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Mike Natal Posted: Sep 25, 2008 08:42 AM	Can closed cell be sprayed over open cell? Can closed cell be sprayed over open cell? The reason Im asking is my rafters in my attic were sprayed with open cell, but the contractor srayed some areas 1/2" thick in some areas and 2" in other areas and 5" in other areas. So he was going to respray the rafter to correct the problem, but only has closed cell to do it with. What would be the pros or cons of this?
mason Posted: Sep 25, 2008 08:50 AM	No, you do not want to spray closed cell foam over open cell foam or fiberglass or cellulose. If you had a roof leak the water would not have anyway to get out. Now you can do the reverse, spray open cell over closed cell so long as you have sufficient thickness of closed cell SPF to prevent potential condensation on the surface of the foam. (typically 1 inch in mixed climates and 2 inches in cold climates.)
Jim Coler Posted: Sep 25, 2008 05:16 PM	Mason, This sounds like the "Flash and Batt" type of approach using open cell foam. I'm assuming you are recommending this because it's in the South and the warm side is the exterior for the majority of the year. So you would want to put your vapor retarder material towards the outside of the building. But this doesn't seem to make sense with what has been described as the probelm in this situation. It seems that there is a condensation issue in the attic already with inconsistent application of .5 lb foam from 1/2" to 6" thick. I would think that if there is a condensation issue then theat means there is a cold surface in a warm moist environment. This would say you might consider using the closed cell on top of the open cell as a vapor retarder material. Overall, open cell is the best to use over open cell.
mason Posted: Sep 26, 2008 09:09 AM	Riversnrocks, No, I am not talking about condensation, (although that is another issue to consider), but actual bulk water from a roof or window leak. If you install closed cell foam over open cell foam, bulk water cannot escape through the closed cell foam and would stay in the open cell foam until the closed cell foam got saturated. By this time you could have significant wood deterioration above the open cell foam. Better idea is to just install more open cell foam until the specified thickness is reached.
Mike Natal Posted: Sep 26, 2008 09:14 AM	So to sum things up, its seems what ya'll are telling me is once my foam guy sprays the correct thickness evenly across the entire roof and he closes up the scattered holes allowing air at the soffit that should resolve my moisture problem all together?? In the mean time, what do you suggest I can do to move some of that moist air out the attic until he can respray? Will eliminating the excess moisture and wettness on the air handlers and duct work help reduce my electirc bill thats sky high right now?
Jim Coler Posted: Sep 26, 2008 09:38 PM	It sounds like you have ductwork in your attic which has condensation occurring on it. Is this correct? Well, the leaky attic is allowing moist air into it and the warm moist air is rushing to the cold ductwork. When the heat of the air is deposited to the ductwork, the moisture it was carrying gets dropped on the surface. So, once you get the air sealing issues under control, it should show improvements to your situation. The air sealing and insulation may not be the only problem resulting in condensation and high utility bills, but as mentioned by others on this forum, you may need to reduce your AC tonnage for it to run longer and remove the additional moisture. So, I would start with properly air sealing and insulating your attic and monitor the results and tae further action if necessary. There is no easy answer as a quick fix for ductwork condensation, other than air sealing and insulating properly. You really have two options: 1: make the air in your attic dryer (hard to do with leaks to the outdoors) or 2: make the ductwork warmer. If you can't control air from coming in from outside, you can't control the moisture in the air of your attic. So, the only quick temporary fix, is to turn off your AC which will make the ductwork warmer. So, get your attic insulation and air sealing fixed fast and then see if you need to do something with your AC system to help further reduce utility bills.
mason Posted: Sep 29, 2008 03:32 PM	Good analysis and advice, Riversnrocks on the attic humidity! There is another suggestion for the duct work in the attic. The 2007 IRC Building Code allows the use of closed cell SPF on ductwork in attics (covered with an ignition barrier.) Insulating the ductwork with SPF can eliminate condensation on the ducts. The humidity in the attic is coming from somewhere either warm moist air from outside or your mechanical system is pumping warm moist air into the attic from your bathrooms, laundry rooms or kitchen. Check out that the air is actually being pumped outside and that the ductwork is sufficiently sealed. Again SPF on the ducts can seal them as well as insulate them.

