Does it matter if one side of a trap is higher than the other?


Old 09-29-20, 07:50 AM
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Does it matter if one side of a trap is higher than the other?

Sometimes I feel like I'm getting dumber with age. On my bathtub replacement project, due to some existing framing stupidity(by the builder 80 years ago), the trap will have to be sort of closer to the middle of the tub and not where you might conventionally located it, immediately under the drain. Does it matter if the outflow side of the trap is higher than the inflow side? I wouldn't think so. My initial instinct is that since the tub is higher than the trap, it really doesn't matter too much what happens before the trap, so long as after the trap there is correct fall to the waste pipe.

Am I correct with this?
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Old 09-29-20, 10:24 AM
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I think this will cause more problems than you think.

With the trap arm (outflow) being higher than the inflow, the horizontal pipe will always have water in it. It will slow down the water draining and could cause clogs. In a tub, you don't have a whole lot going down that's likely to cause clogs, other than hair, but it will likely slow down the draining.

I don't quite understand how you're going to set this up. So the drain/overflow is going to 90-degree towards the center of the tub, run a few inches, then go into a U-trap? I've never seen something like that, and there's probably a reason for that.
Can you sketch it out or take a picture so we can see what you're working with?
Old 09-29-20, 10:50 AM
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If you are subject to plumbing codes you can not install a running trap for the tub.
Old 09-29-20, 11:39 AM
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Pilot Dane - a running trap?

Zorfdt Yeah, so here's the deal... normally the overflow would shoot straight down, pick up the tub drain, then drop immediately into a trap. That's not/can't be the case for me and here's why: The awesome builders of 1966 must not have put much planning into this little bathroom because the alcove for the tub is exactly 60" and right beneath the drain is a DOUBLE FLOOR JOIST. Yeah. Not even just a single, like, just another floor joist. It's a double joist running perpendicular to the other floor joists, so it's obviously a structural piece. it's a 2x8(well, two of them) and the builders had notched into them 4.5" x about 6" long. That's already pretty not cool in my book. So, long story short, I'm not going to notch it any further, and so I have to be very creative getting my overflow and drain pipes over and past that notch, as a trap sits too low. I've got exacly 4.5" from the surface of the 3/4" subfloor in depth and so the conventional tub drain setup just isn't an option. Why not get a right hand drain tub this time? Because there's no room over there either as it's the outside wall. I wish I could have remembered how they had it set in there with the original tub but I forgot. It was of course, all brass fittings and such. Maybe they had some weird low-profile trap or something. This project should NOT be this much trouble lol.

Pictures incoming. stand by.

Last edited by survivalbloke; 09-29-20 at 12:11 PM.
Old 09-29-20, 12:19 PM
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Oh wow, well that's weird, I guess I have two accounts on two browsers. crazy.. well, I'm the OP. I had a thread regarding this a month or so ago but I never got anywhere with it as the bathroom was on hold due to being busy with other things.

OK here are the pics.
floor opening
closer view of floor opening. Double joist notched more than halfway through (builders, not me)
First plan - trap is too deep to clear the notch
Second plan - little wonky but clears the notch

**UPDATE** I'm all set. There was ONE COMBINATION I didn't think of. I'll post pics of it tomorrow. I basically have the trap BEHIND the joist, perpendicular to the waste line. It's brilliant.

Last edited by survivalbloke; 09-29-20 at 02:28 PM.
Old 09-30-20, 05:06 PM
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Here it is. My solution.
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