Attic ceiling insulation in a vented attic question - GreenBuildingAdvisor
Summary
This article discusses a homeowner's inquiry about attic ceiling insulation and the implications of deep burying ductwork in a vented attic, focusing on condensation risks and heat transfer principles.
Why It Matters
Understanding attic insulation and HVAC duct placement is crucial for energy efficiency and preventing moisture issues in homes. This discussion highlights the complexities of building science, particularly in relation to insulation materials and their impact on indoor air quality and comfort.
Key Takeaways
- Deep burying ducts may alter condensation risks due to insulation properties.
- Understanding heat transfer mechanisms is essential for effective insulation strategies.
- Proper air sealing and vapor barriers are critical in preventing moisture accumulation.
Attic ceiling insulation in a vented attic question JeffS1 | Posted in Energy Efficiency and Durability on February 24, 2026 12:21pm I’m a little embarassed to ask a question that has arisen since I decided to redo my attic HVAC and insulation. Background: I’m going to completely air seal the attic ceiling from the house below. The HVAC equipment and ducts really have nowhere else to go so I plan to deep bury the ducts. I’m in CZ 3A. Complete compliance with the code as I understand it seems nearly impossible because R13 ducts are not available, whereas R8 are readily available. My question has arisen after considering the consequences of deep burying new R8 ducts (R13 is code but not available) and avoiding condensation on the outer duct jacket. I understand why no condensation forms on the jacket under the existing conditions (the skin is the same temperature as the attic air). But why does deep burying change the physics if air can go through the blow-in insulation on top of the ducts and contact the duct outer skin? For that matter, the more I thought about this issue and confused myself, why doesn’t that roasting attic summer air just go right through the blown-in insulation and contact the back side of the ceiling drywall, creating the same potential for condensation? I suspect the answer involves me better understanding heat transfer due to conduction versus due to convection. But I suspect someone here can explain it. Recommendations for an air barrier ar...
