adding insulation for finished block interior walls
My den is built over a slab in the area/room that was the house's original (1940) garage. Over 10 years I've been here, I've established that there's no insulation in the floor joists (at least nothing currently in place/functioning, if there ever was) and both the floors and walls (and elec outlet covers) seem to hold on to cold air at this time of year. There is one hot air heat vent in the room and a return, but they do little under the circumstances.
I'm about to paint the room and remember reading or hearing about some sort of insulating board material I could add on top of the block walls (they only have a textured paint on them) that would help to keep the room warmer. If so, now might be the time to do it. Sounds like something I might be able to manage, - but after a quick search on Google and here didn't come up with anything designed for such use. Any suggestions of what to look into, if available at Home Depot or Lowes? I'm expecting I would need to attach it under, and then replace the woodwork. And, how costly and effective could I expect it to be?
A few years ago I was advised to increase ventilation in the open slab area under the room's floor, which I did to no noticeable effect (and now read that thinking about that approach has changed again/more). So - aside from covering the beautiful red pine floor in the room as well as I can to block the cold air, I haven't found any solution I might be able to do myself to help with insulation there... Thus I'm hoping insulating the walls will help a lot.
Any and all advice and/or information would be MUCH appreciated.