Adding an attic bathroom

[soropa]

I have a house that is a hundred years old, has a basement, ground floor, and unfinished attic. I am in the process of converting the attic into liveable space and want to add a bathroom. Currently the house has one bathroom on the ground floor. The main drain is of 4" cast iron and runs horizontal with a gradual decline in the basement. The toilet, lav, and tub drain into the main drain, as well as the kitchen sink, and laundry.Where the toilet attaches to the main drain, from that point the cast iron runs vertically through the house and vents above the roof.

I would like to tie-in to the current 4" cast iron vent upstairs. I have upload a pic to illustrate what I'm talking about. The majority of the pic shows what my current set-up is, the part that is drawn in blue is my proposed set-up. Will this work? What I guess I'm most worried about is venting. I keep reading conflicting reports about venting, wet-venting etc, and what is necessary. I also would like to know if there is a particular order to the drain that is required. For example currenlty I have the new bath lav drain attaching to the new toilet drain and the new tub drain attaching to the new lav drain. Could that be reversed? For example could the new tub attach to the new toilet, and the new lav attach to the new bath instead?

Also you will notice on my proposed set-up in blue that I added an individual vent line for both the new lav and new tub that attach to the main vent at a higher point. Is this necessary? I only added it because I keep seeing plumbing diagrams where each fixture i.e. lav, tub, etc each have an individual vent line that attaches to the main vent. I'm confused as to why this is neccessary as my current set-up does not do this. If you notice my current lav, tub, kitchen sink, laundry just have drains that attach to the main 4" cast iron, and no seperate vents. As I said the house is 100 years old, but for the 10 years I have been here haven't had any problems with plumbing drainage/ or odors. Thanks for any and all help!

[jadnashua]

Won't meet current code...once a vent, always a vent. When you start to use the vent as a drain from above, it is no longer a vent for below. Now, the stuff below isn't vented properly per today's codes, either. Your choices are: run a new drain line down, or a new vent line up. You can combine the vents at 42" above the new stuff (or 6" above the flood plane, whichever is higher) so you maintain one vent through the roof, or just vent it separately, if it's easier.

[soropa]

Thanks for the response. Aside from apply with code-I'm not sure that anything in this house is up to date with current code, however its been functioning well for a hundred years-would the system work? It seems that I'm just making the current vent into a wet-vent right? Is not everything else in the house currently (aside from the toilet) wet vented?

[jadnashua]

What your local inspector requires depends on local rules. Normally, if you don't touch something, you don't have to update it. So, the stuff that's there now can normally stay as it is. The new stuff needs to meet code. So, if you want the new stuff to meet code, you'll need to add a drain line or a new vent. Check with your local inspector. Problem is, especially between floors, if there's a clog somewhere down below, adding waste through the 'vent' as it is in your drawing, could cause it to overflow out of each fixture down below, not a pretty picture. Say you decide to take a nice long shower...all of that waste water could end up on the floor downstairs. If there were a separate vent and drain, you'd notice it backing up and hopefully, turn things off before things got out of hand.

One of the pros will likely confirm my thoughts. But, your best bet may be talking to the local inspector as to what he'd allow.

[cacher_chick]

The age of the house is of no matter.
Anything that you add needs to meet the minimum requirements of the plumbing code.
A new drain stack connected downstream of the existing fixtures would be required.
You cannot wet vent between floors.

[Terry]

Vents can be tied together at 42" above the floor, which also means that the lower vents can only tie in at 42" above the second floor of the second floor vents.

Waste from above needs to tie in below the downstairs plumbing.

Just because you are the car in front, it doesn't give you the right to throw your ice cream cones out the window at the car behind you. That's what the trash bag is for.

[hj]

You are trying to stretch the definition of a wet vent, but it does NOT apply in your situation. Regardless of whether the existing was vented or not 100 years ago, you are changing the dynamics by adding the bathroom upstairs. That would have required changing the venting for the downstairs even 100 years ago. There is no "quick and dirty" way to do what you want to.