Please help with new basement bathroom DWV piping layout.

chachee · Jan 30, 2012

Quick background details, House was built in 1952 with unfinished basement, concrete all the way up to the first floor sills. The main floor bathroom has a 4" cast iron stack that leads out the front of the house, away from the proposed bathroom location and is approximately 20" below finished slab elevation (located by local plumber). Kitchen sink at the back of the house has a 2" pipe with 1- ½" vent drains the kitchen sink (main floor), floor drain, utility sink and clothes washer (basement) and leads out of the back of the house approximately 10" below finished slab grade and is near the location of the proposed bathroom. Having trouble laying out the waste piping and provide the required venting, either through the roof or AAV. Total DFU if I connect to the kitchen pluming = 13 which leads me to 3" piping from the water closet with 2" vent(?). Please offer up suggestions on how to plumb the bathroom drains. Increasing 1.5" vent for kitchen is not feasible as it would require going into wall cavity behind kitchen cabinets with granite counters. Let me know if there are any additional details I need to provide.

chachee · Jan 31, 2012

First attempt at layout

Haven't received any feedback so here is my first attempt at a layout.

Concerns/questions
1. Can an AAV be placed in a wall cavity? where do these usually go?
2. Is there sufficient venting for the shower between the 1-1/2" and 2" AAV?
3. Can the drain and vent for the clothes washer go around the corner in the wall framing?
4. Can I use a Fernco coupling to connect to concrete?
5. I assume I have to use Ductile Iron under the footing?
Any feed back would be greatly appreciated.

Sponsor · 2022-01-29T12:20:58-0800

Cacher_Chick · Jan 31, 2012

If it helps, the vent stack can run across the basement overhead (with pitch) to a more suitable location where it can go up and through the roof.

The WC can be wet vented through the lav. Keep the 3" line as straight as possible and run the 2" lav drain to the 3" line. (not the 3" to the lav drain)

The shower trap must be vented. Run the trap arm towards the outside stud wall so you can run the vent up in the wall to connect to the other vent in the wet wall.

If you connect the floor drain as drawn, it will need to be vented, as the bath drainage would otherwise siphon the trap.

Dlarrivee · Jan 31, 2012

I would avoid the AAV at all costs, you cannot conceal it within a wall.

No problem with coming up somewhere other than behind your fancy cabinets/counter-tops, you can run the vent horizontally between floor joists until you find a good spot to head vertical again.

I'm interested to see how this all ties into the existing 4" drain for the rest of the house?

hj · Feb 1, 2012

The only correct vents are the ones for the washer and lavatory. All the others are either in the wrong place or missing. Why would you use "Fernco" to "connect to the concrete"? Good luck finding a short piece of ductile to go under the wall. It looks like a typical "Handyman or DIY" installation. You cannot connect a toilet to the 2" kitchen drain, but it has nothing to do with "fixture units".

Terry · Feb 1, 2012

Almost none of that works in Seattle.

I will try to look at it better later today. But don't bother putting any of that together.

chachee · Feb 1, 2012

Thanks for the feedback, I will work up another layout to post

Thanks for the feedback cacher_chick and dlarrivee. I will take your recommendations and revise my layout, just haven't had time to work on it yet. I will have to put the vent in a soffit to run to a first floor wall cavity where I will have access to drill the holes out for the 2" vent and take it up through the roof.

HJ - You nailed it, I am a DIY'er who is trying his hand at laying out the plumbing after reading up on some code, that is why I posted the questions to get some help. I have a new found respect for plumbers, it's not as easy as it first would appear. If you can provide any substantive help other than "its wrong" I would appreciate it.

