I installed these shingles about fifteen years ago. My roof has absolutely no ventilation underneath because it is a century old house and has solid wood soffits, not perforated. So I added the nine vents you see and figured that hot air would escape out of the four top vents and cool air will flow in through the bottom five. This part of the roof faces south.
Obviously it did not work. Why? I am curious as to what is wrong with my reasoning. Also, if you notice, the shingles at and above the upper vents have not deteriorated, which is the exact opposite of what I was expecting. Strange.
I am redoing the shingles and plan to eliminate most of the vents, perhaps just leave a couple of the top ones.