Drainage and cleanouts (Chapter 7, Washington)
- Table 703.2: 16/8, 48/35, 256/216. No water closets on 2 inches; 3-inch limits of 4 water closets vertical and 3 horizontal.
- Slope 1/4 inch per foot; 1/8 only for 4-inch and larger with AHJ approval (0.8 factor).
- Cleanouts: at the upper end, every 100 feet, for turns over 135°. Washington clearance 12 or 18 inches, under-floor within 20 feet.
- Ejectors: 20 gpm; a 2-inch ball and 3-inch discharge (single dwelling: 1-1/2-inch ball, 2-inch discharge).
Indirect wastes, vents, and traps (Chapters 8–10)
- Drainage air gap at least 1 inch. Food equipment indirect waste 1 inch minimum, 15 feet maximum. Clothes washer standpipe 18–30 inches, trap 6–18 inches above the floor.
- Vents: individual at least 1-1/4 inches and at least half the drain; 6 inches above the flood rim before turning horizontal; terminal 6 inches above the roof, 10 feet from or 3 feet above openings.
- Trap seal 2–4 inches; trap arms 30/42/60/72/120 inches; water closet 6 feet; tailpiece 24 inches maximum.
Classic Distractors and Why They Are Wrong
| Distractor | Why it is wrong in Washington |
|---|---|
| "UPC Table 422.1 sets the number of fixtures" | Not adopted; Building Code Table 2902.1 applies |
| "Shower minimum 1,024 square inches" | Washington amends it to 900 |
| "Cleanout clearance 18 or 24 inches" | Washington amends it to 12 or 18 |
| "Combustion air 50 cubic feet per 1,000 Btu/h" | UPC 506 is not adopted; the Mechanical Code governs |
| "Gas pipe sizing by longest length" | UPC Chapter 12 is not adopted |
| "Four-inch minimum building sewer in Washington" | Building sewer sections are deleted; there is no such state UPC rule |
| "Hot water is 120°F or more" | Washington defines hot water as 100°F or more |
| "Water test at 100 psi" | The UPC uses working pressure, or 50 psi air |
| "Nail plate 16 gauge within 1-1/4 inches" | The UPC requires 18 gauge within 1 inch |
| "Elevation loss is 0.433 psi per foot" (on Table 610.4 questions) | 610.8 uses 1/2 psi per foot |
| "Lavatory 2 DFU in public use" | Table 702.1 lists 1.0 for a lavatory in all columns |
| "Two flushometer water closets = 80 WSFU" | Table 610.10 gives 70 |
Final Readiness Checklist
| I can… | Section |
|---|---|
| State the exam format, fees, retake rules, and the 90-day certificate deadline | 1.1, 14.1 |
| Recite Table 703.2 with notes, Table 1002.2, and the vent area list from memory | 6.3, 9.2, 8.1 |
| Size every drain and vent on a two-story commercial drawing, including aggregate venting | 11.2, 11.3 |
| Size meter, supply, and branches with Tables 610.3, 610.4, and 610.10 at any pressure | 12.2–12.4 |
| Name each Washington amendment and each non-adopted section | 13.1 |
| Pick the right backflow device for any application, with heights and testing | 5.1–5.4 |
| Apply cleanout, trap, and vent-termination rules to a drawing | 7.1, 9.1, 11.4 |
| Do offset, grade, area, volume, and head calculations | 13.2 |
If any row is uncertain, reread that section and redo its quiz questions before test day.
Which of these statements about testing is correct under the 2015 UPC as adopted in Washington?
DWV piping is tested with at least a 10-foot water head or 5 psi air for 15 minutes, and plastic pipe is not air tested
Shower pans are tested with 2 inches of water for 24 hours
Water supply piping must be tested at 100 psi for 15 minutes
Plastic DWV piping may be tested with 5 psi air
A question asks for the maximum pressure setting of a water heater's pressure relief valve. Which answer is correct under UPC 608.4?
Not more than 150 psi
175 psi
210 psi
125 psi
A practice test answer states that Washington requires a 4-inch minimum building sewer under the UPC. Why is that answer unreliable?
Washington requires a 6-inch minimum
Washington deletes UPC Chapter 7 Part II (Sections 713 through 723), so the state plumbing code sets no building sewer size; the building drain is sized by Table 703.2
The UPC requires 3 inches
Building sewers are sized by Table 610.4
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