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Author	Comments
bob brining Posted: Jul 30, 2008 02:00 PM	condesation I have a newer home in upper michigan. This past winter i pulled away the fiberglass batt insulation in my rim joists and cantilever just to see. What i found was ice and or moisture built up on my OSB. Since the basement is heated I figured the warm air must pass through or around the fiberglass and condense on the OSB rim joist. My question is wether to use an open or close cell foam to insulate the rim joist and how much foam should be put in the cantilever?
mason Posted: Jul 30, 2008 04:17 PM	Yep, that's whats happening. I would use the closed cell foam, because it can act as a secondary barrier to water, air barrier and vapor retarder as well as insulation. You need at least 2-3 inches to stop condensation, but you can use a little more to provide better energy efficiency.
Dan Beecher Posted: Jul 31, 2008 09:47 AM	Check with the building codes people too. Some states like MN want the closed cell for the vapor retarder requirement alone. Open cell is not going to do that. We spray 3-4" of closed cell. Done thousands of them no problems.
Jim Coler Posted: Aug 12, 2008 09:53 AM	You could use open or closed cell. Yes, closed cell acts more as a moisture barrier, but if you have a good flashing and water managament layer outside the structure, it shouldn't matter. You're not talking about leaking mass water in the space, but condensation and both open and closed cell will prevent condensation. The important part about foam is that it acts as air barrier which prevents the warm moist air from getting to the cold surface. The inner surface of the foam is warm so it doesn't condense on the surface. The common thought from many has been just use closed cell because they don't completely understand the open cell or what's happening. The principle we use is to design to keep the moisture out and let it out when it gets in because noone is perfect at keeping it out.
Luke Kujacznski Posted: Aug 12, 2008 10:51 AM	River, I Michigan you cannot spray open cell in rim joist and leave them exposed. This is a code issue. Bren, 2-3 inches of closed cell will do the trick. Luke
Jim Coler Posted: Aug 12, 2008 10:53 AM	Be careful! The test for the rim joists was only performed on closed cell which technically has a larger fuel load than open cell. The objection by fire marshals and officials is the fuel load of exposed material with their tainted experiences of non Class I fire rated foams. Technically, Open cell is a lower fuel load because it is a lower density material. If you ask the ICC, they will tell you that open cell meets the intent of the code and can be left exposed in rim joists like the closed cell because it is a lower fuel load than the closed cell which is tested and approved. Yes, there are some states like MI, CA and NY which have their own code approvals and disapprovals, but most of them recognize the ICC as an acceptable approval body. So, what reasons did they give you for it's disapproval? Fire related code issue (I Assumed)? What's the difference between open and closed cell in a fire? It depends on the specific product used because technically, some of the older closed cells were even more flamable and would be rediculous to be left exposed.
mason Posted: Aug 12, 2008 01:41 PM	Open cell foam requires a vapor retarder element over it in colder climates. The main reason I recommended closed cell foam in the rim joists was to provide a secondary barrier against bulk water entering the space. The reader was correct that open cell foam was not approved at the last ICC code hearing exposed in sill plates. So it would require an ignition barrier over the foam.

Author

Comments

bob brining

Posted: Jul 30, 2008 02:00 PM

condesation

I have a newer home in upper michigan. This past winter i pulled away the fiberglass batt insulation in my rim joists and cantilever just to see. What i found was ice and or moisture built up on my OSB. Since the basement is heated I figured the warm air must pass through or around the fiberglass and condense on the OSB rim joist. My question is wether to use an open or close cell foam to insulate the rim joist and how much foam should be put in the cantilever?

mason

Posted: Jul 30, 2008 04:17 PM

Yep, that's whats happening. I would use the closed cell foam, because it can act as a secondary barrier to water, air barrier and vapor retarder as well as insulation. You need at least 2-3 inches to stop condensation, but you can use a little more to provide better energy efficiency.

Dan Beecher

Posted: Jul 31, 2008 09:47 AM

Check with the building codes people too. Some states like MN want the closed cell for the vapor retarder requirement alone. Open cell is not going to do that. We spray 3-4" of closed cell. Done thousands of them no problems.

Jim Coler

Posted: Aug 12, 2008 09:53 AM

You could use open or closed cell. Yes, closed cell acts more as a moisture barrier, but if you have a good flashing and water managament layer outside the structure, it shouldn't matter. You're not talking about leaking mass water in the space, but condensation and both open and closed cell will prevent condensation. The important part about foam is that it acts as air barrier which prevents the warm moist air from getting to the cold surface. The inner surface of the foam is warm so it doesn't condense on the surface.

The common thought from many has been just use closed cell because they don't completely understand the open cell or what's happening. The principle we use is to design to keep the moisture out and let it out when it gets in because noone is perfect at keeping it out.

Luke Kujacznski

Posted: Aug 12, 2008 10:51 AM

River,

I Michigan you cannot spray open cell in rim joist and leave them exposed. This is a code issue.

Bren,

2-3 inches of closed cell will do the trick.

Luke

Jim Coler

Posted: Aug 12, 2008 10:53 AM

Be careful! The test for the rim joists was only performed on closed cell which technically has a larger fuel load than open cell. The objection by fire marshals and officials is the fuel load of exposed material with their tainted experiences of non Class I fire rated foams. Technically, Open cell is a lower fuel load because it is a lower density material. If you ask the ICC, they will tell you that open cell meets the intent of the code and can be left exposed in rim joists like the closed cell because it is a lower fuel load than the closed cell which is tested and approved. Yes, there are some states like MI, CA and NY which have their own code approvals and disapprovals, but most of them recognize the ICC as an acceptable approval body.

So, what reasons did they give you for it's disapproval? Fire related code issue (I Assumed)? What's the difference between open and closed cell in a fire? It depends on the specific product used because technically, some of the older closed cells were even more flamable and would be rediculous to be left exposed.

mason

Posted: Aug 12, 2008 01:41 PM

Open cell foam requires a vapor retarder element over it in colder climates. The main reason I recommended closed cell foam in the rim joists was to provide a secondary barrier against bulk water entering the space. The reader was correct that open cell foam was not approved at the last ICC code hearing exposed in sill plates. So it would require an ignition barrier over the foam.

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