It would depend upon which major national code your local code is modelled after.

The Uniform Plumbing Code does not require a Main Vent, but rather they require all vents must go through the roof and the combined aggregate cross seetional area of all vents must be equal too or greater than the cross sectional area of the house main drain.

The International Residential Code requires that all structures must have one "Main Vent" which must run undiminished in size from the Main drain through the roof. After that you may reduce the diameter of an auxillary vent to 1/2 the diameter of the line it serves or,
1. You may terminate a vent in the attic space (terrible idea,,never do this cause it will cause excess moisture to form in your attic insulation).
2. Under some very limiting circumstances you may vent throug a side wall (rarely done).
3. For auxillary vents you may use an unlimited number of AAV's.

Under both codes you can offset the vent riser however you may not make a horizontal offset until the vent reaches an elevation 6" higher than the flood level rim of the highest fixture served by that vent. In this case it would be 6" higher than the top of your kitchen sink.

The maximum allowable length of a horizontal offset may not exceed 20% of the total vent height. by example, let us say your drain riser is connect to a horizontal drain one foot under the kitchen floor. The total rise would then be 1 foot to the floor, 8ft floor to ceiling, perhaps 5ft in the attic space and 1 ft above the roof for a total rise of 15ft.

.20 x 15ft would then be 3ft.

3ft would then be the maximum allowable combined horizontal offset, which means the offset under the window plus the return offset in the attic. However there is another option.

In plumbing any pipe which rises at an angle of 45 deg or greater is said to be a vertical rise. You could offset 3' horizontally under the kitchen window, then use a 45deg angled riser from the attic floor to the existing vent stack. The 45deg section in the attic would then be classified as a vertical riser so your total horizontal offset would only be the 3' offset under the window.

Also, when making a horizontal offset the horizontal section must be pitched at 1/4" per foot downward in the direction of flow and in the case of vent the direction of flow is from the roof opening downward towards the drain pipe.

What are people doing for island sinks? Are the mechanical vents that screw into a 1 1/2" fitting allowed in some cases? I have seen them used in mobile home kitchen sinks which follow a HUD code.

Both the IRC and UPC define how to install an "Island Vent" which is a type of loop vent, although they are very different in the actual layouts.

And...what about the mechanical vents? Do they meet any codes?

The UPC will allow a maximum of "One" air Admittance Valve (mechanical vent) with the expressed written permission of the local inspecting authority and generally the inspectors will limit that solely to a kitchen island. All other vents must terminate through the roof.

The IRC requires all structures to have on "Main Vent" which must run undiminished in size from the building main drain through the roof. After that is acheived we may terminate vents in the attic space, through the wall under very strict limitations or an unlimited use of AAV's, however, AAV's may only be used in situations where it would be extremely difficult to achieve a vent by normal means. We may not indescriminantly use an AAV to discontinue the use of an existing vent.

THANK YOU ALL FOR THE VALUABLE INFO AND FURTHER QUESTIONS. I WILL TALK TO A LOCAL PERSON ABOUT CODES ETC.
THAT IS A GOOD POINT ABOUT ISLAND SINKS - THEY DON'T HAVE "CHIMNEYS"!!!!!
GRANNY

This is interesting. From what I read here the vent for my kitchen sink does not appear to meet code. Since I'm doing a major remodeling of that area everything is currently exposed. The sink is on the outside wall, and the vent pipe runs up through the top plate of the wall, then horizontally between the floor joists at least 10 ft, then goes up vertically through a 2nd story wall, attic and roof. I wouldn't be surprised if the horizontal run is at least 50% of the vertical.

Is there anything I can or should do to improve this situation? Would this be a good application of an AAV?

Thanks for any insight.

Tom

Tom
Assuming for the moment that the existing vent is original to the house, we can then assume that it was also inspected and approved during construction. If you are not altering the design, layout or adding additional fixture loads to that line it would then meet approval as being grandfathered from the original construction.

Thanks for the information Lazypup. The only thing I might change is the configuration of the drain for the dish washer, which I've been told is no longer legal (?). Essentially, it's a built-in high loop with 1/2 inch copper pipe going about 4 ft up the wall, then turning 180 deg down to mate up with ABS pipe which then goes through a p-trap and then enters the right side of a 4-way connection. The drain from the sink enters from the left, the vent comes out of the top and the bottom of course is the drain.

Since we have a new dishwasher with built-in high loop should its drain just be connected to the garbage disposal, or can I continue to use the existing drain line? I was thinking of removing that built-into-the-wall high loop and capping off the pipe at the 4-way connection.

Thanks for any info.

Tom

That existing 4' high loop is really delving into a rather gray area of the code. Normally the trap is considered the official point of transition between an appliance drain line and the house DWV system and in that case the manufacturer of the appliance may determine the required diameter of the appliance drain line which is determined by the volume and velocity of the discharge from the appliance. Generally the manufacturer will print a table in the installation guide that defines the size, length and permissible vertical lift of the drain line with recommendations to increase the line size if you need to exceed the length or vertical lift. That table will also define a maximum length or lift which is determined by the output pressure of the pump in relation to pipe friction loss or maximum vertical static head.

