Install your drip edge first nailing up high on the drip edge. Then proceed to lay your shingles andnail in appropriate areas. Make sure the drip edge is tight and plum to the edge of the roof for maximum efficiency. Any ripples in the drip edge might cause the shingles to become inefficient.
The first layer on shingles installed above a drip edge must have a one half inch over hang. You must also double up the first row of shingles. This ensures no gaps on the starter course of shingles.
If you have more than 2 layers of excisting shingles you will need to do a full tear off assuming the underneath sheeting is good you will need to re tarpaper, replace valley tin if you have any. Purchase new shingles and install new drip-edge followed by new shingles.
Well the first step is to install the drip-edge by holding it tight to the fascia and nailing it. Next run 3 to 6 ft. of ice and water shield. Now run a starter shingle or a upsidedown 3tab flush with the edge. Now run your roofing.
you can do this two different ways. you can buy a starter strip that goes down before the shingle does or you can just flip one set of shingles face downand the start shingleing over that. be sure to bring you shingles flush to the edge of your drip edge.