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 Drain-waste-vent system design - advice
Author: sammy412 (CA)

I'm designing a drain-waste-vent system to handle two baths and laundry. I'll be tying into 4" ABS sewage line, that has a 2 inch vent (See figure 1). It's a Single story house with crawl space, in Southern California with very moderate temperature. All venting will go straight up through roof.

Questions:

Are there enough vents (i.e. does the washing machine need its own vent)?
Is the location of the vents correct?
Is the plumbing sized correctly?
Any problems with this design?

Existing plumbing:



Proposed Design:

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 Re: Drain-waste-vent system design - advice
Author: packy (MA)

you've made it way to complicated.
first off, as drawn the washer does need a vent.
next, take the bathroom sink and tie it into the toilet drain and tie the tub into the sink drain. one 2 inch vent will take all of that.
then tie the tub into the other toilet drain and vent that 2 inch.
we really need a side view to get any further.

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 Re: Drain-waste-vent system design - advice
Author: sammy412 (CA)

[i.stack.imgur.com]

I followed the advice from a few forum members. Thank you all so much. The floorplan for Bathroom B has changed and now I have a new design. Many thanks to forum participants for all their tips.

Please let me know if I am on the right path to a good and UPC code worthy design. Is the venting correct?

Post Reply

 Re: Drain-waste-vent system design - advice
Author: packy (MA)

closer but still far away...
eg.. the toilet at the top shows a dry vent taken off the back of a fitting. how long until that dry vent will clog and become useless?? not to mention that it is prohibited to run flat until it is 6 inches above the flood rim of the highest fixture it serves.
no one can tell (here or on any other forum) without a side view of your proposal..

Post Reply

 Re: Drain-waste-vent system design - advice
Author: sum (FL)

Not a plumber but what is the purpose of the 2" vent at the lower right corner off the 4" pipe? What fixture does that serve?

It may be easier to do an ISO to get real opinion as it is hard to comment just on the horizontal without taking into consideration of the vertical. Also for wet venting distance along pipes matter so important to show distances.

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 Re: Drain-waste-vent system design - advice
Author: sum (FL)

Packy just curious is it better to plumb DWV of each "bath group" on their own before tying them together? Or is it better to plumb clusters of fixtures in close proximity?

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 Re: Drain-waste-vent system design - advice
Author: sammy412 (CA)

I have more than 2' vertical space in the crawl space. The runs to Toilet B is about 12". For all the plumbing I had planned to slope the standard 1" per 4' of pluming. Can you let me know how to vent that toilet or would you like me to make an attempt first?

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 Re: Drain-waste-vent system design - advice
Author: packy (MA)

sum, so much depends on the existing framing (floor joist). i have done more keeping the same bathroom piped as a single group but i've done some where the directions of the joist made grouping them impossible.

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 Re: Drain-waste-vent system design - advice
Author: sammy412 (CA)

What are the down sides to keeping venting separate? More holes in the roof, cost??? It seems easier down the road to troubleshoot or repair if they are separate.

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 Re: Drain-waste-vent system design - advice
Author: sum (FL)

In my opinion (and I am not a plumber so...) too many vents can be confusing.

As far as ease of trouble shooting, I think of trouble shooting by yourself the person who did it as well as trouble shooting by someone else not you later on once you sold the place or whatever. The more vents there are I think the more confusing it gets.

Also more vents is more roof penetration which means more chance of moisture penetration. If you re-vent and tie some together in the attic, then your attic is harder to navigate...I go up to the attic to make repairs and vent pipes, rigid electrical conduits, AC duct works are always in the way.

Also more vent pipes in the stud bay going up the walls could put limitations on future improvements. For example you may want to put in a pocket door and a vent is in the way or you want to open up a wall and a vent is in the way.

There are many considerations that goes into a DWV design. Different people tend to optimize their design differently, by cost, by ease of installation, etc...I personally tend to optimize to provide the least number of joints and directional change, and I tend to have the lav and shower tie into the toilet line sooner, so the water from these fixtures could rinse that line when these fixtures are used.

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 Re: Drain-waste-vent system design - advice
Author: sammy412 (CA)

Here is my latest design and I am ready to build once I figure out if is going to work.

Layout (birdseye view):
[imgur.com]

Center Leg of above layout (side view):
[imgur.com]

Right leg of above layout (side view):
[imgur.com]

I want to know if the system will work (odors, clogs, etc). Should I add any cleanouts (i.e. shower tubs etc?) If so do they go upstream or downstream from the p-traps? Do I use sanitary T or a long turn wye for a cleanout?

Please comment so I can get to building.

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