DWV Layout for Bathroom Remodel (2)

Stu27 · Sep 23, 2010

Attached is a drawing of my dwv layout for a master bathroom remodel where we wish to move the lav, shower, and toilet to new locations. I tried to be much clearer than previous post, used 3D, and showed all vents this time. Lav drain is 1.5", shower drain is 2". Is this a good design, will it meet code? Thanks.

Dlarrivee · Sep 23, 2010

Looks pretty good to me, the only area I'm concerned about is the drain for the lav and shower tying in before the vent for the w/c, is that allowed? I'm not a plumber though. Just wondering what software you used?

Sponsor · 2022-01-29T12:20:58-0800

hj · Sep 23, 2010

The 2" vent after the shower is strictly cosmetic and performs absolutely no function.

Dlarrivee · Sep 23, 2010

hj said:
The 2" vent after the shower is strictly cosmetic and performs absolutely no function.

So would the shower be wet vented through the lav without it, or would it be vented through the green "to roof" section?

Stu27 · Sep 23, 2010

I put the wye and 1/8 bend in the same relative position (between the toilet and vent) as it was in the original layout for the tub drain. I could move it downstream to the other side of the main vent, if necessary.

Software is VectorWorks.

Stu27 · Sep 23, 2010

hj said:
The 2" vent after the shower is strictly cosmetic and performs absolutely no function.

The original tub was wet vented and had poor drain performance, so I was focused on finding a way to dry vent each new fixture.

If the 2" vent were removed and if the the lav was running at the same time that the shower was in use, would the shower then be wet vented? If that were the case, would the shower drain performance suffer as compared to leaving the 2" vent in place?

NHmaster3015 · Sep 24, 2010

good, bad or no venting will have no difference on drain performance. Water flows in a pipe just fine without any vent at all

hj · Sep 24, 2010

good, bad or no venting will have no difference on drain performance. Water flows in a pipe just fine without any vent at all

That is true as far as it goes. Vents come into play before AND after the fixture drains, and only slightly while it is draining. Therefore, they have LITTLE to do with the draining, although under the right circumstances a fixture will drain better and faster without a vent. In this case, the shower would use the sink vent, but depending on factors not apparent in the drawing, I would probably NOT connect the shower at that point anyway.

Dlarrivee · Sep 24, 2010

Hj you would rather it take a more direct route than a combo, and those two 90s prior the 45 and wye?

Inspektor Ludwig · Sep 24, 2010

So it looks like you have a horizontal wet vent for your lav and shower and toilet, Like HJ said, the 2"vent downstream of the shower is useless, if you want to dry vent the shower then you need to pull the vent off of the shower trap arm before it ties into the main line of the lav waste. The 2" vent downstream of the toilet is also useless since it appears that the horizontal tie in of the shower and lav is between the toilet and the toilet vent. If you want to dry vent the toilet then the same rules apply as with the shower, you need to put the vent downstream of the toilet but upstream of the shower/lav tie in. If you want to run everything on a horizontal wet vent, then I would eliminate the 2 "optional" vents and use the lav vent only (2"). Of course if you want to use the vents there's no harm in it but it's just more work, more money.

NHmaster3015 · Sep 25, 2010

the vent for the toilet is not doing anything either

Stu27 · Sep 25, 2010

Thanks to all for the feedback so far, I appreciate it!

I've added some photos of the existing plumbing (as-built by home builder) for context. Some limitationsâ€¦
- I was trying to layout the drains so as not to bore any more holes in the floor joists (my thought here was to keep the floor as stiff as possible as the entire area will get tile when done).
- the new lav and shower will be on an exterior wall that has an engineered piece of lumber beneath (thought I'd avoid pipes in this wall altogether)
- existing sanitary tee on its back venting the 3" waste (from my readings here I understand this is not to code). I plan to correct this in the remodel with a combo (already shown in the 3D drawing)

Stu27 · Sep 25, 2010

I will move the 2" drain entering the 3" waste at the wye + 1/8 bend to downstream of the main vent (poor judgement on my partâ€¦ copying the existing layout)

Assuming that change will correct the toilet vent, how best to proceed with the lav and shower drains/vents...

