I have a 2 story brick farm house with a 2x6 rafters in the attic. They are on 16 inch centers and spand about 16 feet. I would like to get to at least a R-30 of blown in insulation. When walking in the attic the ceiling flexes which may loosen the plaster ceilings. Would like to retain the floor in attic for storage. Could I add a 2x12 beside the original rafter for strength but is that enough height for insulation. Or can I put a 2x6 or 2x8 fastened on top of the original rafters but would that add strength to the ceiling to keep from flexing?
Or is there any other way to add strength to the ceiling rafters and add more insulation?