To insulate the ceiling of an unheated basement:
In the Foundation section of the Input screens, enter "None or Undesired Incidental" in the Basement Heating & Cooling section.
This ensures that the model sees the basement ceiling as the thermal envelope of the building as opposed to the basement walls and floor.
The following fields for the basement will then be opened in the Refine screen and you may now enter either Cavity or Continuous Insulation to the basement ceiling.
The Recommendation
Please note:
In the basement recommendation, when basement heating is set to 'None or Undesired Incidental', the following fields are now hidden to better represent the data used in modeling and HPXML:
Basement Rim Joist Treatment
Basement Rim Joist Insulation
Basement Rim Joist Assembly R Value
Basement Rim Joist Insulation Type
This also improves compatibility with certain program guidelines. If the basement is unconditioned, the rim joist is bounding an unconditioned air space on the inside. This would have a minimal impact on heating load. Only a small amount of the insulation is in contact with the floor above and that is generally going to be under the exterior wall rather than adjacent to the conditioned air.