Ask Me Help Desk - Basement 1/2 bath install

I would like to add a half bath in my basement. The planned half bath is just below my kitchen sink on the main level and near the first floor laundry as well. My laundry is just off the kitchen but there is crawl space under it.

In the area where I want to put the half bath, there is a 2" PVC drain pipe for my kitchen sink and my laundry tub connected together, that runs into the basement and into the concrete floor, I would guess into the main sewer line. There is a cleanout "Y" in this line near the basement floor.

I have a couple of questions. First, Can I simply connect my sink drain to this cleanout? Second, can I assume that if I bust the floor near this 2" line I will find the main sewer line to connect my toilet to? Third, I cannot find the vents for either my kitchen sink or the laundry tub in the crawl so I'm guessing that it is in the wall behind the kitchen sink and in the wall between the kitchen and laundry, and of course buried behind finished partitions and cabinetry. So given this information, what is best way to vent my new basement toilet and sink? Do I have to run a new vent pipe up through each floor in the house and out the roof? If that is the only way, how in the heck is that done?

First timer here, thanks for reading and any help you can give.

Hey jforce:

1) No... code forbids anyone to just connect into a cleanout at the base of the stack. But does not mean you cannot connect into pipe... as long as you cut wye fitting in AND you run a separate vent for sink... but read on.. I have a better idea.

2) No.. do not assume that it is becomes 3 inch drain anywhere near that 2" pipe coming out of ground. Here, I would look for the main drain cleanout and try to work my way back toward bathroom area from there. Are there any other pipes coming out of floor besides that 2" pipe..such as a 3 inch stack or 4" stack going upstairs? It may be possible to see that 2" pipe may run over to that larger pipe before it goes upstairs to pick up bathroom(s). So really look at the system and see if you can tie all together.

3) Yes, vent pipe is probably behind the kitchen sink/laundry tub. In terms of the vent for your future 1/2 bath you will need to run a 2" vent for the system. Here, you will probably run a 3 or 4 inch (depending on underground pipe size) waste pipe to toilet, then take a 2" vent off the toilet waste line (rolled above center line of waste to be a valid vent) and run that to the lavatory (sink) and pick up lavatory. This is called a wet vent and is legal by code anywhere if you follow basic rules). From there you continue up with that 2" vent until you can connect into another 2"vent...such as may be by a full bathroom.

How do you do it...? It can be tricky. In alot of these cases I just run a whole new 2" vent line all the way to attic by way of closets (hide pipe in corner.. or can box vent out in closet so knowone sees) and then tie my vent in up in attic at 3" pipe up there.

Anyway, there you go.. a basic rundown. Let me know if you have any more questions. All of us onsite are glad to help when we can.

If my answer helped, please RATE THIS ANSWER by clicking on button below. Thank you.

Thanks for the quick answer. As you can tell, I've never done anything like this before.

Your answer had great information. Not sure exactly by what you mean by the "wet vent", but maybe a schematic would help.

As for other runs in my house, yes there are two others besides the 2" I asked about. One is a 3" and is located in the center of the basement, almost the midpoint of the house. I'd say its 12' on a diagonal line from where the 2" kitchen/laundry drain enters the basement floor. This 3" pipe is the drain (and I can see the vent too) for the first floor powder room and the second floor Main Bath directly above the powder room.

Then on the other side of the basement from where the new bath is intended, perhaps 21' from the 2" on a direct line, is a 4" pipe which is the drain for the master bath on the second floor. If you can imagine, the 2" pipe in the new bathroom area the 3" in the center of the house and the 4" on the opposite side of the basement form a perfect triangle. I would assume then that the drain out to the street is off the 3" (only because it is closest to the street?). Anyway, that's the layout.

Finally, Just above the area anticipated for the new basement 1/2 bath, I went up in the attic and located the vent stack for the kitchen and laundry. It is just a few feet over from my new room and above crawl space. Better yet, the closet for my mud room leading out to the garage is also right there. So I can put a new vent in the framed wall of my new bath above the toilet, carry that over to above the lav and then up into the closet then into the attic above the closet and voilà - the laundry/kitchen vent stack is right there to 'T' into?

As far as I can tell, the only real issue is figuring out from all this how much of my concrete floor I need to tear up to install a toilet drain. I can't assume there is a larger drain pipe just below the 2" drain pipe according to your post, so is it possible the plumber ran a 2" line into the concrete there and then all the way (diagonally) to where the 3" main bath drain is? In that case, in order to connect to a larger drain pipe, I have to tear up 12' or more of floor. Thats the distance between the 2" and the 3" in the center of the basement. That's a ton of concrete.

Again, thanks for your help Massplumber2008.

Hi jforce... A wet vent is used in place of individual vents to each fixture if it meets certain criteria. Here, as in your case, you can run a 2" vent off the toilet waste line underground and run that over to the sink. It is a wetted vent because waste from lavatory will flow down this toilet vent but it is OK because the sink is rarely used at the same time as the toilet.. so code says OK.

