Venting systems: BCIN Plumbing - All Buildings Study Guide

Last updated October 22, 2026

Values this chapter turns on

stack height above which yoke vents are needed: 11 storeys; stack height above which yoke vents are needed
stack height above which a vent stack is needed: 4 storeys; stack height above which a vent stack is needed
max circuit-vented fixtures between vent connections: 8 fixtures; max circuit-vented fixtures between vent connections
min height of a vent terminal above the roof: 150 mm; min height of a vent terminal above the roof

Section 7.5. of Division B protects trap seals by letting air into and out of the drainage system. In a house you mostly meet individual vents, a wet vent and one stack vent. In larger buildings the exam adds circuit venting of rows of fixtures, vent stacks for tall stacks, yoke vents every five storeys, offset relief vents, interceptor and sump vents, and the sizing tables that go with them.

When a trap needs a vent

Every trap is protected by a vent pipe (OBC Div. B 7.5.1.1.), with these exceptions:

Trap	Vent needed?
Floor or hub drain trap, NPS 3 or larger, fixture drain at least 450 mm long, fall not more than its pipe size	no separate vent
Trap serving a subsoil drainage pipe or a storm drainage system	no
Trap that is part of an indirect drainage system	no

The same Article lists every kind of vent the Code recognizes, from branch vents to continuous vents.

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Wet venting

A sanitary drainage pipe may serve as a wet vent (OBC Div. B 7.5.2.1.) if the load fits Table 7.5.8.1., it serves no more than 2 water closets, those closets are downstream of all other fixtures, trap arms and fixture drains on it are NPS 2 or less, and above the first storey no storey adds more than 4 fixture units. It may have one horizontal offset (1.2 m for NPS 2 or less, 2.5 m above NPS 2), its length is not limited, and it is not reduced in size. When sizing the wet vent, leave out the most downstream fixture (or a symmetrically connected pair) (7.5.8.1.).

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Circuit venting

Circuit venting is the classic commercial washroom layout: a row of floor-outlet fixtures on one horizontal branch, vented by a circuit vent connected to that branch (OBC Div. B 7.5.3.1.). The rules:

All circuit-vented fixtures are on the same storey, and no stack connects to the branch upstream of a circuit-vented fixture.
Fixtures with outlet pipes smaller than NPS 2 (lavatories, for example) are not circuit vented; they are separately vented or separately circuit vented.
A relief vent connects downstream of the last circuit-vented fixture. A drainage pipe carrying 6 fixture units or less may act as that relief vent. One symmetrically connected relief vent may serve 2 circuit-vented branches if each has no more than 8 fixtures.
An additional circuit vent is needed for more than 8 fixtures between vent connections, or where the branch turns more than 45° cumulatively between vent connections.
The circuit-vented branch is at least NPS 2 where the traps are smaller than NPS 2, and at least NPS 3 where they are NPS 2 or larger.

Sizes: a circuit vent uses Table 7.5.8.3., with length measured from the horizontal drain connection to the vent stack, stack vent, header or open air (7.5.8.3.). An additional circuit vent or relief vent may be one size smaller than the circuit vent, and never needs to exceed NPS 2 (7.5.7.3.). Length does not count for additional circuit vents and relief vents (7.5.8.5.).

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Stack vents, vent stacks, yoke and offset relief vents

Vent	Trigger	Size rule
Stack vent	top of every stack	Table 7.5.8.4., at least half the stack's base size
Vent stack	stack draining fixtures on more than 4 storeys (not a wet vent stack)	Table 7.5.8.4., at least half the stack's base size
Yoke vent	stack with fixtures on more than 11 storeys: one per 5-storey section counted from the top, and at each offset	one size smaller than the smallest pipe it joins
Offset relief vent	horizontal offset over 1.5 m with the upper stack passing through more than 2 storeys and carrying over 100 fixture units	one size smaller than the stack vent

Sources: 7.5.4.1., 7.5.4.2., 7.5.4.3., 7.5.4.4., 7.5.7.4., 7.5.7.5., 7.5.8.4..

The vent stack joins the stack at or just below the lowest drainage connection. A yoke vent leaves the stack through a drainage fitting at or just below the lowest connection of its section and enters the vent stack at least 1 m above that storey's floor. The yoke can be skipped if the stack and vent stack are cross-connected on every storey with fixtures, using a pipe the size of the branch or NPS 2, whichever is smaller. Up to 8 fixture units of fixtures on the lowest storey may drain into a vent stack under the conditions in 7.5.4.2.

Reading Table 7.5.8.4. Find the stack size, then the load row, then the vent size column, which gives a maximum developed length (from the lower end to open air). For an NPS 4 stack carrying 540 fixture units, an NPS 3 vent may be 46 m long and an NPS 4 vent 177 m. Also remember: every sanitary building drain needs at least one vent of NPS 3 or larger (7.5.7.2.).

