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Old 05-18-2017, 10:28 AM   #1
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Height of P-trap?


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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Old 05-18-2017, 06:29 PM   #2
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Re: Height of P-trap?


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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Old 05-22-2017, 12:50 AM   #3
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Re: Height of P-trap?


Quote:
Originally Posted by TheEplumber View Post
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"
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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Old 05-22-2017, 02:46 AM   #4
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Re: Height of P-trap?


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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Old 05-22-2017, 05:30 AM   #5
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Re: Height of P-trap?


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Originally Posted by MTN REMODEL LLC View Post
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.
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Old 05-22-2017, 12:02 PM   #6
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Re: Height of P-trap?


Quote:
Originally Posted by MTN REMODEL LLC View Post
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.

Last edited by Ghostmaker; 05-22-2017 at 12:09 PM.
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