Ducts Buried in Attic Insulation

For homes with ducted heating and cooling systems, the best place to locate the duct system from an HVAC performance standpoint is within the conditioned space of the home, either in dropped ceilings, or between floors, or in a sealed and insulated basement, crawlspace, or attic. If the ducts must be located within a vented attic, one option for protecting the ducts and helping to minimize heat transfer between ducts and the unconditioned attic is to lay the ducts on the attic floor and cover them with the same blown insulation that is used to cover the attic floor. The ductwork should be installed so that it is in direct contact with the ceiling and/or truss lower cords.

When HVAC ducts are installed in a vented attic in a dry climate, bury the ducts in attic insulation to protect them from temperature extremes in the unconditioned attic space.

• Install ductwork so that it is in direct contact with (i.e., laying on) the ceiling and/or truss lower cords.

• Use metal, flex, or fiber board ducts that are insulated to code. The duct insulation should include a vapor barrier cover.

• Mechanically fasten and mastic-seal all duct connections.

• Test total duct leakage. Add additional sealant if necessary.

• Install loose-fill insulation to cover the ducts and the attic floor to meet or exceed the code-required R value for attic insulation.

• If using this technique in a humid or marine climate, the ducts must be encapsulated with spray foam before installing the blown insulation.