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Code guide

Ontario Plumbing Code: Part 7 of the 2024 Building Code

Ontario's plumbing code is Part 7 of the 2024 Building Code. Scope, traps, venting, drain slope, backflow, relief valves, permits and who may design it.
of Division B holds Ontario's plumbing rules
Part 7
of Division B holds Ontario's plumbing rules
minimum trap seal depth
38 mm
minimum trap seal depth
minimum slope, drain pipes NPS 3 or less
1 in 50
minimum slope, drain pipes NPS 3 or less
minimum building drain and sewer to the public sewer
NPS 4
minimum building drain and sewer to the public sewer

Last updated

Ontario does not have a separate plumbing code: the plumbing rules are Part 7 of Division B of the 2024 Ontario Building Code, which applies to the design and construction of plumbing (OBC Div. B 7.1.1.1.OBC Div. B 7.1.1.1. Application(1) Except as provided in Sentence (2), this Part applies to the design and construction of plumbing. (2) This Part does not apply to industrial process systems unless the industrial process system is interconnected with the plumbing system, in which case the interconnection shall be so designed and installed so that…). Typical numbers people look for are a 38 mm minimum trap seal (OBC Div. B 7.2.3.1.OBC Div. B 7.2.3.1. Traps(1) Except as provided for in Sentence (2), traps shall (a) have a trap seal depth of not less than 38 mm, (b) be so designed that failure of the seal walls will cause exterior leakage, and (c) have a water seal that does not depend on the action of moving parts. (See Note A-7.2.3.1.(1) and (3)) (2) The trap seal…) and a 1 in 50 minimum slope for drain pipes of NPS 3 or less (OBC Div. B 7.4.8.1.OBC Div. B 7.4.8.1. Minimum Slope(1) Except as provided in Sentences (2) and (3) and Articles 7.4.10.8. and 7.4.10.9., drainage pipes that are NPS 3 or less shall have a downward slope in the direction of flow of at least 1 in 50. (See Note A-7.4.8.1.(1)) (2) Sentence (1) does not apply to a force main. (3) Where it is not possible to comply with…).

This guide explains what Part 7 covers, the core ideas (fixture units, traps, venting and backflow), a handful of verified values, permits, and who may design and inspect plumbing. It paraphrases the code. Your building department has the final say on your project.

Key plumbing values at a glance

Item Value Where to look
Trap seal depth, ordinary traps at least 38 mm 7.2.3.1.(1)
Trap seal depth, acid waste fixtures at least 50 mm 7.2.3.1.(2)
Slope, drainage pipes NPS 3 or less at least 1 in 50 7.4.8.1.(1)
Lesser slope allowed only if flow is at least 0.6 m/s 7.4.8.1.(3)
Building drain and sewer to public sewer (downstream of main cleanout) at least NPS 4 7.4.9.4.(1)
Storm building drains and sewers at least NPS 4 7.4.9.4.(2)
Temperature-relief sensing element within the top 150 mm of the tank 7.6.1.7.(2)
Water heater temperature limit the relief valve protects 99°C 7.6.1.7.(2)
Relief valve discharge air break not more than 300 mm 7.6.1.7.(5)

Our own summary of the articles, not a copy of the code. Read the full Sentences before you design or answer an exam question.

What counts as plumbing

The Building Code Act defines plumbing as a drainage system, a venting system and a water system, or parts of them (BCA s. 1, plumbingBCA s. 1 plumbing“plumbing” means a drainage system, a venting system and a water system or parts thereof; (“installation de plomberie”)). Part 7 does not apply to industrial process systems unless they connect to the plumbing, and then the connection must protect the plumbing from contamination (7.1.1.1.(2)OBC Div. B 7.1.1.1. Application(1) Except as provided in Sentence (2), this Part applies to the design and construction of plumbing. (2) This Part does not apply to industrial process systems unless the industrial process system is interconnected with the plumbing system, in which case the interconnection shall be so designed and installed so that…).

How many fixtures a building needs is not in Part 7 itself. It points to Subsection 3.7.4. for Part 3 buildings and Section 9.31. for Part 9 buildings (7.1.1B.1.OBC Div. B 7.1.1B.1. Facilities Required(1) Plumbing facilities shall be provided in accordance with Subsection 3.7.4. and Section 9.31.). Part 7 then governs how those fixtures are drained, vented and supplied.

