- Overview: How the 13 Content Areas Fit Together
- Domain 1: Drainage Waste and Vents
- Domain 2: Indirect Waste
- Domain 3: Water Supply Systems
- Domain 4: Backflow Prevention
- Domain 5: Roof Drains and Storm Drainage Systems
- Domain 6: Plumbing Fixtures
- Domain 7: General Knowledge
- Domain 8: Specialty Plumbing, Interceptors, and Traps
- Domain 9: Fuel Gas
- Domain 10: Septic and Sewer
- Domain 11: Hydronics
- Domain 12: Fire Sprinklers
- Domain 13: Excavation
- How Domain Weight Should Shape Your Prep Time
- FAQ
- The C-37/CR-37 trade outline covers 13 content areas across 100 scored questions in 240 minutes.
- Drainage Waste and Vents is the largest domain - prioritize it in your study schedule.
- The exam is open book with approved references including the 2018 IPC, IMC, IFGC, and specific NFPA standards.
- Passing requires 70%; PSI may add 5-10 unscored experimental items within the same time limit.
Overview: How the 13 Content Areas Fit Together
The Arizona Registrar of Contractors, through PSI, structures the C-37/CR-37 Plumbing trade examination around 13 distinct content areas. Each domain represents a body of code knowledge and field practice that a qualifying party is expected to have mastered before holding a license. Unlike a generic trades quiz, this exam pulls directly from the plumbing, mechanical, and fuel gas codes adopted in Arizona, plus specific NFPA fire protection standards and OSHA excavation safety rules.
If you're just starting your prep, it helps to first understand what AZ-PLB certification actually involves and how the trade exam relates to the separate Statutes and Rules Exam. This guide breaks down every domain so you know exactly what to study and in what order.
Domain 1: Drainage Waste and Vents
Drainage Waste and Vents (DWV)
This is the largest domain on the exam, and it deserves the largest share of your study hours. DWV questions test your ability to size drain, waste, and vent piping; determine fixture unit loads; apply venting methods (wet vents, common vents, circuit vents, air admittance valves); and identify slope, cleanout, and trap arm requirements under the 2018 IPC.
- Fixture unit calculations and pipe sizing tables
- Vent stack, stack vent, and relief vent distinctions
- Cleanout placement and access requirements
- Horizontal and vertical drainage pipe sizing limits
Because DWV touches nearly every other system on the exam, mastering it first gives you a foundation for interpreting related questions in Indirect Waste and Specialty Plumbing.
Domain 2: Indirect Waste
Indirect Waste
This domain covers waste piping that must discharge indirectly into the drainage system rather than connecting directly - think food service equipment, ice makers, and certain mechanical condensate lines.
- When indirect waste receptors are required
- Air gap and air break distinctions
- Special waste piping materials for chemical or acidic waste
Indirect Waste is a smaller domain in scope but shows up in commercial kitchen and mechanical room scenarios that overlap with the Plumbing Fixtures domain.
Domain 3: Water Supply Systems
Water Supply Systems
Water supply questions test pipe sizing methods, water hammer control, pressure loss calculations, and material selection for potable water distribution under the adopted plumbing code.
- Demand-based sizing using fixture units
- Water hammer arrestor placement
- Approved piping materials and joining methods
- Minimum pressure and flow requirements
Domain 4: Backflow Prevention
Backflow Prevention
Cross-connection control is a heavily code-driven topic. Expect questions on device selection based on hazard level, testable versus non-testable assemblies, and installation clearances.
- Backflow preventer types and where each is required
- Air gap sizing for various fixture categories
- Cross-connection hazard classification
Domain 5: Roof Drains and Storm Drainage Systems
Roof Drains and Storm Drainage Systems
This domain focuses on sizing storm drainage piping, roof drain placement, and secondary (overflow) drainage requirements - critical in Arizona's monsoon-driven rainfall design considerations.
- Roof drain sizing based on drainage area and rainfall rate
- Primary vs. secondary (overflow) drain requirements
- Combined vs. separate storm and sanitary systems
Domain 6: Plumbing Fixtures
Plumbing Fixtures (including water heaters and accessibility)
This domain is broad - it spans fixture connections, minimum fixture counts for occupancy types, water heater installation and venting, and accessibility clearances for fixtures under the applicable code sections.
