New Bathroom - Venting and Draining

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by pensfan84, Oct 27, 2009.

  1. pensfan84

    pensfan84 New Member

    Oct 27, 2009
    Pittsburgh, PA
    I'll give some background information and then ask my questions:

    I recently purchased a home and decided to tear our the existing bathroom. So far I've tore out the entire bathroom to the studs and capped the existing supply lines. I'm confident in my skills to re-run the supply and drain lines.

    The old bathroom was rather crazy in its plumbing design - the toilet used a 4" cast iron stack for drainage and venting, the sink used a 2" ABS line for drainage and the 4" cast iron stack for venting, and the tub used the 2" ABS line for drainage and a 2" steel pipe for venting. Crazy, I know. Also, the old tub had drainage problems with no blockage in the drain line - my guess is that the vent is clogged or blocked somehow.

    In the new bathroom, I will be pulling out the old cast iron stack from the roof flashing all the way to the drain into the floor and will be pulling out the 2" steel pipe that was previously used for venting.

    The plumbing, both supply and DWV, will be completely new.

    My questions are regarding the drains and vents. First, what size vent pipe should I use in this application? For this vent, there will be all of the fixtures in the bathroom (lavatory, toilet, whirlpool tub), plus the utility sink in the basement. The total feet from the utility sink to the roof flashing is roughly 25 feet, and from the bathroom to the roof flashing is roughly 20 feet. From reviewing the plumbing code handbook my state uses, it appears that a 2" vent pipe will sufficiently vent all of these fixtures, so I want to be sure that you'd recommend this as well.

    After removing the existing cast iron stack, I will be replacing it with a 4" ABS pipe into the concrete floor. The utility sink in the basement has its own main drain; however, I am wondering what is the best way to tie in all three drains from the bathroom? All three of the drains will be along a single wall that is 8 ft long and are in line with each other (closest to the door, sink->toilet->tub). The critical distance between any of these drains and the vent pipe would be under 8 ft. The sink drain will be 1 1/2", toilet drain 4", whirlpool tub 2".

    The new stack will be at 4" at the base level and taper to 2" above the last drain into the vent stack.

    I had originally planned to install a closet bend for the toilet and connect to the 4" soil stack, critical distance being >6', so I was not going to install an additional vent for this and rely solely on the vent stack.

    The tub will have a 2" P-trap, and will be vented up through the wall and connect to the vent stack.

    The sink will have a 1 1/2" P-trap, and will also be vented up through the wall and connect to the vent stack.

    Also, I will be roughing in for a new bathroom on the second story of the house. This bathroom will be vented up through the attic and will connect to the vent stack near the roof flashing.

    In conclusion - I am pulling out the existing 2" vent and the 4" cast iron vent stack. In its place, I will be putting a 4" ABS pipe into the basement floor and running all DWV pipes off of that.

    My questions are these:

    1.) Am I approaching venting these pipes properly? Properly, in this case, being installing a back vent taken off the horizontal at least 45 degrees above the mid-line and tying back into the stack above flood level of the highest fixture for both the first story lavatory and tub, along with the second story lavatory and toilet. The first story toilet will vent directly into the vent stack since it is <6' from closet bend to waste T.

    2.) What is the best way to tie all of the waste pipes together? I know that this is a loaded question, but a little bit of advice in this area should go a long way. My question here revolves mainly around fittings and couplings.

    Thank you in advance for your advice.
    Last edited: Oct 27, 2009
  2. dcelite

    dcelite Plumber

    Oct 5, 2009
    Los Gatos, CA
    A picture is worth a thousand words. Can you make a drawing of what you're planning to do?
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  4. geniescience

    geniescience Homeowner

    Nov 27, 2005
    humid summers hot, humid winters cold
    Sketch & leave it blank in the middle so someone can fill in the blank to give you the answer you are looking for. Reading your post, I think you need an answer about the Wye's to use to connect the bathroom group together. Toilet, vents, etc. The geometry.

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