building a new room

I think you want to do black plastic on the exterior. The foam board will prevent moisture to pass thru it (providing it is closed cell XPS). I suggest the Dow XPS 1 inch board.
It will much easier to create an air tight seal with the foam than with the plastic (I would think). Neither will allow moisture to pass so unless the interior layer is not tight you shouldn't have an issue. You want to use PL300 adhesive and low expansion closed cell spray foam for your 2 gluing/sealing products.

If you think the plastic will be easier than you can do that. It just seems that would much more difficult.

the interior should be as air tight as I can get. nice close edges then sealed with 2 hvac foil tape.

maybe ill take back the roll of black plastic. shit was 80.00, and could use that for the foam board cost.

DemonTrich said:

the interior should be as air tight as I can get. nice close edges then sealed with 2 hvac foil tape.

maybe ill take back the roll of black plastic. shit was 80.00, and could use that for the foam board cost.

Click to expand...

I'm inclined to agree with you. Even if you were able to get it perfect, it is so susceptible to punctures and tears. If you were to use staples...you might compromise the vapor barrier right there.

I would have stapled the plastic up. im still using 1 layer of 6ml plastic on the floor and ceiling (stapled then taped over the staples), then 3 layers panda film on the floor (1st layer stapled, last 2 taped on the edges), and 1panda film layer on the ceiling over the black plastic. again stapled, then taped over each staple.

what would the benefit be on 1/2", 3/4" or 1" foam board insulation? I grow underground, and my temps are normally 73* year round. when all my room are fired up (3x600 hps, 1x600mh, 2x 2x4' t8 6500) and my a/c on its still 73/74* (all plants are currently grown in tents). and I recirculate all air in my underground grow. I don't pull or exhaust any air outside.

Then you probably don't need it and what you did will be fine. It would have given you some R value if you needed it but it sounds like you don't.