2” or 3” waste pipe?

[sledro1]

Good evening all…

My kitchen sink drains into a 2” waste line that runs around my basement to my main sewer stack. The total length of the run is 41’.

Draining into this 2” waste line in order from kitchen sink to main stack is a dishwasher, kitchen sink, washing machine, laundry sink and master bathroom shower. (Which has two shower heads).

I calculated 12 DFUs for this line which would mean that it needs to have a 3” drain instead of a 2” drain.

Here’s my question: can I start with a 2” line and then transition to a 3” when I get to the extra drainage…such as the washing machine drain? (So that I’m running a 2” line for the kitchen sink and dishwasher and a 3” line for the washing machine, laundry sink and shower)

Please see the photos for better understanding. The first photo shows the existing 2” drain line. The far left is the kitchen sink/dishwasher drop. It then travels all the way to the right and turns 90 degrees before another drain (washing machine) drops into it. The second photo shows where I’m thinking it would be better to have an 3” line to account for the extra drainage. The drops in the second picture are (L-R) washing machine, laundry sink, and shower. The laundry sink drop is behind the ghost board and drywall.

(Your eyes don’t fool you…there are sections where the pipe is going uphill, which is why I’m replacing the run.)

Any help and advice is appreciated. Thank you in advance.

 

[wwhitney]

Draining into this 2” waste line in order from kitchen sink to main stack is a dishwasher, kitchen sink, washing machine, laundry sink and master bathroom shower. (Which has two shower heads).

I calculated 12 DFUs for this line which would mean that it needs to have a 3” drain instead of a 2” drain.

Iowa uses the UPC. If the dishwasher goes into the kitchen sink tailpiece, that's just 2 DFU total; if it has it's own trap and standpipe, that 2 additional DFU.

Likewise, if the washing machine goes into the laundry sink basin, that's just 2 DFU total. If it has its own trap and standpipe, that's an additional 3 DFU.

Two head shower is 3 DFU.

So total is anywhere from 7 to 12 DFU, depending.

Anyway, to answer your question, any portion of the horizontal drain carrying at most 8 DFU may be 2".

Cheers, Wayne

 

[Sponsor]

 

[sledro1]

Iowa uses the UPC. If the dishwasher goes into the kitchen sink tailpiece, that's just 2 DFU total; if it has it's own trap and standpipe, that 2 additional DFU.

Likewise, if the washing machine goes into the laundry sink basin, that's just 2 DFU total. If it has its own trap and standpipe, that's an additional 3 DFU.

Two head shower is 3 DFU.

So total is anywhere from 7 to 12 DFU, depending.

Anyway, to answer your question, any portion of the horizontal drain carrying at most 8 DFU may be 2".

Cheers, Wayne

Ok cool…yeah the dishwasher goes into the sink before the trap. And the washing machine has its own stand pipe. So I’m calculating 2 DFU for the kitchen sink/dishwasher. 3 DFU for the washing machine. 2 for the laundry sink. And 3 for the double shower. For a total of 10 DFUs.

This is above the 8 DFUs allowed on a horizontal run for 2”, so a 3” run is necessary.

To clarify though, does the entire run need to be 3” or can it be 2” until it gets to 8 DFUs?

 

[sledro1]

Ok cool…yeah the dishwasher goes into the sink before the trap. And the washing machine has its own stand pipe. So I’m calculating 2 DFU for the kitchen sink/dishwasher. 3 DFU for the washing machine. 2 for the laundry sink. And 3 for the double shower. For a total of 10 DFUs.

This is above the 8 DFUs allowed on a horizontal run for 2”, so a 3” run is necessary.

To clarify though, does the entire run need to be 3” or can it be 2” until it gets to 8 DFUs?

And thank you for replying I appreciate it!

 

[wwhitney]

To clarify though, does the entire run need to be 3” or can it be 2” until it gets to 8 DFUs?

See my first response.

Cheers, Wayne

 

[sledro1]

See my first response.

Cheers, Wayne

Ha! Sorry…sometimes I read things but don’t comprehend what it’s saying. Thanks again for your response.

 

[ProfessionalPlumbingInc]

It only has to be 3" from the point of connection of the fixture that puts the fixture count to above 8 horizontally.