Because the moving air is in the ductwork for only a short period of time it does not need the insulation r value the attic floor requires.
Duct insulation in attic.
According to rightsuite the software we use the supply ducts have about 560 square feet of surface area and the return ducts 101 square feet.
Most attic ducts are insulated flex ducts that is flex ducts with r 6 or r 8 fiberglass insulation along with an exterior polyethylene jacket.
Air sealing your attic and ducts installing blown cellulose insulation and insulating ductwork will eliminate these problems.
Sometimes the insulation is inside the ductwork.
Install ductwork so that it is in direct contact with i e laying on the ceiling and or truss lower cords.
Flexible ductwork comes with different insulation r values.
Looking at the cooling side only the additional load would be.
Install ductwork so that it is in direct contact with i e laying on the ceiling and or truss lower cords.
When these ducts are exposed to exterior air the plastic jacket never gets cold enough to permit condensation because the hot attic air keeps the plastic jacket warm.
When hvac ducts are installed in a vented attic in any climate encapsulate the hvac ducts in attic insulation to protect them from temperature extremes in the unconditioned attic space.
Other times insulation may be on the outside.
Attic space insufficient attic insulation poor air sealing and uninsulated ductwork are all common problems that will lead to uncomfortable rooms and make your home less efficient.
All the ducts are in the attic.
Use metal flex or fiber board ducts that are insulated to code.