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Draining Systems - Main Vents

Vents in draining systems protects traps against pressure differences that could cause them to siphon or blow out .

Vents protects traps against pressure differences that could cause them to siphon or blow out, leaving occupants unprotected against smell and potential contaminants from the sewer system.

Draining Systems - Main Vents
Pipe Size
Max. Drainage Fixture Units
1 1/4 1
1 /1/2 81)
2 24
2 1/2 48
3 84
4 256

1) No water closets permitted

  • at least one vent should terminate through the roof
  • air admittance valves within the building may be permitted (check local authority)
  • terminating vents in side wall may be permitted (check local authority)

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