Plumbing Venting Example 2

[John_187]

I want to know if this attached picture waste and vent setup is legal. There is a bathroom group and break sinks that are individually vented, and are upstream of floor drain that is not individually vented. I assume this can be a combination waste vent setup, but not sure. Please help, thank you.

 

[bimr]

Underground floor drains connected to a building drain shall be individually vented. Floor drains may be 2-Inch minimum size.

The sink drain line from "KS" (kitchen sink?) should be 1-1/2-Inch instead of 3-Inch.

Sanitary tees should be used at connections from horizontal to vertical pipes.

The "WC" vent should be 3-Inch. The "LAV" vents should be 1-1/2". Each structure should have at least one main vent (the 3-Inch on the "WC").

The building drain outside the structure is generally a minimum of 4-Inch. You can probably use a 3-Inch drain inside the structure. You show it as a 4-Inch drain.

On "KS", use a long sweep elbow at the base where you transition to horizontal.

Use Wye fittings where you connect into the horizontal drain line.

Consider combining all in the vents into the main stack for one roof vent penetration.

You don't say what this structure is and I assume it is a residence. You will need to verify with the AHJ to determine what plumbing code is in effect and the local plumbing requirements.

 

[John_187]

Thanks for the reply. You said that in this instance, the floor drains should have individual vents, but in my other example thread (With urinals and lavs upstream of floor drains), they didn't? Why do you say this, what is the difference?

The only code evidence for why this floor drain can't be treated as a combination waste and vent (that the floor drain needs an individual vent), is section 915.1 of the 2012 IPC. This states the food grinder waste be on a combination waste / vent system. I assume this would apply to the building drain that the combination waste and vent is connected to, as is the case here.

I interpret the 915.1 of the 2012 IPC saying that combination waste and vent can only serve floor drains, lavs, and drinking fountains to mean that those are the fixtures that don't need an individual vent on them. Any fixture (other than a food grinder), can be located upstream of the combination waste and vent as long as it's properly vented and the building drain waste pipe is oversized. Do you agree?

This is a commercial application, the jurisdiction would follow the 2012 plumbing code.

 

[PEDARRIN2]

John187

Your interpretation of 915.1 is partially incorrect in that the at least one of the lavs, drinking fountains, or floor drains must have a vent for the combination drain and vent system (CDV) to be valid.

Your drawing would be acceptable since the floor drain is connected to a ventilated main, with a caveat about the food waste grinder makes it a bit trickier.

Also, you have to remember the CDV philosophy is based on low flow and larger pipes. So you have to be careful about what is flowing upstream which can influence the venting. If you have a washer box upstream, which could flow a lot of water, you might not have a good design to not vent a floor drain. Also, if the floor drain is receiving a lot of flow, say from a kitchen dump kettle, you would likely want to vent it even if it is on a CDV system.

 

[bimr]

Thanks for the reply. You said that in this instance, the floor drains should have individual vents, but in my other example thread (With urinals and lavs upstream of floor drains), they didn't? Why do you say this, what is the difference?

The same comments in the other thread would also apply.

Combination waste and vent ate intended for extensive floor and shower drain systems where venting is impractical. In view of the grease producing potential, commercial kitchen equipment should generally not be connected to a combination waste and vent system.

The design of a commercial kitchen is complex. Here are some additional comments.

"There are other important regulations regarding the installation and operation of kitchen equipment found in the local health department codes. This includes everything from the temperature of the water delivered to the dishwasher and triple-compartment sink, to the type of floor drain used, to the number and location of hand washing lavatories and mop basins. Health department codes also dictate the location of toilet facilities for the kitchen workers and the construction of spaces used for the storage of food and dishware."

"At least one triple-compartment sink will be required."

"A grease interceptor will be required and should receive waste from everything except the dishwasher and food waste grinder (although the ultimate destination of greasy waste discharge from a food waste grinder is currently a topic of discussion)."

"Area drains should be provided throughout the space (wherever needed)."

"All equipment or sinks that are used to prepare food or clean dishes or pots must drain indirectly. (This can be achieved by either spilling indirectly over a floor drain or incorporating a floor drain into the waste branch serving the fixture.)"

Commercial Kitchens

http://www.plumbingpros.com/pdf/dwvents.pdf[/URL]]Additional Illustrations

 

[PEDARRIN2]

bimr,

A problem with commercial kitchens is the architect likes to have half height walls - or no walls at all for a lot of the area. I think they are required to have full height walls separating prep from washing areas, but for other areas, no such requirement exists. So, sometimes the plumbing designer has to utilize combination drain and vent for kitchen designs. As I stated, the approach gets dicey when the floor drains are receiving a lot of flow from something.

Design should generally try to provide vents in a conservative fashion (more is better), but sometimes it is not possible.

 

[John110]

bimr, why you say 3" vent for WC? Where in the code asks for it?

 

[PEDARRIN2]

It is likely the part in the code which requires a single full size vent to be provided. So, if your largest fixture is a water closet and it has a 3" drain, you are supposed to provide a 3" vent from it. With a 4" water closet connection, you are supposed to provide a 4" vent from it.

I have never seen this enforced - always used 2" vents off water closets and increased the size to 3" at the VTR. That being said, if the fixture units in the building require a 4" vent due to developed length and such, I may provide a 4" VTR or i may provide multiple 3" VTR.

 

[bimr]

Typical plumbing codes will state that "each building in which plumbing is installed shall have at least one main stack vent no smaller than 3 inches for each building drain installed".

 

[PEDARRIN2]

The VTR may be 3", but the piping leading to it may not be. A single toilet room with a toilet and lavatory could have a 2" vent from the fixtures to the roof and increase in size to 3" just prior to the roof penetration. This is commonly done and acceptable.

But... I have heard that some older AHJs will interpret the code to mean the vent must be 3" from the fixtures to the roof because of the definition of waste stack and stack vent. This is a rather conservative interpretation of the code in my opinion.

 

[John110]

bimr & PEDARRIN2 Thanks