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Special vents

Item	Rule
Sanitary sump or tank	vent from its top; one size below the largest drain into it, NPS 2 minimum, need not exceed NPS 4
Oil interceptor	2 independent vents at opposite ends, ending at least 2 m above ground at heights at least 300 mm apart, not joined to any other vent
Grease interceptor	vent on the inlet pipe within 1,500 mm of the interceptor, NPS 1½ to NPS 2, with a cleanout
Corrosive waste piping and tanks	vented independently to outdoors
Manhole inside a building	NPS 2 vent
Building trap	NPS 4 fresh air inlet within 1.2 m upstream

Sources: 7.5.5.1., 7.5.5.2., 7.5.5.3., 7.5.5.4., 7.5.7.6., 7.5.7.7.. Every storey where plumbing is or may be installed, basement included, gets a vent pipe of at least NPS 1½ for future connections (7.5.5.5.).

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Arrangement and terminals

Vents slope to drain, connect above the centre line of a horizontal drain (wet vents aside), and rise above the flood level rim of every fixture they serve before joining another vent (7.5.6.1., 7.5.6.2., 7.5.6.4.). A trap arm is at least twice the fixture drain size long, falls no more than its inside diameter, turns no more than 135° (225° for siphonic fixtures) and stays within Table 7.5.6.3. (7.5.6.3.).

Terminals in open air (7.5.6.5.): at least 1 m above or 3.5 m from air inlets, openable windows and doors; 2 m above (or 3.5 m from) a roof with an occupancy; 2 m above ground; 1.8 m from property lines; 150 mm above the roof. Where frost may close it, increase by one size to at least NPS 3 before the roof. A vent run outside the building stays vertical with no bend over 45°, and on buildings of 4 storeys or less ends above the roof.

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Air admittance valves

Air admittance valves may terminate individual and dual vents only, and only in renovations or where a vent connection may not be practical (7.5.9.1., 7.5.9.2.). They sit at least 100 mm above the fixture drain and 150 mm above insulation, serve fixtures on the same storey, connect to the horizontal fixture drain, stay accessible, and are kept out of air plenums and freezing spaces. The system still needs at least one vent to outdoors (7.5.9.3.).

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Common traps

Vent stack trigger is more than 4 storeys; yoke vent trigger is more than 11 storeys.
Lavatories with NPS 1¼ outlets cannot be circuit vented.
Length matters for branch, circuit, continuous and header vents (Table 7.5.8.3.) but not for relief, yoke, offset relief, interceptor, sump or manhole vents.
Oil interceptor vents never join each other or any other vent.

Chapter review

Chapter at a glance

One line per section: the idea to carry into the exam. Then the answers that most often catch candidates out.

Chapter at a glance: the key idea in each section
Section	Key idea
When a trap needs a vent	The same Article lists every kind of vent the Code recognizes, from branch vents to continuous vents.
Wet venting	A sanitary drainage pipe may serve as a wet vent if the load fits, it serves no more than 2 water closets, those closets are downstream of all other fixtures, trap arms and…
Circuit venting	Circuit venting is the classic commercial washroom layout: a row of floor-outlet fixtures on one horizontal branch, vented by a circuit vent connected to that branch.
Stack vents, vent stacks, yoke and offset relief vents	The vent stack joins the stack at or just below the lowest drainage connection.
Special vents	Sources:,,,,,. Every storey where plumbing is or may be installed, basement included, gets a vent pipe of at least NPS 1½ for future connections.
Arrangement and terminals	Vents slope to drain, connect above the centre line of a horizontal drain (wet vents aside), and rise above the flood level rim of every fixture they serve before joining another…
Air admittance valves	Air admittance valves may terminate individual and dual vents only, and only in renovations or where a vent connection may not be practical.

When a trap needs a vent
The same Article lists every kind of vent the Code recognizes, from branch vents to continuous vents.
Wet venting
A sanitary drainage pipe may serve as a wet vent if the load fits, it serves no more than 2 water closets, those closets are downstream of all other fixtures, trap arms and…
Circuit venting
Circuit venting is the classic commercial washroom layout: a row of floor-outlet fixtures on one horizontal branch, vented by a circuit vent connected to that branch.
Stack vents, vent stacks, yoke and offset relief vents
The vent stack joins the stack at or just below the lowest drainage connection.
Special vents
Sources:,,,,,. Every storey where plumbing is or may be installed, basement included, gets a vent pipe of at least NPS 1½ for future connections.
Arrangement and terminals
Vents slope to drain, connect above the centre line of a horizontal drain (wet vents aside), and rise above the flood level rim of every fixture they serve before joining another…
Air admittance valves
Air admittance valves may terminate individual and dual vents only, and only in renovations or where a vent connection may not be practical.

Usual exam traps

Vent stack trigger is more than 4 storeys; yoke vent trigger is more than 11 storeys.
Lavatories with NPS 1¼ outlets cannot be circuit vented.
Length matters for branch, circuit, continuous and header vents (Table 7.5.8.3.) but not for relief, yoke, offset relief, interceptor, sump or manhole vents.
Oil interceptor vents never join each other or any other vent.

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Questions on Venting systems (7.5), in the exam format, every answer explained and cited to its article. Sign in to start; a free account gets the free questions.

