A home with uneven snow on the roof is a sign of excessive air leakage and a lack of insulation. Attic Air Sealing will stop the hot air from leaking out. If insulation is added before air sealing the leaks would still exist and would lower the effectiveness of the insulation. According to the Building Performance Institute it could lower the effective R-Value by almost half. Before adding insulation an Energy Audit needs to be completed to determine the actual leakage. Air Sealing can be completed to seal the home to the Building Air Flow Standard.