Vapor barrier not needed if using foam?

Hi there,
I’m in the midst of re-cellaring after quite a few flood. In trying to get the vapor barrier done right, I came across a reference saying that you don’t need it if spraying with foam. Is this correct?

Also I saw in different spots, people (a) hanging the plastic behind the studs towards the other rooms as well as (b) wrapping the studs themselves in plastic. What is right here?

And what do you do for ceilings? (I’m in the basement.)


Must be closed-cell foam.

Thanks, Dale! Could you elaborate?

I am assuming you mean that if you use foam for insulation, it should be closed-cell foam? Do you also know if you need a vapor barrier if you use closed-cell foam? How about ceiling? Do you do the same as for walls?

Thomas - I built a cellar a couple of years ago and the builder (who specialized in wine cellars) told me the same thing - that there was no need for the vapor barrier when spraying closed cell foam. I also had the ceiling sprayed and my cellar is below grade. So far so good…

Yep, we used closed cell foam insulation for my wine wall (and entire house) and did not need an additional vapor barrier. Highly recommended if you’re redoing your cellar anyway.

thanks! This is super helpful!

No one is worried about the health and environmental issues with sprayed foam insulation?

As pretty much said above, closed cell foam will act as the vapor barrier. Open cell foam (cheaper) will not. So if you are unsure of the difference then ask to be sure you are putting closed cell in assuming you want it to double as the vapor barrier.

Closed cell insulation must be a certain thickness to be considered a vapor barrier. Of course, I forgot what thickness is needed since I used it in my own cellar - but that info should be readily available on the insulation spec sheets from the manufacturer.

Fairly certain that’s only during installation and the first 12-24 hrs. Needs to be properly ventilated during this time and installers should wear proper protective gear. Otherwise I don’t believe it has any health risks, especially when it’s covered with wall material.

From my own research, most say 2" or more for a vapor barrier. The real key is to make sure there aren’t pin holes anywhere. Also, it is expensive and 2" is probably not enough insulation (particularly for ceiling and depending on climate). Can either use more foam or use 2x6s and put fiberglass insulation in once the foam is down.


But you DEFINITELY need protective gear and ventilation when installing. I felt bad for the dudes that did our house. Some nasty stuff for sure.

I used Heatlok Soy 200 - had to look it up in my records. Looks like it reaches vapor barrier at 1.2 inches. I’d still probably spray a minimum of 2 inches just to be on the safe side - the way the foam sets, its impossible for it to be a consistent depth all over and bound to have a few shallow spots. And you’re exactly right 2x6s with some fiberglass on top of the spray is a good way to fill the cavity and be cost efficient. Impossible to fill studs with spray completely without carving off a ton of over spray.