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Code cited in this chapter

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

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 vents,
(g)circuit vents,
(h)yoke vents,
(i)offset relief vents,
(j)additional circuit vents,
(k)wet vents,
(l)individual vents,
(m)dual vents, or
(n)continuous vents.
(3)A trap that serves a floor drain or hub drain need not be protected by a vent pipe separately where
(a)the nominal pipe size of the trap is not less than NPS 3,
(b)the length of the fixture drain is not less than 450 mm,
(c)the fall on the fixture drain does not exceed its nominal pipe size.
(4)A trap need not be protected by a vent pipe
(a)where it serves
(i)a subsoil drainage pipe, or
(ii)a storm drainage system, or
(b)where it forms part of an indirect drainage system. (See also Clause 7.4.2.3.(2)(b))
Open OBC Div. B 7.5.1.1. in the code viewer
OBC Div. B 7.5.2.1. Wet Venting
(1)A sanitary drainage pipe is permitted to serve as a wet vent, provided
(a)the hydraulic load is in accordance with Table 7.5.8.1.,
(b)the number of wet-vented water closets does not exceed 2,
(c)where 2 water closets are installed, they are connected at the same level by means of a double sanitary T fitting if the vent pipe is vertical and by means of a double Y fitting if the vent pipe is horizontal,
(d)the water closets are installed downstream of all other fixtures,
(e)trap arms and fixture drains connected to the wet vent do not exceed NPS 2, except for connections from emergency floor drains in accordance with Sentence 7.5.1.1.(3),
(f)the total hydraulic load on the wet vent does not exceed the limits stated in Table 7.5.8.1. when separately vented branches or fixture drains in the same storey, having a total hydraulic load not greater than 2 fixture units, are connected to the wet vent or a wet-vented water-closet trap arm,
(g)the hydraulic load of separately vented fixtures that drain into the wet vent are not included when sizing the continuous vent that serves the wet vent,
(h)where a wet vent extends through more than one storey, the total discharge from any one storey above the first storey does not exceed 4 fixture units,
(i)there is not more than one nominally horizontal offset in the wet vent, and
(i)the offset does not exceed 1.2 m for pipes of NPS 2 or less, or
(ii)the offset does not exceed 2.5 m for pipes larger than NPS 2,
(j)the wet vented portion is not reduced in size except for the portion that is upstream of floor drains in accordance with Sentence 7.5.1.1.(3),
(k)the length of the wet vent is not limited.
Open OBC Div. B 7.5.2.1. in the code viewer
OBC Div. B Table 7.5.8.1. Maximum Hydraulic Load, Fixture Units
Table 7.5.8.1. — Maximum Hydraulic Load, Fixture Units Forming Part of Sentences 7.5.7.3.(2) and 7.5.8.1.(1) Nominal Pipe Size of Wet Vent, NPS | Not Serving Water Closets | Fixtures, Other Than Water Closets, That Serve Not More Than 2 Water Closets 1½ | 2 | N/A 2 | 4 | 3 3 | 12 | 8 4 | 36 | 14 5 | N/A | 18 6 | N/A | 23
Open OBC Div. B Table 7.5.8.1. in the code viewer
OBC Div. B 7.5.8.1. Hydraulic Loads Draining to Wet Vents
(1)The hydraulic load that drains to a wet vent shall conform to Table 7.5.8.1.
(2)When determining the nominal pipe size of a wet vent, the hydraulic load from the most downstream fixture or symmetrically connected fixtures shall not be included.
Open OBC Div. B 7.5.8.1. in the code viewer
OBC Div. B 7.5.3.1. Circuit Venting
(1)A section of horizontal branch may be circuit-vented provided
(a)a circuit vent is connected to it,
(b)all fixtures served by the circuit vent are located in the same storey,
(c)no stack is connected to it upstream of a circuit-vented fixture.
(2)Fixtures with fixture outlet pipes less than NPS 2 shall be separately vented or separately circuit-vented.
(3)Except as provided in Sentences (4) and (5), a relief vent shall be connected to the branch that forms part of a circuit-vented system, downstream of the connection of the most downstream circuit-vented fixture.
(4)A sanitary drainage pipe having a hydraulic load not greater than 6 fixture units is permitted to act as a relief vent for a branch that is circuit-vented.
(5)A symmetrically connected relief vent is permitted to serve as a combined relief vent for a maximum of 2 branches that are circuit-vented, provided there are not more than 8 circuit-vented fixtures connected between the combined relief vent and each circuit vent.
