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.

Pipe Size (in)	DFU max. (in)
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)

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

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