Can this be used this way?

[JCA1]

Can a wye be used to connect a horizontal pipe to a vertical pipe to connect two vent pipes together just before they go through the roof, or does it have to be a DWV tee?

[LazyPup]

In order to use a wye the offset from the second vent would need to come in at a 45deg angle and the wye would be connected upside down.

Also, If you live in a geographic area which is subject to freezing temperatures in winter, and if this is an auxillary drain which is less than 3" diameter it needs to be increased to 3" at least 1' inside the structure before going through the roof.

The vent must extend a minimum of 10" above the roof or 6" above the average snow line, whichever is greater.

[JCA1]

Ok, what I have is 3-2" vents coming to one side of the house, I plan to bring all 3 of those together just before going through the roof and increasing to 3" before going out. I have 2-1.5" and 1-2" vent on the other side that I planned to carry through the roof on 2", if I understand what you're saying this needs to be 3" as well.

On one side, one is 1.5" off the utility tub, one is 2" off the washer, one is 1.5" off the kitchen sink all originating behind the fixtures. On the other side, one is 2" off of two lavatories, a closet, and a tub. This one originates right behind the downstairs lavatory. The next 2" is off of this same area coming from under the house between the tub, and 3" main, and connecting to another 2" vewnt in the wall(a). The nest 2" is off a lavatory, closet and tub, originating behind the lavatory. One is 2" off one shower and a closet originating off the 3" drain in the wall(a). This is what I have so far but I think I need atleast one more somewhere coming off the 3" main close to the bathrooms. Does this sound OK? I don't expect you to "cyberplumb" my house LazyPup, I am talking to inspectors as well, but I find your info to be much more educated. After all, you are a master plumber and trully the inspectors may know little more about plumbing than I and I want this stuff to work.

[LazyPup]

It sounds like you may have many more vents than what you are actually required to have.

I am attaching an isometric drawing of a typical bathroom group. Note the lenght of the waste arm from the trap to the vent. If the length of the waste arm is equal to or less than the indicated maximum lengths it does not require additional venting.

[JCA1]

Ok I guess I'm in good shape then. Will having more vents than needed have any adverse affects on the system? As a side note I spoke with local inspector earlier. He said that here we are no longer required to have 3" vents. He said just tie the vents together and carry them out the roof on 2". What advantages would 3" have over the 2"? It seems to me like it would allow much more vaccum if more than one 2" vent was needed at a time. Say if someone was running water in the sink in two baths at once?

[LazyPup]

Both the International Residential Code and the Uniform Plumbing Code require all structures to have one main vent that runs undiminished in size from the main drain through the roof, however, The Uniform Plumbing Code does allows an option to the main venting rule that is sometimes adopted by local code authority;

The total area of vents must be equal to or greater than the main buiding drain. (UPC 904.1)

All piping in the drain system must be sized in such a manner that when the pipe is carrying its full rated flow a horizontal run will only be 1/2 full. That allows enough liquid flow to carry any solids that might be present in the line, while still keeping the upper half of the pipe open to permit the free transfer of vent air.

If a pipe is overloaded it then runs full and vent air cannot transfer which results in sucking water out of the traps, which would then leave the traps open and potentially dangerous sewer gases could get into the structure. If a pipe is too big the water level is too low to carry solids, which then pile up and clog the pipe.

In order to have a uniform method of sizing the pipe we work from tables in the code book that use an index called a DFU (Drainage Fixture Unit).

The code specifies the diameter of trap that is required for each fixture in the structure. The bathroom lavatory has the smallest diameter trap which is required to be 1-1/4"

In order to develope the DFU system they first measured how much water could discharge through an 1-1/4 drain under gravity flow in one minute and found that to be 7.5gals. which is 1 DFU.

The code has tables listing all the fixtures that can be found in a structure and a DFU value for each fixture.

Example:
lavatory 1 DFU
Bath tub/shower 2 DFU
Shower Stall 2 DFU
Water closet >1.6gal 4DFU
Water closet <1.6gal 3DFU
Kitchen sink 2DFU
Clothes washer standpipe 2DFU
etc, etc,etc

In additon to the DFU tables there is another table that lists the minimum size trap that may be attached to a fixture, which means that would also be the minimum size line that may serve that fixture.

In the post above I listed the maximum distances a horizontal pipe may run from the vent to the trap without adding additional venting. If the horizontal lenght exceeds those limits we must then install an auxillary vent.
Once we have the DFU load for any given section of pipe we then check the pipe size chart to determime proper size:

Pipe size-------------Horizontal ------- Vertical
1-1/4" 1 1
1-1/2" 3 4
2" 6 10
2-1/2" 12 30
3" 20 48
4" 160 240

There are other tables for the main drain and building sewer line.

A vent may be reduced to 1/2 the diameter of the pipe it serves, except, if the lenght of a vent exceeds 40' in must be increased one nominal trade size.

Contrary to public opinion there is no guessing in plumbing just as there can be no guessing in the electrical trade. We simply compute the load and select the appropriate size of pipe in the same manner an electrician would determine wire guage from charts in his code book.

Once we have the DWV system figured out, we must then use the same system to compute the water distribution piping throughout the structure from a different set of Fixture Unit Tables.

[JCA1]

Ok that makes sence. Thats very similar to the fules line sizing charts I use everyday so I'm somewhat farmiliar to those. According to the basic info. you posted above I should be OK. I do not have a 3" main vent but the total area of my vents are greater than the 3" main, and my trap arm distances are within those limilts and are adequately sized for the DFU they serve. Thanks very much for this information and all your help. I'm starting to feel like one of your apprentices...he-he.

[LazyPup]

If you haven't already done so, pop up and read my post at the top of the Plumbing forum labelled "Thank You All" and you will see why I and the other guys in here take the time to answer all these questions.

[JCA1]

Thats great LazyPup, people like me really appreciate your willingness to provide your hard earned knowledge. In fact I'm writing "LazyPup" on that closet drain you helped me with in honor of you. Before it's over the inside of my walls will look like a notebook I'm sure, and you'll be there.