Insulation, Radiant and Vapor Barriers - Closed or Open cell foam insulation

I am currently getting bids on having the shallow crawl space under my late 1800's farm house insulated with sprayed foam insulation. I am getting conflicting information as to whether closed or open cell should be used.

The closed cell guy says go with it because it is a potentially moist environment and the closed cell will serve as a vapor barrier. The open cell guy says that the additional cost of the closed cell is not worth it and he has never had a problem with using open cell in similar applications to mine.

Anyone have enough experience to weigh in on this? Thanks in advance for your thoughts.

Closed cell is the way to go. As he said it will keep the moisture from the wood.

If your crawl space has a dirt floor make sure you add a full heavy duty vapor battier over the floor and up the foundation half a foot or so and seal it to whatever is there concrete or foam. Once you seal up the air leakage down there with the foam, moisture will need to be managed, possible a dehumidifier, but the VB over the floor should be fine.

And I agree with airman, close cell.

Bud

Closed cell is the only choice for your application.

If your crawl space has a dirt floor make sure you add a full heavy duty vapor battier over the floor and up the foundation half a foot or so and seal it to whatever is there concrete or foam. Once you seal up the air leakage down there with the foam, moisture will need to be managed, possible a dehumidifier, but the VB over the floor should be fine.

And I agree with airman, close cell.

Bud

Thank you all for your comments. Let me provide some additional information that Bud brought up.

Installation of vapor barrier is part of the working I am getting bids on and I will continue to run a dehumidifier in the space once the work is done.

When I started this process my homework lead me to believe closed cell was the way to go. But the one contractor insisted that although he could blow closed cell there was no reason for me to pay the extra cost as the vapor barrier would keep any moisture away from the foam and open cell was the way to go. He claims in the 15+ years he had been doing foam he had never had a problem with open cell used in a situation like mine as long as it was done right. There is a considerable cost difference between the two.

There's also considerable R-value difference between open and closed cell. Are the quotes for open cell for the same R-value or the same number of inches?

Doug M.

Also the closed cell air seals. I don't think there is any real cost between the two. Id get a couple more prices.

There's also considerable R-value difference between open and closed cell. Are the quotes for open cell for the same R-value or the same number of inches?

Doug M.

All quotes so far are for approximate inches installed, not R value. Yes, I know there is a difference in the R value between the two types.

Also the closed cell air seals. I don't think there is any real cost between the two. Id get a couple more prices.

I have read that closed cell is more expensive and the quotes certainly support that.

The guy who says I don't need closed cell is using the cost as one of his reasons. He says the cost is not justified and he doesn't want to spend my money unnecessarily. Of course that puts his bid at the low end.

If we take the R value difference out of the equation, what is the real reason I need closed cell? If I have a poly vapor barrier installed up onto the foundation walls and the foam is sprayed from the joist pocket/band board down to and slightly onto the poly then where is the moisture going to come from that makes the closed cell the product of choice? Through the foundation wall?

I appreciate the discussion.

For me being a "partially moist environment" is the key.
If you were not concerned about this then fiberglass could be thrown into your choices.
Although it does not spread quite as quickly as with fibreglass, a breach in your vapor barrier or an unexpected flood would affect the *open cell foam.
*Open cell will absorb and retain water within the cell structure.
Open cell also means open to absorb and hold water.

As an example I have dismantled many older home built commercial freezers that were insulated with six inches of open rather than closed cell insulation.
Because of improper or failed vapor barrier the stacked three inch sheets had to be broken into small pieces to be removed.
They has gained so much weight with retained water that they would be too heavy to carry and drip when squeezed .
I am only sorry I didn't weight them to see the actual amount of water they would hold.

I would view the installation of closed cell as long term and open cell as having the potential of being temporary in the event of the unforeseen .

Although it does not spread quite as quickly as with fibreglass, a breach in your vapor barrier or an unexpected flood would affect the closed cell foam.
Closed cell will absorb and retain water within the cell structure.


I thought closed cell foam was essentially impervious to moisture penetration and that was why it was such a great vapor/air barrier. Am I wrong about this?