THIS saves you from having to run a vent for toilet AND an individual vent for the sink.. just has to run full size two inch pipe all the way as posted in my last post. READ this post and the other post again.. see if makes sense. Let me know.

And yes... sounds like you understood the rest of my post.. and yes.. 12 feet is a good length of concrete... but breaks away pretty easy once you get a good hole started.

Let me know if you need any more info.. could try to draw out if you want.

Please rate this answer if this was helpful

Massplumber2008 I think I've got it. Thank you very much!

The 'wet vent' for the toilet doubles as the drain line for the lav. I have to put a 'wye' into the toilet drain below grade but above or slight angled up from 90 degress so sewage from the toilet can't flow up the vent, right? That is very cool. Thanks again and if I got it wrong, please correct me.

J

Quote:

The 'wet vent' for the toilet doubles as the drain line for the lav.

Not quite. The lavatory drain will serve as a wet vent for the toilet when it's connected to the toilet drain and, if local codes permit and if you wish to add a tub/shower you may connect to the lavatory drain and it will be wet vented also. Good luck, Tom

Jforce... for your purposes... you got it dead on. Understood me exactly... looking for a job?

If my answers helped please RATE THIS ANSWER by clicking on button below. Thank you.

And if you need more info... just let us know.

Thank you both. If I get into a bind, you'll hear from me. I could always use a job, but think I'll stick with sales.

J

Quote:

The 'wet vent' for the toilet doubles as the drain line for the lav.

Quote:

The lavatory drain will serve as a wet vent for the toilet

Sorry Mass! Just read it wrong and then said the same thing. MY BAD!

Just wanted to post an update for others considering a basement half bath install and for the experts that helped me with this question. My new half bath is installed! This was my first time doing anythying like this. A real experience. For others out there contemplating such a project, it can be done, but with a lot of hard work and the mother of all messes (cutting into the floor). I would say the only thing I could think of worse than the mess I made cutting into the concrete floor would be a flood. So, learn from my 'mistakes' and save yourselves some of what I went through. First of all, I have new respect for how hard concrete is. In order to locate my 3" drain line via the recommendations posted here, I cold chiseled thru the floor at a spot that looked promising. It took me 2.5 hours to open up a small 5" hole. Digging around this hole with a screwdriver, I located the 3" drain line. I noticed right off that my 2" drain discussed in the original question was Wye-d off this 3" and that I would subsequently saw thru it when I cut the floor (which is what happened - but its no big deal. I had to duct tape the cuts in order to wash clothes for a few days until we could re-plumb).

In order to make this story shorter, it is possible to locate the 3" drain by following the tips these people gave me in the answers above (I was so happy to locate the 3" line after 2.5 hours of sweat!). Next I was ready to cut into the floor. Here is where you can do yourself a big favor. Hire a concrete saw company to come in and do it. Pay them. Don't do this yourself like I did. It cost me 3 days of cleaning up the mess. Compared with the mess made sanding a floor or sanding drywall this was incredible. I'm talking about a cloud of dust. A respirator is absolutely necessary. I could not put enough water on the saw to keep the dust down. If you hire a saw, they come in with a saw that will minimize the dust and put more water on the floor. Your options are not good for doing it yourself. You either expose yourself to CO from a gas powered saw or you use an electric saw with water? I began cutting the floor on a Saturday around 2 in the afternoon. By midnight that night, I was able to clean up enough to turn the furnace back on. I spent the entire next day cleaning up. Everything in the basement gets thickly covered with the dust. So remove everything first. I did not. And I had to touch and clean every single thing, tool, box, everything. The dust is so fine that it actually goes thru the thin gage poly coverings I put on some of the items in my basement. So tarping doesn't cut it. Remove everything first.

OK so we got thru it. We then plumbed the new toilet and sink drain as suggested here. We wet vented the sink and the only departure from Massplumber's recommendation is that I used a studor vent, hiding it in the new wet wall because I have a pedestal sink otherwise the studor vent, which is acceptable here code-wise where I live, can be hidden under a vanity. Mine is a perfect application for these types of vents. It saved me from running a new 2" vent up through a closet and into the attic and out the roof. I put it in the wall right behind the toilet teeing off the sink drain/wet vent. You have to have air access to these things so I used an HVAC cold air return cover to cover a hole in the drywall on the backside of the wall behind the vent and marked it "1/2 bath vent". We can use Studor vents here but it needs to be accessible for servicing.

So thanks to those of you that helped. I could have done this with a lot less work, but that's the difference between amatueurs and pros I guess!

If anyone reading this would like more of my experience with this, just ask. I have pictures of how I plumbed it. I did everything in my basement finishing project from soup to nuts, but this was the most formidable task by far. Not impossible, not ridiculous, just hard. Two lessons I take away from this experience. Never buy a slab home and always pre-plumb the basement with a drain line when building.