How to Insulate a Garage

Last summer it got so hot in my garage, my air conditioner would not operate. I decided to install a whirlybird in the roof to let the heat out. My garage was getting to 50 degrees celsius on hot days. I decided to use silver sarking to insulate the walls and roof of the garage. This made a huge difference. I can now operate my air conditioner on days above 40 deg c.