Do you need vapor barrier for open cell insulation

[69gp]

Just had my garage insulated. 2nd floor ceilings were 3" of closed cell with 6" of open cell. My concern is on the garage level where I have 5.5" of open cell in the walls. Insulation contractor says that a vapor barrier is not needed unless the building inspector wants one. Just looking to see what everyone's opinion is on this. Blueboard goes up in about 2 weeks so I have plenty of time to add this in later if needed.

 

[billconner]

Following. I think the permeability of open cell justifies a vapor barrier, but interested in what others have to say.

 

[mrbill55]

Better to have it and not need it, then to need it and not have it. If it was mine, for the additional cost of material and labor, I'd install the vapor barrier, throw on some sheetrock, and at least have piece of mind.


Bill S.

 

[jack stand]

Following. I think the permeability of open cell justifies a vapor barrier, but interested in what others have to say.

I would say is there a negative side of doing a layer of poly?
It's such an easy and inexpensive item to do and with your scissor lift....
I'd stop by https://www.greenbuildingtalk.com/
and ask them over there.
I'd be inclined to do it as I don't understand why anyone would select open cell over closed.

 

[kj_mustang]

If your heat source is pumping out water vapor in the winter, I would want a barrier installed.

 

[Hank11]

I don’t know the answer but my concern would be whether the wall assembly could breath or dry to the outside after you sealed up the inside with plastic.

 

[69gp]

I would say is there a negative side of doing a layer of poly?
It's such an easy and inexpensive item to do and with your scissor lift....
I'd stop by https://www.greenbuildingtalk.com/
and ask them over there.
I'd be inclined to do it as I don't understand why anyone would select open cell over closed.

The cost of closed cell in the walls was going to almost double the cost of insulation.

 

[69gp]

If your heat source is pumping out water vapor in the winter, I would want a barrier installed.

I have radiant heat in the floor on the new garage section. Where the old garage is located I will be installing radiant in the ceiling.

 

[b-boy]

Correct me if I'm wrong, but the closed cell foam is essentially a vapor barrier and insulation. If you cover the open cell with another vapor barrier, will there be there anywhere for moisture to go if it gets between the layers?

I had my attic done a few months ago. I know an attic is not exactly the same, but the contractor would only do closed cell in the NE.

 

[Jbullfrog]

The reason the closed cell is double is that you don't have to take it out when your studs start to rot. The idea of insulation is to stop heat transfer, but if you don't seal the wall, you still have air and moisture moving thru it. What is your outer shell?

 

[billconner]

The cost of closed cell in the walls was going to almost double the cost of insulation.

Even though for same R value it's only takes about 2/3 for closed cell, plus cost of vapor barrier? Not critical, just trying to learn.