- Minimum fixture counts by occupancy classification
- Water heater relief valve and venting requirements
- Accessible fixture clearance and mounting height rules
- Fixture trap and connection requirements
Domain 7: General Knowledge
General Knowledge
This domain tests broader trade knowledge that doesn't fit neatly into a single system - administrative code provisions, general definitions, materials standards, and inspection/testing procedures that apply across multiple plumbing systems.
- Code definitions and administrative provisions
- General testing and inspection procedures
- Materials approval and listing standards
Domain 8: Specialty Plumbing, Interceptors, and Traps
Specialty Plumbing, Interceptors, and Traps
Grease interceptors, oil separators, and specialty trap configurations live here. Expect scenario questions about sizing interceptors for commercial kitchens and selecting the correct trap type for unusual fixture arrangements.
- Grease interceptor and grease trap sizing
- Oil and sand interceptor requirements
- Trap seal protection and prohibited trap types
Domain 9: Fuel Gas
Fuel Gas
Fuel Gas questions draw from the 2018 IFGC and test gas pipe sizing, appliance venting, shutoff valve placement, and clearance requirements for gas-fired equipment.
- Gas pipe sizing based on demand and length
- Appliance connector and shutoff valve requirements
- Venting categories for gas appliances
Domain 10: Septic and Sewer
Septic and Sewer
Arizona's onsite-wastewater rules are part of the approved reference list, and this domain draws directly from them. Expect questions on building sewer sizing, septic system components, and connection requirements to public or private sewer systems.
- Building sewer material and slope requirements
- Onsite wastewater (septic) system components
- Connection requirements per Arizona onsite-wastewater rules
Domain 11: Hydronics
Hydronics
Hydronic piping systems - used for heating and cooling water circulation - are tested under the adopted mechanical code. Questions typically involve piping materials, expansion, and safety controls for closed hydronic loops.
- Hydronic piping material and pressure ratings
- Expansion tank sizing and placement
- Relief valve and safety control requirements
Domain 12: Fire Sprinklers
Fire Sprinklers
This domain pulls from NFPA 13 (2016), NFPA 13D (2007), and NFPA 13R (2007) - three distinct standards covering commercial, one- and two-family dwelling, and residential occupancy sprinkler systems respectively. Know which standard applies to which building type.
- Differences between NFPA 13, 13D, and 13R applicability
- Sprinkler system water supply and piping basics
- Occupancy classification impact on system design
Domain 13: Excavation
Excavation
Excavation questions are grounded in OSHA 1926 safety requirements as applied to trenching for plumbing installations - shoring, sloping, and trench safety fundamentals.
- Trench shoring and sloping requirements
- Excavation safety and protective system selection
- Underground utility protection during trenching
How Domain Weight Should Shape Your Prep Time
With 13 domains compressed into 100 scored questions, not every content area carries equal weight. Drainage Waste and Vents is explicitly the largest domain, which means it warrants disproportionate study time relative to narrower domains like Indirect Waste or Excavation. That doesn't mean you can skip the smaller domains - a single missed question in Fire Sprinklers counts the same as one in DWV - but your study calendar should reflect where the volume of questions is likely concentrated.
Foundation Domains
- Drainage Waste and Vents (largest domain - start here)
- Water Supply Systems
- Plumbing Fixtures
Code-Heavy Systems
- Fuel Gas
- Backflow Prevention
- Roof Drains and Storm Drainage Systems
Specialty and Support Systems
- Specialty Plumbing, Interceptors, and Traps
- Indirect Waste
- Hydronics
- Septic and Sewer
Standards-Based Domains and Review
- Fire Sprinklers (NFPA 13/13D/13R distinctions)
- Excavation (OSHA 1926)
- General Knowledge
- Full open-book timed practice run
For a fuller breakdown of pacing and reference-tabbing strategy, see the AZ-PLB Study Guide 2026. And if you're still weighing whether the license is right for your career path, the ROI analysis on AZ-PLB certification covers that in depth.