I can see (now) that in my proposed 3D layout the shower would vent off the lav vent and the 2" shower vent was not helpful.

Can I simply move the lav drain tie-in to a point on the 2" drain that is downstream of the shower vent, thus giving both fixtures dedicated, functional vents (like in the attached layout)? If that is overkill (or pathetic), any suggestions are appreciated.

I want to do this right (hey - that's why i'm here). Thanks again for the helpâ€¦

Geniescience · Sep 25, 2010

Now you the joists are visible, I'll say that it is best NOT to use the existing holes in the joists. You can strengthen your joists every easily later if you want them stiffer. It's not a challenge.

New holes to be cut would not be in the center of the span, so that is another (minor) good thing if you want to overthink this. New holes would be near the shower drain. The waster water would follow a far more direct route.

my opinion.

hj · Sep 25, 2010

Is there a reason you are NOT utilizing the existing connection and holes in the joists? Without a floor plan showing HOW the shower is being installed, it is not possible to optimize your piping, but it appears you are doing it the hardest way possible.

Stu27 · Sep 25, 2010

hj -- yes, I am using all existing holes in the joists (four total). The only change from the existing tub drain location is the preferred center drain for the shower which would add one new joist hole nearest to the shower trap, then pick up the original tub trap arm joist hole. The 2" drain continues and picks up the final three existing joist holes to run across to tie-in to the 3" waste. So, as configured, I'm only adding one new hole next to the shower trap).

Geniescience · Sep 25, 2010

stu27, in my response, posted at the same time as hj's i thought you were indeed re-using joist holes. Imagine for a minute there are no joists in the way. Then, plan a DWV route. Then, bring that ideal plan into the joist structure, without any big changes. Doing this you will have a couple 1/8 bends instead of three 1/4 bends. If you do this, you will have unused holes. Having seen the photo, I know you have a clear space to put a reinforcement onto the joist. Search "sister joist" in a search engine.

Stu27 · Sep 25, 2010

geniescience -- I wound up with this spaghetti drain layout trying to get the venting right and using existing joist holes. I was trying to avoid wet venting which I had blamed for previously poor tub drain performance, but have been corrected on that.

If the drain layout were optimized for the shower, I can see bringing the trap arm off the drain 135 degrees CW of what I've shown and one 1/8 bend down to the main drain tie-in (and that only requires one joist hole). I'll have to noodle on how to vent the shower in that config, given the framing limitations...

Attached is another drawing with no plumbing changes -- only added framing, again for context (that's a roof line on the other side of the darker rear wall and you can see the solid lumber structural member below the floor of the rear wall preventing me from plumbing the rear wall).

Stu27 · Sep 25, 2010

In this version, the shower drain is run in a more direct manner (which ignores the easy access it had previously to a wall with a vent). I like the direct routing of the 2" shower drain. The centerline length from the weir to the 3" vent is roughly 9 feet. That length requires some type of vent, right? It won't maintain an air gap at 1/4" per foot of slope over 9 feet. Is the (wet) vent from the lav enough? Or should the shower get a dedicated vent (need some ideas on how...)? Feel like I'm close... thanks for the patience with the questions.

Geniescience · Sep 25, 2010

keeping it as drawn now, imagine you move your Lav drain over, way over, by going through the wall studs. Come down into the joist bay where it will meet the new 1/8 bend of your new shower drain. This puts the (wet) vent closer. Also, the lav drain doesn't have to turn corners. This is what I meant when I said to imagine the best possible configuration without the joists. As it turns out, you only have to drill one new hole. Also, you get a clean run of joist to "sister" and strengthen. But, hey, what do I know, this might be all wrong. Wait for at least one other post confirming this. If you do this, you also have to figure out where to put a clean out. A shower niche or a shower bench will be a good means to hide the access panel to a clean out.

DWV Layout for Bathroom Remodel (2)

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