(6)Additional circuit vents shall be required
(a)where each cumulative horizontal change in direction of a branch served by a circuit vent exceeds 45° between vent pipe connections, or
(b)where more than 8 circuit-vented fixtures are connected to a branch between vent pipe connections.
(7)A sanitary drainage pipe is permitted to serve as an additional circuit vent in accordance with Sentence (6), provided the sanitary drainage pipe is sized as a wet vent in conformance with Article 7.5.8.1. and is not less than NPS 2.
(8)Connections to circuit vents and additional circuit vents in accordance with Sentence (6) shall conform to Sentence 7.5.4.5.(1).
(9)A circuit-vented branch, including the fixture drain downstream of the circuit vent connection, shall be sized in accordance with Articles 7.4.10.7. and 7.10.4.8., except that it shall be not less than
(a)NPS 2, where traps less than NPS 2 are circuit-vented, or
(b)NPS 3, where traps of NPS 2 or larger are circuit-vented.
(10)Additional circuit vents shall be sized in accordance with Table 7.5.7.1. and Sentence 7.5.7.3.(1).
(11)The hydraulic load on a circuit vent shall include the hydraulic load from fixtures connected to the branch served by the circuit vent, but shall not include the hydraulic load from fixtures permitted by Sentences (3), (4) and (5).
Open OBC Div. B 7.5.3.1. in the code viewer
OBC Div. B Table 7.5.8.3. Maximum Length of Vent Pipe, m[1]
Table 7.5.8.3. — Maximum Length of Vent Pipe, m[1] Forming Part of Article 7.5.8.3. Total Hydraulic Load Served by Vent Pipe, fixture units | Nominal Pipe Size of Vent Pipe, NPS: 1¼ | Nominal Pipe Size of Vent Pipe, NPS: 1½ | Nominal Pipe Size of Vent Pipe, NPS: 2 | Nominal Pipe Size of Vent Pipe, NPS: 3 | Nominal Pipe Size of Vent Pipe, NPS: 4 | Nominal Pipe Size of Vent Pipe, NPS: 5 | Nominal Pipe Size of Vent Pipe, NPS: 6 | Nominal Pipe Size of Vent Pipe, NPS: 8 2 | 9 | NL | NL | NL | NL | NL | NL | NL 8 | 9 | 30 | 61 | NL | NL | NL | NL | NL 20 | 7.5 | 15 | 46 | NL | NL | NL | NL | NL 24 | 4.5 | 9 | 30 | NL | NL | NL | NL | NL 42 | NP | 9 | 30 | NL | NL | NL | NL | NL 60 | NP | 4.5 | 15 | 120 | NL | NL | NL | NL 100 | NP | NP | 11 | 79 | 305 | NL | NL | NL 200 | NP | NP | 9 | 76 | 275 | NL | NL | NL 500 | NP | NP | 6 | 55 | 215 | NL | NL | NL 1,100 | NP | NP | NP | 15 | 61 | 215 | NL | NL 1,900 | NP | NP | NP | 6 | 21 | 61 | 215 | NL 2,200 | NP | NP | NP | NP | 9 | 27 | 105 | 335 3,600 | NP | NP | NP | NP | 7.5 | 18 | 76 | 245 5,600 | NP | NP | NP | NP | NP | 7.5 | 18 | 76 Notes to Table 7.5.8.3.: (1) NP = not permitted and NL = not limited
Open OBC Div. B Table 7.5.8.3. in the code viewer
OBC Div. B 7.5.8.3. Branch Vents, Vent Headers, Continuous Vents and Circuit Vents
(1)Branch vents, vent headers, circuit vents and continuous vents shall be sized in accordance with Table 7.5.8.3., unless they are individual vents or dual vents.
(2)For the purposes of Table 7.5.8.3., the length of a branch vent shall be its developed length from the most distant sanitary drainage pipe connection to a vent stack, stack vent, header or open air.
(3)For the purposes of Table 7.5.8.3., the length of a vent header shall be its developed length from the most distant sanitary drainage pipe connection to open air.
(4)For the purposes of Table 7.5.8.3., the length of a circuit vent shall be its developed length from the horizontal sanitary drainage pipe connection to a vent stack, stack vent, vent header or open air.
(5)For the purposes of Table 7.5.8.3., the length of a continuous vent shall be its developed length from the vertical sanitary drainage pipe connection to a vent stack, stack vent, vent header or open air.
Open OBC Div. B 7.5.8.3. in the code viewer
OBC Div. B 7.5.7.3. Additional Circuit Vents and Relief Vents
(1)Except as provided in Article 7.5.7.1. and Sentence 7.5.3.1.(7), the minimum nominal pipe size of an additional circuit vent or relief vent installed in conjunction with a circuit vent is permitted to be one NPS smaller than the required nominal pipe size of the circuit vent, but need not be larger than NPS 2.
(2)The nominal pipe size of the sanitary drainage pipe acting as a relief vent in accordance with Sentence 7.5.3.1.(4) shall be in conformance with Table 7.4.10.6.-A, 7.4.10.6.-B or 7.5.8.1., and Article 7.5.7.1., whichever nominal pipe size is the largest considering the hydraulic load drained into the sanitary drainage pipe.
Open OBC Div. B 7.5.7.3. in the code viewer

