Shingles should be layered on a roof so that each layer overlaps the shingle layer below it by a distance specified by the shingle manufacturer. For example, some manufacturers state that their shingles should be installed so that there is a 5 5/8-inch distance between overlapping shingle edges.
It is best to start at one of the lowermost corners of the roof and work toward the top when layering shingles. Begin by laying a shingle starter strip along the perimeter of the roof edge. The starter strip should extend at least 1/8 inch over the side of the roof to divert water away from the edge of roof and to prevent water damage to the roof. Lay the first row of shingles, starting from the corner of the roof, so that the edges of the shingles are flush with the edge of the starter strip. Secure the shingles with roofing nails.
Lay another piece of starter strip material above the new shingles. It is important to make sure that the shingle seams of different rows do not line up with one another. For architectural shingles that come in long strips, trim each row so that they are different lengths to make it easier to stagger the shingle seams when they are laid down. Work up toward the peak of the roof, laying starter strips and staggering the shingle seams until the entire roof is covered.