My house was pretty hot this early summer, i decide to check on the attic. I found out that my attic has some old insulation for about 3 inches thick. No wonder it is hot and cold in the summer / winter. I bought some R30 and roll out in my attic. Installed a Gable Fan (1260CFM), now today when it is 105F, inside is only 84F. I m pretty happy with the result. I read another article, someone suggest to increase exhaust air to about 1/4 of house cubic feet, and it will help to reduce the house temperature. In this autumn, i m going to add radiation barrier in my attic and install another electric gable fan. Will update how the temperature dropped by addition gable fan and radiation barrier

Thats great news. However I do not suggest that you install a 2nd power fan in conjuction with the one you already have. Fans are typically used when natural ventilation does not pull enough air out of the attic. It sounds that you have enough air flow now. Using two can cause one to work against the other.