Hi, this is my first post here. Looks like a very helpful place.

I've taken on the task of roughing in the plumbing for my new house. I haven't rented the trencher yet - probably about 2 weeks out from doing that. I have some experience with plumbing, but I have never done the under-slab work, so that is where I need help. This will be a thickened edge monolithic concrete slab with post-tensioning (I'm in Louisiana with expansive clay soil - post tensioning is very popular here and highly recommended).

So what I can't find in any of my code books or resource manuals is how deep should I take the initial vertical element of the drain which is farthest from the sewer tie-in? I understand what pitch to place on all the runs, and that the farthest drain from the tie-in will of course be the shallowest. But how deep should it be before it goes horizontally toward the sewer? I assume it should be deep enough to be deeper than the post tension footings. Is that enough?

Post Tension Footing ? You mean Post Tention Slab, correct ?

If you have PTS in your house, you should only score the slab and carefully break the slab avoiding buried cables. Also, plan your cuts so you don't interfere with end tension plugs on side of slab. If you break slab too close to the outside edge, the end plug will snap violently.

Just start with the toilet and proceed at 1/4" per foot (3"pipe) or 1/8" per foot (4"pipe) towards outside. Once you hit the foundation you can drill it or undermine it. Install Clean Out within 24" of the exterior foundation. Bring new sewer to the location of your existing main sewer. If you are too high, use 2 - 45 degree bends to bring it down onto the same level with old sewer line. There, cut existing sewer, install Y and connect new sewer to it.

Milo, thank you for your help. You're correct - the footings themselves will not be post-tensioned. Just the slab will be post-tensioned, but there will be more footings than in a normal slab and they will be deeper.

Remember there is no slab yet - I've got just dirt right now. So I'm not making any cuts (of course if I screw up I just may have to break some stuff out later on - let's hope it doesn't come to that!).

So I would start then with the toilet drain at an elevation which is just under what will eventually be the bottom of the slab?

If you post sketch of your new bath including position of plumbing fixtures, I will draw you drain / vent lay-out, UPC version.

Hey Jellyroll...

To answer your last question (Milo missed it :p) you will start with the toilet drain at an elevation that is about 6" below the slab as you want to be sure the pipe is covered by a few inches of dirt and you want to be able to roll fittings above the center line of the toilet pipe for the toilet vent without the vent ending up in the concrete... and then pitch the pipe 1/4" per foot(3") or 1/8" per foot(4").

As Milo said, he'll draw up a UPC version of drains/vents for you. Or if you don't fall under UPC, let us know and we will see what else we can do.

MARK

Milo, If you're going to make a drawing why not make two. One depicting UPC with all those vents you guys love so well and another with wet vents. That way the OP has a choice if he doesn't fall under UPC. Regards, Tom

I'm about to expose my abundant ignorance. What is a "wet vent"?

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Originally Posted by jlisenbe

I'm about to expose my abundant ignorance. What is a "wet vent"?

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In the world of indoor plumbing, a wet vent,(see image) is a connection between an air pipe (vent) and the main drain pipe (soil stack) that occurs lower on the soil stack than a connection between that same soil stack and any other drain (toilet, shower, sink). Ideally, the vent pipes, which equalize air pressure within the entire drain waste vent system should connect to the soil stack above any drains so the vents don't get clogged up with waste, but this option may not be feasible for certain types of plumbing projects, such as adding a bathroom on a lower floor. A wet vent is essentially a plumbing compromise that uses the main drain pipe as both a drain and a vent when access to the top of the soil stack is not available. In the image the shower's wet vented by the lavatory vent.
Regards, Tom

Jlisebe: In my area, wet venting is not allowed and is against the Code. We run dedicated vent for each plumbing fixture. Vents can connect about 48" above the floor and continue with one single pipe to the attic. That's why it is important to know what Code your project falls under. According to UPC , Tom's drawing would be missing Shower vent and Toilet vent. Also, no clean out of any sort are present and Drum Trap is something you see in B&W movies from the silent era .

Thanks everybody. As requested I am attaching the drawing. We use the 2006 IRC as the building code, but the plumbing code is the 2000 Louisiana State Plumbing Code, which comprises the 1994 Standard Plumbing Code published by the Southern Building Code with some 1999 Louisiana modifications. Phew! That was a mouth full!

I think with the exception of some local edits (like no AAV and so forth) I'm probably fine if I stick with UPC. I don't know however if wet venting is allowed. Perhaps you can tell from the architect's drawing?

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Tom's drawing would be missing Shower vent and Toilet vent. Also, no clean out of any sort are present and Drum Trap is something you see in B&W movies from the silent era.

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This drawing is just pointing out the principles of wet venting. In my area we don't run a dedicated vent on everything but the family dog and While a clean out on every fixture might be just dandy in your area we consider it to be overkill and I AM something you would see in B&W movies from the silent era. Cheers, Tom

Lol!

After reviewing the code it appears that wet venting is allowed, as long as some specific conditions are met regarding size of venting and distance of fixture to vent, et cetera.

Still, the way the architect has the riser diagram drawn, many of the fixtures look to be way too far from the nearest vent to roof (look at the master bathroom for example).

Jellyroll...

Where are all the vents for the sinks..? All sinks need to have their own vent. What about the washing machine vent... where is that?

I have to say...this is the oddest plumbing design I have ever seen RESIDENTIALLY..?

