July 12, 2013
Q: When insulating an unvented attic assembly in a retrofit, what does one do with the existing blown-in insulation on the floor of the attic?
A: In an unvented attic assembly, conditioned air from the living space below should slowly infiltrate the attic space. Therefore, the fiberglass insulation would be removed.
Q: What happens if the blown-in insulation is left in place?
A: The blown-in insulation slows the heat transfer into the attic so the space is hotter in the summer and colder in the winter. Without the blown in insulation, the energy efficiency is better since the space is typically within 2 to 3 C (5 to 7 F) of the interior temperature.
Q: What is the best way to insulate an attic space if there is no ductwork or HVAC equipment within it?
A: A vented attic assembly would be more efficient if there is no ductwork or HVAC equipment in the attic. However, it is important to remember to air-seal the floor of the attic to minimize heat transfer through gaps, cracks, and voids from penetrations to the attic space.
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