Do I need Attic Fan in Garage?
Roofs need to be ventilated to remove excess moisture and to inprove teh effectiveness of your insulation.  In the summer, improper ventilation can cause attic heat to build in excess of 160°F. This super-heated air eventually penetrates the ceiling insulation into the living area below.
  In the winter, warm interior air leaking through the insulation can cause condensation and can contribute to excess moisture build-up. Improperly ventilated attics will allow this moisture to collect and cling to the underside of the roof. The moisture will condense and fall, soaking the attic insulation and reducing its efficiency.
  You should install roof vents.  There should be a air passageway that allows air from the eaves to be drawn in and exit through roof vents. This all can be passive and does not require a fan.