- The trade exam has 101 questions (100 scored) in 240 minutes; Business and Law has 55 questions (50 scored) in 120 minutes.
- Passing score is 70% on each part; testing fees total $138 for the standard trade-plus-Business-and-Law route.
- Drainage, Waste, and Sanitary Vents alone is 24% of scored trade content - the single biggest domain.
- A failed portion means a 60-day wait before you can retest that section.
Fees & Fast Facts
If you need the numbers in one place before test day, here they are. The Ohio Construction Industry Licensing Board (OCILB), under the Ohio Department of Commerce's Division of Industrial Compliance, sets application and licensing requirements, while PSI actually administers the Plumbing Contractor examination. Keeping these two entities straight matters because fees flow through both channels.
- Certifying/administering bodies: OCILB (Ohio Department of Commerce) sets policy; PSI delivers the computer-based test.
- Application fee: $25 to the Board.
- License issuance fee: $25 to the Board.
- Exam registration: $69 per attempt through PSI.
- Standard combined testing cost: $138 (trade exam + Business and Law).
- Renewal: $60 annually with 10 continuing education hours.
For a deeper look at what these numbers mean for your budget and timeline, the OH-PLB Requirements guide lays out every prerequisite step alongside the associated costs.
Exam Format at a Glance
OH-PLB testing happens at PSI test centers on computer, using multiple-choice questions. It is open-book, but only in the sense that you may bring approved trade references - there is no internet access, and only the onscreen calculator PSI provides is permitted during testing.
| Exam Part | Total Questions | Scored Items | Time Allowed | Passing Score |
|---|---|---|---|---|
| Plumbing Trade Exam | 101 | 100 (1 unscored pretest) | 240 minutes | 70% |
| Business and Law Exam | 55 | 50 (5 unscored) | 120 minutes | 70% |
Notice the pretest item on the trade exam and the five unscored items on Business and Law - you won't know which questions those are, so treat every item as scored. For a detailed explanation of how the 70% threshold is calculated and what it means practically, see the OH-PLB Passing Score guide.
Key Takeaway
Budget your 240 minutes across roughly 100 scored trade questions - that's a little under two and a half minutes per question, but domains like Isometric Analysis often take longer per item than General Knowledge questions.
Domain Breakdown (100 Scored Items)
PSI's official allocation splits the 100 scored trade items across nine domains. Three of them - Drainage, Waste, and Sanitary Vents; General Regulations; and Isometric Analysis - combine for 64% of the scored trade exam. If you only have time to master three domains cold, these are the ones.
Domain 5: Drainage, Waste, and Sanitary Vents (24%)
The largest single domain. Expect questions on pipe sizing, trap arrangements, vent configurations, and drainage fixture unit calculations tied to the Ohio Plumbing Code.
- Master fixture unit tables and minimum pipe diameters
- Know vent types and when each is required
Domain 2: General Regulations (20%)
Covers code administration, permitting concepts, and general regulatory provisions found throughout the Ohio Plumbing Code.
- Understand code enforcement scope and definitions
- Review inspection and approval sequencing
Domain 9: Isometric Analysis (20%)
Tests your ability to read and interpret isometric drawings of plumbing systems - a skill that rewards practice with diagrams, not just text memorization.
- Practice tracing DWV and water supply runs on isometric sketches
- Identify code violations visually, not just numerically
Domain 4: Water Supply Systems (10%)
Sizing, materials, and layout principles for potable water distribution.
- Know pipe sizing methods and water demand calculations
- Understand backflow prevention basics
Domain 1: General Knowledge (8%)
Foundational terminology and broad plumbing concepts that underpin the more specialized domains.
- Solidify terminology before tackling denser domains
Domain 3: Plumbing Fixtures (6%)
Fixture requirements, minimum clearances, and fixture-specific code provisions.
- Review minimum fixture counts by occupancy type
Domain 8: Specialty Plumbing (5%)
Covers less-common systems and applications outside standard residential/commercial installs.
- Skim specialty system sections in the code rather than deep-diving
Domain 7: Roof Drain Piping (4%)
Sizing and layout rules for roof drainage systems.
- Know roof drain sizing tables tied to roof area
Domain 6: Indirect Wastes (3%)
The smallest domain but still worth a quick review of indirect waste receptor requirements.
- Learn when indirect waste connections are mandatory
For narrative walkthroughs of each domain with more context on question style, the OH-PLB Exam Domains guide expands on every one of these nine areas. If you're still gauging overall difficulty before committing to a study plan, How Hard Is the OH-PLB Exam? is a useful companion read.
Approved References & Testing Rules
The current PSI bulletin (cover revision dated February 7, 2024) names the specific references you're permitted to use at the test center for the trade exam:
- Ohio Plumbing Code (2024)
- International Fuel Gas Code (2024)
- Mathematics for Plumbers and Pipefitters, 8th edition (2013)
- Modern Plumbing, 9th edition (2022)
For the Business and Law exam, the center provides the Ohio NASCLA Contractors Guide to Business, Law and Project Management, 4th edition - and this copy must not be marked in any way.