Fixture units and pipe sizing

Drain sizing in Part 7 runs on fixture units, a measure of the hydraulic load a fixture puts on the drainage system based on its discharge rate, time of operation and frequency of use (Div. A 1.4.1.2.OBC Div. A 1.4.1.2.(1) Fixture unitFixture unit, as applying to a drainage system, means the unit of measure based on the rate of discharge, time of operation and frequency of use of a fixture that expresses the hydraulic load that is imposed by that fixture on the drainage system.). The load on any pipe is the total from every fixture upstream of it, every fixture provided for future connection, and every roof or paved area that drains into it (7.4.10.1.OBC Div. B 7.4.10.1. Total Load on a Pipe(1) The hydraulic load on a pipe is the total load from (a) every fixture that is connected to the system upstream of the pipe, (b) every fixture for which provision is made for future connection upstream of the pipe, and (c) all roofs and paved surfaces that drain into the system upstream of the pipe.). Fixtures listed in Table 7.4.9.3. take the fixture unit value given there; others are rated by the size of their trap (7.4.10.2.OBC Div. B 7.4.10.2. Hydraulic Loads for Fixtures(1) The hydraulic load from a fixture that is listed in Table 7.4.9.3. is the number of fixture units set forth in the Table. (2) Except as provided in Sentence (1), the hydraulic load from a fixture that is not listed in Table 7.4.9.3. is the number of fixture units set forth in Table 7.4.10.2. for the nominal pipe…).

You then compare the total with the allowable load for the pipe size and slope in the hydraulic load tables. Sizes are written as nominal pipe size (NPS). The worked method is in our plumbing sizing calculation.

Traps and venting

Every fixture needs a trap so that sewer gas cannot enter the building. Traps need a seal of at least 38 mm, must leak to the outside if the seal wall fails, and must not depend on moving parts. Bell traps and drum traps are not allowed, and bottle traps are limited to laboratory-type uses (7.2.3.1.OBC Div. B 7.2.3.1. Traps(1) Except as provided for in Sentence (2), traps shall (a) have a trap seal depth of not less than 38 mm, (b) be so designed that failure of the seal walls will cause exterior leakage, and (c) have a water seal that does not depend on the action of moving parts. (See Note A-7.2.3.1.(1) and (3)) (2) The trap seal…).

Traps are protected by vent pipes so the seal is not siphoned out (7.5.1.1.(1)OBC Div. B 7.5.1.1. Venting for Traps(1) Except as provided in Sentences (3) and (4), traps shall be protected by a vent pipe. (2) Drainage systems may require additional protection as provided in Subsections 7.5.4. and 7.5.5. by the installation of (a) branch vents, (b) vent stacks, (c) stack vents, (d) vent headers, (e) fresh air inlets, (f) relief…). The code lists the venting methods it recognizes, such as individual, branch, wet, circuit and stack vents, and allows a few traps without a separate vent: for example, a floor drain trap of at least NPS 3 with a fixture drain at least 450 mm long and a fall no greater than its pipe size (7.5.1.1.(3)OBC Div. B 7.5.1.1. Venting for Traps(1) Except as provided in Sentences (3) and (4), traps shall be protected by a vent pipe. (2) Drainage systems may require additional protection as provided in Subsections 7.5.4. and 7.5.5. by the installation of (a) branch vents, (b) vent stacks, (c) stack vents, (d) vent headers, (e) fresh air inlets, (f) relief…). Air admittance valves are covered in Subsection 7.5.9.

Backflow and water heaters

Part 7 protects the drinking water supply from backflow:

  • Hose bibbs. Outdoor hose bibbs, those in garages, and any in an area with an identifiable contamination risk must be protected against backflow (7.6.2.7.OBC Div. B 7.6.2.7. Hose Bibb(1) Where a hose bibb is installed outside a building, inside a garage or in an area where there is an identifiable risk of contamination, the potable water system shall be protected against backflow through the hose bibb.).
  • Premise isolation. Buildings with a moderate or severe backflow hazard need a backflow preventer at the service. Part 9 residential buildings are not required to be isolated unless they have an auxiliary water supply, such as a well (7.6.2.6.OBC Div. B 7.6.2.6. Premise Isolation(1) Buildings or facilities where a moderate hazard or severe hazard may be caused by backflow shall be provided with premise isolation of the potable water system by the installation of a backflow preventer selected in accordance with Clauses 5.3.4.2.(b) and (c) of CSA B64.10, "Selection and installation of backflow…).
  • Backwater valves. A backwater valve that blocks air circulation is not allowed in a building drain or sewer, except a normally open type serving not more than one dwelling unit (7.4.6.4.OBC Div. B 7.4.6.4. Protection from Backflow(1) Except as permitted in Sentence (2), a backwater valve that would prevent free circulation of air shall not be installed in a building drain or in a building sewer. (2) A backwater valve may be installed in a building drain provided that, (a) it is a "normally open" design conforming to, (i) CAN/CSA-B70, "Cast…).
  • Water heaters. Storage water heaters need a temperature-relief valve with its sensor in the top 150 mm of the tank, set to keep the water below 99°C. The discharge pipe must be rigid, slope down, have no thread at the outlet, and end over a floor drain or other safe place with an air break of not more than 300 mm. No shut-off valve may sit between the tank and the relief valve (7.6.1.7.OBC Div. B 7.6.1.7. Relief Valves(1) Every pressure vessel that is part of a plumbing system or connected to a plumbing system shall be equipped with a pressure-relief valve designed to open when the water pressure in the tank reaches the rated working pressure of the tank, and so located that the pressure in the tank shall not exceed 1,100 kPa or…).

