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Unread 12-10-2007, 05:38 AM   #1
ShowerSam
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Question Drain Rough in

I am replacing a bath tub with a shower. The plumbing for the tub did not have a visible p-trap to the iron waste pipe. Do I need to put a p-trap in? I am using a Kerdi drain and kerdi membrane system. As it is there is a elbow from the drain to a 2" street elbow that fits into a black doughnut that is installed in a 4" iron pipe. Is it customary that the p-trap is part of the iron pipe rough in? I need to know before I cover everything up with the shower pan.

For the shower walls, I have installed hardi board over a plastic vapor barrier on the wall studs. The joints in the hardi board are taped and the hardi board has been floated with mortar to build it up to the same level as the sheetrock. I am ready to put the shower pan in and then the membrane.

Thanks for the advice.

Last edited by ShowerSam; 12-10-2007 at 05:56 AM.
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Unread 12-10-2007, 06:02 AM   #2
ddmoit
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Hi Sam, and welcome to the forum.

Smart choice to use Kerdi for your shower. Since you are replacing a tub, your existing drain line is probably 1.5". Code almost everywhere for a shower is 2", so your current P-trap configuration doesn't matter since you'll be replacing it.

Your new P-trap will reside directly under the drain. Sounds like everything you have is iron right now. Your new material will be either PVC or ABS, depending on which is used in your area. Be certain to order the Kerdi drain that matches what you use.

As for connecting the new stuff to the existing 4" iron, there's always a way. A good plumbing supply store should be able to tell you what you need, or one of the experts here might know.
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Unread 12-10-2007, 06:07 AM   #3
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Hey Sam,

I see that you've added some information to your post while I was posting. If you're using the Kerdi system, you do not want the vapor barrier behind your cement board - and you can use drywall instead of cement board if you want.

The Kerdi drain is not like other drains, and it is meant to be used with the Kerdi membrane. Kerdi shower pan construction is different (easier) than a ordinary shower pan.
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Unread 12-10-2007, 06:23 AM   #4
ShowerSam
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OK , the walls are already finished. I assume that the vapor barrier is overkill at this point since the walls are finished. My concern is that right now there is no PVC ptrap between the drain opening where the Kerdi drain attaches and the iron pipe with the doughnut. When I took the bath tub plumbing out there was not a ptrap either. Is the ptrap part of the iron pipe rough in or do I need to install one. Another question is whether I need to have this remodel inspected. I have done all of the work myself. The original layout was a separate shower and a bath. Now I have a larger shower with a drain at both ends. I am planning to have a peak in the center of the shower pan, sloping toward each drain; dual shower, one with body sprays.
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Unread 12-10-2007, 07:31 AM   #5
muskymike
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Hi Sam, you don't need a vapor barrier with Kerdi. I'll move ya over to the Advice Forum. As far as inspection, it depends where you are at.
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Unread 12-10-2007, 08:32 AM   #6
esobocinski
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Hi Sam. Sounds like you're still trying to figure out the P-trap requirement.

You always need one P-trap between the drain and the rest of the waste plumbing system. The basic purpose is to create a water barrier to prevent gases and fetid smells from getting into the home through the drain. It isn't surprising that the iron pipe itself doesn't have a P-trap, since the trap is almost always part of the tub drain assembly and would have been removed with the tub. On very old houses in my area, I have seen a couple of cases where the trap wasn't directly under the tub because there wasn't room in a shallow floor, so they put an elbow to get to a nearby wall, then plumbed a trap in the waste line itself as the first part of the vertical drop down the wall. Unconventional, but was allowed if it was close to the tub. Check to see if they did this to you. If your tub truly had no trap at all, then it was wrong.

As ddmoit already said, a shower drain is 2" by code, but most tub drains are only 1 1/2". The logic here is that most drains in your home simply need to drain, and if the drain gets slow, the water just stays in the tub or basin until it gets through. In a shower, you want the water to drain immediately, and 2" gives you the margin to make sure that happens.

If your existing pipe really is 2", then you got lucky. First, take another look at the route and make sure that they didn't already include a trap somewhere else along the 2" line. If there is one then you don't want to add a second one, because that'll create an airlock between them and will prevent draining. Assuming that you don't have this strangeness, then you will want to add a trap to the PVC or ABS tail coming off of your new shower drain.

Double check though that you really have a 2" line. A 1 1/2" trade size is almost 2" at the outside diameter, but only 1 1/2" (or a little larger) on the inside. It can get confusing if you eyeball it.

--eric (a DIY'er, but I actually read code books )
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Unread 12-10-2007, 08:46 AM   #7
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I guess I can add that, since you have two drains in a single shower, it's your choice whether to tie them together and use one trap for both (into a single waste line) or to trap them separately. I personally would do separate traps anyway, because in my experience it is easier to clear plumbing problems that way, but it doesn't really matter.
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Unread 12-10-2007, 01:46 PM   #8
ShowerSam
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Eric,

First thanks for the reply.

I understand the need and pupose for the P-trap. As I described, I have converted a shower/bathtub into a 2 head shower, shower dimensions are 34" x 112". The drain for the old shower definitely went to a P-trap. When I removed the old bathtub I don't remember seeing a P-trap from the bath drain to the sewer pipe (4" iron pipe). There was a rubber flange in iron pipe with a reducer from 2" to 1 1/2". Everything after the reducer was 1 1/2" . As I recall, there was the pipe from the bathtub drain to a T-fitting, the top of the T was plumbed to the tub overflow, the bottom went to the reducer in the iron pipe. I have had the drain plumbed and it has about 2" of concrete over it to bring it up to the level of the foundation (slab). I have no odor from the drain and I can hear nothing from the drain if I flush any toilet in house, it has been like this for about 2 months while I built the new enclosure. This tells me that the 2 drains probably tie into a common P-trap. I understand it would be uncommon to have a P-trap in the iron pipe. I also understand that I don't want 2 traps in the same line. I should have verified all this prior to concreting over the new drain, that's why I not a plumber! Is there any other way to tell if the old bathtub drain has a P-trap somewhere that I didn't see? If it matters the house was built in 1985.

Any help is appreciated.

Thanks
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Unread 12-14-2007, 01:54 PM   #9
esobocinski
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Glad to help.

I suppose that anything I have to say after this point is probably bad news. :-( The remote tee arrangement is a old-style workaround. Your house is new enough that it's pretty doubtful that you'd have one of those. In modern plumbing, the trap would have been attached to the bottom of the tee you described connecting the overflow and drain.

Current plumbing codes usually require the trap to be within 30" of the drain. They also require the trap to be "self-scouring", meaning that the water needs to be flowing turbulently enough through the trap to prevent normal grit and gunk from settling into the bottom of the trap and clogging it. Putting the trap right under the fixture solves all the problems, and cheaply. Putting the trap a distance away requires funny tricks to make it work correctly. Your house isn't old enough for the requirements to have been much different back when it was built.

You've described your drain run in enough detail that I'm pretty confident that you would have remembered seeing the trap in a funny place if it was there. If you remember that 1 1/2" pipe emptying directly into the 4" drain as a straight run, then you have no trap.

I don't have a good idea for how to test for a trap, but here's my best shot: If you get a short length of 2" pvc and can seal one end against the shower drain while blowing into the other end, you should be able to "gargle" the trap water. If you haven't used this drain line in a while, pour a glass of water down the drain first to make sure there's water in the trap (if it's there). If there's no air resistance when you blow, then you don't have a trap.

You still have the problem that your shower drain pipe is smaller than code requires. I suppose that it's on your conscience to decide if you're going to fix it.
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