Plumbing new shower drain 2" from 1.5"

[madosta]

I have an existing master bath, but I want to upgrade to a shower.

I need help with the venting, my plumber can't make it today, so I figured I would see what you guys thought.

Existing plumbing, I cannot find a vent. The sink elbows into the wall and does not go up through the roof.

Proposed would be to tap the 2" directly into the 3" trunk between the toiled and the sink, but this doesn't seem right.

Proposed. Moving it over to center it in the shower and not cut any joists.

I feel like I need a vent, but the house is newer (2009) approved plumbing inspection, and I don't understand. (Yes I am having a plumber do it, just wanted some opinions.)

 

[bmwpowere36m3]

You need to know where the vents are.... you're allowed a certain number of inches on a horizontal before a vent. For a 2" drainage line (sloped 1/4" per ft) that's 8 ft.

 

[madosta]

What is really weird is that I climbed in the attic and pulled the p-trap off the sink, and there is no vent at this end of the house. I don't get it.

 

[holt2ton]

My old house had anti siphon valves​ on every sink to prevent toilet flushing from sucking the water out of the p-trap. Also does the same if you fill up the sink and then drain it. The quick introduction of water causes the valve to open letting air into the drain line and ​preventing the trap from being siphoned dry.

 

[The Cobbler]

does the sink drain turn down at the wall or does it run horizontal in the wall?
if it is horizontal in the wall, likely the vent comes off the horizontal run of the drain & vents to the stack at the other end.

sometimes home owners /builders request this type of stuff to eliminate extra flashings etc.
when I was apprenticing for plumber, we had a homeowner ( new house) where they didn't want any copper lines fastened to the underside of the joists . we had to drill each joist and run the copper thru them. it meant that we roughed in before the brick went on the outside, we ran a lot of the pipe (that was perpendicular to the joists) from the outside to eliminate short pcs.

 

[madosta]

does the sink drain turn down at the wall or does it run horizontal in the wall?
if it is horizontal in the wall, likely the vent comes off the horizontal run of the drain & vents to the stack at the other end.

sometimes home owners /builders request this type of stuff to eliminate extra flashings etc.
when I was apprenticing for plumber, we had a homeowner ( new house) where they didn't want any copper lines fastened to the underside of the joists . we had to drill each joist and run the copper thru them. it meant that we roughed in before the brick went on the outside, we ran a lot of the pipe (that was perpendicular to the joists) from the outside to eliminate short pcs.

The sink p trap goes into an elbow straight down. I'm going to have to look down the trunk to see if there's a vent hidden somewhere.

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[mires]

I can't see your pics but I think you may be thinking too much into it. If everything drains just fine and it passed inspection, then the venting is fine. When you switch to a shower, just use a reducer coupling to switch to 2'' pipe since that is what the shower is designed for.

 

[s14kev]

I can't see your pics but I think you may be thinking too much into it. If everything drains just fine and it passed inspection, then the venting is fine. When you switch to a shower, just use a reducer coupling to switch to 2'' pipe since that is what the shower is designed for.

This is not necessarily up to code in all regions. I would be cautious with a 1.5-2" restrictor. Many require 2" all the way to the main stack. I just went through this and found the 1.5" did not drain well in one bathroom. Changing to 2" fixed the issue.

 

[Lunker]

2" is code on a shower 1.5" on a tub

 

[scottydosnntkno]

This is the one item I dont understand about modern plumbing code. Taking a 40-80 gallon tub of water(standard vs jacuzzi tub), popping the drain the letting it all drain at once through a 1.5" pipe is perfectly fine.

But if you have a shower, with a 1.5gpm low flow head(90% of showers) , or even say two rain heads and body sprays running 8gpm, you need a 2" drain? It definitely does not take s tub 5 minutes to drain, so why does the lower flow fixture require a bigger drain.

 

[Lunker]

This is the one item I dont understand about modern plumbing code. Taking a 40-80 gallon tub of water(standard vs jacuzzi tub), popping the drain the letting it all drain at once through a 1.5" pipe is perfectly fine.

But if you have a shower, with a 1.5gpm low flow head(90% of showers) , or even say two rain heads and body sprays running 8gpm, you need a 2" drain? It definitely does not take s tub 5 minutes to drain, so why does the lower flow fixture require a bigger drain.

I think it's because exactly what you described the tub can hold a lot of water but shower pan cannot.

 

[scottydosnntkno]

I think it's because exactly what you described the tub can hold a lot of water but shower pan cannot.

So the tub, holding more water, gets to drain into a smaller drain? That doesn't make sense

Or your saying because a tub spout, even left wide open could theoretically never overrun a 1.5" drain capacity? That's more likely. But when it gets to the tub overflow, they are always so small I never see them keeping up with the flow if the main drain gets clogged/stopped

 

[ddawg16]

So the tub, holding more water, gets to drain into a smaller drain? That doesn't make sense

Or your saying because a tub spout, even left wide open could theoretically never overrun a 1.5" drain capacity? That's more likely. But when it gets to the tub overflow, they are always so small I never see them keeping up with the flow if the main drain gets clogged/stopped

You are kinda missing the point.

If a tub can't drain...the water sits there. It has an overflow....if you leave the water on, it drains out the overflow.

But the shower? No over flow...no storage capacity....

With the tub, you have a lot more buffer (time) if things go wrong. Shower? Nadda.

 

[madosta]

I've heard as well that the 2" is for a quick recovery. Think if you dropped a wash cloth that covered the shower drain and then remove it, the 2" will clear it faster. The overflow for the shower is the floor so yea, we don't want that.

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