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attic question Post New Topic | Post Reply
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SPFer
Posted: Apr 20, 2010 05:34 PM
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attic question
I've got a contractor who is building a small addition. The owner wants the following system: 2" of closed cell on the attic floor covered by 17" cellulose. Nothing new there, however, they also want 2" of closed cell directly under the roof creating an enclosed, airtight attic. There will be ductwork through the space, but no heating or cooling units. We will need to cover the exposed insulation on the roof with a thermal barrier.Does anyone have any objections to this attic system? |
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Ivan Pauliuchenka
Posted: Apr 20, 2010 09:08 PM
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You better off just spraying ducts with foam to eliminate heat loss and I would imagine 17" of cellulose would cover all the the ducts. Don`t seal the attic - air will stall in there. Let the attic vent this way. Or why don`t you just spray like 7" of closed cell wouldn`t this be close enough price??? have a good one |
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Ivan Pauliuchenka
Posted: Apr 20, 2010 09:15 PM
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to above.... 7" of cc to underside of the roof... later |
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Greg Pruitt
Posted: Apr 23, 2010 07:07 AM
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My understanding is that it does not meet code to spray the duct work. The foam is considered a plastic, and does not meet code when applied to the duct work. |
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John Shockney
Posted: Apr 23, 2010 09:59 AM
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It looks like you have almost enough foam figured to spray 4inches on the underside of the roof. What is the cost of the 17inches of blown in insulation? Couldn’t you just use the money budgeted for the blown in insulation to add more foam and just spray the underside of the roof? Thanks Airpro |
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Derek Dwyer
Posted: Jun 21, 2010 05:17 PM
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The bigger issue here is vapor retarder qualities of the closed cell foam products. According to R806.4, there is to be no interior vapor retarder installed on the ceiling side (attic floor) of the unvented attic assembly. A typical closed cell application will achieve a perm rating of less than 1 at a thickness of 2 inches. This would mean the foam is a type II vapor retarder and the assembly would not be code compliant. You must choose one or the other, not both. |
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mason
Posted: Jun 22, 2010 03:08 PM
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Caddis, Sprayfoam is acceptable on ductwork in residential attics but not commercial attics. Use the same rules as any foam plastic, cover it with an ignition barrier such as fiberglass (unfaced) Be sure to use sufficient thickness of foam to stop condensation |