Author

Comments

Mike Natal

Posted: Sep 25, 2008 08:42 AM

Can closed cell be sprayed over open cell?

Can closed cell be sprayed over open cell?

The reason Im asking is my rafters in my attic were sprayed with open cell, but the contractor srayed some areas 1/2" thick in some areas and 2" in other areas and 5" in other areas. So he was going to respray the rafter to correct the problem, but only has closed cell to do it with.

What would be the pros or cons of this?

mason

Posted: Sep 25, 2008 08:50 AM

No, you do not want to spray closed cell foam over open cell foam or fiberglass or cellulose. If you had a roof leak the water would not have anyway to get out.

Now you can do the reverse, spray open cell over closed cell so long as you have sufficient thickness of closed cell SPF to prevent potential condensation on the surface of the foam. (typically 1 inch in mixed climates and 2 inches in cold climates.)

Jim Coler

Posted: Sep 25, 2008 05:16 PM

Mason,
This sounds like the "Flash and Batt" type of approach using open cell foam. I'm assuming you are recommending this because it's in the South and the warm side is the exterior for the majority of the year. So you would want to put your vapor retarder material towards the outside of the building.

But this doesn't seem to make sense with what has been described as the probelm in this situation. It seems that there is a condensation issue in the attic already with inconsistent application of .5 lb foam from 1/2" to 6" thick. I would think that if there is a condensation issue then theat means there is a cold surface in a warm moist environment. This would say you might consider using the closed cell on top of the open cell as a vapor retarder material.

Overall, open cell is the best to use over open cell.

mason

Posted: Sep 26, 2008 09:09 AM

Riversnrocks,

No, I am not talking about condensation, (although that is another issue to consider), but actual bulk water from a roof or window leak. If you install closed cell foam over open cell foam, bulk water cannot escape through the closed cell foam and would stay in the open cell foam until the closed cell foam got saturated. By this time you could have significant wood deterioration above the open cell foam.

Better idea is to just install more open cell foam until the specified thickness is reached.

Mike Natal

Posted: Sep 26, 2008 09:14 AM

So to sum things up, its seems what ya'll are telling me is once my foam guy sprays the correct thickness evenly across the entire roof and he closes up the scattered holes allowing air at the soffit that should resolve my moisture problem all together?? In the mean time, what do you suggest I can do to move some of that moist air out the attic until he can respray? Will eliminating the excess moisture and wettness on the air handlers and duct work help reduce my electirc bill thats sky high right now?

Jim Coler

Posted: Sep 26, 2008 09:38 PM

It sounds like you have ductwork in your attic which has condensation occurring on it. Is this correct? Well, the leaky attic is allowing moist air into it and the warm moist air is rushing to the cold ductwork. When the heat of the air is deposited to the ductwork, the moisture it was carrying gets dropped on the surface. So, once you get the air sealing issues under control, it should show improvements to your situation. The air sealing and insulation may not be the only problem resulting in condensation and high utility bills, but as mentioned by others on this forum, you may need to reduce your AC tonnage for it to run longer and remove the additional moisture. So, I would start with properly air sealing and insulating your attic and monitor the results and tae further action if necessary.

There is no easy answer as a quick fix for ductwork condensation, other than air sealing and insulating properly. You really have two options: 1: make the air in your attic dryer (hard to do with leaks to the outdoors) or 2: make the ductwork warmer. If you can't control air from coming in from outside, you can't control the moisture in the air of your attic. So, the only quick temporary fix, is to turn off your AC which will make the ductwork warmer.

So, get your attic insulation and air sealing fixed fast and then see if you need to do something with your AC system to help further reduce utility bills.

mason

Posted: Sep 29, 2008 03:32 PM

Good analysis and advice, Riversnrocks on the attic humidity!

There is another suggestion for the duct work in the attic. The 2007 IRC Building Code allows the use of closed cell SPF on ductwork in attics (covered with an ignition barrier.) Insulating the ductwork with SPF can eliminate condensation on the ducts.

The humidity in the attic is coming from somewhere either warm moist air from outside or your mechanical system is pumping warm moist air into the attic from your bathrooms, laundry rooms or kitchen. Check out that the air is actually being pumped outside and that the ductwork is sufficiently sealed. Again SPF on the ducts can seal them as well as insulate them.

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