My metal roof has a cap but there is no air space through which air can escape. Under the metal roofing there is at least one layer of old shingles (all this was there when I bought the house.). Around the attic I have 9-8x16 in. soffit vents, and the 2 big circular gable vents.
Answer:
I think you'll be far better off to invest in the ridge vents because your gable end vents are not doing a whole lot for you during the summer (which is when you need most to keep the attic temperature down) unless the wind is blowing directly against one of them. I prefer to see baffled ridge vents going from gable to gable and even then, if you don't have good soffit ventilation, there is a negative impact on roof structure. It is all but impossible to over ventilate an attic as long as you do not compromise it's structural integrity and keep nature's elements out of it.