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OBC Div. B 7.5.8.5. Lengths for Other Vent Pipes
(1)When sizing an additional circuit vent, offset relief vent, relief vent, yoke vent and the vent pipe for an interceptor, dilution tank, sanitary sewage tank, sump, or manhole, length is not taken into consideration.
Open OBC Div. B 7.5.8.5. in the code viewer
OBC Div. B Table 7.5.8.4. Maximum Length of Stack Vent or Vent Stack, m[1]
Table 7.5.8.4. — Maximum Length of Stack Vent or Vent Stack, m[1] Forming Part of Sentences 7.5.8.4.(1) and (2) Nominal Pipe Size of Stack, NPS[2] | Total Hydraulic Load Being Vented, fixture units | Water Occupied Area | Nominal Pipe Size of Stack Vent or Vent Stack, NPS: 1¼ | Nominal Pipe Size of Stack Vent or Vent Stack, NPS: 1½ | Nominal Pipe Size of Stack Vent or Vent Stack, NPS: 2 | Nominal Pipe Size of Stack Vent or Vent Stack, NPS: 3 | Nominal Pipe Size of Stack Vent or Vent Stack, NPS: 4 | Nominal Pipe Size of Stack Vent or Vent Stack, NPS: 5 | Nominal Pipe Size of Stack Vent or Vent Stack, NPS: 6 | Nominal Pipe Size of Stack Vent or Vent Stack, NPS: 8 | Nominal Pipe Size of Stack Vent or Vent Stack, NPS: 10 | Nominal Pipe Size of Stack Vent or Vent Stack, NPS: 12 1¼ | 2 | 0.29 | 9 | NL | NL | NL | NL | NL | NL | NL | NL | NL 1½ | 8 | 0.25 | 15 | 46 | NL | NL | NL | NL | NL | NL | NL | NL 2 | 12 | 0.25 | 9 | 23 | 61 | NL | NL | NL | NL | NL | NL | NL 2 | 24 | 0.29 | 8 | 15 | 46 | NL | NL | NL | NL | NL | NL | NL 3 | 10 | 0.15 | NP | 13 | 46 | 317 | NL | NL | NL | NL | NL | NL 3 | 21 | 0.20 | NP | 10 | 33.5 | 247 | NL | NL | NL | NL | NL | NL 3 | 53 | 0.25 | NP | 8 | 28.5 | 207 | NL | NL | NL | NL | NL | NL 3 | 102 | 0.29 | NP | 7.5 | 26 | 189 | NL | NL | NL | NL | NL | NL 4 | 43 | 0.15 | NP | NP | 10.5 | 76 | 299 | NL | NL | NL | NL | NL 4 | 140 | 0.20 | NP | NP | 8 | 61 | 229 | NL | NL | NL | NL | NL 4 | 320 | 0.25 | NP | NP | 7 | 52 | 195 | NL | NL | NL | NL | NL 4 | 540 | 0.29 | NP | NP | 6.5 | 46 | 177 | NL | NL | NL | NL | NL 5 | 190 | 0.15 | NP | NP | NP | 25 | 97.5 | 302 | NL | NL | NL | NL 5 | 490 | 0.20 | NP | NP | NP | 19 | 76 | 232 | NL | NL | NL | NL 5 | 940 | 0.25 | NP | NP | NP | 16 | 64 | 204 | NL | NL | NL | NL 5 | 1400 | 0.29 | NP | NP | NP | 15 | 58 | 180 | NL | NL | NL | NL 6 | 500 | 0.15 | NP | NP | NP | 10 | 39.5 | 122 | 305 | NL | NL | NL 6 | 1 100 | 0.20 | NP | NP | NP | 8 | 30.5 | 94.5 | 238 | NL | NL | NL 6 | 2 000 | 0.25 | NP | NP | NP | 6.5 | 25.5 | 79 | 201 | NL | NL | NL 6 | 2 900 | 0.29 | NP | NP | NP | 6 | 23.5 | 73 | 183 | NL | NL | NL 8 | 1 800 | 0.15 | NP | NP | NP | NP | 9.5 | 29 | 73 | 287 | NL | NL 8 | 3 400 | 0.20 | NP | NP | NP | NP | 7 | 22 | 58 | 219.5 | NL | NL 8 | 5 600 | 0.25 | NP | NP | NP | NP | 6 | 19 | 49 | 186 | NL | NL 8 | 7 600 | 0.29 | NP | NP | NP | NP | 5.5 | 17 | 43 | 170.5 | NL | NL 10 | 4 000 | 0.15 | NP | NP | NP | NP | NP | 9.5 | 24 | 94.5 | 292.5 | NL 10 | 7 200 | 0.20 | NP | NP | NP | NP | NP | 7 | 18 | 73 | 225.5 | NL 10 | 11 000 | 0.25 | NP | NP | NP | NP | NP | 6 | 15.5 | 61 | 192 | NL 10 | 15 000 | 0.29 | NP | NP | NP | NP | NP | 5.5 | 14 | 55 | 174 | NL 12 | 7 300 | 0.15 | NP | NP | NP | NP | NP | NP | 9.5 | 36.5 | 116 | 287 12 | 13 000 | 0.20 | NP | NP | NP | NP | NP | NP | 7 | 28.5 | 91 | 219.5 12 | 20 000 | 0.25 | NP | NP | NP | NP | NP | NP | 6 | 24 | 76 | 186 12 | 26 000 | 0.29 | NP | NP | NP | NP | NP | NP | 5.5 | 22 | 70 | 152 15 | 15 000 | 0.15 | NP | NP | NP | NP | NP | NP | NP | 12 | 39.5 | 94.5 15 | 25 000 | 0.20 | NP | NP | NP | NP | NP | NP | NP | 9.5 | 29 | 73 15 | 38 000 | 0.25 | NP | NP | NP | NP | NP | NP | NP | 8 | 24.5 | 61 15 | 50 000 | 0.29 | NP | NP | NP | NP | NP | NP | NP | 7 | 22.5 | 55 Notes to Table 7.5.8.4.: (1) NP = not permitted and NL = not limited. (2) Stacks shall be sized using Table 7.4.10.6.-A.
Open OBC Div. B Table 7.5.8.4. in the code viewer
OBC Div. B 7.5.4.1. Stack Vents
(1)The upper end of every stack shall terminate in a stack vent and the stack vent shall terminate in open air outside the building, or connect directly or through a header to another stack vent or vent stack that does terminate in open air outside the building.
Open OBC Div. B 7.5.4.1. in the code viewer
OBC Div. B 7.5.4.2. Vent Stacks
(1)Except as provided in Sentence (2), every stack that drains fixtures from more than 4 storeys containing plumbing fixtures shall have a vent stack.
(2)A stack that serves as a wet vent does not require a vent stack.
(3)The vent stack required by Sentence (1) shall be connected to a vertical section of the stack at or immediately below the lowest sanitary drainage pipe connected to the stack.
(4)Fixtures are permitted to be connected to a vent stack, provided
(a)the total hydraulic load of the connected fixtures does not exceed 8 fixture units,
(b)at least one fixture is connected to a vertical portion of the vent stack and upstream of any other fixtures,
(c)no other fixture is connected downstream of a water closet,