Mchild,

Is this a vented crawlspace or unvented? I'm assuming it is vented and unconditioned as you are pricing having the ceiling of the crawl insualted vs. the walls. If it's vented then just a 6 mil vapor barrier on the floor may be enough to let the vents control the moisture. The downside with vents is the cold air unless you close them in the winter. Closing them can also provide a moisture issue in the winter if there is no air movement. A dehumidifier would help but I don't know what area of space you are trying to dehumidify and what size dehumidifier is beinf used.

Yes you will get moisture penetration through the foundation walls. Are you planning to foam them as well? Regardless of how tight you try to make a structure it is inevitable that moisture will be an issue and that is why most people here are suggesting closed cell directly against the flooring surface .

Would the installers spray an inch of closed first as a vapor barrier and then open cell the rest of the way? It would be similar to insulating with fiberglass in that you have the vapor barrier installed against the surface and then a "breathable" insulation below it.

I thought closed cell foam was essentially impervious to moisture penetration and that was why it was such a great vapor/air barrier. Am I wrong about this?

Mchild,

Is this a vented crawlspace or unvented? I'm assuming it is vented and unconditioned as you are pricing having the ceiling of the crawl insualted vs. the walls. If it's vented then just a 6 mil vapor barrier on the floor may be enough to let the vents control the moisture. The downside with vents is the cold air unless you close them in the winter. Closing them can also provide a moisture issue in the winter if there is no air movement. A dehumidifier would help but I don't know what area of space you are trying to dehumidify and what size dehumidifier is beinf used.

Yes you will get moisture penetration through the foundation walls. Are you planning to foam them as well? Regardless of how tight you try to make a structure it is inevitable that moisture will be an issue and that is why most people here are suggesting closed cell directly against the flooring surface .

Would the installers spray an inch of closed first as a vapor barrier and then open cell the rest of the way? It would be similar to insulating with fiberglass in that you have the vapor barrier installed against the surface and then a "breathable" insulation below it.

shane21,

I think you may have misinterpreted what I am doing. I am having the foundation walls up and into the joist bay at the band board. I am not doing the ceiling (underside of the floor) with foam. Once it is done it will then be closed crawl and the humidity will be controlled with a dehumidifier. It will then be considered conditioned space.

Hate to get you off in another direction. But if this is a crawl space and you go with the spray foam Id have them put a flash coat on all the wood (decking studs beams etc). This will keep moisture away from the wood and a dehumidifier will not be necessary. You can only do this if you go with the closed cell because the open will let moisture penetrate.

This is a typo:

Although it does not spread quite as quickly as with fibreglass, a breach in your vapor barrier or an unexpected flood would affect the closed cell foam.
Closed cell will absorb and retain water within the cell structure.

Too much open and closed talk goin' on here. :D

This is a typo:



Too much open and closed talk goin' on here. :D

I was tracking with you - not a problem. Thanks!

Hate to get you off in another direction. But if this is a crawl space and you go with the spray foam Id have them put a flash coat on all the wood (decking studs beams etc). This will keep moisture away from the wood and a dehumidifier will not be necessary. You can only do this if you go with the closed cell because the open will let moisture penetrate.

I thought you weren't supposed to insulate both the walls and the joists/ceilings in a crawl space? I never understood why not if the space is also conditioned but everything I have ever been able to read says one or the other but never both.

Yes mchild i was mistaken as i thought you were foaming the joists/ceiling and not the walls.

I still don't know about the dehumidifier handling all the moisture in that crawlspace but I cannot say because I don't have a clue how (or even if) you can calculate how many sq. ft. a dehumidifier can handle.

Hate to get you off in another direction. But if this is a crawl space and you go with the spray foam Id have them put a flash coat on all the wood (decking studs beams etc). This will keep moisture away from the wood and a dehumidifier will not be necessary. You can only do this if you go with the closed cell because the open will let moisture penetrate.

Is the flash coat sprayed on? What material is used?

I still don't know about the dehumidifier handling all the moisture in that crawlspace but I cannot say because I don't have a clue how (or even if) you can calculate how many sq. ft. a dehumidifier can handle.

There are sites that provide that info - try Thermastor. I have a separate crawl 16x39x4 under a newer addition (with vapor barrier) that I use a 35 pint/day dehumidifier. Works very well keeping the space not more than 50% RH. I will be using the same model of unit under the old part of the house once it has been sealed and insulated.

Yes just a 1 inch coating over anything that supports mold growth.