I have a brick house built in the 50's, in Maryland. I have about 2 or 3 inches of what looks to be blown in(fiberglass). There are no soffit vents. I only have gable vents. I want to put more insulation in the attic. Should I just blow more on top of the old stuff. Is there anything I should do to incease venaltion? I have an attic fan, but that runs in the summer. Thanks