You have 1.5" vents going through the roof (called VTR on the print)... that is not acceptable anywhere that I know of. Minimum vent penetration in all states that I know of is 2"

The shower drain is only 1.5"... no shower drains are 1.5" anywhere... period! All shower drains and shower strainers are 2".

You don't have wet vents... you don't have many individual vents and I don't see any mechanical vents mentioned.

The way it is drawn it wouldn't pass code in any state that I know of. Wonder what the other experts think?

MARK

Massplumber, I agree with you - I wondered where all the vents were too when I studied the diagram. I don't think the architect is expert at plumbing.

Looks like I REALLY need the help of this forum :)

I don't think the architect had a clue! You didn't pay for this did you?

If you give me some time I will try to draw up a better design then this last guy had.
I would draw up a wet vented system.

Otherwise, if Milo or Tom wants to draw this up vented and wet vented.. no problem! Just let me know Milo or Tom..OK?

We'll let you know, Jellyroll!

MARK

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Originally Posted by massplumber2008

Jellyroll...

Where are all the vents for the sinks...?? All sinks need to have their own vent. What about the washing machine vent...where is that??

I have to say...this is the oddest plumbing design I have ever seen RESIDENTIALLY...???

You have 1.5" vents going through the roof (called VTR on the print)...that is not acceptable anywhere that I know of. Minimum vent penetration in all states that I know of is 2"

The shower drain is only 1.5"...no shower drains are 1.5" anywhere...period! All shower drains and shower strainers are 2".

You don't have wet vents...you don't have many individual vents and I don't see any mechanical vents mentioned.

The way it is drawn it wouldn't pass code in any state that I know of. Wonder what the other experts think??

MARK

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Mark, it is quite common to run 1 1/2" vent through the roof under UPC. Just go to Home Depot and see how many of those roof jacks they have on shelf for this purpose...

You can vent a shower, or sink, or a tub with 1 1/2" vent and go all the way through the roof if framing doesn't allow you to combine it with other, larger, vents. Of course, toilet requires 2" vent.


Wet venting is frequently used in the situation as yours. As far as legalities according to Code it varies depending on which jurisdiction you are under. The UPC is considerably stricter with its rules than the IPC or most other codes.

When wet-venting the shower into the toilet (or any fixture drain) according to the UPC you are required to upsize the toilet vent one pipe size in the wet-vented section. That would require the toilet vent to be 2-1/2” where the shower enters and anywhere downstream of that entry. Since we do not use 2-1/2” it would cause us to use 3” for that section. Actually all we would do is use a 3 x 2 x 2 spigot sanitary tee on top of the 3” sanitary tee for the toilet and then the toilet vent and the shower vent would continue on combined in a 2” section which could have other vents connected upstream.

The restrictions encountered are the length of the dirty arm or trap arm. UPC requires a shower to have a 2” trap and arm whereas a tub-shower combination can be served with an 1-1/2” trap and arm. The 2” arm can be 5' in length from the weir of the trap to the entry of the vent. The 1-1/2” must not be more than 3' 6”. These are UPC rules but these distances are likely the same under both codes.

Following these parameters if you were to wet-vent the tub into the shower vent (only required to be 1-1/2” per UPC) all you need do is make sure the shower vent is 2-inch instead of 1-1/2” until you have the tub sanitary tee (2 x 1-1/2 x 1-1/2) installed then the 1-1/2” vent will serve both fixtures.

As I said earlier, other codes are not that restrictive and your area may well be under something other than the UPC. You may run into a less experienced plumber who categorically rejects one system over the other. But both systems work and will server you for many years w/o problems. UPC is more elaborate system and requires more materials. But in exchange, you will have each fixture with its own vent. Other system are simplified, not as heavy on materials. But in both cases, set rules have to be followed. Still it is not too difficult to comply with these rules and by following them - it does insure that you will have a good functioning system.

Yes, I agree with previous post: your blueprint is drawn by the "old" rules. In my area, and for residential projects, we don't get plumbing drawing showing drains and vents in place. We get only location of plumbing fixtures with necessary distances and clearances and we apply the most recent Code requirements to rough-it in. It is the opposite in Commercial projects. There, plumbing page includes location and sizes of drains and vents and sometimes even number of fittings required to complete the project.

Good Luck... Milo

Milo sez,

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your blueprint is drawn by the "old" rules.

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Yeah! Back in the late 1800's or early 1900's. While your code allows wet vents it doesn't allow "S" traps and I counted nine of them in the isometric drawing. Have you ran this past the Building Department yet? Let us know what they say. Fire the architect and hire AskMeHerlpDesk. We may work cheap but at least we attempt to kerep it in code. Like Milo , We get the As-Built Plans and lay the drainage out according to code. Good luck, Tom

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Just let me know Milo or Tom.. OK?

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Run with it Mark If I did it I'd have to copy the plans, hand draw in the vents and then scan it to disk. You have a much easier way to do it. Go git them! Cheers, Tom

Well of course if any of you have the time to make a drawing I would be eternally grateful. You've all been incredibly helpful already. I like this place!

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Originally Posted by Jellyroll

Well of course if any of you have the time to make a drawing I would be eternally grateful. You've all been incredibly helpful already. I like this place!

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Hey Jelly,
That's why we're here. Glad you like it here because we're all likable guys.
If you think we're nice here you ought to party with us on the weekends!! You have yourself a good one while Mark draws you up a set of plans that won't get you laughed at. Cheers, Tom