View Full Version : “extra” Cast Iron Vent pipe still needed? NSPC

06-03-2010, 09:29 AM
Per my town building inspector in Northeast NJ, code no longer requires a 4” cast iron DWV pipe that rises up from my house’s main Drain-Waste-Vent pipe just before it exits my house. Is there any reason to keep this pipe? I need to cut and cap it, or cut and replace it with re-routed PVC, so I can have an electrician replace my electrical service (the cast iron is about 2’ from my fuze boxes). My approx. 100-year old 3-story (3-apartment) house has a vertical cast iron DWV pipe that penetrates my roof and which the 4 bathrooms tie into. This main DWV pipe leads into the horizontal one under my basement slab, which then runs about 40’ where this “extra” vent pipe and then 2 clean-outs rise up from the horizontal DWV pipe just before it exits my house. This apparent “extra” vent pipe rises straight up approx. 5’, then runs horizontally about 6’ where it exits my house through an above ground penetration in the side of my foundation. I assume it’s 4” cast iron buried under my slab since everything else above the basement slab is cast iron, but I was told the pipe from my house to the city sewer is clay pipe. If current plumbing code does not require this “extra” vent pipe, is there still good reason to replace it with PVC instead of just capping it? I assume the original installers did it for a reason. Does it significantly help the flow of waste and help prevent my old clay pipe from getting clogged? Is it an emergency escape path for sewage if the sewer feed pipe does clog - letting the waste flow out of the side of your house instead of out of a first-floor bathroom? If so, the later-installed basement bathroom renders this benefit useless. Regarding vent pipes, my house also has a 2 inch vent pipe that exits the roof above 2 kitchen sinks. Any feedback/suggestion would be greatly appreciated. Thanks, Craig

06-03-2010, 01:20 PM
A lot of areas wouldn't allow clay pipe inside the house it had to be changed to cast iron when it entered. Without knowing EXACTLY what that pipe is for I wouldn't touch it, you could be removing part of your plumbing system.

06-04-2010, 08:08 AM
I wouldn't even try to follow your description. You may not need a 4" pipe through the roof, but you still need SOMETHING, and normally, you have to have the equivalent area through the roof, meaning something like four 2" vents, or two 3" ones, etc. ANy combination which gives an area, NOT a diameter, equal to a 4" pipe.

06-07-2010, 12:03 PM
thanks for the advice/input. Just to clarify, my house does have a vertical 4" cast iron DWV pipe that penetrates the roof and which services 4 bathrooms (stacked one on top of the other). It also has what looks like a 2" vertical DWV pipe coming up through the roof above 2 kitchen sinks. The "extra" pipe (4" cast iron) that vents out my foundation (above ground) rises up from the cast iron drain pipe under my basement floor just before this main drain pipe exits my house for the city sewer.

this "extra" pipe is somewhat common in my neighborhood. And my house is actually 1 of 5 houses in a row that were built at the same time with this "extra" pipe. 2 of the 5 have since had it removed - not sure if its caused problems, but I'll see if I can find any knowleadgable local plumbers who are familiar with this type of design.


06-07-2010, 02:21 PM
Maybe this extra vent is for a house trap or something?