how would i insulate a brick house that has 12 inch thick brick walls ? not sure if it has any studding in the outside walls. the inside partition walls are oak studs with plaster slats and plaster. high heat bills are making me want to re-stud over the existing plaster walls and insulate with r-13 fiberglass rolls. i am wondering if this cause condensation between the walls and cause more problems ? thanks !

The best way to handle this would be to use a blown in type of insulation. In your case you would drill holes on the top of the inside walls to where the insulation will fill up each cavity of the studding (frame) you will have to this to each and every cavity and then blaster over the holes you made. But will be well worth it.

The other choice you have would be to remove all the blaster from the exterior walls, insulate with the thickest insulation you can fit in and then of course re-Sheetrock , trim and paint. The blown in way on a older house and one made of brick / concrete will give you the better bang for the buck.