Is putting poly over rigid foam boards going to cause a double vapor barrier issue?

You're definately creating a **double vapor barrier** if you pull that poly down over the rigid foam. If you've got 2-inch XPS (the pink stuff), that board is allready a vapor retarder. Slapping a sheet of 6-mil poly over it creates a moisture sandwich that will eventually rot your studs. Once moisture gets trapped between those two impermeable layers, there’s no way for the wall to dry out. Since you've already taped the seams and tucked the foam between the studs, your main concern is the wood itself. If you've used spray foam or high-quality tape to seal the rigid board to the studs, you've already created an effective air and vapor seal. Adding plastic on top is overkill and actualy dangerous for the longevity of the framing.

Stop the poly right at the top plate. You want a continuous air seal, but that doesn't mean the material has to be the same. Use some **acoustic sealant** (the messy black stuff) to goop the ceiling poly to the top plate of your wall. This keeps the ceiling assembly airtight while letting the wall breathe slightly toward the interior if it ever needs to.

In colder climates like Canada, the goal is to keep the vapor barrier on the warm side of the insulation, but you have to pick one. If you have at least R-10 of foam, the dew point shoud stay within the foam itself rather than hitting the foundation wall. Adding poly over the studs just invites condensation to form on the back of the plastic, wich then drips onto your bottom plate. Not a situation you want to deal with in five years.

I was honestly about to do the same thing because I thougt the whole room had to be wrapped like a giant gift. If I'm skipping the poly on the walls, what do I do about the tiny gaps where the rigid board meets the studs? My cuts weren't exactly perfect, and some of the tape is already peeling. Should I go over those edges with some of that canned expanding spray foam to keep it airtight? I really don't want drafts coming through once the drywall is up if I'm not using the plastic sheet to catch everthing.

defintely skip the poly. I’ve seen guys pull it down and when they renovate five years later, the studs are black with mold. If your cuts aren't perfect, grab a pro-grade foam gun and some low-expansion spray foam. It’s way better than tape for those tricky stud-to-foam gaps. Also, don't forget to seal the bottom of the foam to the floor or the bottom plate. If air leaks under there, it doesn't matter how well the rest is taped. A bead of acoustic sealant or a quick spray of foam at the footer makes a huge difference in keeping that basement from feeling drafty.