Moving sink, venting options, help

19 years ago

I am converting a full bath to a half bath on the 1st floor. No bedrooms down there, so I do not need it. I want to put the sink where the shower was and have a few questions about my venting options.

The bathrom sits on a slab.

1. Drain the sink into the old shower drain. Do I still need to vent the sink, or can I assume the shower was properly vented? I do know it vents into a "wet" vent stack shared by the toilet and the upstairs baths. Problem is, the drain goes into the floor about 20 inches from the back wall, so it will be in the front part of the vanity, and since I want an open vanity, it might be seen were it enters the floor.

2. There is an old laundry drain behind the wall. However, there is about 5 feet from where I can tap into the drain and where it hits the same vented stack as option 1, seems to be the same option as the shower drain, but I can get it to disappear. Again, would I need to vent seperatley?

3. Above the location of the sink is the drain for another sink, which is no longer used, and is capped. I was thinking about connecting the vent to this, but It will not be 6" above the fixtures that feed in from the 2nd floor. I know this is against code.

4. Run the old vent over to the new location. Lots of work, but possible. If I do this, I will most likely tap the drain into the old laundry drain.

I know I can do 4 and not 3, but what are my options for 1 and 2?

TIA

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Comment (1)

lazypup
19 years ago
No matter which option you choose you may not tie a vent into that stack until the vent reaches an elevation 6" higher than the highest fixture served by that stack. (6" above the highest fixture on the 2nd floor).

option 1 -the shower drain:
Code prohibits double trapping and the shower drain already has a trap so before you could tie a drain line into it you would need to remove that trap.

You cannot use the shower trap for the sink because the maximum permitted vertical drop from the drain opening inside the sink bowl to the input of the trap is 24" (12" in some jurisdictions).

By necsssity there is always a section of horizontal pipe from a trap to a vented stack or vented drain line. That section of pipe is properly called the fixture arm and it serves as both the drain and the vent for that distance. The minimum allowable length of the fixture arm is 2x the pipe dismeter. The maximum length would depend upon what code you are under.

Under the International Residential Code(IRC) the maximum length of a fixture arm may be mathematically computed by dividing the line diameter by the pitch, thus a 2" line run with a 1/4" per foot pitch would be 2"/.25"=8'.

The Unifrom Plumbing Code(UPC) uses fundamentally the same formula then they derate the length by approximately 40% therefore under the UPC the maximum length of a 2" fixture arm is 5'.

When the length of the horizontal run exceeds the prescribed limits we must install an auxillary vent within the limit.

OPTION 2 The Old Laundry Drain

You may connect the drain line to that line but you would still need an auxillary vent and the aux.vent would need to rise to a point 6" higher than the highest fixture on the second floor before being tied into the stack.

OPTION 3 -You already ruled out option three and cited the correct reason.

Option 4. Here again, that vent would need to be 6" above the highest fixture on the second floor before being combined into the stack.

OPTION 5

The IRC permits an unlimited number or AAV's (Air inlet valves) and the UPC permits a maximum of 1 AAV per structure. You could install an AAV on the lavatory drain line.
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