In most cases the code will require that the appliance drain must be in an accessible location to permit servicing in the event that line should become obstructed.

Whenever a drain line is permanently installed in the wall it is then classified as a portion of the structure DWV system and it would require that there must be a trap at the beginning of the concealed section of the line and the minimum permissible diamter of the line would then be determined by the DFU (drainage fixture unit) load value of the appliance or fixture being served by that drain. In the case of a dishwasher the DFU load is 2DFU's which would require a minimum of an 1-1/2" drain line.

The plumbing codes also require that a dishwasher, washing machine, HVAC unit or a home water treatment discharge line must also be connected by means of an "indirect waste receptor". Under some local codes you could achieve the indirect waste receptor by installing an "Air Gap" or they may require you to install a standpipe on the trap and connect the dishwasher drain to a standpipe in the same manner as a washing machine line is commonly connected to a standpipe. (Some codes require all dishwashers to have an air gap, regardless of how the drain is connected. Check your local code.)

Under the UPC whenever we have two common vented gravity flow drains connecting to the same vertical riser we are required to use a "Back to Back Tee" (4-way) however code prohibits connecting two commonly vented drains by means of a Back-to-back if one of those drains is receiving the discharge from a powered drain I.E. a dishwasher or washing machine.

The discharge from a powered drain is required to be connected by means of a directional fitting (baffled Tee) and generally the baffled tee should be placed lower than the gravity drain.

In your case the simple solution would be to connect the dishwasher to the disposal input port, providing that is permitted by your local code as well. (For reasons known only to the AHJ some codes prohibit connecting a dishwasher to a disposal input port..One code that immediately comes to mind here is the Illinois State Code.)

Your screen name is Tom-in-Seattle so I am assuming that you are actually in Seattle. I am not certain but i believe your code is modelled after the UPC (Uniform Plumbing Code). If so the defined trap and waste arm size for a kitchen sink is 1-1/2" but under the UPC all vertical risers and drain lines serving a kitchen drain must be a minimum of 2" pipe.

You may use an 1-1/2" pipe for the vent.

There is some question about whether the length of the horizontal offset on the vent in your attic would pass, but I doubt that it would even come into play unless you happen upon a hardnose inspector that is really intent on finding a problem.

Thanks for all the information.

Yes, I am in the Seattle area... Sammamish to be exact.

I think the best thing to do is post a picture of the existing dishwasher and sink drain configuration, which I will do later. If all I was doing was installing a new dishwasher I would not consider any changes, but since all the sheetrock is off the walls I figure this would be a good time to update the old configuration if it's out of date, or not up to current code.

Tom

1. You may terminate a vent in the attic space (terrible idea,,never do this cause it will cause excess moisture to form in your attic insulation).
Thats a terrible idea... Could be very stankie!

2. Under some very limiting circumstances you may vent throug a side wall (rarely done).
Also not a great idea even though the IPC does permit it!

3. For auxillary vents you may use an unlimited number of AAV's.
An AAV should be a vent of last resort and is not allowed in many locations.

If you want to degrade your plumbing to the level found in tin houses on wheels by using AAV's because the ever so lenient IPC allows it go ahead.

Here is a link that might be useful: {{gwi:2022354}}

The Loop vent illustrated in the link is configured in accordance with the Uniform Plumbing Code.

Under the International Residential Code you may use 1/4 bends on the top of the risers and make a flat crossover connecting the risers. The IRC does not require nor would it permit the horizontal vent run under the floor as shown on the lower left of the illustration.

The vent in the lower left would be pitched, Other codes will not allow the use of 1/4 bends on the top as it would be a flat vent below the flood rim of the sink.

In Plumbing any line which rises at an angle of 44 degrees or less above horizontal is defined as a horizontal line, while any line which rises at an angle of 45 degree or more above horizontal is defined as a vertical line thus the angled lines at the top of the two risers in the illustration are technically defined as vertical lines even though they are angled to the point of attachment at the top.

Under the International Residential Code (IRC) we are permitted a flat horizontal line to connect the two risers of an Island Vent even though that crossover is below the flood level rim of the sink. This is the only instance in the IRC where we may have a horizontal vent below an elevation of 6" above the flood level rim of the highest fixture served by the vent. Thus under the IRC the horizontal vent under the floor as shown in the illustration would not be permitted.

Hi: I have a jenn-air stove top and wish to modify the vent tubes located under the counter (sitting on a shelf). I want to raise the vent tubes up so I can use the shelf. Thinking about going from 6" dia. to 4" Dia. Is this safe and up to code? The vent goes from under the stove (about 4 feet) out to a side outside vent.