Venting systems (7.5): BCIN Plumbing

Last updated October 22, 2026

Values this chapter turns on

max trap arm length for an NPS 1¼ trap: 1.5 m; max trap arm length for an NPS 1¼ trap
max number of wet-vented water closets: 2; max number of wet-vented water closets
minimum vent terminal height above the roof: 150 mm; minimum vent terminal height above the roof
minimum vent terminal distance to property line: 1.8 m; minimum vent terminal distance to property line

Venting protects trap seals by letting air in and out of the drainage system. On the house exam, venting is the biggest single topic: trap arm lengths, vent sizes, wet venting limits, terminal locations and air admittance valves. Circuit venting, yoke vents and offset relief vents are excluded from this syllabus, so do not spend time there.

Vent pipes for traps

Every trap is protected by a vent pipe unless an exception applies (OBC Div. B 7.5.1.1.). The exceptions:

Trap	Condition
Floor drain or hub drain	trap at least NPS 3, fixture drain at least 450 mm long, and fall on the fixture drain not more than its pipe size
Subsoil drainage pipe or storm drainage system trap	no vent needed
Part of an indirect drainage system	no vent needed

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Wet venting

A sanitary drainage pipe may serve as a wet vent if all the conditions in OBC Div. B 7.5.2.1. are met. The ones exams ask about:

load within Table 7.5.8.1.,
not more than 2 wet-vented water closets, at the same level, joined by a double sanitary T (vertical vent) or double Y (horizontal vent),
water closets downstream of all other fixtures,
trap arms and fixture drains on the wet vent not over NPS 2,
through more than one storey: not more than 4 fixture units from any one storey above the first,
not more than one horizontal offset: up to 1.2 m for NPS 2 or less, 2.5 m for larger pipe,
the wet vent is not reduced in size, and its length is not limited.

When sizing a wet vent, leave out the load of the most downstream fixture or symmetrically connected fixtures (7.5.8.1.(2)).

Wet vent NPS	Load, no water closets	Other fixtures, serving up to 2 water closets
1½	2	not permitted
2	4	3
3	12	8
4	36	14

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Stack vents, vent stacks and miscellaneous vents

Every stack ends in a stack vent that goes to open air, directly or through a header (7.5.4.1.).
A vent stack is needed only on a stack draining fixtures on more than 4 storeys (7.5.4.2.), so a house rarely needs one.
A sanitary sump gets a vent connected to its top (7.5.5.1.).
A building trap needs a fresh air inlet of at least NPS 4 within 1.2 m upstream (7.5.5.4.).
Every storey where plumbing is or may be installed, including the basement, must have a vent pipe of at least NPS 1½ extended into it or passing through it for future connections (OBC Div. B 7.5.5.5.).

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Arrangement of vent pipes

Vents must have no sags where moisture can collect, and waste pipes are back vented when installed (7.5.6.1.).
Except for wet vents, a vent connects to a horizontal drain above the drain's horizontal centre line (7.5.6.2.).
Except for wet vents, a vent rises above the flood level rim of every fixture it serves before joining another vent (7.5.6.4.).

Trap arm rules (OBC Div. B 7.5.6.3.):

Rule	Limit
Minimum trap arm length	twice the NPS of the fixture drain
Total fall of the trap arm	not more than its inside diameter
Change of direction	not more than 135° total (225° for water closets and siphonic fixtures)
Water closet vent distance	within 1 m vertically and 3 m horizontally of the fixture connection

Maximum trap arm lengths (Table 7.5.6.3.):

Trap NPS	Max length	Slope
1¼	1.5 m	1 in 50
1½	1.8 m	1 in 50
2	2.4 m	1 in 50
3	3.6 m	1 in 50
4	4.9 m, or 9.8 m at 1 in 100

Terminals (OBC Div. B 7.5.6.5.):

Rule	Value
From air inlets, openable windows and doors	at least 1 m above or 3.5 m in any other direction
From a roof that supports an occupancy	at least 2 m above or 3.5 m in any other direction
Above ground	at least 2 m
From a property line	at least 1.8 m
Above the roof or ponding water	at least 150 mm
Frost closure protection	increase one NPS, to at least NPS 3, before the roof, or insulate
Flashing on a shingled roof	at least 500 mm by 500 mm

A vent run outside the building may change direction by no more than 45° at a time, must be nominally vertical, and on a building of 4 storeys or less must end above the roof.

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Sizing vent pipes

Start with Table 7.5.7.1.: minimum vent size from the trap served. Trap 1¼ or 1½: vent 1¼. Trap 2, 3 or 4: vent 1½. Trap 5 or 6: vent 2. Individual and dual vents use this table only, sized on the largest trap, and length is ignored (7.5.8.2.).

Other size rules:

A branch vent, stack vent or vent header is never smaller than the vent pipe connected to it (7.5.7.2.(1)).
Every sanitary building drain needs at least one vent of NPS 3 or more, normally the soil stack's stack vent (7.5.7.2.(2)).
A stack vent is at least half the NPS of the stack at its base (7.5.8.4.(3)).
Sewage sump vents: one NPS smaller than the largest drain into the sump, but not less than NPS 2 (and need not exceed NPS 4). A macerating toilet sump vent is at least NPS 1½ (OBC Div. B 7.5.7.7.).