(d)all fixtures are located in the lowest storey served by the vent stack, and
(e)the section of the vent pipe that acts as a wet vent conforms to the requirements regarding wet vents.
Open OBC Div. B 7.5.4.2. in the code viewer
OBC Div. B 7.5.4.3. Yoke Vents
(1)Except as provided in Sentence (4), where a stack receives the discharge from fixtures located on more than 11 storeys, a yoke vent shall be installed
(a)for each section of 5 storeys or part of them counted from the top down, and
(b)at or immediately above each offset or double offset.
(2)The yoke vent shall be connected to the stack by means of a drainage fitting at or immediately below the lowest sanitary drainage pipe from the lowest storey of the sections described in Sentence (1).
(3)The yoke vent shall connect to the vent stack at least 1 m above the floor level of the lowest storey in the section described in Sentence (1).
(4)A yoke vent need not be installed provided the stack is interconnected with the vent stack in each storey of the section in which fixtures are located by means of a vent pipe equal in nominal pipe size to the branch or fixture drain or NPS 2, whichever is smaller.
Open OBC Div. B 7.5.4.3. in the code viewer
OBC Div. B 7.5.4.4. Offset Relief Vents
(1)A stack that has a nominally horizontal offset more than 1.5 m long and above which the upper vertical portion of the stack passes through more than 2 storeys and receives a hydraulic load of more than 100 fixture units shall be vented by an offset relief vent connected to the vertical section immediately above the offset and by another offset relief vent
(a)connected to the lower vertical section at or above the highest sanitary drainage pipe connection, or
(b)extended as a vertical continuation of the lower section.
Open OBC Div. B 7.5.4.4. in the code viewer
OBC Div. B 7.5.7.4. Offset Relief Vents
(1)Except as provided in Article 7.5.7.1., the minimum nominal pipe size of an offset relief vent is permitted to be one NPS smaller than the NPS of the stack vent..
Open OBC Div. B 7.5.7.4. in the code viewer
OBC Div. B 7.5.7.5. Yoke Vents
(1)Yoke vents required by Sentence 7.5.4.3.(1) are permitted to be one NPS smaller than the NPS of the smallest pipe to which they are connected
Open OBC Div. B 7.5.7.5. in the code viewer
OBC Div. B 7.5.8.4. Vent Stacks or Stack Vents
(1)A vent stack or stack vent shall be sized in accordance with Table 7.5.8.4. based on
(a)the length of the vent stack or stack vent, and
(b)the total hydraulic load that is drained to the lowest section of a stack served by the vent pipe, plus any additional vent loads connected to the vent stack or stack vent.
(2)For the purposes of Table 7.5.8.4., the length of a stack vent or vent stack shall be its developed length from its lower end to open air.
(3)The minimum nominal pipe size of a vent stack or stack vent shall be one-half the NPS of the stack at its base.
(4)A stack vent serving a wet vent stack that is over 4 storeys high shall extend the full size of the wet vent to open air.
(5)Sanitary building drains shall be provided with at least one vent that is not less than NPS 3.
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OBC Div. B 7.5.7.2. Size Restriction
(1)The nominal pipe size of a branch vent, stack vent, vent stack or vent header shall be not less than the nominal pipe size of the vent pipe to which it is connected.
(2)Sanitary building drains shall be provided with at least one vent that is not less than NPS 3.
(3)A vent referred to in Sentence (2) shall be a soil stack if one is available and may be a vent stack or waste stack that provides at least NPS 3 stack vent and that goes to open air above the roof, either directly or through a header.
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OBC Div. B 7.5.5.1. Venting of Sanitary Sewage Sumps
(1)Every sump or tank that receives sanitary sewage shall be provided with a vent pipe that is connected to the top of the sump or tank. (See Article 7.5.7.7. for sizing of these vents.)
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OBC Div. B 7.5.5.2. Venting of Interceptors
(1)Every oil interceptor shall be provided with 2 vent pipes that
(a)connect to the interceptor at opposite ends,
(b)extend independently to open air,
(c)terminate not less than 2 m above ground and at elevations differing by at least 300 mm, and
(d)do not connect to each other or any other vent pipe.
(2)Adjacent compartments within every oil interceptor shall be connected to each other by a vent opening.
(3)Where a secondary receiver for oil is installed in conjunction with an oil interceptor, it shall be vented in accordance with the manufacturer's recommendations, and the vent pipe shall
(a)in no case be less than NPS 11/2,
(b)extend independently to open air, and
(c)terminate not less than 2 m above ground.
(4)The vent pipes referred to in Sentence (1) are permitted to be one NPS smaller than the largest connected drainage pipe but not less than NPS 1½, or can be sized in accordance with the manufacturer's recommendations.
