Creating a retrofit conditioned attic when I cannot get to cathedral ceiling portion – GreenBuildingAdvisor

Hey folks, I posted some of this in an article comment but it probably suits this forum better. I just bought a home that was built in 2021 and I want to condition the attic since it has two HVAC/furnace units in the attic plus ductwork. The contractor can get to all areas of the attic that have the ductwork and the HVAC units, but there is at least one cathedral ceiling that comes off the side of the house where the top of the cathedral connects inside the attic to the area that would get foam and sealed. Therefore, the cathedral would have open soffit venting at the bottom, but be closed off at the top. Is this OK or should I not create an unvented assembly in the rest of the attic since it would cut that venting of the cathedral off?