Insulation, Radiant and Vapor Barriers - vapor barrier question re: drywall

So I've got a piece of greenboard, facing the kitchen on one side of the wall. The other side of the wall is the garage. Because the utility sink is close to this area, and the back part of the greenboard doesn't have the barrier, I attached 3mil poly to protect the backside of the greenboard from spashes.

Now, I want to rock the garage. I want to put greenboard on the garage side in the areas around the sink. The rock will not go all the way down to the garage floor, because the plumbing in the garage butts out past the wall. I know vapor barriers on both sides of a wall can cause mold; so my question is this:

Should I just rock it with greenboard, and since it's not going all the way to the wall, it wouldn't be considered a vapor barrer because airflow could still get in?

Should I remove the 3mil from the backside of the kitchen greenboard, then put up the greenboard in the garage?

Of course the rock not going all the way to the floor is most likely a fire code issue, but it is not possible without some plumbing mods with I don't have the skill to do.

Thanks all !

Rock should NEVER be on the floor leave 1/2 inch off plastic on inside will be fine.

what I meant by 'floor' was just as you said, with a small gap at the bottom. So all I need is 1/2" and I can have plastic on both sides, without any problem?

Doesn't seem right.

You keep the rock 1/2 inch so it wouldn't get wet from spills and weep water out of concrete. Id only put VB on inside of wall.

doesn't greenboard have a vapor barrier also? If it does then it would be on the outside of the garage wall. There is already a 3mil poly barrier on the inside of the kitchen wall. I definately need greenboard on the garage side. So should I remove the 3mil on the inside of the kitchen wall?

Vapor retarder goes on heated side of wall.

Vapor barriers go on the warm or conditioned side of the fiberglass insulation.

If you are putting up any kind of a board with any openings in or around it, it is not a vapor barrier.

Dick

Thanks Dick. That was my thinking as well. The original purpose of putting up the 3mil on the garage side was to protect the backside of the greenboard from spashing from the sink.

I just wanted to make sure that if I put up greenboard on the garage side, the 3mil wouldn't be a problem for mold.

But it makes sense that if air can get in there, and it will be able to, that it is not a vapor barrier and therefore not an issue with mold growth.

Thanks.

Did you check on fire code there You said 1/2" drywall. Most codes call for 5/8" drywall for fire stop on a wall from the garage to the home.

ED;)

Ed, I think the 1/2" was the gap from the bottom of the rock to the floor. Yes, I plan to use 5/8" as the code here requires 1 hour fire-rating.

Thanks.