Insulation, Radiant and Vapor Barriers - Finishing attic ... what about the floor?

I'm refinishing my attic to make it studio space. Do I insultate the attic floor? It's over a living space. One source said insulating the floor will create a vapor trap, another said "it couldn't hurt". What are the issues? Is the big factor whether the living space below provides the heat (unheated attic) or if the attic has its own source of heat?

Thanks.

It is uneccesary to insulate the floor of the attic, only the ceiling.

You could insulate the floor as well for sound-dampening but that would also prevent residual heat from the stories below from heating the space.

There are no issues with insulation between heated stories.

Insulation place between heated stories does not use a vapor retarder.

Is there currently a ceiling (drywall) over the rafters? If not, then you will need to consider how you will vent the underside of the roof while ensuring you have insulation in the ceiling space.

No, there is no sheetrock. I'll be putting up rafter vents (1.5") and R-19 insultation (6.25") in the dormer spaces (most of the area of up there) except for behind the kickwall space (R-38 in those spots). There is no flat ceiling because of the low headroom when finished (estimated at 6'8" so none of this will qualify as "livable" space).

So for the rafters I'll be putting up scabbed-on 2X4s and 1X2s on top of my existing 2X4s using mending plates. That should give me enough loft for the vents and insulation.

Sound like an okay plan?

And I'll remove the existing loose fill insulation in the floor ... since I won't need it and because it's a brownish wood fiber product that apparently catches fire like tinder. Probably installed around 1917.