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rick wade Posted: Feb 12, 2009 03:35 PM	metal building w/ wood frame inside question I am building a house inside a metal building. The metal building is 6" purlin and I beam with a 2x6 wood frame interior. I need to spray foam next week and I am very confused with how to have the contractors do it. The ones that I have had bid it, all have a different opinion. It's in North Texas (hot summers, mild winters). I have been told 1" closed cell and 5" open cell on the sheet metal walls and the underside of the roof with no insulation in the ceiling joists. To me that means I am heating and cooling my attic. Some have said just do 2" of closed on the walls and underside roof. Some recommend 1" CC 5" OC on the walls 1" underside, with conventional fill in the ceiling joist. I am worried about condensation on the underside roof but I don't want to HVAC my attic. I would appreciate your advice. Thanks, Rick
mason Posted: Feb 13, 2009 01:17 PM	Trackhoeguy, While it seems contradictory, spraying foam to the underside of the metal deck is more energy efficient that spraying the ceiling. Without adding any additional cooling or heating, the attic space will maintain temperatures within 7-8 degrees of the interior temperatures. This is due to air infiltration from the interior to the attic. This makes the HVAC unit not work so hard to cool and heat the interior environments. On a 95 degree day, a vented attic would be over 110 degrees F. Your HVAC would have to cool the interior temperature more than 40 degrees. But, by having an unvented attic, the attic temperatures are around 85 degrees (without cooling) so, you only have to have your HVAC reduce temperature by 15 degrees. A big difference. The same thing happens in the winter. If the temperature outside is 25 degrees the vented attic would be around 30 degrees so the furnace would have to make up more than 40 degrees. As for how much foam, 1 inch of closed cell and 5 inches of open cell sounds about right. I would however spray the purlins (overspray from filling in between the purlins should do the job). This will prevent thermal bridging and potential energy loss and condensation.
rick wade Posted: Feb 13, 2009 08:45 PM	Thank you very much Mason. I feel much better with your recommendation.

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rick wade

Posted: Feb 12, 2009 03:35 PM

metal building w/ wood frame inside question

I am building a house inside a metal building. The metal building is 6" purlin and I beam with a 2x6 wood frame interior. I need to spray foam next week and I am very confused with how to have the contractors do it. The ones that I have had bid it, all have a different opinion. It's in North Texas (hot summers, mild winters). I have been told 1" closed cell and 5" open cell on the sheet metal walls and the underside of the roof with no insulation in the ceiling joists. To me that means I am heating and cooling my attic. Some have said just do 2" of closed on the walls and underside roof. Some recommend 1" CC 5" OC on the walls 1" underside, with conventional fill in the ceiling joist. I am worried about condensation on the underside roof but I don't want to HVAC my attic. I would appreciate your advice. Thanks, Rick

mason

Posted: Feb 13, 2009 01:17 PM

Trackhoeguy,

While it seems contradictory, spraying foam to the underside of the metal deck is more energy efficient that spraying the ceiling. Without adding any additional cooling or heating, the attic space will maintain temperatures within 7-8 degrees of the interior temperatures. This is due to air infiltration from the interior to the attic. This makes the HVAC unit not work so hard to cool and heat the interior environments. On a 95 degree day, a vented attic would be over 110 degrees F. Your HVAC would have to cool the interior temperature more than 40 degrees. But, by having an unvented attic, the attic temperatures are around 85 degrees (without cooling) so, you only have to have your HVAC reduce temperature by 15 degrees. A big difference. The same thing happens in the winter. If the temperature outside is 25 degrees the vented attic would be around 30 degrees so the furnace would have to make up more than 40 degrees.

As for how much foam, 1 inch of closed cell and 5 inches of open cell sounds about right. I would however spray the purlins (overspray from filling in between the purlins should do the job). This will prevent thermal bridging and potential energy loss and condensation.

rick wade

Posted: Feb 13, 2009 08:45 PM

Thank you very much Mason. I feel much better with your recommendation.

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