kerdi drain - connections only abs and pvc?

cmc_in_sfApril 25, 2008

Hi Experts,

We live in San Francisco, CA and the code here requires us to use iron pipes only for our plumbing (no PVC nor ABS). Can we use the Kerdi Drain/System if the connection only come in ABS or PVC? What would be a good alternative? I was all excited about going Kerdi, but DH husband just pointed this out. Can the Kerdi membrane only be used with the Kerdi drain? I heard the system was build around said drain. Please advise.



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Are you certain about SF being cast iron only? You've gotten that from someone in the building department and not by word of mouth, either through a friend, a builder, or even a plumber?

It strikes me as odd simply due to CI being brittle and SF being seismic.

Hubless connectors with stainless clamps can be used to join CI and PVC.


    Bookmark   April 25, 2008 at 9:03AM
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Hi Mongo,

Thanks. Hubby said, CI is required per SF building dept., because of the seismic factor (he actually thinks it's because it's to keep the union workers working). But he thinks CI iron isn't any more brittle than PVC (since PVC can crack). In any case, we have the stuff running everywhere in the new addition and it passed inspection.

I'll have more questions as we get further into this. Right now, we're still researching (and DH isn't completely sold on Kerdi yet). So, please stay tuned or look out for more post from me (and of course I'll search the archives first as I don't want to flood the forum with indulgent Kerdi questions) :). Thanks!!!


    Bookmark   April 25, 2008 at 11:45AM
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Hey Mongo or anyone else who might be tuned in,

I'm convinced we should go Kerdi, but I think the drain thing is the only thing keeping my DH from buying into the idea. Before I call the SF building dept. (and probably get humiliated), do you know if the PVC connector counts as part of the pipe system that they inspect (in your experience)? If it is, it sounds like we won't be able to use the drain. Is there an alternative? Does the Kerdi drain have to be used with the Kerdi system? Thanks again!

    Bookmark   April 28, 2008 at 1:02PM
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My rough plumbing inspections are done prior to the Kerdi drain being installed.

Look at Fernco's website, they have connectors for transitioning from one material to another. The are approved for use in enclosed framing bays as well. If you drop the "Fernco" name he should recognize the connector.

I don't see why, even given your restrictions, you couldn't use the PVC Kerdi Drain, a Schedule 40 PVC trap, then transition to a cast iron drain pipe after the trap. Or even connect the PVC Kerdi Drain to a cast iron P-trap.

The Kerdi Drain does have to be used with Kerdi membrane. There's no way you could effectively use it with typical CPVC or CPE membranes.

I'm one of the only guys around here that still uses cast iron, though I couple it with PVC. CI provides a nice quiet DWV system.

I'm not sure if this is worth anything, but I always get better results with a building department when I have a face-to-face discussion. They can be too prone to easily dismissing you over the phone.


    Bookmark   April 28, 2008 at 2:25PM
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hope i'm not overstepping here, but i think your question about Can the Kerdi membrane only be used with the Kerdi drain? may have been read to mean the opposite of what you're asking (or maybe i'm doing that). are you asking this: "if i am stuck using a traditional drain, can i still use the kerdi membrane somewhere in my shower?"

i believe you can use the kerdi membrane on the walls of a shower & transition to a more traditional shower pan & drain system, but you cannot use the kerdi brand drain without using the kerdi membrane.

hope i didn't add confusion to the mix :)


    Bookmark   April 28, 2008 at 4:35PM
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Thanks Mongo. That's all great info.

Just to give you some background info, we had our rough plumbing inspection a couple of weeks ago and it passed, but with some corrections. One of the corrections is to make the shower pan liner higher up the wall and do a flood test (he wants to see the shower pan hold water the next time he's here.)So, this is before I thought of doing the Kerdi system. I guess he would check that all that after the Kerdi is installed? That would suck if he wouldn't let us have the drain after it was all installed. I'll check around and consult w/DH on our next move. Again, thanks for your input from your experience!

    Bookmark   April 28, 2008 at 9:53PM
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Lisa, thanks for clarifying my statement. Yes, I was asking can we still use the Kerdi membrane with a non-Kerdi drain (if we can't use the Kerdi drain).

So, we can?

    Bookmark   April 29, 2008 at 1:02AM
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Please keep us updated on your findings. We are in SF as well and planning on getting our shower redone with Kerdi. As far as I know our tub and shower drains are copper (1-1/2" tub and 2" shower)
According to
The 2007 San Francisco Plumbing Code consists of the 2007 California Plumbing Code with San Francisco Amendments

You can find San Francisco Amendments here:

One thing to note is this was in final proposals for amendments in Jan 2007 (

Section 701.1.2.1 - DSA is proposing to repeal this amendment to Section 701 of the Uniform Plumbing Code, which restricts the use of ABS and PVC as drainage pipe. Section 701 of the Uniform Plumbing Code otherwise permits the use of ABS and PVC as drainage pipe with specified conditions. Section 903 of the 2001 CPC as adopted by DSA-SS permits the use of ABS and PVC pipe materials for use as vent piping, which is associated with the sanitary drainage system. DSA has no rationale or reason to continue this restriction on the use of drainage pipe materials that are otherwise permitted by the Uniform Plumbing Code.

It may have passed since i don't see any of it in San Francisco Amendments.

But to make sure I think its best to make a trip to the SF Public Library and look at the latest Plumbing Code publications.

Sorry about so many links, but this is some info that I was able to find.


    Bookmark   April 29, 2008 at 1:30AM
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I've been lurking at John Bridge tile forums (author of Kerdi Shower Book) and as far as I know you won't be able to use Kerdi membrane on the floor with other type of drain.

If I'm correct Lisa was saying same thing.

Kerdi Drain wih Kerdi Membrane = OK
Non-Kerdi Drain with Kerdi Membrane = NO NO! ;)

    Bookmark   April 29, 2008 at 2:31AM
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Ah, thanks morozgrafix. No Kerdi drain, then no Kerdi membrane. Got it. Also thanks for the SF Plumbing Code info. That stuff is hard to read through! But I'll let you know if I find anything and please continue to keep me posted on your findings.

    Bookmark   April 29, 2008 at 10:44AM
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It's perhaps too late for your project, however Schluter markets a "Kerdi Hat" that accomodates any drain for about $22. See:

    Bookmark   December 8, 2008 at 10:12PM
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