I'm in the process of attempting to design the plumbing for an in-law unit behind my house. The only plumbing I will have is a lavatory, wc, and shower. My calculations gave me a whopping grand total of 6 DFU's under the UPC.

Everywhere I have looked, the house drain is supposed to be 4", but this seems like way overkill for the small number of fixture units I have and, based on what I've read, I might run the risk of using pipe that is too large thereby increasing the likelihood of blockages down the line (no pun intended).

I'm wondering then, if the drain from the in-law unit (which I referred to above as the "house drain") to main house drain (approximately 40' away) would even be considered a house drain, or can I consider it a horizontal branch drain and size accordingly (I'm thinking 3" would be more than adequate).

Thanks.

Hi Bergs4:

Sounds like a BRANCH drain to me... ;)

3" pipe should be fine here. Be sure to include an accessible end cleanout at the in-law apartment and if possible install another in line cleanout (called a dandy clean out or a test tee) just before the drain connects into the house main drain line.

Bring the cleanouts to grade and then install a cleanout cover (see image... sold at all plumbing supply stores)... ;)

MARK

Another thing to check is your local Building Department for code requirements in your area. In the county I live in a 3" toilet drain under the slab's acceptable while the next county south of me mandates 4". Same SPC PlumbingCode but different mandates. Good luck, Tom

Massplumber --

Thanks. I will go with 3" then and install the cleanouts as you suggested.

That cleanout cover looks MUCH better than the cheapo thing the previous owner installed at the main house drain.

Speedball -- I will check with the building department and see what they say. Thanks.

I've completed my rough design of the plumbing and was wondering if there are any problems with it (I've attached a sketch). I'm most concerned about the wet vent, and if I've done it correctly and sized it appropriately.

Oh, and I forgot to include the cleanouts in the sketch, but will make sure they're included as per the suggestions when the pipe is installed.

Thanks.

Bergs4, you got excellent advice from our Experts. In addition: use 4" pipe only if you have problem with slope. Otherwise, as said above, 3" is fine. Usually, being 40' away brings you at least 20" deep at the point of connection. That's where 4" pipe and its 1/8" per foot slope becomes handy.

Did you measure your elevations ? Do you know how deep is your existing sewer at the point of proposed connection ? You should know that information before you start. It will make the project lot easier.


Your drawing is incorrect. You are missing vent for shower and toilet. You can down-size sink vent to 1 1/2". 3" is overkill. Vents can be connected in the wall ( 48" above the floor or higher ) or in the ceiling. You can penetrate roof with one, 2" vent that will carry all three fixtures.

Preferable location of toilet clean out would be at the end of the horizontal run. If you can, extend the new sewer past the toilet, all the way to the outside. But you are also allowed to come up the nearest wall with same size pipe as the main run and put in Tapped Clean Out Tee with flat plug. This clean out has to be as close to the toilet as possible but not further than 5' away. Reduce this Clean Out Tee to 2" and continue with 2" pipe towards the roof. That is you toilet vent and Clean Out in one. Use long 90's for vertical to horizontal transitions. Horizontal vents have to slop backwards (towards the fixture) at 1/4" per foot. Also, under UPC you will need clean out for each plumbing fixture installed on slab. See the sketch... Red dots are clean outs.

Milo'scorrect. Your drawing won't fly. You can't discharge a major fixture past a unvented minor one. Having said that Milo gave you a drawing from his code (UPC) which has three vents. Let m\e tell you about the code in my area,(SPC) that allows wet vents and only uses one vent for the group.
It goes like this. Toilet to main, shower to lavatory drain line and lavatory to main for the drain and out the roof to vent the group. The toilet and shower will be wet vented by the lav vent tnrough the roof. This is how we put in bathroom groups in my area.
Check with your local Building Department to be sure wet vents are allowed.. Outside of the vents I agree with Milo on all counts. Just giving you more options, Tom

Milo --

Your information and drawing are very helpful. I did measure the depth of my connection at the main house line, and you are right, I'm about 40 inches.

The toilet abuts an exterior wall so I should have no problem installing the cleanout as you suggested.

Is it okay that the toilet is not at the lowest point of the horizontal line in this configuration? For some reason I thought that was a requirement unless you had some sort of wet vent.

Speedball --

I too am under the UPC so I guess it would be safer to go with the configuration Milo has suggested.

Thanks again.

bergs4: Good question...

Toilet has to be last fixture on the run (branch). In the situation when bathroom layout requires toilet to be first, and then followed by sink and shower, you do it as in the sketch bellow ( it is a simplified version just to support my point ). You simply branch off past toilet vent with new pipe servicing sink and shower.

Lets say, if you would branch off between the toilet and its vent - then UPC will consider it as wet venting - which is not allowed.

Hope that will answer your question.

Good luck with your project. Don't forget to let us know how you did ! Milo

Milo--

Thanks for the explanation. That makes sense.

I will post the results of the project, although it's probably going to be a week or two as I'm about to head away for vacation.

I got taken away from the project for a bit:mad:

I've done a revised drawing based on your suggestions and my understanding of them. I was wondering if, as drawn, my plan will work? Also, I wanted to know if if the 2" line serving the shower and lavatory is acceptable. Oh, and also, do I have do the reduction in pipe size (from 2" to 1.5") for all the cleanouts or just the toilet (from 3" to 2")?

Thanks!

Looks good...

Do not reduce clean out at the toilet. Clean out should match the size of the drain pipe. Therefore : Toilet 3" cleanout. Then reduce to 2" and continue up. Shower 2" clean out, sink 1 1/2" clean out.

Otherwise, it looks good to me...

Great!

I'll let you know how the project goes as I progress.

Thanks for all your help.

After I busted up a good part of the slab, I began to lay some pipe. However, I realized that I was going to have a problem doing the cleanout / vent as you suggested for the toilet. The reason, is, due to space considerations, I would have to bring the 3" pipe through my weanie 2x4 sill plate which would basically mean I'd have to cut a portion of the sill plate off, which I didn't think would be the best idea from a structural standpoint. So, I drew (and attached) a workaround which I'm hoping will fly.

Also, if it helps, the cleanout will be about 4ft. From the toilet and would be easily accesible from grade level.


Any comments which be much appreciated.

Thanks.

No attachment, please, try again...

In the meantime: it is structurally perfectly OK to drill 3 1/4" hole through the plate to accommodate the pipe. ( At least in my area ). Also, you can cut the plate completely and install 12" x 1 1/2" metal plate across the cut, one on each side, designed for this purpose. Nail with 8d sinkers.

That's good to know -- based on what you say about the workaround, I'll revisit the original plan.

Here's the attachment.

It makes sense the way you drew it, too. You can always snake drain by removing toilet. But if you have clean out, it is good to install it as close to the end of the line as possible...

Thanks for the quick response. I think I'll go with what you originally suggested and sister the sill plate with the metal straps.

Milo --

Hopefully this is my last question for awhile --

Is it okay to use a combo fitting to transition from the toilet trap arm to the toilet vent line. I feel like it would make it harder to snake from the vent line to the toilet this way (since you'd have to go in the opposite direction of the curve in the combo) -- is there another fitting to use, or is this how it's done?

Thanks.

I bet you your toilet will never clog bet. The toilet inlet and the clean out. If it does, than you remove the toilet and snake it through toilet mounting ring opening.

However, yes, the do sell this "double combo" fitting you are mentioning in your previous post. If you feel that's what you want to do, than do it. It won't hurt the system.

Milo --

That makes sense. I'll go with how it was originally then. I REALLY appreciate all of the help.

Seth