Bathroom sink drain size (1.5" vs. 2")

[EthylOH]

I'm plumbing in the PVC drain line for a single bathroom sink. It's about 5 feet away from the main stack in the house.

I just assumed I would use 2" pipe, but I've also read that 1.5" may actually be better due to the fact that less solids will build up. (Other than toothpaste and hair, I don't really see other solids being present).

Which should I use?

 

[Terry]

You will need a vent within 42" of the p-trap and before it enters a main waste stack.
1.5" is fine.
If plumbing for a double lav, you would want 2"

 

[Sponsor]

 

[EthylOH]

You will need a vent within 42" of the p-trap and before it enters a main waste stack.
1.5" is fine.
If plumbing for a double lav, you would want 2"

Thanks Terry. I spent the night attempting to install the vent.

As luck would have it, the damn ceiling joist is immediately over the center of the top plate in the wall.

Fortunately, since the stack also runs through the wall about 5 feet over, they built that section out another 5 inches when the house was originally constructed. So I have to run the vent pipe over through a couple of studs before running it to the attic.

 

[EthylOH]

Also Terry, am I better off using the 1.5" vs. 2" in the case of a single sink?

 

[Terry]

The 1.5" is fine.
I still think up to the vent is better though. Not that you're going to notice it anyway.

 

[Standardairconditioner]

I would use 2" pipe, but I've also read that 1.5" may actually be better due to the fact that less solids will build up.

Where did you read this, can you please quote credible references?

 

[EthylOH]

Where did you read this, can you please quote credible references?

I don't have credible references.

It's just from another forum (although I guess it does make sense intuitively).

First comment by "lazypup" in this thread:
http://ths.gardenweb.com/discussions/2509860/drain-pipe-size-from-toilet-to-septic-tank

 

[Hated DIY & engineer]

Hi Terry,

I've got a Master And Hall Bath that are back to back. The original has a 4way that goes to a2in drain pipe,with 1.5 in ABS vent pipe.

I'm adding a second sink in the hall bath, about 16in over, on its own drop to the sewer drain. I can drop down with a1.5 in vertical to the 2in drain line (fortunately,is at the end of the line,so that part is easy). For the vent,I plan on continuing up into the attic with 1.5 in vent pipe. Can I use a 45 and wye into the existing 1.5 in vent stack? The pipe verticals are about 16 in apart. Is this an issue having the 3 sinks on the 1.5 in roof vent? Should I switch to 2 in from the vent wye to the roof?

 

[Hated DIY & engineer]

Hi Terry,

I've got a Master And Hall Bath that are back to back. The original has a 4way that goes to a2in drain pipe,with 1.5 in ABS vent pipe.

I'm adding a second sink in the hall bath, about 16in over, on its own drop to the sewer drain. I can drop down with a1.5 in vertical to the 2in drain line (fortunately,is at the end of the line,so that part is easy). For the vent,I plan on continuing up into the attic with 1.5 in vent pipe. Can I use a 45 and wye into the existing 1.5 in vent stack? The pipe verticals are about 16 in apart. Is this an issue having the 3 sinks on the 1.5 in roof vent? Should I switch to 2 in from the vent wye to the roof?

 

[FullySprinklered]

Hereabouts, you would have to drain the new lav into 2in. Inspector over in Jackson County thinks so, anyway. Everything else looks good.

 

[Asktom]

You could use an inverted san tee and 1/4 bend on the vent in the attic and avoid the square root of two. UPC would allow 1 1/2 on a lavatory drain, 2 if it is a laundry tray.

 

[Hated DIY & engineer]

You could use an inverted san tee and 1/4 bend on the vent in the attic and avoid the square root of two. UPC would allow 1 1/2 on a lavatory drain, 2 if it is a laundry tray.

Thanks guys! Sounds like UPC is ok with the 1.5 in drain in this case? I thought that is what I read....

To make sure I understand your point on the vent: go with a 90 at the top of the new vent, then run horizontal over to am inverted sanitary tee? That way I avoid the angle section? thanks in advance!

 

[Hated DIY & engineer]

Went together well in a day's time (which is good for me since some was under the house,behind the wall,and in the attic). Thanks for the feedback!