Complete Strategic Guide: Obtaining the RBQ 15.5 Licence – Owner-Builder for Plumbing

1. What Is the RBQ 15.5 Licence and Who Needs It?

The RBQ 15.5 licence — Owner-Builder for Plumbing (Constructeur-propriétaire en plomberie) — is a specialized licence issued by the Régie du bâtiment du Québec (RBQ) for contractors who install, maintain and modify plumbing systems. It authorizes construction work reserved exclusively to master pipe mechanics involving:

• Hot and cold water supply distribution — piping from the water service entrance to every fixture in the building;
• Sanitary drainage — soil, waste and vent piping that carries used water and sewage to the building drain;
• Trap venting — vent piping that protects trap water seals from siphonage and back-pressure;
• Stormwater drainage — piping that collects and conveys rainwater from roof drains and leaders to the storm sewer;
• Gas piping — installation, pressure regulation and testing of gas supply piping per CAN/CSA-B149.1;
• Plumbing fixtures and appliances — installation, connection and testing of all plumbing fixtures.

With 107 skills across 4 modules and 16 competency elements, the RBQ 15.5 is one of the most comprehensive plumbing exams in the RBQ system. Module 4 alone accounts for 68 of the 107 skills (64%), reflecting the depth of practical installation knowledge required across water supply, drainage, venting, stormwater and gas systems.

2. Scope of the Licence: Complete Plumbing Systems

The RBQ 15.5 covers the installation, modification and repair of complete plumbing systems — from the water service connection at the property line to every fixture outlet, and from every fixture drain back to the building sewer. What makes this licence unique within category 15 is that it addresses both the supply side (pressurized water distribution) and the drainage side (gravity-flow waste and vent systems), requiring candidates to master two fundamentally different hydraulic principles.

The plumbing system is a complete cycle: water service (connection to the municipal water main, water meter, backflow prevention), water distribution (hot and cold water piping sized by fixture supply units, water heater connections, pressure regulation), drainage (fixture traps, branch drains, soil stacks, waste stacks, building drain — all sized by drainage fixture units), venting (individual vents, wet vents, stack vents, vent stacks, air admittance valves — all protecting trap seals), stormwater (roof drains, leaders, storm building drain — sized by roof area and rainfall intensity), and gas piping (sizing, pressure testing and connection to gas-fired water heaters and appliances per CAN/CSA-B149.1).

A distinctive feature of the RBQ 15.5 is the calculation intensity — candidates must size piping for multiple systems using different methodologies: fixture supply units for water supply, drainage fixture units for waste piping, minimum vent diameters based on trap size and developed length, and roof area with rainfall intensity for stormwater. Each system has its own sizing tables in the National Plumbing Code.

3. RBQ Exam Format: What to Expect

• Question type: Multiple choice (MCQ)
• Duration: 3 hours (180 minutes)
• Passing grade: 60%
• Languages: French or English
• Skills assessed: 107 skills across 16 competency elements
• Exam type: Mixed (2 open-book documents + 3 closed-book documents)
• Tools provided: Calculator, ruler, paper and pencil

With 107 skills and only 2 open-book documents, the RBQ 15.5 requires extensive memorization. The two provided codes — the Quebec Construction Code Chapter III and the National Plumbing Code — contain the sizing tables you will need, but the calculation methods from Bolduc and the CMMTQ diagrams must be known from memory.

4. Exam Documentation: Open Book vs. Closed Book

The RBQ 15.5 exam is a mixed exam with 2 documents provided (open book) and 3 to memorize (closed book) — 5 documents total.

Documents PROVIDED During the Exam (Open Book)

• Quebec Construction Code, Chapter III — Plumbing (R.S.Q., c. B-1.1, r.0.01.01) — The Quebec-specific plumbing code containing all provincial amendments to the National Plumbing Code, including pipe sizing tables, fixture unit tables and installation requirements.
• National Plumbing Code — Canada 2015 (modified) — The federal plumbing code as adopted and modified by Quebec, providing the complete normative framework for water supply, drainage, venting and stormwater systems.

Documents to MEMORIZE (Closed Book)

• Building Act (R.S.Q., c. B-1.1) — The foundational statute governing construction, safety, and contractor qualifications in Quebec.
• Explanatory Diagrams — Plumbing (CMMTQ, 2021 Edition) — The CMMTQ publication containing schematic diagrams that illustrate plumbing system configurations, venting arrangements and code-compliant installation details.
• Drainage and Potable Water Supply for Buildings by Michel Bolduc — The comprehensive reference covering drainage and water supply system design, calculation methods, pipe sizing procedures and installation practices for Quebec buildings.