Key Takeaway
Study Drainage Waste and Vents first and most thoroughly since it's the largest domain, then move through code-heavy domains like Fuel Gas and Backflow Prevention before tackling the standards-specific Fire Sprinklers content.
Registration and Exam-Day Mechanics You Need to Know
Beyond content, the AZ-PLB trade exam has specific logistics that affect how you prepare. The trade fee is $66 per attempt, separate from the $61 Statutes and Rules Exam (SRE) delivered online through GMetrix. You can test at a PSI test center or through remote proctoring, but the rules differ: test centers allow a basic silent, nonprinting, nonprogrammable, nonscientific calculator, while remote sessions prohibit scratch paper and breaks entirely.
Your references - the 2018 IPC, IMC, and IFGC, NFPA 13 (2016), NFPA 13D (2007), NFPA 13R (2007), OSHA 1926, and the listed Arizona onsite-wastewater rules - can carry pre-existing notes, highlighting, and permanent tabs. Loose papers and writing in the books during the exam itself are not allowed. If you fail, retake waits are 30 days, extending to 90 days after three failed attempts, so treat each attempt seriously.
For the exact fee structure across both exams, review the AZ-PLB Certification Cost breakdown, and check current exam dates and scheduling windows before locking in a test day.
| Exam Detail | Specification |
|---|---|
| Scored Questions | 100 |
| Unscored Experimental Questions | 5-10 (same time allowance) |
| Time Allowed | 240 minutes |
| Passing Score | 70% |
| Trade Exam Fee | $66 per attempt |
| Format | Computer-based multiple choice, open book |
| Content Areas | 13 domains |
Who Actually Needs to Master All 13 Domains
The C-37/CR-37 exam is taken by qualifying parties for plumbing contracting businesses in Arizona. C-37 covers commercial plumbing work; CR-37 is the dual commercial/residential classification, meaning CR-37 candidates need working knowledge across residential and commercial applications within these same 13 domains. The separate R-37R exam covers residential-only work and isn't the focus of this outline.
Employers hiring for supervisory or qualifying-party roles typically expect candidates to already have four years of practical or management trade experience, including two within the preceding ten years, with qualifying technical education able to substitute for up to two of those years. If you're mapping out whether you meet these thresholds, the AZ-PLB Requirements guide details eligibility in full, and AZ-PLB Jobs outlines where licensed contractors typically find work across residential and commercial plumbing sectors.
Turning Domain Knowledge Into Exam-Day Confidence
Reading code sections is necessary but not sufficient. Because the exam mixes questions from all 13 domains in a single continuous session, you need practice that simulates that unpredictability rather than studying one domain in isolation and moving on permanently. Rotate practice questions across domains you've already covered so DWV concepts stay fresh even while you're deep into Fuel Gas or Hydronics material.
Working through realistic practice questions on our AZ-PLB practice test platform lets you drill each of these 13 domains individually or in mixed sets that mirror actual exam conditions. If you want a deeper look at how difficult the exam tends to feel across domains, the AZ-PLB difficulty guide breaks down where most candidates report the most friction, and the passing score explainer clarifies exactly what 70% means in practice.
Before test day, run through a condensed reference like the AZ-PLB Cheat Sheet to confirm you haven't overlooked a smaller domain like Indirect Waste or Excavation in favor of the bigger ones.
Frequently Asked Questions
Start with Drainage Waste and Vents since it's explicitly the largest domain on the exam. Building that foundation also makes related domains like Indirect Waste and Specialty Plumbing easier to understand.
No. Drainage Waste and Vents is confirmed as the largest domain, meaning it likely generates more scored questions than smaller domains like Indirect Waste or Excavation, even though every domain contributes to the 100 scored questions.
Yes. CR-37 is the dual commercial/residential classification, so candidates should be comfortable applying these 13 domains to both commercial and residential scenarios, unlike C-37, which is commercial only.
Pre-existing notes, highlighting, and permanent tabs in your approved references are permitted. However, you cannot bring extra loose papers or write in the references during the exam itself.
Fire Sprinklers draws from three distinct NFPA standards - NFPA 13 (2016) for commercial systems, NFPA 13D (2007) for one- and two-family dwellings, and NFPA 13R (2007) for residential occupancies - so you need to know which standard applies to which building type.