attic insulation with air handlers

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  #1  
Old 09-14-10, 08:58 AM
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attic insulation with air handlers

I would like to try to solve an ice dam problem in my custom built cape. The attic has 15" of cellulose insulation and all the recessed lights have been sealed as well as all plumbing and wiring openings to the living space below. I have two air handlers located in the attic in the un-conditioned space. The ducts have an R-8 foil insulation but the units themselves are not insulated. I believe that this is where my roof melting is originating from.
Would it be a good idea to add R30 or R38 (unfaced) batts to the roof joists and create a conditioned space for the air handlers? Would I need to add a vapor barrior as well?
 
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Old 09-15-10, 06:56 PM
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The AHUs or insulated on the inside
 
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Old 09-16-10, 04:26 AM
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they cant be insulated to a great degree (R4 maybe). I have one section of roof with the rafters insulated where they create a roof over our deck. The snow above the insulated surface (in the area of the attic with the air handlers) consitently melts and creates ice dams on the cold roof surface below.
 
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Old 09-16-10, 04:45 AM
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A couple of additional steps. Any ducts and AHUs in the unconditioned space need to be air sealed, usually not done at install. Leaks on the supply side dump conditioned air and leaks on the return side pull in unconditioned air.

In addition to increasing the insulation on the ducts and AHU, you need to make sure you have adequate ventilation. Cold air needs a place to enter in large quantities and warm air must have lots of exit space. Since this process relies on heat, the very component you want to eliminate, the better the ventilation the less heat required to make the convection process work.

Bud
 
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