Is a vapor barrier needed for this situation?


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Old 04-10-12, 10:00 AM
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Is a vapor barrier needed for this situation?

I am looking to insulate the floor of a finished attic. The ceiling of the attic has insulation in it and I was told that its probably R9. Would I need to put a vapor barrier in the floor insulation? I live in New Jersey if that makes a difference.
 
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Old 04-10-12, 07:05 PM
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Why are u insulating the floor? There will be no gain in doing so.
 
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Old 04-11-12, 08:48 AM
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I was told that due to lower R value in the roof, cold air was coming through the attic and falling through the house. Insulating the floor of the attic would stop some of the cold air from getting to the lower floors.
 
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Old 04-11-12, 09:54 AM
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If the attic is living space, you need to insulate higher.
 
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Old 04-11-12, 12:12 PM
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That makes sense however the way it was described to me it's an issue of cost. To better insulate the ceiling of the attic I would have to rip out what's there and frame it out to accommodate thicker insulation. Since the attic would just serve as a guest bedroom we thought it might be more cost effective to make sure the lower floors were kept warm and sacrifice on warmth in the attic which would be infrequently used. I could be approaching this all wrong so I really appreciate the feedback.
 
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Old 04-11-12, 02:08 PM
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Are you going to heat the attic only when occupied?
 
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Old 04-11-12, 02:21 PM
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In our current situation we would have to use space heaters so yes, only when occupied.
 
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Old 04-13-12, 01:44 PM
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If someone told you that cold air comes in from the attic and falls down through the house, that's nonsense.
Warm air rises and can draw cold air in from the outside if you are not properly draughtproofed.
Don't bother insulating your ceiling (waste of time) as the warmth will eventually find its way to the attic. You are best insulating the attic ceiling and that will keep the house a little warmer.
 
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Old 04-13-12, 02:27 PM
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How big is this room in the attic space? Does it occupy the entire attic?
 
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Old 04-13-12, 03:20 PM
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It's roughly a 28x15 space and it does occupy the entire attic.
 
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Old 05-02-12, 08:59 PM
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You should not insulate the floor of a finished attic. The reason for this is that the floor is within the "Thermal and Pressure Boundaries" of your house. "Dew Point" can occur which may result in mold and mildew in the finished attic when not in use.

Francis R. Lazaro
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NJ certifed energy auditor since 1984
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