# Height of P-trap?



## Borisw37 (May 31, 2010)

I'm putting in a washing machine outlet box. The drainage pipe branch that I'm planning on connecting to is ~10' away and 18" above floor.
This means that my P-Trap outlet will be 20.5" above floor (1/4" slope) with a 10' horizontal run.

A number of places specify 6" to 18" P-Trap outlet height.
How critical is it? What will be effected if it is higher?


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## TheEplumber (Jul 20, 2010)

The rule you refer to is old but still in place per the UPC model code.
The idea is that the trap is between 6"- 18" above floor. The stand pipe is then 18"-30" long. The idea is to have the top of the stand pipe at 36" maximum. This would equal your other counter top heights.
Example- trap is 6" AFF plus a 30" stand pipe = 36" overall. Trap at 18" AFF plus a 18" standpipe = 36"

IMO, this is old code that needs amendment. I see no problem putting the trap higher than 18" as long as you stay within the 18"-30" standpipe length.

UPC minimum pipe size on a washer is 2", IPC minimum is 3"


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## MTN REMODEL LLC (Sep 11, 2010)

TheEplumber said:


> The rule you refer to is old but still in place per the UPC model code.
> The idea is that the trap is between 6"- 18" above floor. The stand pipe is then 18"-30" long. The idea is to have the top of the stand pipe at 36" maximum. This would equal your other counter top heights.
> Example- trap is 6" AFF plus a 30" stand pipe = 36" overall. Trap at 18" AFF plus a 18" standpipe = 36"
> 
> ...


And I find it interesting that washing machines are using significantly less and less water. I' m certainly not a industry knowledgeable person about machines..... but I can't believe any residential machines require anything near a 3" drain.... and a 3'' drain can be darn difficult to run in most conventional framing . ... but god forbid if one should ever overflow.


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## ddawg16 (Aug 15, 2011)

3"? Wow.....

I went through the same issue 16 years ago during my first kitchen remodel 

I ended up asking the inspector about it. He gave me the same basic story above....and then said "You have a crawl space, if it was me, I'd put the trap down there so I could access it."


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## BIG Johnson (Apr 9, 2017)

MTN REMODEL LLC said:


> And I find it interesting that washing machines are using significantly less and less water. I' m certainly not a industry knowledgeable person about machines..... but I can't believe any residential machines require anything near a 3" drain.... and a 3'' drain can be darn difficult to run in most conventional framing . ... but god forbid if one should ever overflow.



Maybe they're pumping faster. :vs_mad:


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## Ghostmaker (Mar 2, 2013)

MTN REMODEL LLC said:


> And I find it interesting that washing machines are using significantly less and less water. I' m certainly not a industry knowledgeable person about machines..... but I can't believe any residential machines require anything near a 3" drain.... and a 3'' drain can be darn difficult to run in most conventional framing . ... but god forbid if one should ever overflow.



It's not about the amount of water its about a washer being a pumped discharge. Larger pipe tends to make it relax faster. Also IPC is 3 inch once you become a branch drain. More then one fixture. You are trying to minimize the effect of the pressurized discharge on the other fixtures.

406.3 *Waste connection*. The waste from an automatic clothes washer shall discharge through an air break into a standpipe in accordance with Section  802.4 or into a laundry sink. The trap and fixture drain for an automatic clothes washer standpipe shall be a minimum of 2 inches (51 mm) in diameter. The automatic clothes washer fixture drain shall connect to a *branch drain or drainage stack a minimum of 3 inches * (76 mm) in diameter. Automatic clothes washers that discharge by gravity shall be permitted to drain to a waste receptor or an approved trench drain.


*FIXTURE BRANCH.* A drain serving two or more fixtures that discharges to another drain or to a stack.

As 1 fixture 2 inch is the size. Unless it is a stack.


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