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Vent Stack
Purpose:
to maintain
atmospheric pressure throughout the
length of the soil and waste stacks,
provide a convenient connection point for
individual, branch and stack
vents.
Definition:
"Vent Stack means a
vent pipe that is connected at its upper
end to a header or is terminated in an
open air and that is used to limit
pressure differential in a soil or waste
stack."
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Installation:
7.5.3.2.(1)
Vent Stack must be installed in conjunction with the soil or
waste stack
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in any building of 2 or more
storeys except residential ,
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in residential buildings of 4
storeys and more,
where back vents, relief vents or
circuit vents (vent piping in general) are
installed.
7.5.3.2.(2)
A vent stack is not required to be
installed in conjunction with the soil or waste stack in
a residential building of 3 storeys or less.
Connection (lower end):
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in residential buildings of 4 and
more storeys, other buildings of 2 and more
storeys:
7.5.3.2.(3)(a)(i) "...at or below the lowest horizontal sanitary
drainage pipe connected to the waste or soil
stack":
  
7.5.3.2.(3)(a)(ii)
"...to the building drain immediately
downstream of the stack connection":
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in residential buildings of 3 and
less storeys:
fixtures individual vents can be
the beginning of the vent stack
see also Code: A-1.1.3.2.
On this pictures Vent Stack is not installed in conjunction with
the soil or waste stack see
why.
Connection ( vent pipes to the
vent stack ):
"The upper end of every vent pipe
shall be above the flood level rim of the highest fixture
it serves before connecting to another vent pipe."
"No vent pipe shall be so arranged
that it will serve as a bypass in the event of an
obstruction in the drainage pipe."
Sizing
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diameter
As a rule size of the Vent Stack is
half the size of the soil or waste stack at the lowest
point of connection
Table 7.4.10.5.B.
Usually the reason to increase the
diameter of a vent stack is the connection of branch
vents, stack vents and individual vents, not the overall
developed length.
7.5.7.2. Branch Vent Sizing
- No branch vent and its connecting branch
shall be smaller in diameter than the diameter calculated
in accordance with Table 7.5.7.2.A and where Table 7.4.10.5.B. is not applicable to the vent,
the maximum length of the vent shall be calculated in
accordance with Table 7.5.7.2.B.
- For the purpose of Table 7.4.10.5.B. and Table
7.5.7.2.B., the length of a vent stack or vent
shall be its developed length of vent piping from the
vent stack or stack vent where the header terminates to
the most distant vent or stack connected to it.
7.5.7.3.(1) Developed Length
For the purpose of Table 7.4.10.5.B and Table 7.5.7.2.B, the length of a vent stack or
stack vent shall be its developed length from its lower
end where it connects to the drainage piping to its upper
end where it connects to a header or goes directly to
open air.
A vent stack shall at each point of
interconnection with a branch vent be not smaller than
the minimum size permitted by Table 7.5.7.2. A..
Fixtures can be connected to a vent stack:
if
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total hydraulic does not exceed 8
fixture units,
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at least 1 fixture is connected to
the vertical portion of the vent stack and upstream of
any other fixture,
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no other fixtures is connected
downstream of a water closet,
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all fixtures are located at the
lowest storey served by the vent stack.
Visualization of how it might be if
to connect modified stack venting to the vent
stack:
Aditional Requirements
Termination ( connection of the upper end):
7.5.5.5.(1)
The upper end of every vent pipe that
is not terminated in open air shall be connected to a
venting system that is terminated in open air:
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