Ask Me Help Desk - Trap Diameter requirements

Tom,

I had asked some questions previously for roughing in plumbing for a basement. I have a few more questions for you.

1) Does code require the trap to be the same diameter as the trap/waste arm? For my wetbar I ran a 2" horizontal waste line to where it is roughed at of the wall. Does this mean I need a 2" P-trap or can I reduce to an 1" or 1.5". My distance from trap to vent will be about 2-3 feet.

2) From my toilet flange to vent is approximately 15" (measure around the closet bend - combination of vertical and horizontal distance). I've read that code requires 2 times the pipe diameter (6" in my case), so is my method of measuring correct or do I measure horizontal distance from the flange to the vent?

3) I have a 1.5" line for my sink drain and it looks like I will have about 4-5 ft from my P-Trap to vent. Do I need to move my vent to the left a couple of feet to make it compliant to code? I think the distance from P-Trap to vent is 3' 6" for 1.5" pipe? My fall is 1/4 per ft so I have about a 1" fall right now which is less than the 1.5" max fall.

Hi mike, Welcome back,

1) Does code require the trap to be the same diameter as the trap/waste arm? For my wetbar I ran a 2" horizontal waste line to where it is roughed at of the wall. Does this mean I need a 2" P-trap or can I reduce to an 1" or 1".

You may reduce lavatory and wet bar traps down to 1 1/4" if you wish. However all other traps should be 2". As a rule we run a 2" trap with a nylon reducing bushing to pick up the lavatory tail piece.

2) From my toilet flange to vent is approximately 15" (measure around the closet bend - combination of vertical and horizontal distance). I've read that code requires 2 times the pipe diameter (6" in my case), so is my method of measuring correct or do I measure horizontal distance from the flange to the vent?
Your toilet's wet vented, as is the tub/shower by the lavatory vent. Don't sweat it.

3) I have a 1.5" line for my sink drain and it looks like I will have about 4-5 ft from my P-Trap to vent. Do I need to move my vent to the left a couple of feet to make it compliant to code? I think the distance from P-Trap to vent is 3' 6" for 1.5" pipe? My fall is 1/4 per ft so I have about a 1" fall right now which is less than the 1.5" max fall.

To comply with code a 1 1/2" drain must not be over 3.5 ft from trap to vent. However if the job's not going to be inspected you can "fudge" a bit on the length of the drain with no negative results.
Good luck, Tom

Thanks Tom - I have a few other questions based on your response. I was asking below about the toilet venting distance and that it was not an issue because it is wet vented through by Lavatory.

Here is what I was planning to do and why I think I need a separate line for the toilet vent. The bathroom I'm adding is in the basement and I am tying into one of my secondary stacks (3") that runs into the basement floor and ties into the main line. The vertical stack currently has 1 Dbl Sanitary Tee for the first floor (1 connection goes directly to the toilet and the other goes to the rest of the 1st floor bath fixtures). I want to cut into the stack at about 15" off the basement concrete and add a sanitary T to run to my lavatory for about a 5' horizontal run. Then under the concrete I will remove the existing 90 and replace the a 45-Y combo to reconnect the vertical stack to the existing horizontal line and use the other side to connect my toilet.

Therefore my toilet would have to be wet vented through the existing 3" vertical stack for 15" until it reach the lavatory tie in. Therefore my upstairs toilet would be in the vent path of my basement toilet which I'm pretty certain does not meet code. So I was going to add a separate vent between the 45-Y combo and my closet bend for my basement toilet and run it up above ground and tie into the lavatory vent which will then tie into the vent above the existing vertical waste stack.

My questions are can I have the existing Dbl Sanitary T and add another T in the basement for the lavatory on the same vertical stack? And if so, is the method of venting I mentioned above acceptable?

Hi Mike,

"under the concrete I will remove the existing 90 and replace the a 45-Y combo to reconnect the vertical stack to the existing horizontal line and use the other side to connect my toilet."

OK, you've removed the quarter bend and replaced it with a combo. I assume the stack runs against the wall. This would put the open part of the combo facing the wall if I read you right. How do you plan on connecting the toilet? Some sort of a plan would sure be helpful at this point.

"my toilet would have to be wet vented through the existing 3" vertical stack for 15" until it reach the lavatory tie in. Therefore my upstairs toilet would be in the vent path of my basement toilet which I'm pretty certain does not meet code."
This is called a "common vent" and unless your local code forbids it then I don't think a 15" common wet vent will get you redtagged. ( check with local plumbing codes.)

"My questions are can I have the existing Dbl Sanitary T and add another T in the basement for the lavatory on the same vertical stack? And if so, is the method of venting I mentioned above acceptable?"

As long as the basement lav's vented you may add it on the 3" stack. You may also run the toilet vent,(if required) and revent it back to the lav. Good luck, Tom

Tom

The stack is actually in the middle of the basement next to the furnace and water heater so no issue with using the combo fitting and running into the wall. Is there anyway to load pictures other than using the URL link.

Quote:

Originally Posted by mikejct

Tom

The stack is actually in the middle of the basement next to the furnance and water heater so no issue with using the combo fitting and running into the wall. Is there anyway to load pictures other than using the URL link.

If you have bends under the cement I would use short or long sweeps in place of quarter bends.
I'm not a computer whiz. I don't know the drill on sending me anything. I barely manage to to attach images and drawn plans myself. Cheers, Tom