Toilet venting: does my code say two opposing things?

[Zenon]

My bottom line question: how can one connect a vent pipe to the vertical leg of a water closet drain AND simultaneously NEVER run a horizontal vent pipe below the flood rim level of the water closet?

Those two things cannot coexist, right?. Unless I don't understand physics or geometry...

See the photo.

See the part where it says "Vent pipe may be connected to the vertical leg". Isn't this, by definition, a horizontal vent pipe below the flood level of the fixture?

Is 7.5.6.2(1) in direct opposition to 7.5.6.3(5) - see below? And what is better: avoiding horizontal vents at all costs, but having long trap arms (but still vented within the specified distance)? Or providing vent air right at the vertical leg, but having a horizontal run (I would insist on a clean out in the vent piping, above flood level).

I've read enough posts here to understand that true professionals and plumbing "purists" would never run horizontal (dry) vents below flood rim levels. Codes that do allow such things seem to be considered far too lax, for lazy plumbers, etc. But seriously - how bad is it to stick a vent connection on the vertical leg? Is it just begging for it to get clogged with human waste?

Here is the code excerpt (relevant sections in red):

7.5.6.2. Vent Pipe Connections

(1) Every vent pipe 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 soil or waste pipe, the connection shall be above the horizontal centre line of the soil or waste pipe.

(3) Unused vent pipes installed for future connections shall be permanently capped with an end cleanout or an adapter and plug.

7.5.6.3. Location of Vent Pipes

(1) Except as provided in Sentences (2) and (3), a vent pipe that protects a fixture trap shall be located so that,
(a) the developed length of the trap arm is not less than twice the size 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, S-trap standards or 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 shall not exceed,
(a) 1 000 mm in the vertical plane, and
(b) 3 m in the horizontal plane.

(4) The maximum length and minimum slope of every trap arm shall conform to Table 7.5.6.3.

(5) The vent pipe from a water closet or any other fixture that has an integral siphonic flushing action may be connected to the vertical leg of its drainage pipe.

 

[wwhitney]

I assume the solution is that "where structurally possible" includes the notion that the vent pipes are to be run unexposed. So that if the only structural cavity available to run the vent pipe in is the horizontal joist bay, then a horizontal dry vent below the flood rim level is allowed.

US codes would require that the fittings on such a vent located below the flood rim level be drainage fittings, e.g. a long turn 90 where the horizontal vent turns up into a wall.

Cheers, Wayne

 

[Sponsor]

 

[Zenon]

Excellent point, Wayne. If that line was ever to clog, and your horizontal vent filled with nasty stuff, you would want the best chance of it draining itself back out, hence the long-sweep fittings, right?

 

[wwhitney]

Right.