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I have Insulated AC flex duct work in my attic. Am I correct in that since its insulated already if I lay insulation over the duct work it is fine as long as the duct work is sealed properly? I have R11 4' x 100' rolls and it might be difficult to get the entire roll under the flex ductwork. I could cut the rolls down and line them up but was hoping for one continuous roll out.

  • Where in the world are you? In many climate zones, an unvented insulated compact roof is a better bet than trying to faff about with plugging every last air leak in insulated ducts located in a vented attic. – ThreePhaseEel Dec 14 '15 at 2:54
  • I'm in NY. The attic is vented and the duct work is already sealed. Can I lay insulation over the insulated flex duct work ?? – Santo Dec 14 '15 at 3:06
  • what part of New York? (Some parts of upstate get too much snow for an unvented roof.) – ThreePhaseEel Dec 14 '15 at 3:09
  • My attic is vented and I'm located on Long Island. I just want to know if I can cover the insulated AC ducts with more unfaced insulation? – Santo Dec 15 '15 at 13:26
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You can cover the ducts with more insulation -- just make sure to mark where they are, and provide a way for the HVAC tech to access any dampers, etal.

(Sidenote: given your location, an unvented, insulated compact roof could very well be a better bet -- this makes the attic part of the conditioned space, and eliminates the hunt for duct leaks.)

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  • Thank you very much. I'll add more of the R11 insulation blankets I have and just roll them over the duct work. They're 4' wide so it'll cover the entire duct. Each one is 4' x 100' so I'll cut it down to the specific lengths and cover them all. – Santo Dec 16 '15 at 0:09

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