Replies

1. 
   rdesigns | Aug 06, 2009 05:33pm | #1

   The total combined flow could be as much as 15 gpm if you have 4 heads and 2 body sprays.

   Table 7-1 of the UPC lists showers with 1 head as 2 fixture units, and each additional head as 1 fixture unit. With this approach, you would figure 6 fixture units. The Code is not really clear on your specific question, because Table 7-5 lists 2" horizontal pipe as having the capacity for 8 fixture units, but section 702.1 lists a 2" trap and trap arm as having a 4 fixture unit capacity. Then again, Table 7-4 ("Discharge Capacity in Gallons/minute for Intermittent Flow") lists 6 fixture units as equivalent to 30-50 gallons/minute.

   Confused? Me too.

   The IPC is not any clearer. It simply lists showers at 2 fixture units and requires 1-1/2" for shower trap size, but lists nothing for multiple-head showers. For unlisted fixtures, it  requires 4" (!!) for 6 fixture units.

   This is a case where your local inspector or AHJ could go either way--2" or 3". Best to call him and see what he says.

   Don't assume that he'll be OK with 3" because oversized traps tend to lose their self-scouring properties and the Code (UPC,Table 7-3, footnote 7) cautions against it.

   FWIW, my opinion is that 2" will be OK. But, you should also check with Kohler to see if they've developed any written guidelines on this. I couldn't find anything on their Website that was helpful. You will probably find that they (Kohler) will fall back on the usual response of manufacturers:  installation must be in accord local codes. So you're back to your local inspector.

2. 
   MikeHennessy | Aug 06, 2009 05:41pm | #2

   What rdesign said, but no matter how many shower heads you have, they won't be able to deliver more than your supply can, and the supply is generally the limiting factor. So you might want to consider your max delivered flow from your supply when sizing the drain.

   Mike Hennessy
   Pittsburgh, PA
   Everything fits, until you put glue on it.

3. 
   Mongo | Aug 06, 2009 08:00pm | #3

   For draining the water, a 2" drain and 2" drain line are fine for the supply fixtures that you're specifying. I'd only add a second floor drain if the shower was unusually large and the flow was coming from differing walls. A second drain in a large shower can help minimize the depth of the mudbed, depending on the size and shape of the shower.

   Another consideration is venting. But that's somewhat separate from this question.

   
   

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   Edited 8/6/2009 1:13 pm ET by Mongo