View Full Version : adding attic bathroom. cast iron stack questions

09-22-2008, 06:29 AM
i am thinking about adding a toilet and sink to my attic and was thinking that it would make most sense to add it directly above the bathroom below it to tie into the existing cast iron stack.

how would one tie into the cast iron stack?

i'm not going to do it myself (i'll do the rest of the plumbing)
but i'd like to know the process.....

would i cut (or snap) away a section, and leave the cast iron out to the roof still (supported prior to cut of course)

and if so, what is used to tie the new PVC into the cast? a fernco?

thanks for the info.
always curious of this stuff.


09-22-2008, 06:43 AM
A no-hub connector (Fernco makes some) would be used. But, you'd need to revent the lower floor. Using it's vent as a waste pipe changes its use from a vent to a waste line.

There has been some discussion about inserting PVC into a cast iron vertical stack. If I remember, it is not allowed in some places. The considerable weight of the CI might have long term problems on the PVC in the middle. They do make no-hub CI bits, then you could transition to pvc for the new horizontal stuff, if that's an issue. You'd crack out a section of CI, insert a new Y in CI, then transition to pvc.

09-22-2008, 06:46 AM
Back the truck up! That cast iron stack coming up through the roof is the vent from the lower floors. You absolutely CANNOT put waste from your attic bathroom into that. You will need a new vent from the lower floors.

09-22-2008, 07:32 AM
Depending on how the lower floor plumbing is installed it is probably IMPOSSIBLE to isolate it so you could install a separate vent for it. You will probably have to run a new drain line down from the attic and tie it into the drain system below the first floor. This usually means you can put the bathroom anywhere you want it, within reason.

09-22-2008, 07:40 AM
sorry for my confusion guys.

the main stack is a waste line for the toilet on the 2nd floor.
the kitchen sink on the first.
it's also a waste line for a slop sink in the basement.

doesn't it ALSO operate as a vent for the toilet?


09-22-2008, 08:16 AM
All the vents should tie in above the highest fixture that is dumping waste into the stack. I'm with HJ on this! Run a new pipe to the basement it is easier.

09-22-2008, 09:28 AM
What constitutes a vent above the waste lines can't be used as a waste line without redoing the vents it is compromising...as I said, you'd have to redo the vents from below. Depending on the layout, it may be easier to run the waste from the new bathroom down to the lower floor (maybe all the way to the basement) below where the pipe you see in the attic becomes a vent. Keep in mind that the waste for a toilet needs to be at least 3", and the vent line may not be that big.

10-24-2008, 06:10 AM
thanks for all the help guys.

i've got this question about this vent stack:
if the only one fixture (toilet on the 2nd floor) uses this stack as it's waste and vent, then can a toilet be added above it on the 3rd floor?

all other fixtures in the house have/use a different vent....

thanks again.

10-25-2008, 07:43 AM
It makes no difference whether the toilet below it is on the first or second floor. UNLESS that toilet is set up with a vent separate from the main stack, and usually there would be no good reason to do it that way, it CANNOT be used as a drain for something/anything on a floor above it.