New bathroom. Is this drain layout OK?

OHIOresident · Feb 3, 2012

I am adding a new bathroom to my house. I am going to tie into the existing 3 inch drain pipe. There is currently a 2 inch sink drain that runs to the existing 3 inch drain. My new bathroom goes right between that sink and the main drain. I have created the attached drawing of what I am proposing. is this planned drain run ok? Any advice is greatly appreciated. Thanks.

OHIOresident · Feb 3, 2012

Thanks Chad. I agree about the tub drain. My bad. It would have to be 2 inch if wet vented. This is why I ask questions on this site. People here give good advise. I don't know about the lav arm though. It is not part of the venting and don't know if it is considered a wet vent. I thought I read in the code that it could be 1 1/2 inch. Hopefully someone can also comment on that. Thanks again. I really appreciate the advise.

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Terry · Feb 3, 2012

You can wet vent a bathroom group.
The sink that is not part of the bathroom will need to tie in after the bathroom if you are maintaining the wet vent. Is that a kitchen sink?

The trap arm for the tub and the lav can be 1.5"

OHIOresident · Feb 3, 2012

Terry, the sink that comes in on the right is just a utility sink and it also has a vent off of it. So, I am ok then?

Cacher_Chick · Feb 3, 2012

The code is very clear on this- the only thing that can run through the wet vented section of piping are bath group fixtures.

Dlarrivee · Feb 3, 2012

Chad Schloss said:
I am no plumber, but I know enough that if you are going to wet vent a tub like that, you have to run 2" the entire run, so take out that 1.5" after the tub trap and use 2". someone else will probably chime in with more info soon. i think the arm after the sink trap has to be 2" as well, not sure though.

Not sure why you suggest the trap arm on the lav would have anything to do with the wet vent...

Also not sure why you suggest that everything needs to be 2", the wet-vent doesn't carry into the trap arm for the bathtub.

Although there is nothing wrong with using 2" for said trap arm, there's also nothing wrong with using 1.5" under plenty of different codes.

Chad are you sure you understand the purpose of the wet vent?

OHIOresident · Feb 3, 2012

So, if I take the sink drain from the other room out of the mix, does everything else look good then? Thanks to everyone for the replys. I know this is a pretty simple bathroom, but I am also not a plumber and all of you have been helping a lot.

Cacher_Chick · Feb 4, 2012

Your layout looks fine.

You could actually reduce your dry vent stack to 1-1/2, but either way it must be increased to 3" a minimum of 12" below the line where it goes through the roof. This is to prevent frost closure.

OHIOresident · Feb 4, 2012

Thank you for the advise. I'm not trying to save any money, just making sure I do it right. So I will keep the 2 inch dry vent and tie that into the existing 3 inch vent going up through the roof. The 2 inch dry vent is about 6 feet left of the existing 3 inch roof vent. I can easily tie into that 3 inch 2 or 3 feet below where it goes through the roof. I will put the appropriate drops to make sure everything flows toward the main drain. Thanks again.

Tom Sawyer · Feb 4, 2012

You have to know what code you are under here. Under the latest version of the IPC you can vent the whole bath group through an 1 1/2" vent but not all codes will allow 1 1/2 and may want 2" which really, for the cost of the pipe I would much rather use anyway. Of course, under the IPC the toilet to vent distance is unlimited.

Dlarrivee · Feb 4, 2012

I've always been confused why people would go with 1.5" instead of 2" for a vent just because they can...

I don't find 2" hard to work with...?

Cacher_Chick · Feb 4, 2012

Ohio falls under IPC.

In the case of this vent, either is fine.

I would always rather drill a smaller hole than a bigger one, but that's just my preference.

Dlarrivee · Feb 4, 2012

Maybe it's the usual dollars and cents DIY thinking I'm getting at... "If I just use a smaller pipe I don't need a $20 drill bit, I can get away with a $10 one!".

Cacher_Chick · Feb 4, 2012

Maybe in some other person's case.

I'm thinking more about having to bore a stud wall for a section of horizontal vent.
Code does not allow holes through 2x4 wall studs big enough to fit 2" pipe.

A few years ago friends of mine were having carpet installed. The installer had one end of the carpet stretcher against the baseboard on the wall opposite of the bathroom, and when he applied the force of the stretcher, there was a tremendous "crunch".

Right next to the main stack where the bottom plate was drilled through, he had pushed in the bathroom wall 4".

A few more nails during the construction & piping would have went a long way, but nobody knew that until 10 years later.

Tom Sawyer · Feb 4, 2012

cacher, I would rather have my apprentice drill all the holes while I drink coffee and yell at him

Dlarrivee · Feb 4, 2012

I guess I just run my piping in such a way that I don't need to cut through studs for horizontal venting... Top and bottom plates, yes, but not studs.

Between joists or in the attic would be a much better place to go horizontal with a vent, wouldn't you agree?

I'm also always confused as to why people would go through the trouble of running a horizontal line in studs below a window for a kitchen sink... your trap arm can head towards an open stud bay to the left or right of the window in every case I've seen.

Cacher_Chick · Feb 4, 2012

I tend to side with the method that meets code and takes the least effort. I will go to lengths to avoid crawling around in someone's attic if I can avoid it.

If the joists run in the same direction as the plumbing, that is a nice bonus.

Things are not built like they used to be, with a single vent and drain stack. Most of the older houses here have no vents outside the bath. The kitchen piping is always combination drain and vent. I've never heard anyone complain because their traps are siphoned dry. Once in a while a dry floor drain will get someone's attention.

Some of the new houses in my neighborhood have 6 vents going through the roof. All the homeowners are up in arms because the neoprene seals on their roof jacks only last a couple of years and then the rain is leaking in. I put a roof on a couple of years ago and my 50 year old lead flashing looks as good as it did when the house was built.

IMO, the guys that plumbed houses 50 years ago were a lot more skilled than most of those today.

Plastic people and their plastic plumbing.

"Progress", they say.
I'm not always so sure.

Dlarrivee · Feb 4, 2012

Funny you mention plastic.

If you wanted to plumb your house in cast you could, but then you'd have the same rubber that is failing on vent jackets inside your banded couplings.

Hackney plumbing · Feb 4, 2012

cacher_chick said:
I tend to side with the method that meets code and takes the least effort. I will go to lengths to avoid crawling around in someone's attic if I can avoid it.

If the joists run in the same direction as the plumbing, that is a nice bonus.

Things are not built like they used to be, with a single vent and drain stack. Most of the older houses here have no vents outside the bath. The kitchen piping is always combination drain and vent. I've never heard anyone complain because their traps are siphoned dry. Once in a while a dry floor drain will get someone's attention.

Some of the new houses in my neighborhood have 6 vents going through the roof. All the homeowners are up in arms because the neoprene seals on their roof jacks only last a couple of years and then the rain is leaking in. I put a roof on a couple of years ago and my 50 year old lead flashing looks as good as it did when the house was built.

IMO, the guys that plumbed houses 50 years ago were a lot more skilled than most of those today.

Plastic people and their plastic plumbing.

"Progress", they say.
I'm not always so sure.

Labor wise cast iron is harder to install but with leaded cast iron joints you can cheat angles...with pvc fittings you cannot cheat angles and still make a technically correct install. UV causes those roof jacks to break down....they should be outlawed,just another part of the plumbing code thats an absolute joke.

New bathroom. Is this drain layout OK?

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