My attic is insulated at the roof sheathing, not the ceiling. My attic is basically 'inside' the house, from an airflow perspective. It peaks around 87°F in late June. Not ideal, but workable.
Conditioned attics are the new rage. Once it's conditioned, you can move other mechanical devices up there like HVAC etc to reduce the amount of ducting your home needs (especially if it's single-story).
It's nice because that loose, shredded insulation is garbage and so easy to mess up (walking on it can change it from R40 to R20, for example). With a conditioned attic you use standard batting in between the roof members -- impossible to mess up.
Sounds like a nightmare for your energy bills. At least with interior ductwork the losses go to heating/cooling your home instead of your attic, which even with insulation is going to act like a giant heatsink that you get nothing out of.
I don't think so -- you _are_ paying to condition that part of your house, sure, but it becomes just another part of the overall envelope and acts like a buffer between the weather and the actually livable parts of your home. Anecdotally, in my home in the summer months, when unconditioned the attic is 50 degrees on a summer day it literally radiates heat down through the ceiling on the floor below into the rooms there. The attic acts like a heat battery -- long after the sun goes down the attic is radiating heat into the upper floors of my house. Not sure why it retains heat so well it's got louvres and vents ...
When you have ductwork in the attic your heating/cooling efficiency is hurt by the amount of heat lost through the roof and out into the environment. When the ductwork is all in interior walls, there's no efficiency lost because those losses go into the rooms the system was trying to heat/cool already.
Where I live, we have extreme ranges of temperature (both hot and cold) and almost all ductwork is on the interior for this reason. You'd be spending a fortune in the winter heating an attic when it's getting lost to -17C air temps outside...
> Pros: Less noise, easier cable runs.
> Cons: can get hot depending on where you live, roof leaks, humidity/condensation, and creepy at night.
Where do attics not get hot? I live in northern climate, and ours regularly gets hotter than 140F during sunny summer days.
And I say hotter, because the remote temp sensor I have up there maxes out at 140F. I wouldn't be surprised if it actually gets up to 150F or more.