Ask Me Help Desk - Why 6" above flood rim of highest fixture?

hey tom, how goes it?

I just completed my cast to pvc conversion of my attic reomodel. I did revent all my existing fixtures up so that they are 6" above the flood rim of my 2nd floor lav. My question is why? :confused: I can't seem to come up with a decent reason. Could you enlighten me? Also, I plan on using a studor vent on my attic lav, and from applications I heve seen, they are installed only a minimum of 6 inches above the tee. What gives?

to sum up:

1)why do the fixtures have to be revented 6 inches above flood rim of highest fixture?

2)why doesn't this apply if I use a studor vent on that highest fixture?

thanks again for all of you professional advise.

louie

Quote:

Originally Posted by atticguy

hey tom, how goes it?

i just completed my cast to pvc conversion of my attic reomodel. i did revent all my existing fixtures up so that they are 6" above the flood rim of my 2nd floor lav. my question is why? :confused: i can't seem to come up with a decent reason. could you enlighten me? also, i plan on using a studor vent on my attic lav, and from applications i heve seen, they are installed only a minimum of 6 inches above the tee. what gives?

to sum up:

1)why do the fixtures have to be revented 6 inches above flood rim of highest fixture?

2)why doesn't this apply if i use a studor vent on that highest fixture?

thanks again for all of you professional advise.

louie

Good morning Louie, Welcome back, How did your attic installation go? I still have the diagrams that you sent me on file.
I'll answer your questions in order.
(1) )why do the fixtures have to be revented 6 inches above flood rim of highest fixture?
Because Chapter 14,(Vents and Venting) Section 1406.3(Height above fixtures) of The Standard Plumbing Code says so. And Studor AAV manufacture agrees with them in their installation specs.
(2)why doesn't this apply if I use a studor vent on that highest fixture? Where did you get this information from? It applies to all installations,
(3)i plan on using a studor vent on my attic lav, and from applications I heve seen, they are installed only a minimum of 6 inches above the tee. What gives? That's the MINIMUM of 6 inches, the maximum can be as high as you wish. Where did you wish to install it?

Plumbing codes are written to address the worst possible scenario. Lay it out on paper, if you left a open vent or revent below the water level in a fixture and since water will seek its own level you will get a backflow into the vent system.

Good luck Louie and don't be such a strainger. Tom

"How did your attic installation go?"

Reasonably well. After bracing about two feet of cast below my roofline, and removed a chunk of cast to the floor. I was then able to cut the cast right below the cast tee on the first floor which was a current revent. I then lifted the stack through the wall and into the attic, it wasn't as heavy as I would have thought. Sawzalled though all connections first though. My one hang up was cutting the sink vent. The vibration threw something out of whack and I ended up with a snapped drain-thankfully not inside the wall-! Always something eh? Then converted each vent to pvc and reconnected them to the main stack in attic. I still have to run the drain line for attic lav. That is what I'm hashing out now. It is stubbed out from the stack already.

1) the attic sink will be vented via a studor vent, this studor vent, (which must be a min. of 6" from tee), must extend upwards until it is 6" above flood rim of the same sink that it is venting right?

Quote:

Originally Posted by atticguy

"How did your attic installation go?"

reasonably well. after bracing about two feet of cast below my roofline, and removed a chunk of cast to the floor. i was then able to cut the cast right below the cast tee on the first floor which was a current revent. i then lifted the stack through the wall and into the attic, it wasn't as heavy as i would have thought. sawzalled though all connections first though. my one hang up was cutting the sink vent. the vibration threw something out of whack and i ended up with a snapped drain-thankfully not inside the wall-!. always something eh? then converted each vent to pvc and reconnected them to the main stack in attic. i still have to run the drain line for attic lav. that is what i'm hashing out now. it is stubbed out from the stack already.

1) the attic sink will be vented via a studor vent, this studor vent, (which must be a min. of 6" from tee), must extend upwards until it is 6" above flood rim of the same sink that it is venting right?

No! Go to the Studor web site , scroll to the bottom of the page and click on "installations". The Lavatory may be vented directly behind the trap under the cabinet. Cheers, Tom

Hey Speedball,
The schematics for loop vents used in island sinks break the 6" above highest floodline rule and I'm wondering if a loop vent can be applied to any other fixtures. How about a dishwasher that is not directly adjacent to a sink? Or a shower stall?

Jason

Quote:

Originally Posted by tanman

Hey Speedball,
The schematics for loop vents used in island sinks break the 6" above highest floodline rule and I'm wondering if a loop vent can be applied to any other fixtures. How about a dishwasher that is not directly adjacent to a sink? Or a shower stall?

jason

A shower stall is usually found in a bathroom where it's wet vented by the lavatory vent so there would be no reason to install a loop vent and dish washers are usually found in the kitchen where a separate drain and vent aren't necessary. However I suppose that if no drain and vent were available you could enclose the dishwasher and install a drain with a loop vent. While it's true we aren't held to the 6" rule with loop vents you have to understand how they're put together. In a island sink loop vent the bottom of the loop is the drain and we set the "P" trap lower then usual while looplng up as high as we can in the cabinet with the return loop. When the sink drains it drains past the "P" trap and goes down into the lower drain pipe. The higher vent pipe is looped almost to the flood rim so unless there's a blockage the discharge never reaches the vent pipe. The loop prevents this from happening. While a lavatory with the vent installed below the flood rim will feed by gravity back into the vent when you drain a full basin. Hope this explains this to your satisfaction. Regards, Tom

I was just thinking about those fancy installations like a shower/tub in the center of a large bathroom or even a bedroom.

Thanks for the reply... love this website.
Jason

Quote:

Originally Posted by tanman

I was just thinking about those fancy installations like a shower/tub in the center of a large bathroom or even a bedroom.

thanks for the reply... love this website.
jason

While I've never done it that loop ventwould be the easiest since the drain's so low. Tom