Attic Insulation
The U.S. Department of Energy recommends a minimum R-38 level of attic insulation for the Houston area. This is roughly 12 - 13 inches of loose fiberglass.
Insulation is designed to slow the transfer of heat, but it does not inhibit the movement of air (hot or cold). For this reason, it is very important to have the attic floor sealed prior to installing new insulation. This will provide you with the maximum efficiency from your new insulation, and will help prevent the dust from the insulation from infiltrating into your home.