I just tore out a part of the metal drip edge on my 4/12 slope roof to find why I had a leak into the soffit area. Maybe someone can tell me if I found bad construction: the roof is plywood sheathing covered with felt and then 10-year-old asphalt shingles. From the outside all looked well--a metal drip edge jutting out about 1/2 inch over the gutter, shingle starter course upside down, then the first course. First I found the drip edge nailed every 12 inches. I thought water might be entering the nail hole cause the shingles slanted up a bit at the edge and water ran under the shingles probably even up to the top of the drip edge. But then I found that there are two "fascia" boards (if that's what you call them). The plywood sheathing and felt end at the edge of the rafters. Then there is a one-inch wide board nailed onto the rafters and a 3/4 inch (actual measurements) cedar board nailed onto that and then the gutter nailed to the cedar. BUT, the 1-inch piece is about 1/2 inch LOWER than the edge of the sheathing, and the cedar board is slighter HIGHER than the edge of the sheathing, thus creating a nice little trough at the edge of the roof for water to collect, should any leak into that area. It's as if the roofers added the fascia board(s) as an afterthought and figured the drip edge would cover it all. But since the cedar outer board is ever so slightly higher than the sheathing, the whole roof edge, shingles and all, tip upward a bit, inviting water to roll under the shingles. The whole overhang is only about 6 inches leaving barely enough room for a continuous metal soffit vent below (through which the water dripped and tipped me off). I took this vent out to look under the roof and am pretty sure that the leak is confined to the edge area only.
I hope this is clear. Help! What should I do?