I have been designing a drainage plan for an old home. The plan is a little weird because I have to work around duct work and some other things. I would appreciate any thoughts or pointers as to the easiest and best way to setup this system. One thing I am wondering is if I may be able to shrink the vent stack down to 2" so the roof penetration is not as large?

Hi mrjmb:

To begin, you cannot reduce the size of the roof penetration to 2". All homes must, at a minimum, have at least one penetration through the roof that is 3" pipe. However, you note that the pipe is 4" in the basement. If you start out 4" in the basement then my code says you must exit the roof full size 4". If you are pulling permits I am confident that this will be required.

The area with the washing machine will require an additional vent for the sink. The sink cannot use the washing machine vent as a vent for the sink. ALL sinks must have their own vent.

That being said, I see that the only sink you vented is the kitchen sink. You will need to add an individual vent at all sinks in the home.

The bathtub also appears to have no vent. Here, if your local code permits you may be able to connect into the sink drain and use the sink vent as a WET VENT for the bathtub. Here, the pipe size must be 2" for the drain and the vent. The 2" vent from the sink runs full size 2" until it connects into a 2" vent upstairs.

The shower also appears questionable (sorry... ;)) in terms of venting as I see that you also connect a sink drain into the stack at the same level. Here, again, if wet venting is allowed you can connect the shower drain into the sink drain and use the 2" sink vent to wet vent the shower.

SO, basically, you need to add vents to the sinks and use these sink vents to wet vent the tub and the shower.

I would also recommend that you install a full size cleanout at the base of the waste stack... code required. You will also need to add 2" cleanouts on the kitchen sink drain line UNDER the sink and at the base of the 2" pipe going from the basement to the kitchen sink. I would also add a cleanout at the washing machine and at the bathtub/sink area.

For now, check with your local plumbing inspector and see if wet venting is allowed in your area.

A shower drain requires a 2" drain. A washing machine requires a 2" drain with a 2" ptrap with a standpipe about 30" tall. All underground piping (if any) must be 2" minimum pipe size.

Let me know any questions you may have... O.K?

MARK

Some of this plumbing is preexisting and I'm hoping that I can avoid too much work.

So the vents are no problem to install. However the drain lines coming from the washer and sinks will require a bit of concrete removal in order to ty them into the existing toilet in the floor. Can I run the 2" washer and sink line through the wall to the stack as well as the laundry sink?

Another thing is that the stack is 3" right now. There is a 4" pipe coming into the house then it is reduced to 3" at the 90. Can I run a 3" vent from the top of the stack? Or do I need to take the reducer out and put in a 4" stack?

The existing system seems to work considering that there is only one vent in the entire system which is coming from the kitchen sink.

This house was built in 1939 by the way.

There are a couple other things I was thinking that I forgot to mention in my last post.

Is it OK to us AAV's in the basement?

Also the sink on the far right will be used as a salon sink for now so it needs to be at the edge of the counter. The reason I designed the 2" pipe to run around through the wall is in case someone in the future wished to move the sink more towards the center of the counter space and use it as a kitchen sink instead.

Nice visual.. Mark is offering good advice. In addition to it, here are 2 cents from a plumber who works under UPC Code:

Please, keep in mind that you don't have to connect all vents to 3" stack. That kitchen vent and washer/sink vent can to through the roof on its own... or they can be combined in the attic and penetrate roof as one vent. That can save you some crawling in tight spaces...