5. The 4 Training and Competency Modules

Module 1 — Definitions and Types of Systems (16 skills)

Covers the foundational knowledge of plumbing systems: types of water supply networks (direct, gravity, pressurized), types of drainage systems (sanitary, stormwater, combined), types of venting systems (individual, wet, circuit, stack, air admittance valves), types of piping materials (copper, PVC, ABS, cast iron, PEX — each with specific applications and joining methods), types of plumbing fixtures (sinks, lavatories, water closets, bathtubs, showers, floor drains — each with specific trap sizes and fixture unit values), and types of water heaters (storage, tankless, indirect). Also covers basic hydraulic principles: pressure, flow rate, head loss in supply systems and gravity flow in drainage systems.

Module 2 — Legislative, Normative and Regulatory Framework (15 skills)

Covers the regulatory framework for plumbing: the Building Act, the Quebec Construction Code Chapter III — Plumbing, the National Plumbing Code — Canada 2015, the Master Pipe Mechanics Act, CAN/CSA-B149.1 for gas piping, the Safety Code, and the Occupational Health and Safety Act. This module tests the candidate's understanding of the hierarchy of legislation and codes, jurisdictional responsibilities, permit requirements, and the roles of the CMMTQ (Corporation des maîtres mécaniciens en tuyauterie du Québec) and the RBQ.

Module 3 — Plan and Specification Reading (8 skills)

Covers the ability to read and interpret plumbing plans and specifications: floor plans showing piping layouts and fixture locations, riser diagrams showing vertical drainage and vent stacks, isometric drawings of plumbing systems, plumbing symbols and abbreviations, fixture schedules, pipe size annotations, and the National Master Specification (section 01550). This module tests the candidate's ability to extract installation requirements from architectural and mechanical drawings and to perform quantity surveys for plumbing materials.

Module 4 — Standards and Work Execution (68 skills, 64%)

The most heavily weighted module on the exam. This module covers the full plumbing installation workflow: project planning and coordination, water service connection and meter installation, hot and cold water distribution piping (sizing by fixture supply units, materials, supports, thermal expansion), sanitary drainage piping (sizing by drainage fixture units, trap installation, cleanouts, grade requirements), trap venting systems (individual vents, wet vents, stack vents, vent sizing, developed length calculations), stormwater drainage (roof drains, leaders, horizontal piping — sizing by roof area and rainfall intensity), gas piping installation (sizing, pressure testing, purging per CAN/CSA-B149.1), fixture installation and connection, pressure testing and leak detection, system commissioning, and quality control procedures.

6. Key Competencies and Technical Requirements (Official Context)

Water Supply Sizing: Fixture Supply Units and the National Plumbing Code

Water supply pipe sizing is one of the most heavily tested calculation skills on the RBQ 15.5 exam. The methodology is based on fixture supply units (FSU) — a standardized value assigned to each type of plumbing fixture based on its expected water demand. The exam tests the complete sizing process: (1) counting the fixtures on each branch and assigning their FSU values from the code table, (2) summing the total FSU for each pipe section, (3) converting the total FSU to a probable demand flow rate (GPM or L/s) using the code's demand curve, (4) determining the available pressure at the most remote fixture (street pressure minus static head loss, minus friction losses through the water meter, backflow preventer and piping), and (5) selecting a pipe diameter that delivers the required flow at an acceptable velocity (typically 2.4 m/s maximum for supply piping). The water service pipe — the connection from the municipal main to the building — has its own sizing methodology based on the total building demand, the available street pressure and the length of the service run.

Sanitary Drainage: Drainage Fixture Units and Pipe Sizing

The drainage system operates by gravity — and the sizing methodology is fundamentally different from the pressurized supply system. The National Plumbing Code assigns drainage fixture units (DFU) to each fixture based on the volume and rate of its discharge. The exam tests candidates on the complete drainage sizing chain: assigning DFU values to fixtures, summing DFU for each branch drain, sizing branch drains (based on DFU and pipe slope — typically 1:50 for pipes 3 inches and smaller, 1:100 for 4 inches and larger), sizing soil and waste stacks (based on total DFU and stack height — with limits on the DFU load per branch interval), and sizing the building drain (based on total DFU and pipe slope). The exam also tests cleanout placement (maximum spacing, required locations at direction changes and at the base of stacks), trap sizes (minimum sizes based on fixture type) and the critical rule that no drainage pipe may be reduced in size in the direction of flow.

