I plan to install a toilet, lavatory, and a laundry tub in our basement. Will break out the floor and hook into 4" DWV line. The run from the main line to the toilet is about 5 1/2' feet. I figure that if I vent at the point where the new toilet drain line enters the 4" main line, I should be okay. Basin and tub will be directly above the main line. My question is about the vent pipe. According to the information I can find from on-line articles, it seems that a toilet draws 4 "fixture units", the basin draws 1 and the laundry tub 2. That's 7 "fixture points" altogether.

There is a single laundry drain pipe nearby that drains into another drain pipe (3") which then runs directly into the vertical stack next to the basement wall (can't use it for my purposes). The vertical stack runs directly into the 4" line under the basement floor. That 2" laundry drain is vented by a 1 1/2" pipe that goes to the roof. Also in that same small system is the kitchen sink (with dishwasher and disposal). The kitchen sink and laundry drains work excellently. The vent pipe is actually 2" where the kitchen drain hooks into it, but then it converts to 1 1/2 " as it turns to go through the floor upstairs. If only that were a 2" vent stack (which should be able to handle 16 fixture units..more than enough for everything)!

Am I risking too much by hooking the vent line for the new half bath and laundry tub into that 1 1/2" line? Will it do the job? I certainly can't run a vent pipe from the basement to the roof. I can get to a 2" vent line that is currently only serving a toilet and washbasin...but it will be very difficult to get to it (have to tear out some finished areas, including first floor vanity and wall, etc., and will have a very tight working area to get to the vertical stack above that first floor sink. Need some expert advice on this. Thanks.

speedball1

Hi John,

I see you've done your homework. Your fixture units are right on. However, fixture units address drainage and wet venting. Not the vent stacks themselves. I have to know up front, will this job have a permit pulled and be inspected?
Our inspector allows 1 1/2" vent stacks but will tell you he much prefers to see 2"".
You have a venting problem from the git-go. As I understand what you're planing you will use the one vent coming off the 4" main to vent the rest of your fixtures because they are so close to the 4" main.
That's not gonna fly, (even without a inspection). You will leave the lavatory and the laundry tray with "S" traps, (outlawed in every state and Canada). Every fixture that's trapped must be vented. This means that each "P" trap must come off a tee and the top part of the tee must tie into a vent. There are no exceptions to this.
This doesn't mean that that your job's impossible, it just means you can't configure it the way you planed. Let me give you a another option.
Go 4" from the toilet to the main. Tie the lavatory drain, (2") into the 5 1/2" toilet branch and the laundry tray,(2") into the lavatory drain. That's your drainage.
For the vents you have options. (1) You can run a common 1 1/2" vent up and tie the lavatory and the laundry tray together and connect them to the 1 1/2 vent and the toilet will be wet vented, or (2)) you can install a 2" AAV (Air Admittance Valve) on each tee and your group will be vented that way. A AAV is a mechanical spring loaded valve used in remodel jobs where you can't get to a vent. If you're interested in venting with AAV's click on; http://www.studor.com/homeowners.htm
to check them out. Studore vents are manufactureda little north of where I live and I've used them with no problems. Good luck and let me know what you decide. Tom

miscojohn

I appreciate your response, Tom. I was not clear concerning how I intended to drain the lavatory sink and the laundry sink. I planned to do it nearly as you suggested, only I was going to put a separate "y" in the 4" underground main just for the 2 sinks. Your way is better...can I just go "4" until the sinks branch off and then 3" the rest of the way to the toilet?

As far as venting, I was not planning to use an "s" trap...rather to come up from underneath the slab with a vertical drain pipe and "t", hooking the lav into one side ("P" trap) and the laundry tub to the other side ("P" trap)...and then going straight up vertically with the vent and hooking into the 1 1/2" line above where the washing machine vent pipe and kitchen sink vent pipe hook into it. Was hoping the toilet vent could also be "y"ed into the sink vent pipes (because it's about a 5' run from that vent pipe to the stool).

As I listened to what you said your inspector said, I am starting to waver on hooking into the 1 1/2" vent pipe for the whole basement project. My original question concerned whether or not 1 1/2" was enough to vent that toilet, etc.

I've figured out that I can get to a 2" vent pipe by pushing a pipe from the basement up to the 1st floor bathroom, taking off the mirror in front of the sink, cutting open that wall behind the mirror and "t-ing" into that vent pipe (that only vents a lav sink and toilet) which goes all the way to the roof.

You asked if I planned to get project inspected. In our part of the country, the county website says that only licensed plumbers can do plumbing work, period. Same for electricians. However, when I've called them, they've told me that first, but then when I asked questions, they said, "bring your project in and let's look at it", implying that maybe they might let me do the work. I've done a few projects, added some circuits, finished off most of the basement (including building a large home theatre room with ceiling projector and 8' screen, elaborate sound system, etc.) without taking out the permits or getting the inspections. Am quite confident of the workmanship so am not afraid to sign off at house sale time. But this question of 1 1/2" or 2" has caused me to pause. I've done everything else according to code and would prefer to do this that way, too. So I've decided to go the more difficult but correct route and hooking into the 2" vent pipe. Right now, I'm also planning on calling the local department and checking out to see if they will let me do my own work. I work with people most of the time and this home construction is a hobby and passion that gives me a lot of satisfaction.

Thanks for your help.

speedball1

Hi John,
"Can I just go "4" until the sinks branch off and then 3" the rest of the way to the toilet?
You could go 3" all the way to the toilet if ths was a 1st. or 2nd. floor installation. But since this is under cement you must stay 4" all the way for the branch. Since you got the building department involved my guess is they will look at your plans and then make you pull a permit. Pick up a copy of local codes while your down there. You may save youself a lot of hassle if they'll let you use AAV valves for vents. If you run it the way I suggested you won't need a "toilet vent" it will be wetvented by the lavatory vent.
Good luck and keep me informed. Tom

miscojohn

Thanks...will do. I've already read the county regulations (they are on-line). "Only licensed plumbers may do plumbing installations in Howard County"

speedball1

Good morning John,
"Only licensed plumbers may do plumbing installations in Howard County"

Now I'm not telling you to break the law. That would be wrong. However, you sound to me knowledgeable enough to tackle the job by yourself. It's unfortunate you got the county involved. Where do you go from here? Regards, Tom