basement bathroom rough in how-to help needed

[rayethan]

I need some advice on roughing-in/installing a basement bathroom.

I've already cut the slab and the drain pipe is exposed. I have about a two foot wide trench cut with the existing drain pipe running parallel and just off the center of the trench. It appears to be a 4 inch pipe. All pvc.

This drain pipe enters the basement floor and serves the second floor bathroom.

I want to add a toilet, shower, vanity sink and a utility sink. (The utility sink is going to be outside the bathroom).

I was thinking that I would just run another drain pipe to serve the toilet, shower and vanity and then just tie that pipe into the existing drain pipe.

I am going to have this inspected so it needs to be code. I live in Michigan.

Are there any space issues regarding the fixtures? I know I need 15" on each side of the toilet and if I use a 36" shower, the drain will be 18" from the wall. I'm concerned about the amount of space bewteen the toilet and the vanity which are across from each other.

Will this "flow" of how things are connected to the new drain work? Vanity -> Toilet -> Shower -> Utility sink.

What pipe sizes do I need for each fixture?

Venting is going to be a problem. What size vents to I need for each fixture?

I'd like to run the vents up the bathroom walls and tie them all together. The problem is finding where to vent them to. There are no existing vents in the basement. I was thinking of running this vent horizontally for about 20 feet to the sidewall of the house. I have a washer drain there and there is a vent pipe through the roof. Run this vent up the wall and tie into the vent pipe in the attic.

Any knowledge you can pass on is appreciated.
Thanks,
Ethan

[Tom R]

I'll try to help a little here. Although 15" on each side of the toilet is up to code and will work, 18" on each side is more comfortable if you have the space. I believe the minimum between the adjacent toilet and sink is 22", but again, - - more is better, - - I try to achieve a 24" minimum. You gotta go with a 'round' bowl, rather than an 'oval', when space is tight, and if you need to, you can go with an 18" deep vanity, instead of a 21".

I'm gonna say you need minimum 3" drain for the toilet, and minimum 1 1/2" drains for the rest (though I would use 2"), - - it all really depends on your local codes.

[bkrahmer]

I don't know how friendly your inspectors are there, but our plumbing inspectors here are willing to check over your plans before you get started. I would call them and see if that's a possibility. Then, you can sketch out what you think will work, ask if it will work, and they will probably design the darn thing for you if you did anything wrong. Even if you have to pay for an inspection visit just to go over your plan, you'll surely be money ahead compared to plumber rates...

It's odd that a drain for an upper floor enters the basement slab. That's not allowed here in ID. In ID, you also cannot have drain line smaller then 2" in the slab. Don't know about MI.

Again, local codes will dictate, but you should plan on venting each fixture before it joins a 'main line'. I don't believe there will be a problem with a 20' horizontal run, as long as the pipe is large enough for the fixtures it serves.

[mjpliv]

Use sanitary "Y" fittings for waste connections and use "T" conections only for vent connections. You should only need a single vent line for the whole system.