Trap Venting: Protecting the Water Seal

Venting is the most conceptually challenging aspect of plumbing — and the exam tests it extensively. Every trap requires a vent to protect its water seal (the water retained in the trap that prevents sewer gases from entering the building). Without proper venting, the flow of water in the drainage system can create siphonage (negative pressure that pulls water out of the trap) or back-pressure (positive pressure that pushes water and gases through the trap). The exam tests multiple venting methods: individual vents (a dedicated vent pipe from each trap to the vent stack — the most reliable but most material-intensive method), wet vents (a pipe that serves as both a drain for one fixture and a vent for another — with strict limitations on pipe size, fixture unit load and configuration), circuit vents (a single vent serving a group of fixtures on a branch — limited to floor-mounted fixtures), stack vents (the extension of a soil or waste stack above the highest fixture drain connection), and air admittance valves (mechanical devices that open under negative pressure to admit air — with specific restrictions on where they may be used).

Stormwater Drainage: Roof Area and Rainfall Intensity

Stormwater drainage pipe sizing uses a completely different methodology from sanitary drainage — based on roof area and rainfall intensity rather than fixture units. The exam tests the complete sizing process: (1) determining the horizontal projected roof area served by each leader (including additional area for walls adjacent to the roof that may redirect water onto it), (2) applying the local rainfall intensity factor (a 15-minute duration rainfall event with a specified return period — the value varies by municipality and is provided in the code), (3) using the code's sizing table to select a leader diameter based on the roof area and rainfall intensity, (4) sizing horizontal storm building drains based on total connected roof area and pipe slope. The exam also tests controlled flow roof drainage (systems that intentionally restrict the flow rate to reduce peak demand on the storm sewer — using orifice plates or controlled-flow roof drains) and combined drainage rules (when sanitary and storm drainage are combined in a single system).

Gas Piping in Plumbing Systems: CAN/CSA-B149.1

Although the RBQ 15.5 is primarily a plumbing licence, it also covers gas piping installation — the supply piping from the gas meter to gas-fired plumbing appliances (water heaters, boilers). The exam tests gas piping requirements per CAN/CSA-B149.1: pipe sizing using the longest-run method (based on the total connected BTU/h load and the equivalent length of the longest pipe run), approved materials and joining methods for gas piping, pressure testing (at 1.5× operating pressure for the required duration), purging procedures (removing air from gas lines before ignition — a critical safety procedure), and burial requirements for underground gas piping. Candidates must understand the distinction between the plumbing code (Chapter III) and the gas code (CAN/CSA-B149.1) and know when each applies.

Quality Control: Testing and Commissioning

The exam tests the complete quality control process for plumbing systems — a critical set of skills that ensures the installed system meets code requirements before being placed in service. For drainage, waste and vent (DWV) systems, the primary test is the water test: the system is filled with water to the level of the highest vent opening, and all joints are inspected for leaks. Alternative tests include the air test (pressurizing the system with air) for situations where water testing is impractical. For water supply systems, the test involves pressurizing the piping to the street pressure (or a minimum specified pressure) and monitoring for pressure loss over a defined period. The exam also tests final inspection procedures: fixture flow tests, trap seal verification, backflow preventer testing, and gas piping leak detection using approved methods.

7. Preparation Strategy and Tips for Success

The RBQ 15.5 exam covers 107 skills across 4 modules with 2 open-book and 3 closed-book documents. Here is a recommended strategy:

Phase 1 — Master the National Plumbing Code (provided at the exam). The National Plumbing Code and the Quebec Construction Code Chapter III are your two open-book references — and they contain all the sizing tables you need. Focus on learning where the key tables are located: fixture supply unit tables, demand curves, drainage fixture unit tables, branch drain sizing, stack sizing, vent sizing, and stormwater sizing. Practise navigating to these tables quickly — with 107 skills in 180 minutes, you have roughly 101 seconds per question.

Phase 2 — Memorize the Bolduc reference and the CMMTQ diagrams. "Drainage and Potable Water Supply for Buildings" by Michel Bolduc and the "Explanatory Diagrams — Plumbing" from the CMMTQ are the two closed-book references that contain calculation methods and schematic configurations you must know from memory. Focus on water supply sizing methodology, drainage pipe sizing procedures, and the standard venting configurations illustrated in the CMMTQ diagrams.

Phase 3 — Master the calculation skills. The RBQ 15.5 tests multiple sizing methodologies — each with its own tables and procedures. Practise fixture supply unit calculations, drainage fixture unit sizing, vent pipe sizing (diameter based on trap size and developed length), and stormwater sizing (roof area × rainfall intensity). Use Prof-RBQ.ca's step-by-step exercises to build speed and accuracy.

Phase 4 — Memorize the Building Act. The Building Act is common to all RBQ licences and provides the legislative foundation for contractor qualifications, permit requirements and enforcement provisions.

Phase 5 — Complete full timed simulations. With 107 skills and only 2 open-book documents, you need to be fast and precise with code lookups. Practice complete exam simulations under timed conditions with Prof-RBQ.ca to build the speed and confidence you need.

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