Permits and inspections

The Act's definition of "building" includes a structure of 10 m² or less that contains plumbing, and plumbing not located in a structure (BCA s. 1, buildingBCA s. 1 building“building” means, (a) a structure occupying an area greater than ten square metres consisting of a wall, roof and floor or any of them or a structural system serving the function thereof including all plumbing, works, fixtures and service systems appurtenant thereto, (b) a structure occupying an area of ten square…). So plumbing work is construction of a building, and a permit is required to construct (BCA s. 8BCA s. 8 Building permits(1) No person shall construct or demolish a building or cause a building to be constructed or demolished unless a permit has been issued therefor by the chief building official. (1.1) An application for a permit to construct or demolish a building may be made by a person specified by regulation and the prescribed form…). Once you have a permit, you must tell the building department when drains, sewers, water service pipes, venting, the water distribution system and fixtures are ready for inspection and testing (Div. C 1.3.5.1.OBC Div. C 1.3.5.1. Prescribed Notices(1) This Article sets out the notices that are required under section 10.2 of the Act. (2) The person to whom a permit under section 8 of the Act is issued shall notify the chief building official or, where a registered code agency is appointed under the Act in respect of the construction to which the notice relates…). Part 7 also sets the water and air tests for drainage and venting systems in Subsection 7.3.6.

Who may design and inspect plumbing

Design and inspection of plumbing are separate BCIN qualifications (Div. C Table 3.5.2.1.OBC Div. C Table 3.5.2.1. Classes of Registration and Categories of Qualifications for Inspectors and Persons Who Carry Out Design Activities[1][2] — Forming Part of Sentence 3.5.2.1.(1)Table 3.5.2.1. — Classes of Registration and Categories of Qualifications for Inspectors and Persons Who Carry Out Design Activities[1][2] — Forming Part of Sentence 3.5.2.1.(1) Item | Classes of Registration for Inspectors and Persons Who Carry out Design Activities | Categories of Qualifications for Inspectors and…):

  • Plumbing - House: all Part 7 plumbing serving a house.
  • Plumbing - All Buildings: all Part 7 plumbing, including houses.

A House or Small Buildings qualification does not cover plumbing design. Trade licensing for the people who install plumbing is a separate system outside the Building Code.

Common mistakes

  1. Looking for a stand-alone "Ontario Plumbing Code". It is Part 7 of the Building Code.
  2. Using 2012 pipe sizes or numbering. Part 7 now expresses sizes as NPS, and article numbers moved.
  3. Forgetting future fixtures when adding up fixture units.
  4. Putting a valve on the relief line, or threading its outlet.
  5. Leaving a hose bibb unprotected in a garage.

How to look it up yourself

Open the 2024 Compendium, Volume 1, Division B, Part 7, Plumbing (Part 7 in our viewer). Search terms that appear in the code text: "trap seal depth", "Minimum Slope", "Hydraulic Loads", "Venting for Traps", "Premise Isolation", "Hose Bibb" and "Relief Valves". The fixture unit tables are numbered 7.4.9.3. and 7.4.10.2.

The BCIN exam angle

Part 7 is the core of the Plumbing - House exam and the Plumbing - All Buildings exam. Start with the free chapters on Part 7 general rules and drainage sizing and hydraulic loads, then practise the plumbing sizing method. Not sure which plumbing exam you need? Plumbing - All Buildings also grants Plumbing - House; see which BCIN exams do I need.

Based on the official 2024 Building Code Compendium on ontario.ca.

© King's Printer for Ontario, 2024. Reproduced with permission.

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Frequently asked questions

Is there a separate plumbing code in Ontario?
No. Plumbing rules are Part 7 of Division B of the 2024 Ontario Building Code, which applies to the design and construction of plumbing (Division B, Article 7.1.1.1.). Plumbing fixtures required in buildings are set by Subsection 3.7.4. and Section 9.31.
What is the minimum trap seal depth in Ontario?
38 mm for ordinary traps, and 50 mm on fixtures draining to an acid waste system (Division B, Article 7.2.3.1.).
What slope do drain pipes need?
Drainage pipes of NPS 3 or less need a downward slope of at least 1 in 50. A lesser slope is allowed only where 1 in 50 is not possible and the pipe still gives a gravity flow of at least 0.6 m per second (Division B, Article 7.4.8.1.).
Do I need a permit for plumbing work in Ontario?
New plumbing and material alterations to plumbing generally need a permit, because the Building Code Act counts plumbing, even plumbing not in a structure, as a building. Ask your building department whether a like-for-like fixture swap needs one.
Can a BCIN designer design plumbing?
Only with the matching qualification. Plumbing - House covers Part 7 plumbing serving a house, and Plumbing - All Buildings covers all Part 7 plumbing (Division C, Table 3.5.2.1.). A House qualification alone does not include plumbing design.