(5)A vent pipe that serves an oil interceptor and is located outside a building shall be not less than NPS 3 in areas where it may be subject to frost closure.
(6)Every grease interceptor inlet pipe shall be provided with a vent pipe
(a)within 1,500 mm of the inlet to the grease interceptor,
(b)not less than NPS 1½ for inlet pipes up to NPS 4, but not larger than NPS 2, and
(c)complete with a cleanout to provide cleaning of the vent pipe.
(7)Where an acid waste dilution tank is installed, it shall be provided with a vent pipe connected at the top of the tank and that is sized in accordance with Article 7.5.7.7.
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OBC Div. B 7.5.5.3. Venting of Drain Piping and Dilution Tanks for Corrosive Waste
(1)Venting systems for drain piping, neutralizing tanks, or dilution tanks conveying corrosive waste shall extend independently and terminate outdoors. (See Article 7.5.7.7. for sizing of these vents.)
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OBC Div. B 7.5.5.4. Fresh Air Inlets
(1)Where a building trap is installed, a fresh air inlet not less than NPS 4 shall be connected upstream and within 1.2 m of the building trap and downstream of any other connection.
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OBC Div. B 7.5.7.6. Vent Pipes for Manholes
(1)The minimum nominal pipe size of a vent pipe that serves a manhole within a building shall be NPS 2.
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OBC Div. B 7.5.7.7. Vents for Sewage Sumps, Neutralizing and Dilution Tanks, and Macerating Toilet Systems
(1)Except as provided in Sentences (2) and (3), the minimum nominal pipe size of the vent pipe for a sewage sump or neutralizing or dilution tank shall be one NPS smaller than the NPS of the largest branch or fixture drain draining to the sump.
(2)The nominal pipe size of every vent pipe for a sewage sump or neutralizing or dilution tank shall be not less than NPS 2, but need not be greater than NPS 4.
(3)The nominal pipe size of a vent pipe for a macerating toilet system with a sump shall be not less than NPS 1½.
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OBC Div. B 7.5.5.5. Provision for Future Installations
(1)Where provision is made for a fixture to be installed in the future, the drainage system and venting system shall be sized accordingly and provision made for the necessary future connections.
(2)Except as required in Sentence 7.5.7.7.(2), where a plumbing system is installed in a building, every storey in which plumbing is or may be installed, including the basement of a building, shall have extended into it or passing through it a vent pipe that is at least NPS 1½ for the provision of future connections.
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OBC Div. B 7.5.6.1. Drainage of Vent Pipes
(1)Vent pipes shall be installed without depression in which moisture can collect.
(2)Waste pipes shall be installed and back vented at the same time.
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OBC Div. B 7.5.6.2. Vent Pipe Connections
(1)Vent pipes in a plumbing system shall be installed so as to be direct as possible to a vent stack or open air, as the case may be, and so that any horizontal run below the flood level of the fixture to which the vent pipe is installed is eliminated where structurally possible.
(2)Except for wet vents, where a vent pipe is connected to a nominally horizontal sanitary drainage pipe, the connection shall be above the horizontal centre line of the sanitary drainage pipe.
(3)Unused vent pipes installed for future connections shall be permanently capped with an end cleanout or an adapter and plug.
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OBC Div. B 7.5.6.4. Connection of Vents Above Fixtures Served
(1)Except for a wet vent, every vent pipe shall extend above the flood level rim of every fixture that it serves before being connected to another vent pipe.
(2)No vent pipe shall be connected in such a manner that a blockage in a soil or waste pipe would cause waste to drain through the vent pipe to the drainage system.
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OBC Div. B Table 7.5.6.3. Length of Trap Arm
Table 7.5.6.3. Length of Trap Arm Forming Part of Sentence 7.5.6.3.(4) Nominal Pipe Size of Trap Served, NPS | Maximum Length of Trap Arm, m | Minimum Slope 1¼ | 1.5 | 1 in 50 1½ | 1.8 | 1 in 50 2 | 2.4 | 1 in 50 3 | 3.6 | 1 in 50 4 | 4.9 | 1 in 50 4 | 9.8 | 1 in 100
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OBC Div. B 7.5.6.3. Location of Vent Pipes
(1)Except as provided in Sentences (2) and (3), vent pipes that protects a fixture trap shall be located so that
(a)the developed length of the trap arm is not less than twice the NPS of the fixture drain,
(b)the total fall of the trap arm is not greater than its inside diameter, and
