Heat Issue? Try RockWool

I have a friend's BH has heat issue. The highest temp is ~32degC. He decided to try out Rockwool from Roxul. After changed, at 3pm, the max temp only 29.5degC.

He told me that there are 6 pcs of Rockwool in a box. Each Rockwool is 4x2 feet and 2" thick. The cost of 1 box is RM75. Imaging if your BH is 20x70' which is around 1400 sqr feet, after minus the open roof entrance area and some other non critical area, only 1200 sqr feet of area need to cover by Rockwool. 1 box can cover 48 sqr feet. You will need 25 boxes which are around RM1875.

If I were to design another BH, I will definitely consider Rockwool rather than 2" Styrofoam. With the global warming effect, you better take it seriously the roof insulator design.