This is one of the most concrete, exam-specific mechanics candidates overlook. Spend an evening tabbing your Ohio Plumbing Code and Mathematics for Plumbers and Pipefitters by topic - matched to the domain weights above - before you ever sit for the exam. The OH-PLB Study Guide walks through a tabbing strategy in more detail.
Eligibility Snapshot
Before you're authorized to test, OCILB has to approve your application, and that approval depends on meeting age, status, and experience thresholds.
- Minimum age 18, with required U.S. citizenship or legal-status documentation.
- Standard route: five years of trade experience immediately preceding application, five consecutive years of tax records, plus one accepted supporting document - qualifying permits, an active journeyman card, an approved apprenticeship certificate, or 40 nonduplicated hours of approved trade-code education.
- Engineer route: Ohio-registered professional engineer with three years of relevant construction-business experience.
- Inspector route: five years as an Ohio government inspector in the trade.
Key Takeaway
The 40-hour education option is supporting evidence for the standard route - it does not replace the five years of trade experience or substitute for the other three routes. Confirm your specific path on the OH-PLB Requirements page before you apply.
Once approved, applicants still go through state and federal background checks. Your examination authorization then expires one year after the completed criminal-records check is received, so don't apply for approval and then sit on it - schedule promptly.
Retakes, Authorization Windows & Renewal
A few timeline rules are easy to miss but can derail a candidate who isn't tracking them:
- Fail a portion? You must wait 60 days before retesting that section.
- Five failed attempts without passing means you must reapply under Ohio Revised Code 4740.06 - essentially starting the process over.
- Your exam authorization is tied to your background check and lapses one year after that check is received.
- Pass Business and Law but not the trade exam? That Business and Law pass can count toward another approved trade exam for three years from license issuance - useful if you're pursuing more than one trade credential.
After licensure, you'll need at least $500,000 in contractor liability coverage and assignment to a contracting company to activate the license. Renewal runs $60 annually with 10 approved CE hours, though licensees who qualify for the Compliant Contractor Program (after one year of demonstrated compliance) get flexible options: $60/year with 8 CE hours, or $180 every three years with 24 CE hours. These renewal mechanics and the CE math are broken down further in the certification cost article.
Last-Mile Review Schedule
In the final weeks before your test date, structure review sessions around domain weight rather than alphabetical order or textbook sequence. This isn't a generic study calendar - it's built specifically around the 100-item scored allocation.
Drainage, Waste, and Sanitary Vents + Isometric Analysis
- Work fixture-unit and vent-sizing problems from the Ohio Plumbing Code
- Practice reading isometric drawings for DWV runs
General Regulations + Water Supply Systems
- Review code administration sections and permitting language
- Drill water demand and pipe sizing calculations
General Knowledge, Plumbing Fixtures, Specialty Plumbing, Roof Drain Piping, Indirect Wastes
- Sweep the five smaller domains together - together they're still 26% of the exam
- Finish tabbing your approved references by domain
Business and Law + Full Timed Practice
- Study the Ohio NASCLA Contractors Guide topics without marking your own notes into it
- Run full 240-minute and 120-minute timed practice sessions
Running realistic timed sessions on our OH-PLB practice test platform before test day helps you calibrate pacing against the real 240-minute and 120-minute limits, rather than guessing how far 100 questions will actually take you.
How to Actually Use This Page
Print this article or keep it open on a second screen during your final review pass. It's designed to answer the "wait, what was the fee again?" and "which domain was biggest?" questions that pop up in the last 48 hours before your exam - not to replace deep study.
If you're earlier in the process and still deciding whether this credential fits your career plans, the ROI analysis and salary guide cover the bigger-picture questions. And if you're simply trying to confirm scheduling logistics, OH-PLB Exam Dates covers testing windows and deadlines in detail.
For candidates who want a broader orientation before diving into domain-level prep, start with What Is OH-PLB? or run a few sample questions on the main practice test site to see where your baseline knowledge stands.
FAQ
The trade exam has 101 total questions - 100 scored plus one unscored pretest item - with 240 minutes to complete it. A 70% score on the scored items is required to pass.
PSI charges $69 per exam registration. Taking both the trade exam and the Business and Law exam brings total testing fees to $138, separate from the Board's $25 application fee and $25 license issuance fee.
No. You may highlight, underline, and index your approved trade references in advance, but written notes and any loose or attached papers are prohibited at the test center.
You must wait 60 days before retesting that portion. If you haven't passed after five total attempts, you're required to reapply under Ohio Revised Code 4740.06.
Focus first on Drainage, Waste, and Sanitary Vents (24%), General Regulations (20%), and Isometric Analysis (20%). Together these three domains make up 64% of the scored trade exam.