(c)the trap arm does not have a cumulative change in direction of more than 135°.
(2)The trap arm of water closets, of S-trap standards or of any other fixture that also discharges vertically and depends on siphonic action for its proper functioning shall not have a cumulative change in direction of more than 225°.
(3)A vent pipe that protects a water closet or any other fixture that also depends on siphonic action for its proper functioning shall be located so that the distance between the connections of the fixture drain to the fixture and the vent pipe does not exceed
(a)1 m in the vertical plane, and
(b)3 m in the horizontal plane.
(4)The maximum length of every trap arm shall conform to Table 7.5.6.3.
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OBC Div. B 7.5.6.5. Terminals
(1)Except as provided in Sentence (3), the upper end of every vent pipe that is not terminated in open air shall be connected to a venting system that terminates through a roof to open air.
(2)The upper end of every vent pipe that is terminated in open air, other than a vent pipe that serves an oil interceptor or a fresh air inlet, shall be extended above the roof.
(3)A vent pipe is permitted to be erected outside a building, provided that
(a)no single change of direction of the vent pipe exceeds 45°,
(b)all parts of the vent pipe are nominally vertical,
(c)in areas where the vent pipe may be subject to frost closure, it is increased to not less than NPS 3 before penetrating a wall or roof, and
(d)where the building is 4 storeys or less in height, the vent pipe terminates above the roof of the building.
(4)Except for a fresh air inlet, where a vent pipe is terminated in open air, the terminal shall be located
(a)not less than 1 m above and not less than 3.5 m in any other direction from every air inlet, openable window or door,
(b)not less than 2 m above and not less than 3.5 m in any other direction from a roof that supports an occupancy,
(c)not less than 2 m above ground, and
(d)not less than 1.8 m from every property line.
(5)Where a vent pipe passes through a roof, it shall
(a)be terminated high enough to prevent the entry of roof drainage but not less than 150 mm above the roof or above the surface of storm water, which could pond on the roof, and
(b)be provided with flashing to prevent the entry of water between the vent pipe and the roof. (See Article 7.2.10.14.)
(6)Where a vent pipe passes through a roof and may be subject to frost closure, it shall be protected from frost closure by
(a)increasing its diameter at least one NPS, but not less than NPS 3, immediately before it penetrates the roof,
(b)insulating the pipe, or
(c)protecting it in some other manner.
(See Article 7.3.4.7.)
(7)Where a vent pipe is located 2 m or more above a roof, it shall be so constructed as to be stable and secure.
(8)Flashing shall be of material specified in Article 7.2.10.14. and on a shingled roof shall have a minimum dimension of 500 mm by 500 mm.
(9)Where a sleeve flashing is installed on a flat roof, it shall extend at least 150 mm above the flood level and on a sloped roof shall be at least 150 mm high on the short side.
(10)No bore of a vent stack or stack vent shall be reduced or obstructed by the installation of a flashing.
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OBC Div. B 7.5.9.1. Air Admittance Valve as a Vent Terminal
(1)Individual vents and dual vents are permitted to terminate with a connection to an air admittance valve as provided in Articles 7.5.9.2. and 7.5.9.3. (See also Sentence 7.2.10.16.(1))
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OBC Div. B 7.5.9.2. Air Admittance Valves
(1)Air admittance valves shall only be used to vent
(a)fixtures in buildings undergoing renovation, and
(b)installations where connection to a vent may not be practical.
(2)Air admittance valves shall be located
(a)not less than 100 mm above the fixture drain being vented,
(b)within the maximum developed length permitted for the vent, and
(c)not less than 150 mm above insulation materials.
(3)Air admittance valves shall
(a)only vent fixtures located on the same storey, and
(b)be connected to the horizontal fixture drain.
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OBC Div. B 7.5.9.3. Installation Conditions
(1)Air admittance valves shall not be installed in supply or return air plenums, or in locations where they may be exposed to freezing temperatures.
(2)Air admittance valves shall be installed in accordance with the manufacturer's installation instructions.
(3)Air admittance valves shall be rated for the nominal pipe size of vent pipe to which they are connected.
(4)Installed air admittance valves shall be
(a)accessible, and
(b)located in a space that allows air to enter the valve.
(5)Drainage systems shall have at least one vent that terminates to the outdoors in conformance with Sentence 7.5.6.5.(1).
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