Are ridge vents necessary, if...?
If your attic roof isn't insulated, if your attic is unfinished, and if you have the proper venting per sq footage, then you should be OK.
Sometimes, contractors/builders put soffit vents between every OTHER rafter. And sometimes, they're just bore-holes covered w/soffet vent. So, if the vents are UNDERSIZED, you may need more help.
Assuming you understand the Physics of this process, passive venting is usually sufficient. The addition of a draw fan or an exhaust fan, that's mounted in a Gable Vent, could add problems. To know if you don't need a fan, one test is to 'feel' how hot your ceiling gets in the top-most rooms in your house, just below the attic. For example, in summer, if the ceiling in your bedroom is really, REALLY warm, or if you feel the air getting warmer as you climb higher in the house, then perhaps warm air is being drawn into the living space via the attic!
Funny thing - In my neighborhood, we all have the same house. 3 neighbors have portable fans on their 2nd floor that just 'circulate' air because it gets so hot up there. Me - I have NOOOOOO problem whatsoever! I think that either their attic insulation is 'bad', they have no attic insulation, the insulation job was poorly done or inadequate, or their HVAC system is drawing warm air from the attic into the living space via 'leaks' between the 2 spaces (like attic pull-down stairs, drywall cracks, or the like.)
Good luck! My best to ya and hope this helps.
Jay J -Moderator
PS: God BLess America!