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Old 12-31-2017, 10:40 AM   #1
Mike_Qtile
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Handling buried vent pipe in shower bed

I took out an old basement shower, the vent pipe went up a cubicle wall.

Have re-routed this to the side of the shower but of course the ~horizontal vent pipe section is about 4 inches above the slab.

Can I mud this shower using a thicker mud bed to cover this pipe(and support underneath), so the mud thickness would go to 6 or 7 inches with appropriate slopes from shower wall to drain pipe and allowing 2inches of mud over the vent pipe. With wire reinforcing and maybe an enhanced mud mix?

The other problem/uncertainty is that the center of the shower has about 9 inches x 9 inches of pure gravel around the drain going through the floor slab so possibly it might be better to pour a thin concrete slab to give better support to the shower base before mudding?

Shower is only 36inches x 32inches.
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Old 12-31-2017, 10:59 AM   #2
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Welcome Mike.

Is there no way to have the vent within an existing wall and have it horizontal in the floor joists above? Vents can be pretty convoluted as long as they don't have negative slope.

Perhaps a photo would be helpful for suggestions.

Building the floor up would be my last choice. What's ceiling height?
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Old 12-31-2017, 01:57 PM   #3
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Mike, I don't see a problem with adding cement to support the drain. Is this shower going to have a traditional pan liner? I'm not sure if 6-7 inches of mud will work or not. I vote for a picture as well.
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Old 12-31-2017, 08:04 PM   #4
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For the vent to be that high implies the trap is as well. Is the drain line low enough where you could lower the whole thing, and thus get the vent line beneath the slab? IMHO, building up the shower pan that far above the rest of the room is not a good thing. I was in a shower done like that in a small hotel in London one time...almost killed myself getting out of the thing more than once during that trip!

Cracking up the slab isn't really all that hard. The cleanest way is to pay a pro to do it with a saw. They take care of carting all of the debris out, too, which is sometimes the worst part of it.
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Old 01-01-2018, 09:17 AM   #5
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Here is a picture of the piping and drain coming through the slab. (not cleaned up)

The previous shower floor was built up(thick) with the vent pipe going ~horizontal and then into a vertical cubicle wall which has been removed.

The shower height will be restricted but similar to what it was before. At ~36 x 32 it is a small shower.
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Old 01-01-2018, 10:23 AM   #6
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Looks like you're well into the shower construction Mike. I see what looks like new tile backer on walls.

Without seeing what's in wall and floor, I can't say with certainty how I would address, but my first inclination would be to lower trap and drain and subsequently vent. By the looks of it there's been some remodeling or addition at some point. Venting for the drain would typically be accomplished by a wye to save height, but without info on how it ties into rest of system, it's just conjecture.

I guess it boils down to this: If you want to bury existing vent in concrete you probably could successfully. If you'd rather not have that step up, there may be a way, but you'll have to uncover more of the system to determine viability.

Is that just rubble in the pan area or it there some concrete there? The adjacent floor looks like it might sleepers on a slab, but hard to tell from photo.
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Old 01-01-2018, 10:39 AM   #7
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Redo the plumbing to lower that horizontal vent line:

Remove that tee or wye with vertical coupling and street 90. Replace it with a tee rolled so its side entry is about 45 degrees off vertical, followed by a street 45 to go horizontal. If you want the street 45 exit to point at the vent in the wall, you can probably achieve by rolling the tee a little farther downward, and then rolling the street 45 to the side. Run the horizontal vent line into the wall, notching out the mud sill and chipping out concrete as required. Or possibly you could enter the wall with two 45s to reduce the concrete chipping required, if that wouldn't interfere with your shower mud bed. You'll probably need to use one shielded rubber coupling in the wall to connect up to the existing vent line.

Cheers, Wayne
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Old 01-02-2018, 07:42 AM   #8
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You may not have an option or may be far enough underway already, but a horizontal vent line below the shower floor isn't to code. The way to vent that is to have the trap arm from the shower head toward a wall and pick up the vent there. Or to wet vent the shower so there would be e.g. a (vented) drain line from the vanity under the shower pan to pick up the shower drain. Might be a good question to ask over at terry love's plumbing site.

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Old 01-02-2018, 08:01 AM   #9
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OK

Thanks Everybody for the input.

For not to code, (use a wet vent or go to the wall) I guess the problem was generated when the shower was first put in with a horizontal vent imbedded in the shower floor. Reluctant to cut the slab to fix it, it sounds like a lot of work.(but could do it, will investigate)

As suggested will dig out the gravel base and see if lowering the vent a few inches might be done. Vent pipe would still come out above the slab but not as severely. So the mud base thickness could be reduced a couple inches. Will still have to support mud somehow in the gravel area; maybe a custom steel plate? It is only 10x10 or so.
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Old 01-02-2018, 12:18 PM   #10
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Quote:
Originally Posted by Bruce
You may not have an option or may be far enough underway already, but a horizontal vent line below the shower floor isn't to code.
OK, thanks for motivating me to look up the code. It looks like your statement is true for the IPC (905.5 says in part "Horizontal vent pipes forming branch vents, relief vents or loop vents shall be at least 6 inches above the flood level rim of the highest fixture served.") However the UPC provides more flexibility, see below for the details.

