considering cutting out 4" C.I. Vent stack, replacing with 4" PVC.... need help with how to run sink drains to it....

[Jim Jensen]

2 bath sinks are back to back, have cast iron pipes that are leaded?? Oakum'd ?? into the 4" c.i. vent stack I would like to eventually replace all the cast iron under the house, and while I am remodeling the master bath, figured I should cut out the vent stack, and replace it, down to the floor, at least.... There is room behind the pipe to get a soil pipe cutter chain around it, as the wall is framed with 2 x 8's.... I have not removed the sink and toilet yet, as I don't want to go down to 1 bathroom, til I have to.... these 2 sinks have been slow draining, off and on, for last 2 years, I figure there is corrosion in those small 1" or 1 -1/2" horizontal (lead??) drain pipes.... and, *why* did they wrap them in what looks like window screen.....???

 

[breplum]

If there are other vents in the house, you don't even need a single 4".
The UPC states that the total vent area must equal the largest required building drain, which depending on how many bathrooms you have could be 3" and if there are other bathrooms you could go to 2" or 3".

 

[Jim Jensen]

There is a 2" waaaayyyy out in the garage (far end of the house), and then another 2" at the kitchen sink, so only 3 vents, total. Only 2 bathrooms. I just figured I would go back with 4", to make it fit the hole already there in the roof (it is a "torch-down" very low slope asphalt roof) thanks !!!

 

[breplum]

2" would work, for sure.
You can snap the 4" up high and use a 4 x 2 no hub type coupling, then support the rig.