I am trying to warm an exercise floor in an unfinished attic and save on heating at the same time. I want to evaluate whether covering the rafters in my attic with various materials will be worthwhile to warm the space and to save on the heating bill. I have a pyramid shaped attic. I would separate the peak from the main space with rigid foam, drop a knee-wall of blankets around the perimeter and then close off and connecting the two spaces formed thereby by stapling a layer of plastic sheeting or bubble wrap to the still exposed rafters in between. I think the foam and blankets will help. I am thinking that connecting them by sheeting spaces between the rafters will cut down on draftiness and maybe add r value. Does this plan sound worthwhile implementing for a season or three until I can afford a better system?
First of all, foam and plastic are fire hazards. Don't turn your attic into a giant match head for your house.
It sounds like your attic ceiling is not yet insulated, so that is where you should start. The fiberglass stuff goes on sale pretty regularly at the big box homecenters. You want the paper backed stuff. The paper makes it easy to staple to rafters and it will stay put once it's up. Your roof requires some air circulation, so before putting up insulation between the rafters you will need to put up ventilation channels. The big box stores sell them, though I can't recall the brand. If you can't buy it all at once, do it a roll at a time until the whole ceiling is insulated.
When you have the entire ceiling insulated you will probably be surprised at how much warmer it is.
But your job isn't really done at this point. The craft paper backed insulation must be covered with drywall in order to pass any type of fire code (I'm not a fire code expert, but the insulation says so right on it). So once it's insulated, put up drywall. No need to plaster or paint yet, jut get the insulation covered. Start by making a peak ceiling and then fill that whole space with fluffy insulation. Then would you way down until you're ready to do the kneewall. Drywall is also fairly cheap. Just requires time and probably a friend to install.
If you close off the space first and it still is not warm it is VERY difficult to insulate after the fact.