- The CO-RP Exam Blueprint
- Domain 1: Water Supply
- Domain 2: Vents
- Domain 3: Fixtures and Equipment
- Domain 4: General Regulations
- Domain 5: Traps
- Domain 6: Sanitary Drainage Systems
- Domain 7: Residential Fire Sprinklers
- Domain 8: Water Heaters
- Exam Day Mechanics That Interact With Content
- Building a Domain-Weighted Study Schedule
- Who Hires Around This Scope
- FAQs
- Vents and Sanitary Drainage Systems each carry 21 of 100 scored questions - the two heaviest domains.
- Water Supply follows close behind at 18 questions; together the top three domains are more than half the exam.
- Residential Fire Sprinklers is the lightest domain at just 4 questions, so budget study time accordingly.
- You need 70 of 100 scored questions correct to pass; the 10 unscored pilot items don't count either way.
The CO-RP Exam Blueprint
The Colorado Residential Plumber License Exam (CO-RP) is a computer-based, multiple-choice test administered by PSI Services LLC under the authority of the Colorado State Plumbing Board and the Colorado Department of Regulatory Agencies (DORA). Candidates get 240 minutes to answer 100 scored questions, and PSI may slip in up to 10 additional unscored questions with 30 extra minutes tacked on for that purpose. Those pilot questions look identical to scored ones, so there's no reliable way to skip them - the only sound strategy is to treat every question on screen as if it counts.
What actually separates a comfortable pass from a stressful retake is understanding how the 100 scored questions are distributed across eight content domains. The blueprint is not evenly weighted. Two domains - Vents and Sanitary Drainage Systems - tie for the largest share at 21 questions apiece, while Residential Fire Sprinklers accounts for a mere 4. That's a massive gap in emphasis, and it should directly shape how you allocate study hours. For a broader look at how difficulty stacks up across the whole exam, see How Hard Is the CO-RP Exam? Complete Difficulty Guide 2026.
| Domain | Scored Questions | Share of 100 |
|---|---|---|
| 1. Water Supply | 18 | 18% |
| 2. Vents | 21 | 21% |
| 3. Fixtures and Equipment | 12 | 12% |
| 4. General Regulations | 11 | 11% |
| 5. Traps | 5 | 5% |
| 6. Sanitary Drainage Systems | 21 | 21% |
| 7. Residential Fire Sprinklers | 4 | 4% |
| 8. Water Heaters | 8 | 8% |
Domain 1: Water Supply
Water Supply - 18 scored questions
This domain covers the systems that bring potable water into a one- to four-family dwelling and distribute it safely to fixtures. Expect questions on pipe sizing logic, water distribution layout, backflow prevention concepts, and material compatibility rules drawn from the 2021 International Plumbing Code (IPC) and 2021 International Residential Code (IRC).
- Supply pipe sizing and fixture unit relationships
- Backflow prevention and cross-connection control
- Water service and distribution system requirements
- Material and installation standards for supply piping
Because Water Supply is the third-largest domain, it deserves dedicated study blocks rather than a quick review pass. Candidates who treat this domain as an afterthought commonly find themselves guessing on sizing-table questions during the actual exam.
Domain 2: Vents
Vents - 21 scored questions
Tied for the heaviest domain on the exam, Vents tests your understanding of how drainage systems stay properly aired to prevent trap seal loss and sewer gas intrusion. Expect scenario-based questions requiring you to identify correct vent type, sizing, and connection points for residential configurations.
- Vent sizing based on fixture unit load and pipe diameter
- Individual, common, wet, and circuit venting configurations
- Vent termination location and distance requirements
- Relief and re-vent requirements for island fixtures and complex layouts
Key Takeaway
Since Vents and Sanitary Drainage Systems together make up 42 of the 100 scored questions, mastering how venting and drainage interact - not just each topic in isolation - is the single highest-leverage study activity for the CO-RP exam.
Domain 3: Fixtures and Equipment
Fixtures and Equipment - 12 scored questions
This domain focuses on the installation, clearance, and connection requirements for residential plumbing fixtures - sinks, tubs, toilets, showers, and related equipment - as governed by the IPC and IRC.
- Minimum clearance and access requirements around fixtures
- Fixture connection and support requirements
- Accessibility and required fixture counts for dwelling units
- Equipment installation standards tied to manufacturer and code specifications
Domain 4: General Regulations
General Regulations - 11 scored questions
General Regulations covers the administrative and code-application rules that frame every other domain - permitting concepts, inspection requirements, and the scope limitations that define what a residential license actually covers.
- Scope of work permitted under a residential plumber license
- Code application hierarchy between the IPC and IRC
- Inspection and approval process concepts
- General safety and workmanship provisions
Remember that the residential scope itself is legally bounded: a residential license covers one- through four-family dwellings no more than two stories aboveground, and plumbing contractor registration is a separate credential. Questions in this domain frequently test whether you understand where that boundary sits. For the full eligibility picture before you even sit for the exam, see CO-RP Requirements 2026: Eligibility, Prerequisites & How to Qualify.
Domain 5: Traps
Traps - 5 scored questions
Traps is one of the lightest domains, but don't dismiss it entirely - its 5 questions are still worth studying since trap-seal and sizing logic connects directly to the much larger Vents and Sanitary Drainage Systems domains.
- Trap seal depth and protection requirements
- Prohibited trap types and double-trapping rules
- Trap sizing relative to the fixture it serves
Domain 6: Sanitary Drainage Systems
Sanitary Drainage Systems - 21 scored questions
Tied with Vents as the largest domain, Sanitary Drainage Systems tests how waste and drainage piping is sized, sloped, and connected throughout a residential structure.
