A properly insulated attic not only improves energy performance, but it also helps your home maintain a comfortable temperature all year-round. Energy Star states that central California homes should add R25 to R38 insulation in attics that are already insulated and R30 to R60 insulation in uninsulated attics. The best type of insulation for your attic depends on the type of insulation already in it, its age and your home’s sun exposure.