Branch vents, vent headers and continuous vents use Table 7.5.8.3.: find the load row, then read the maximum developed length under each vent size (7.5.8.3.). NL means not limited and NP means not permitted. For example, at 24 fixture units an NPS 1½ vent may be 9 m long and an NPS 2 vent 30 m. Stack vents use Table 7.5.8.4., entered by stack size and load.

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Worked example: a lavatory trap arm

A lavatory has an NPS 1¼ trap and fixture drain. The vent must be at least 2 x 1¼ = 2½ in. of trap arm away from the weir, the trap arm may be at most 1.5 m long at 1 in 50, and its total fall cannot exceed the pipe's inside diameter. Over 1.5 m at 1 in 50 the fall is 30 mm, which is under the roughly 32 mm bore, so the slope and fall both work. The vent itself may be NPS 1¼ (Table 7.5.7.1.).

Air admittance valves

An air admittance valve may terminate an individual or dual vent (7.5.9.1.), but only for fixtures in buildings undergoing renovation or where a vent connection may not be practical (OBC Div. B 7.5.9.2.). It must be at least 100 mm above the fixture drain it vents, within the maximum developed length for the vent, at least 150 mm above insulation, serve fixtures on the same storey only, and connect to the horizontal fixture drain. It may not be in a supply or return air plenum or where it could freeze, must be accessible with room for air to enter, and the drainage system still needs at least one vent to outdoors (7.5.9.3.).

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Common traps

Venting a water closet with a horizontal distance over 3 m.
Allowing an air admittance valve on a branch vent. Only individual and dual vents qualify.
Using the 1 in 100 trap arm length (9.8 m) for anything other than an NPS 4 trap.
Forgetting the 4 fixture unit per storey cap on a multi-storey wet 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
Vent pipes for traps	Every trap is protected by a vent pipe unless an exception applies.
Wet venting	A sanitary drainage pipe may serve as a wet vent if all the conditions in are met.
Arrangement of vent pipes	A vent run outside the building may change direction by no more than 45° at a time, must be nominally vertical, and on a building of 4 storeys or less must end above the roof.
Sizing vent pipes	Start with: minimum vent size from the trap served.
Air admittance valves	An air admittance valve may terminate an individual or dual vent, but only for fixtures in buildings undergoing renovation or where a vent connection may not be practical.

Vent pipes for traps
Every trap is protected by a vent pipe unless an exception applies.
Wet venting
A sanitary drainage pipe may serve as a wet vent if all the conditions in are met.
Arrangement of vent pipes
A vent run outside the building may change direction by no more than 45° at a time, must be nominally vertical, and on a building of 4 storeys or less must end above the roof.
Sizing vent pipes
Start with: minimum vent size from the trap served.
Air admittance valves
An air admittance valve may terminate an individual or dual vent, but only for fixtures in buildings undergoing renovation or where a vent connection may not be practical.

Usual exam traps

Venting a water closet with a horizontal distance over 3 m.
Allowing an air admittance valve on a branch vent. Only individual and dual vents qualify.
Using the 1 in 100 trap arm length (9.8 m) for anything other than an NPS 4 trap.
Forgetting the 4 fixture unit per storey cap on a multi-storey wet 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 7.5.4.1. 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 7.5.5.1. 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.)
Open OBC Div. B 7.5.5.1. in the code viewer
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.
Open OBC Div. B 7.5.5.4. in the code viewer

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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.
Open OBC Div. B 7.5.5.5. in the code viewer
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.
Open OBC Div. B 7.5.6.1. in the code viewer
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.
Open OBC Div. B 7.5.6.2. in the code viewer
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.
Open OBC Div. B 7.5.6.4. in the code viewer
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.
Open OBC Div. B 7.5.6.3. in the code viewer
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
Open OBC Div. B Table 7.5.6.3. in the code viewer
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.
Open OBC Div. B 7.5.6.5. in the code viewer
OBC Div. B Table 7.5.7.1. Minimum Permitted Size of Vent Pipe Based on Size of Trap Served
Table 7.5.7.1. — Minimum Permitted Size of Vent Pipe Based on Size of Trap Served Forming Part of Sentences 7.5.7.1.(1) and 7.5.8.2.(1) Nominal Pipe Size of Trap Served, NPS | Minimum Nominal Pipe Size of Vent Pipe, NPS 1¼ | 1¼ 1½ | 1¼ 2 | 1½ 3 | 1½ 4 | 1½ 5 | 2 6 | 2
Open OBC Div. B Table 7.5.7.1. in the code viewer
OBC Div. B 7.5.8.2. Individual Vents and Dual Vents
(1)The nominal pipe size of individual vents and dual vents shall be determined using Table 7.5.7.1. based on the largest trap served.
(2)When sizing an individual vent or a dual vent, the length is not taken into consideration.
Open OBC Div. B 7.5.8.2. in the code viewer
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.
Open OBC Div. B 7.5.7.2. 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.
Open OBC Div. B 7.5.8.4. in the code viewer
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.
Open OBC Div. B 7.5.7.7. 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 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 7.5.9.1. 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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