Is there a max slope for shower drain? - Plumbing Forum

markcool · 10-19-2011, 11:42 AM

I'm roughing in a bathroom in my attic, and the best way I've been able to find to tie into the stack with the shower drain gives me a slope of 4" over 3.5'. That's a little more than an inch per foot.

I haven't been able to find anything in the code book about a max slope, only a minimum.

Is there any reason that this would not pass inspection?

Thanks!

**Otahyoni** · 10-19-2011, 11:57 AM

As long as you have a proper trap at the shower, i doubt it would matter if the drain went straight down.

I'm not a plumber and i dont know the code in your area.

markcool · 10-19-2011, 04:30 PM

If it goes straight down, then it's an S trap, which is not allowed.

Flat slope facilitates self-cleaning of any solids. The only solids I anticipate in the shower are probably hairs.

I just want to be sure the slope's not too steep before the inspector comes.

**FlushMasta** · 10-19-2011, 11:32 PM

Quote:

Originally Posted by markcool

If it goes straight down, then it's an S trap, which is not allowed.

not neccesarily true. i don't know how your current venting configuration is, but i hope this diagram can explain.

the top trap is what im guessing what you're asking. that is considered an s-trap, and that is what you should avoid. basically the weir of the trap is higher than your tie-in making the vent obsolete. again i hope my diagram can help. but! if you have your trap vented properly, you can have as much fall as you'd like

**Otahyoni** · 10-20-2011, 12:23 AM

Thats why i said i'm not a plumber. I don't know everything.

So an "s" trap will siphon itself out? Is that why you can use them?

**FlushMasta** · 10-20-2011, 01:18 AM

it can, and yes

**Caduceus** · 10-20-2011, 01:33 AM

The only concern that I could see is with such fast fall on a horizontal pipe connecting to a vertical stack the pipe would not be completely seated into the hub. I hope that made sense.
The inspector may surmise that the pipe and the hub don't seat squarely enough to give a reliable joint. It may pass test, but over a period of time could develop a leak.

**phishfood** · 10-20-2011, 01:48 AM

If the stack is the vent for the trap on the shower, than 4" of fall is too much, refer back to FlushMasta's illustration.

**Caduceus** · 10-20-2011, 02:10 AM

Yeah, that too. Sorry, forgot to reinforce the importance of FlushMasta's drawing. Thanks, phish. I've had the hydraulic grade conversation too many times with some apprentices and they still don't get it. Should copy and print it.

markcool · 10-20-2011, 11:50 AM

It's like Flushmasta said, mine looks like the diagram. As far as seating, I think the joints are solid. I am tying into a 45 that drops inside the wall, where the 2" drain connects to the 3" stack via a 3 x 2 Wye.

To recap; there's a 2" trap with a 39" arm descending at a slope of 1"+ per foot to 2 street 45's, which go into the 3 x 2 wye.

The reason I'm having to drop it is because I'm in a 1940's house with 2 x 6 joists. The weir of the 2" trap is proud of the subfloor. In the shower, it's np, as I'll be pouring concrete for a shower pan, so IK can work around it. Once it gets out of the shower, I need it to be below the floor.

The only other way I could think to do it is to add 2 45's to the trap arm to dip it, which would essentially create two smoother slopes over the 39" with a dip. Is this any better? I have about 2' before it leaves the shower area.

The trap is 7", so can I go 14", then twist it downward to another, lower path with two 45s?

Alternately, can I add a vertical 2" vent inside the wall, go straight from the trap to the vent, then drop to the drain?

I would have to run the 2" vent inside the wall to tie it into the 3" stack.

Thanks again for all the feedback, I appreciate it.

Trying to do it right the first time.