Need advice on DWV layout for small cafe (commercial space)

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Mliu

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I'm working on a small bakery & cafe. I'll need to install new drain lines, tying into an existing waste line in the service corridor behind the shop. (The existing line flows to a grease interceptor that services the building.) I'm planning the shop layout and need some advice on the design of the DWV lines.

The shop is on the ground floor with a concrete slab. There is a rise in elevation between the main shop floor and the back office (and service corridor) floor, but the existing line is 3 feet below grade, so fall won't be a problem.

There will be 3 floor sinks, 3 floor drains, 2 hand washing sinks, and 1 mop sink. The following is how each fixture will be configured:

Floor Sink #1: Indirect drain for a "water station" for filling glasses of water (and may get an occasional cup of coffee dumped into it. The water station is rated at 2.2 gpm and has a 3/4" drain. Also indirectly draining into this floor sink is the drain line for a small, under-counter ice maker. This floor sink will have a 2" outlet. Based on the size of the floor sink outlet, the load should be 2 DFUs. But based on what is actually emptying into the floor sink, it's probably equivalent to a water fountain at 0.5 DFU. I'm not sure which load number is required to be used in this case.

Floor Sink #2: Indirect drain for a small sink in a food prep worktable. This sink will mostly be used as a source of water for making receipes (meaning, very little water will be going down the drain). Nevertheless, the sink is comparable to a bar sink and I beleive it should be rated as such. Again, there is confusion as I've seen some sources list bar sinks as 1 DFU and others list them as 2 DFU. This floor sink will also have a 2" outlet, so that may force the load to be 2 DFU.

Floor Sink #3: Indirect drain for a 3-comp sink used for ware washing. This floor sink will have a 3" outlet. The load rating, based on the 3-comp sink, will be 6 DFU.

Floor Drains #1, #2, & #3: For draining any water spills and for washing down the floors. Each will have a 2" outlet and each will contribute 2 DFUs.

Hand Sinks #1 & #2: Each has a 1.5" outlet and each contributes 1 DFU.

Mop Sink: The mop sink has a 2" outlet. According to IPC Table 709.1, a service sink is assigned 2 DFUs. However, I have seen other sources list mop sinks specifically at 3 DFUs. Again, the requirement is not clear.​

This is my proposed layout for the branches (Note: I only labeled the two Wyes where the major branches join):

DWV Plan.png

My desire is to have this installed as a Combination Waste and Vent design in accordance with IPC Section 915. The branches will be sized as follows:

  • Floor Sink #1 and Hand Sink #1 plumbed to Wye #1 with 2" pipe.
  • Floor Drain #1 plumbed to Wye #1 with 2" pipe.
  • Wye #1 plumbed to Floor Sink #2 with 3" pipe.
  • Floor Sink #2 plumbed to the Double Wye with 3" pipe.
  • Floor Drain #2 and Floor Drain #3 plumbed to the Double Wye with 2" pipe.
  • Double Wye plumbed to Wye #2 with 3" pipe.
  • Floor Sink #3 plumbed to Wye #2 with 3" pipe.
  • Hand Sink #2 and Mop Sink plumbed to the Floor Sink #3 branch with 2" pipe.
  • Wye #2 plumbed to the existing cleanout in the service corridor with 4" pipe.

Each branch up to Wye #2 will have 1/4" per foot slope. From Wye #2 to the existing cleanout, I'm not sure if the slope should be less than or greater than 1/4" per foot.

Next comes the question of venting. Since it will be more difficult to install vent pipes inside the existing perimeter walls, I propose to add a dry vent in one of the new partition walls at the point marked with a red triangle between Wye #1 and Floor Sink #2. My question is, will that one vent be sufficient for the entire system. Two possible problems: there are 9 total fixtures. I'm not sure if the "8 fixture max" requirement for Circuit Venting applies here. The other possible problem arises from IPC Table 915.2.2. If I have to use the max DFU values listed above, then the total load after Wye #2 is 21 DFUs. So then the question becomes: is the pipe after Wye #2 considered a "horizontal branch" or is it considered part of the "building drain"? If the latter, then no problem. But if considered a horizontal branch, then 21 DFUs exceeds the rating of 20 DFUs for a 4" pipe. But I can't go larger because the existing drain line in the service corridor is a 4" pipe.

The other questions I have regarding venting has to do with the hand sinks. How does one plumb from the P-trap under the sink to the horizontal drain branch under the floor without dropping straight down and creating an S-trap? Is it enough to have several inches of horizontal waste arm after the P-trap before turning down vertically?

My final question has to do with cleanouts. I think I should add a cleanout in the service corridor just prior to the existing one, and directed upstream back into the shop. But I'm not sure that that complies with IPC 708.1.8 which states that a cleanout must enable cleaning only in the direction of drainage flow. But there's an exception for the use of a two-way cleanout so it seems like two back-to-back cleanouts, one facing downstream and one facing upstream would be comparable. Also, I don't know if other cleanouts are required. And if so, where?

I would greatly appreciate any advice, answers, or additional code references. Btw, I'm located in Colorado.


P.S. I'm sure this question will come up, so I'll answer it in advance. Yes, I shall be hiring a licensed plumber for this job. However, I'm asking for advice and guidance for the following reasons:
  1. I need to ensure my floorplan and fixture layout will work within the requirements of the plumbing.
  2. I want to fully understand the plumbing system for the shop.
  3. As mentioned earlier, I've seen conflicting requirements published by various sources. So I don't want to assume that the plumber I hire will have all the correct answers.
  4. I enjoy learning about this stuff.
 

hj

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1. ALL the combined W&V drains have to be oversized. The drops from the floor sinks, etc., have to be at least one size larger with a reducer on the bottom of the drain. NO DRAINS can be 2" pipe. You will need a vent where the pipe exits the building and probably one at the very upstream location. You cannot exceed the 1/4" per foot slope requirement. IF any of the sinks discharge grease you will need an interceptor and it CANNOT drain into a W&V sytsten
 
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