Washing machine P-trap question, under floor?

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Interlodge

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Washing machine p trap question.
I see many comments about the washer p trap being requred on the same floor as the machine. We are in NJ and covered under the 2oo6 National Standard plumbing code. In that code I can find no requirement for the same floor. Simply 2 “ minimum standpipe size no more than 48 nor less than 18†above it’s trap.
The washer I have requires 24 to 36 above the floor with “the lower height preferable.â€
The reason I ask is I can mount the trap directly below the floor, have crawl space access as well as simplifying horizontal drain line to main stack. It will also tremendously simplify vent line.
So I could use a 30 or so standpipe above the floor to meet washer requirement and then the trap would be just inches below that, well with the NJ code length and even within well within other code’s lengths.
Do you see any problems with that? Is the reasoning of the code requirement in orther codes on same floor simply because of standpipe excess length issues, . Without that requirement in NJ, are there any other issues to think about?
Local jurisdiction has no modifications to code
 

NHmaster

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All traps must be installed on the same floor as the fixture served with the exception of tubs and showers. You can probably find that code bit in the DWV section, not necessarily under washing machines. In any case putting it below the floor would violate the maximum length of the stand pipe code which is 30"
 

Interlodge

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I don’t know why you are referencing the other codes. As I said I am under the National Standard Plumbing Code
I did check under traps, trap placement, drain and waste, general provision etc and can’t find any reference at all. As I said the code has a specific exemption to the normal 24” vertical distance limit saying specifically “2 “ minimum standpipe size no more than 48 nor less than 18” above it’s trap” As the washer only requires 24” above floor for the standpipe height, I can easily be around 30, well within the NJ code. Up to 48” might be excessive in the light of other codes but it’s stated clearly there but I’ll be much more conservative given other codes views on siphoning. I’m trying to understand the rational behind the rule in the other codes as long as you are within specs, NJ has some unique code provisions like “S traps of uniform internal dimensions” are prohibited. One size larger vertical drain line and it’s allowed. I’m not asking you to read the code and find all the applicable parts of my code, (unless you’d like to be really helpful) I’m trying to understand what logical rational and what the issues could possibly be, or why you are saying I need to worry about other code specifics.
 
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Jadnashua

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I'm assuming you have a front loading machine, as you'd need a higher standpipe for a normal top loader. I'd be surprised if the standpipe couldn't be higher, as the pump should easily allow it to work in any retrofitted situation when replacing a top loader. Having it low could make it difficult when you sell the house.
 

Interlodge

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Jim, I hear you, and as I thought about it and the machine allows up to 36 why not get it as close to normal as possible. Yes the machine is a front loader and a water saver, very low water usage. As far as under the flooe, I visited my local wawa at coffee rush time this am and talked to two local plumbers who said above floor is "preferrable" but below is allowed and routinely done. Preferrable had to do with freeze protection in the unheated space but they said to try to keep it in the joist space within the regular insulation, otherwise take other steps.
so even at 32-36 above floor, I'd easily be only less than 40 total length of standpipe and while all the codes differ on that, ours allows uop to 48" (doesn't that 48" length almost seems like a compatible compliment to allowing under floor?)
 

Export!

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In NJ I would put it above the floor. If the P-Trap did freeze up (and this is a real possibility if there are any drafts through the crawlspace (there always are)) you would have an INSTANT disaster on your hands when the washer ejects. This would not be a problem that creeps up on you and shows symptoms. Instant carnage.
 

Gary Swart

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There really isn't much argument that the trap should be above the floor. Just because some plumbers may get away with putting them under the floor doesn't make it right. You are of course free to take our free advice or leave it. In your favor, it is likely that there will be no problems with putting it under the floor as long as you can prevent it from freezing.
 

Interlodge

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I hear you on that concern but he offered he's never seen or heard of one freezzing when it's up in the joist insulation and even the ones in the older homes below the joists and before they required a sealed box never freeze unless the home heat were to fail. (likethe recent storms and some homes losing peower for 3+ days) On that note, it's always amazed me that in is customary to run all supply piping down there, often cross joist and exposed, and there are never any issues, (except when a 3 say power outage hits and lots of home damage with those supply lines) These were seasonal homes and all were built with easily accesible shutoffs and drains but many people never use them and that can be a real mess in an unoccupied home.
 

Interlodge

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Gary, I wrote that to the previous poster, but your concern is appreciated too. That's what I'm trying to understand... If the only reason for the on the same floor requirement is to prevent freezing, I can understand that and will then take my local code and what it allows and requires. and make my own best decision. For instance, why would that be a concern in Miami? why include it in their code? Are there other legit reason's?

I will check with the town on Monday but it appears to be a common and allowed practice locally based on the Nj code
 

Export!

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It sounds like you're willing to convince yourself that it's OK to put it under the floor so go ahead and do it. It will probably be fine.

In a perfect world, you can easily access the P-Trap and cleanout at the fixture location for (I'm sure) a variety of reasons.
 

Interlodge

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"Just because some plumbers may get away with putting them under the floor doesn't make it right."
This is exactly what I'm trying to grasp? why say it's not right when apparantly the code allows it, the town allows it, the plumbers do it and no ones ever had an issue. The first floor showers and tubs are there in every house in the town (almost all homes have some bedrooms, full baths or showers on the first floo) and I realize they'll get hot water when started but they are in the same exact place (all house have the same foundation crawlspace setup) I realize other codes specifically have an exemption for them in their own requirements but we weem to have no such requirement in the first place. I appreciate everyoe's advice but wish people would be careful when they say " get away with putting them under the floor doesn't make it right." These are repscted plumbers in this town. . My question is what could be "not right" if it is allowed under code and by the town and no one ever has an issue with it.
 

Interlodge

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The advantage is it allows the vent to go up through an adjacent wall through the second floor and out. The wall ithe trap would be in would require a very small boxed soffit as it cannot go through the pate as it has double 2x10's 2nd floor joists resting right above it. (technically the first floor wall is not lead bearing as these 2nd floor joists are engineered as self supporting) Hence you can come up through the bottom plate but not exit the top plate, so a small jut ou would be required.

The alternative would be that modified S trap, but that will really get people talking.....or a small bump out soffit at the top of the closet to bypass those joists which could easily be done, but why if there is no valid reason?
 

NHmaster

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well, I read your code and from what I can tell, your code would allow the trap to be beneath the floor. The IPC and the UPC both specifically do not allow it to be beneath the floor. They also do not allow a 48" standpipe. But I guess what I don't understand is that if it's allowed, why not go ahead and do what you want to do? The main reason why we don't do it is because with a maximum 30" standpipe length you can't put the trap below the floor and still have the inlet above the flood level rim of the washing machine.
 

Interlodge

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sorry, I might not of explained before, Only "S traps of uniform internal Dimensions" are prohibited iunder NJ code Technically I could run a two inch trap above the floor but make the vertical exit 3" (one pipe size larger) as long as it is vented within the regular required distance downstream of that.
 

Interlodge

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Thank You Peter, that's the kind of info I am looking for. The reason is as it started to sound confusing, I wanted to check with the town to be sure. I initially though it would be a simple answer. I really appreciate you taking the time to look through the code. That was above and beyond, I was trying to highlight the relevent sections that might be appropriate so you could avoid it but I appreviate the extra effort. If I understand rhe reasoning though, I can make a better decision, even when it's allowed.... Outhouses were allowed once too
 
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