Any ideas of how to pass under the footing if I am not able to find any ductile iron pipe? The new 3" (or I may go with 4") pipe will be connecting to existing 4" concrete pipe just outside the footing.

chachee · Feb 1, 2012

Revised Layout

Here is a revised layout

3 inch from the water closet straight out to the drain connection outside.
WC wet vented through 2" Lav connection - route vent through roof via soffit, joist bay, main floor wall cavity, attic.
Utility sink connection moved above the drain line to vent separately to the revent line.
Shower ran to exterior wall to vent up to stack. (not sure how this connection will work if I have to use DI under the footing, ie fitting will be too close to footing.)

Sorry for the rough sketch. Didn't have time to draft it up.

chachee · Feb 4, 2012

connection

I spent the afternoon digging a hole to confirm the connection point. The 2" comes out of the house and connects to the 4" concrete pipe about 2 feet from the foundation wall. You can see the 4" connects via a wye, the upstream end is a roof downspout from NW corner of the house (combined sewer). If I am able to find some 4" DI pipe, what type of coupling should I use to connect to the ex. concrete pipe?

chachee · Feb 4, 2012

Any thoughts or suggestions on the revised layout above?

Dlarrivee · Feb 4, 2012

Why iron pipe underground?

chachee · Feb 5, 2012

Didn't think I should put PVC/ABS beneath the foundation. Is ABS allowed beneath a footing?

Cacher_Chick · Feb 5, 2012

I can't comment much more on your layout because the detail is too small and it would be easy to misinterpret what you are planning. If you were to draw an isometric diagram detailing the distances, sizes, and fittings being used, then it would be more clear.
Hopefully you are not doing this work without a permit. Here we must submit an isometric as part of the permit process. This kind of work really needs to be permitted and inspected.

I would pipe C.I. out to the concrete and connect with a reducing fernco of the appropriate size. The existing concrete will need to be cut and the existing drain piped into a new wye. There needs to be a cleanout at grade on the outside of the building near where you are digging.

I'm not from Washington, nor am I a plumber, so take it for what it is worth.

chachee · Feb 6, 2012

I will try to add detail to the layout to show lengths. Might have time tonight. The work will be permitted I am trying to find a solution to the plumbing to get the permit...

Good idea about adding the cleanout.

chachee · Feb 6, 2012

Revised ISO with distances. Let me know if there is anything glaring...
I think I have too many fixtures on the existing 1.5" vent (washer, kitchen sink, utility sink, shower, floor drain)

chachee · Feb 6, 2012

moved shower vent to new 2" vent.

Cacher_Chick · Feb 7, 2012

Your shower vent would not fly here.

A vent cannot run horizontally until it is at least 6" above the flood rim of the highest fixture served.

This it why I suggested that you run the drain to the outside wall. The vent must be vertical.

chachee · Feb 7, 2012

Then is the water closet not properly vented either? This is why the original layout had the drain going to the back wall to vent the WC and connect the lav. Should I go back towards that layout?

Cacher_Chick · Feb 8, 2012

The WC is wet vented through the lavatory vent, which is allowed. Given your layout, the shower vent must be vented with it's own dry vent, which must be vertical at least until it is at least 6" above the flood rim of the highest fixture.

Again, my state does not fall under your plumbing code , so my references are general, and may not pass inspection in your state.

chachee · Feb 9, 2012

Lets try this again. This time I am leaving the kitchen/floor/laundry drain alone and connecting the new bathroom pluming to the 4" CI from the bathroom at the front of the house. There is a lot more distance to travel (cutting through ex. slab) but I believe it makes the plumbing a bit more straight forward.

Connection point is 13"+ to center of pipe. Assuming that the long sweep 90 is directly attached to the wye with cleanout just above FF. At 30' of pipe, 1/4"/ft equals 7.5" of fall. Should be enough to get the shower drain tied in just below the slab.

FYI King County (governing jurisdiction) allows wet venting for bathrooms.

See 4th bullet down "Bathroom (Horizontal) Wet Venting"
I believe that this layout adheres to this criteria - but I open it up for discussion. I am going to go in on Monday to get my permits so I would like to figure this out quickly.

Thanks for all your help!

Please help with new basement bathroom DWV piping layout.

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