Noob Vent Question

[Chris Carroll]

Just curious on the following scenario. I have a 4" horizontal main drain line. I've branched all my 2" and 3" drains off this with each fixture having it's own vent line tying together in the attic to go out the roof. Since each branch line (fixture) is vented do I still need to run the main drain up to the attic for venting as well?

 

[hj]

That depends on your code. Some DO want the main line extended out through the roof with a "full sized" pipe all the way. Other areas you can combine and/or reduce the sizes as long as the AREA, not diameters, (i.e., it takes four 2" pipes to equal a 4" pipe), of the pipes going through the roof equal the area of the pipe coming in to the building.