My husband and I have a home which is 26 years old. It has blown in insulation. We were told that blown in insulation settles after time and is not as efficient at insulating. We would like to add more blown in insulation on top of the old to help defray heating and cooling costs, but my husband is worried about the possibility that the extra weight on our drywall ceilings may pose a problem. Does anyone have an answer to this question? Can you safely add MORE blown in insulation on top of old and will it sugnificantly help defray energy costs?