- Drainage fixture unit values and pipe sizing tables
- Slope and grade requirements for horizontal drainage piping
- Cleanout placement and spacing requirements
- Building drain and building sewer connection requirements
Domain 7: Residential Fire Sprinklers
Residential Fire Sprinklers - 4 scored questions
The smallest domain on the exam, Residential Fire Sprinklers still requires familiarity with basic residential sprinkler system concepts as they apply within the scope of a one- to four-family dwelling.
- General residential sprinkler system components
- Coordination points between sprinkler and domestic water piping
- Basic code-reference awareness for residential fire protection
Because this domain carries so little weight, spending more than a light review session here is usually inefficient - that time is better redirected toward Vents or Sanitary Drainage Systems.
Domain 8: Water Heaters
Water Heaters - 8 scored questions
This domain covers installation, venting, and safety-device requirements for residential water heating equipment.
- Temperature and pressure relief valve requirements
- Combustion air and venting requirements for fuel-fired units
- Seismic and support strapping requirements
- Pan and drainage requirements for water heater installations
Exam Day Mechanics That Interact With Content
Understanding the domains is only half the picture - knowing how the exam is administered changes how you prepare for them. The CO-RP is a closed-book exam in the sense that you cannot bring your own references: the test center supplies the code books, and writing, highlighting, underlining, or indexing in those supplied books is strictly prohibited. That means any tabbing or annotation strategy you'd use with a personal code book is off the table on exam day - you need to already know your way around the 2021 IPC and 2021 IRC structure before you sit down.
An onscreen calculator is available for domains like Water Supply and Sanitary Drainage Systems where sizing math comes up, but formulas are not supplied and you may not bring additional reference material of any kind. Practicing pipe-sizing and fixture-unit calculations by hand - without a formula sheet - before test day is essential.
It's also worth noting that Colorado amendments to the plumbing code are not tested - the PSI bulletin bases the exam strictly on the 2021 IPC and 2021 IRC. Candidates who study a state-specific amendment guide instead of the base codes sometimes waste preparation time on material that won't appear on the exam.
Building a Domain-Weighted Study Schedule
A generic study calendar treats every topic equally. That approach doesn't work well for the CO-RP because the domain weights are so lopsided - 21 questions on Vents deserves far more attention than 4 questions on Residential Fire Sprinklers. Instead, build your schedule around the actual point value of each domain, and use spaced repetition only within that weighted structure, not as a substitute for it.
Vents and Sanitary Drainage Systems (42 combined questions)
- Work through vent sizing tables and drainage fixture unit charts side by side
- Drill cleanout placement and vent termination scenarios daily
Water Supply (18 questions)
- Practice supply pipe sizing without a formula sheet, using the onscreen-calculator style you'll have on test day
- Review backflow prevention device categories
Fixtures and Equipment, General Regulations (23 combined questions)
- Study fixture clearance tables and required fixture counts
- Reinforce the residential license scope boundaries
Water Heaters, Traps, Residential Fire Sprinklers (17 combined questions)
- Cover relief valve and venting rules for water heaters
- Finish with a light review of trap seal depth and sprinkler basics
- Run a full-length timed practice exam under 240-minute conditions
For a more detailed week-by-week methodology and additional practice-question strategy, see CO-RP Study Guide 2026: How to Pass on Your First Attempt. If you want a compact reference to keep nearby during final review, the CO-RP Cheat Sheet 2026: One-Page Review of Must-Know Facts condenses the highest-weight domains into a single page. You can also run through full-length simulated exams on our practice test platform to see how these domain weights feel under real time pressure.
Who Hires Around This Scope
Because the residential license scope is capped at one- through four-family dwellings no more than two stories aboveground, employers hiring CO-RP-licensed plumbers are typically residential service companies, new-home builders, and remodeling contractors rather than large commercial mechanical firms. Passing the exam is the technical gate, but DORA also requires 3,400 hours of verified practical plumbing experience - verified by a master plumber or registered plumbing contractor, never self-verified - before a license application can move forward. If you're still assembling those hours or wondering whether the credential pays off relative to the effort, Is the CO-RP Certification Worth It? Complete ROI Analysis 2026 and CO-RP Salary Guide 2026: Complete Earnings Analysis walk through the broader career picture.
Once licensed, staying active requires eight hours of continuing education every 12 months (after a first-renewal exemption), including at least four code hours and no more than two safety hours per 24 months, plus an attestation that you've read the current Colorado Plumbing Code. Keep those CE records for six years - DORA can request them.
FAQs
Vents and Sanitary Drainage Systems are tied for the largest domain, each contributing 21 of the 100 scored questions - 42% of the exam combined.
Residential Fire Sprinklers is the smallest domain, worth only 4 scored questions, followed by Traps at 5.
No. The PSI bulletin lists the 2021 International Plumbing Code and 2021 International Residential Code as the examination references, and Colorado amendments are not tested.
No. The test center supplies the code books, and personal references along with writing, highlighting, underlining, or indexing in the supplied books are prohibited.
You need 70% of the scored questions correct, which is 70 of the 100 scored items on the CO-RP exam. Unscored pilot questions do not count toward this total.
For details on scheduling, retest windows, and deadlines around the exam itself, visit CO-RP Exam Dates 2026: Testing Windows, Deadlines & Scheduling, and if you want to gauge where you currently stand against these domain weights, try a full simulated run on our CO-RP practice exam platform before you commit to a test date.