Your 18' x 18' forms a hip at top, no horizontal ridge. Add an 8x8 turtle vent: http://www.owenscorning.com/roofing/...ic-slant-back/ on each side to meet the 1/300 min. code requirement as the faced 4" attic deck insulation is probably a vapor barrier- fiberglass or foam board? Open the foamed over hole if you can, add screening for bugs.
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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?