Drain pipes and vent stack sizing
Vents transports sewer gas through the building to open air space. Properly installed the vents prevents traps siphoning and sewage gas to leak into the interior building.
Different codes in different jurisdictions exists and must be adhered to locally. In general we talk about
- individual vents
- relief vents
- circuit vents
- branch vents
- stack vents
Individual vents serve individual fixtures.
This vents only one fixture but may connect into an other vent that extends to open air.
- an individual vent should be at least one-half the size of the drain it vents (no less than 1 1/4", 32 mm)
Relief vents provide additional air to the drainage system where the primary vent is too far from the fixture.
- an relief vent should be at least one-half the size of the drain it vents (no less than 1 1/4", 32 mm)
Circuit vents are used with more than one fixtures. A circuit vent is installed before the last fixture extend up to open air or connects to an other vent that extend to the outside
- an circuit vent should be at least one-half the size of the drain it vents (no less than 1 1/4", 32 mm)
Branch vents are vents extending horizontally that connects multiple vents together.
A vent stack is used only for the purpose of venting.
Vents are normally sized by using the "Developed Length" (total linear footage of pipe making up the vent) method.
Maximum length of vent stacks and relief vents
|Maximum length of vent stacks and relief vents (ft) |
|Size of Soil Waste Stack|
|Fixture Units Connected||Diameter of Required Vent Stack (in)|
|1 1/4||1 1/2||2||2 1/2||3||4||5|