I would say that about 80% of the homes I inspect have inadequate attic insulation for our area. Here in La Plata we are in climate zone 5. For a regular non-cathedral ceiling, the department of energy recommends an attic insulation value of R38-R60 for our zone. R value is a measure of the resistance of an insulating or building material to heat flow, expressed as R-11, R-20, and so on; the higher the number, the greater the resistance to heat flow. Different insulation types have different R values. To get to the suggested R38 you would need at least 12 Inches insulation. To get to R60 you would need at least 15 inches. Adding additional insulation over the top of what you have is a easy DIY project. Home Depot will let you barrow their attic blowing tool if you buy enough loose fill fiberglass. If you do it yourself make sure you don’t blow in fiberglass over your soffit vents. They make easily installed baffles to prevent this.