So Mike, which state are you in, and does it use the International Plumbing Code or the Uniform Plumbing Code? Even if it's the IPC, unless you want to add that wall back in, the best you could easily do would be to comply with the UPC provisions. [Edit: and maybe I'm misinterpreting the IPC, I'm not as familiar with it.]

Cheers, Wayne


Here's what the 2015 UPC has to say:

Quote:
905.2 Horizontal Drainage Pipe. Where vents connect to a horizontal drainage pipe, each vent pipe shall have its invert taken off above the drainage center line of such pipe downstream of the trap being served.

905.3 Vent Pipe Rise. Unless prohibited by structural conditions, each vent shall rise vertically to a point not less than 6 inches above the flood-level rim of the fixture served before offsetting horizontally, [. . .] Vents less than 6 inches above the flood-level rim of the fixture shall be installed with approved drainage fittings, material, and grade to drain.
The OP's situation I would say falls under the "prohibited by structural conditions" clause. So the vent can go horizontal immediately to get to the wall with the vertical vent riser. The portion of the vent below 6" above the shower curb will need to plumbed as if it were a drain. That means using a tee to take off like I suggested is no good, it needs to be a properly oriented wye. Probably locating it a bit downstream of the OP's current vent takeoff would work best for the angles.

I am slightly unclear on the import of 905.2. The "invert" of the pipe is the lowest interior point of its cross section. So certainly on a 2" drain line, the horizontal vent has to be at least 1" higher than the drain line at the point of take off. Possibly 905.2 also requires that the wye for the take off is rolled at least 45 degrees towards vertical, so the invert in the wye branch of fitting is high enough. Probably safest to keep the wye at 45 degrees towards vertical, then I think in the OP's case two 45 degree bends would be enough to get the horizontal vent line pointed towards the wall. Not 100% sure on that, you might need a 45 and a 60, it's a question most easily answered by playing around with the fittings in situ.
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Old 01-03-2018, 12:03 PM   #11
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Are you sure the vent needs to be under the slab. The wye for the vent need not be right at the trap. You would need to look up the code for your jurisdiction and the size pipe you are using to see how long the horizontal run can be before the vent wye. If I recall correctly for the bathtub in my house the allowed length before the vent was 5 feet.
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Old 01-03-2018, 05:33 PM   #12
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Typically, the vent line comes off of the trap arm where the drain line turns down. With a 2" pipe, depending on the code in use, that must happen within 5' of the trap. That 5' should get the trap arm outside of the shower, and then it can use a sanitary T (I think) with the bottom being the drain, and the top, the beginning of the vent. Note, that vent line can combine with other vents as long as it goes up at least 6" above the flood rim of the other devices using that vent. Typically, they want it to go up at least 42" to account for a 36" counter, plus the 6". A 45-degree or steeper angle is considered vertical. The entire vent line must have slope like the drain to allow condensation and precipitation to drain out.

Cracking some concrete isn't often that big of a deal UNLESS it is a post-tensioned slab...then, it can be dangerous to cut things if you hit one of the cables.
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Old 01-03-2018, 09:13 PM   #13
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Quote:
Originally Posted by Jim
Typically, the vent line comes off of the trap arm where the drain line turns down.
Typically, yes, for a vanity or kitchen sink, say. But if you're in a situation where you don't want the drain to drop down, e.g. under a slab, you don't have to have it drop down. You can take off the vent with a wye and keep your drain line horizontal.

Cheers, Wayne

P.S. If your vent is going to rise immediately to 6" above the flood-rim level of the fixture, you can take off the vent with a sanitary-tee on its back. That wouldn't usually be the case under a slab, unless you intercept the drain right where it runs under a wall. If you need to go horizontal before reaching 6" above the flood-rim level, you need to use drainage fittings, so you can't use a sanitary-tee on its back.
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Old 01-03-2018, 10:26 PM   #14
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WIth a horizontal vent pipe, it can become clogged, and with nothing to wash it clean, lead to problems down the road.

IF the drain line allows it (i.e., it is low enough beneath the slab), you really want to crack some slab and use a conventional hookup.
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Old 01-04-2018, 12:31 AM   #15
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Quote:
Originally Posted by Jim
WIth a horizontal vent pipe, it can become clogged, and with nothing to wash it clean, lead to problems down the road.
The vent takeoff can't be flat, it has to be above the midline of the drain pipe. So you could use a wye rolled at least 45 degrees above flat.

Cheers, Wayne
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