Question about Wet Venting

[Peter Langevin]

I live in a 1 1/2 story home, one bathroom on the first floor. I had a remodeling contractor out last week to give me an estimate to add a second bathroom to the upstairs bedroom. His quote came back significantly ($5000) higher than the other 2 I got, and when I asked him what the difference was he said it was due to a "wet venting issue." I mentioned that 2 other contractors hadn't mentioned it, and he essentially told me that they didn't know what they were doing.

I'd like to see who is "all wet" so I know who to believe. The layout is pretty simple and to the best of my notes I'll try to recall what the last guy said.

I have a single bathroom (tub/lav/toilet) on the first floor, as well as a kitchen sink and dishwasher. A single 3" PVC pipe is used for the drain on all of those items, and it extends straight up through the roof without anything else connecting to it.

The bathroom on the second floor would be right next to the 3" pipe, and the other contractors said they could just drain right into it, and that it would also serve as the vent, as long as everything was within 5' of it upstairs.

The last guy said that you can't drain fixtures from the second floor into the same drain used for the first floor, since the first floor fixtures are being "wet vented" into that pipe. To add the bathroom upstairs would mean that you would have fixtures "wet vented" above others that were also "wet vented." This contractor says the extra $$ is to add a second 3" PVC drain all the way to the basement and extend it through the roof. When I spoke to the first 2 contractors they told me that he was nuts, and that they could absolutely be vented and drained into the same "stack" and that the "DFUs" were not exceeded. No idea what a DFU is.

So, help! Who is correct? Can I add the second bathroom upstairs with the same vent/waste pipe?

Thanks all!

[Dan]

Your plumber knows what he is talking about and is proposing to do the job right- The other two are hacks and clearly don't understand code requirements for venting- DFU is drain fixture unit, has nothing to do with this situation-

Dan

[m Ransley]

The wet vent guy is all wet for an extra 5000

[Joseph Meehan]

As I recall, when you are talking about a bathroom the more expensive contractor is correct and you do want to follow his procedure or you may find you will loose the water forming the traps in the lower baths when the upper toilet is flushed.

[m Ransley]

Then what does a high rise building do, you dont see 100 vents comming out of a 100 story building. My 3 story apt gas 1 stack per 3 toilets

[m Ransley]

Ive also looked at many roofs of 3 storey houses with multiple baths one on every floor using the same stack and have instaled 4 basement apts using the same stack as the 2 above, Ive not had a problem in 15 yrs on 4 conversions. Im no plumber but Ive " shared" stacks. You are talking "Air" venting which should not " suck " anything out of a different toilet . I ve also been on a few larger apt building roofs , I have only seen 1 stack per run. If that were the case then large buildings of 100 - 500 toilets would have the roofs covered with stack vents. Pouring 5 gallon of water down a vent won`t creat a suction, maybe pouring 500 gallons in a few seconds will. I still say the 5000+ guy is wrong , unless it is a 1/4 " pipe which it surely is not. . It is most likely 3" or 4 " venting.

[John Gilmer]

I own a high rise condo. I don't know the details but the "vent function" is accomplished without any obvious vent. There are 26 floors in each building and about 30 bathrooms and 20 kitchens per floor. Note that during extreme weather you can see the water level in the toilet bowl vary a good fraction of an inch.

[m Ransley]

John Im sure you have 1 stack per run through the roof. So you may only have 1 if everything is inline. It may only extend up 5" with a vent hood but it is there, perhaps hidden among other roofing equipment as to not be obvious or in the open.

[Eric Tonks]

Simple, an apartment building combines all the drains into one that leaves the building. The vent works the same way they are all combined into one vent that runs through the roof. Basically you only need one drain stack and one vent stack to handle all plumbing. Sometimes because of horizontal spacing you may have more than one vent through the roof.

The more expensive plumber is correct in that you need a vent stack from the bottom to parallel the drain stack, which can combine together in the attic to vent through the roof.

[Speedy Jim]

The last guy is 100% correct.

Here is why: When you flush the upstairs toilet, the slug of water rushing down the stack will create a vacuum as it passes the lower toilet and will try (might succeed) to siphon the water out of the bowl.

In addition, the sinks/tubs on the 1st floor have vent connections into the stack using TEE fittings. That slug of water from the 2nd floor will easily branch off into those vent lines, disrupting trap seals on the sinks.

In h-rise bldgs, there is not one single stack. There will be at least one soil stack and a separate vent stack. All waste will drop into the soil stack and all traps will be connected to the vent stack.

Go to the BigBox store and get a basic plumbing book or go the local library. Good books will have pics showing how it is correctly done.

Or, call the town inspector and ask. After all, the 2 guys with the low bids *will* be getting permits. Right??

It's a big job in a residence to add another stack thru existing walls.

Jim

[Brian Barnson]

I asked a venting question here a while back and someone posted this instructive link:

Brian, in Cedar

[m Ransley]

Now im getting a bit confused, I put in basement apatments and hooked everything to the main 4" or so drain that takes care of 2 upper floors and all is fine for years. I thought the main drain was the vent as it terminated out the roof. or am I wrong. It all works well though.

[Andy Hill]

DFU = "Drainage Fixture Unit"

It's been a couple of years since I've had to deal with this, but last time I checked most residential codes only allow wet venting for fixtures on the same floor, so if they're planning on just dumping the 2nd story waste into the existing vent stack, that's a no-no.

That's not to say that a new soil stack all the way to basement is needed -- if the existing soil stack (and associated vent stack) is big enough (that's where the DFU issue comes in), then it might be possible to use the existing vent stack as the 2nd story soil stack (sliced off accordingly), and run a new vent stack (starting at the existing hole in the roof). down to the 2nd and 1st floors.

I'm not a plumber by trade, 'tho, so something may've changed in one of the codes in the last couple of years.

[Pop]

Thanks, Brian; great link!

Pop

[JerryMouse]

That's only if the water moves like a cylindrical hunk of Jello. I can't imagine the amount of water it would take to fill the cross-section of a

3-4" pipe under the influence of gravity. I don't think you can do it absent much higher pressure, like a fire hose. The water is going to run down the sides of the pipe maybe 1/16" thick.

Now is some kind of SOLID plug (like a diaper or football) is moving down the drain, maybe you can generate a vacuum. Water alone won't do it.

Here's a compromise: Do the remodel without the new stack. If it doesn't work, retrofit enough parts to make it work.

[Greg O]

All the vents can be ran back together into one at some point. The problem here is one stack for drain and vent, a big no no! Greg

[Greg O]

It may work, but it is not up to code in most areas. Just 'cuz it works, don't mean it is right! Greg

[NoSpamFANatic]

[Calvin Henry-Cotnam]

I believe in our code (and probably others) a wet stack may be used for venting only where it carries a single sink or tub, but not a toilet, from above.

Even so, I lean towards only using only dry stacks for venting.

Dry stacks start with the vent on the roof and proceed down to each fixture they serve. Branches for each fixture must take off the main stack above the flood line for the fixture. Therefore, no fixture can ever have water from it flow into the dry stack.

[CR]

I don't know about you, but when I use the toilet there is a hell of a lot more than water going down the waste line, not quite a football but close. And if you have any women in the house, the amount or toilet paper used is incredible. With a wife and two daughters they can use over a roll a day. What's up with that anyway? They roll about 20' of it around their hand just to dab off after they pee and then repeat once or twice.

CR