1. Ducts in attic w/ R8 insulation are popular because it’s price competitive (aka cheap) to build and install, in most cases. Fact is, HVAC equipment should never be designed and installed in a ventilated attic, and a properly designed, installed and commissioned system, inside the conditioned space, costs a lot less than a system that is not; or at least that is my experience for the last 15-20 years.