I would suggest increasing your loose fill fiberglass to 16 inches, at least. I would use fiberglass because the density of the product will be the same as what you currently have. While Cellulose is a fantastic product, if you were to use it, you would have to put the full R-30 to R-38 amount into your attic because it is more dense that fiberglass and would compress the existing insulation, making it lose its R-value. Also, be certain that your attic ventilation is adequate.

Humidity is not a factor in using Cellulose; however, if you have moisture issues, you will need to find the cause of them and fix it immediately to prevent future damage.

Bryan Vance
Vance Installations
BPI Certified Building Analyst

Sounds like you have an R-factor of about 15 and you will need a total R-factor of 38. We don't use fiberglass for health reasons, and instead, we use stabilized cellulose with glue binder to stick fibers together with an R-value of 4 per inch.

Humidity is not at all a problem for cellulose in the Houston area. However, it is important to consider air ventilation in your attic. We have our own line of solar fans that work great with a vented attic.

Pat Rist
AtticDr.com